Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Sweet taste exposure and the subsequent acceptance and preference for sweet taste in the diet : Systematic review of the published literature
    Appleton, Km ; Tuorila, H. ; Bertenshaw, Ej ; Graaf, C. De; Mela, Dj - \ 2018
    American Journal of Clinical Nutrition 107 (2018)3. - ISSN 0002-9165 - p. 405 - 419.
    exposure - food choice - food intake - food preferences - sweet taste
    Background There are consistent, evidence-based global public health recommendations to reduce intakes of free sugars. However, the corresponding evidence for recommending reduced exposure to sweetness is less clear. Objective Our aim was to identify and review the published evidence investigating the impact of dietary exposure to sweet-tasting foods or beverages on the subsequent generalized acceptance, preference, or choice of sweet foods and beverages in the diet. Design Systematic searches were conducted to identify all studies testing relations of variation in exposure to sweetness through foods and beverages with subsequent variation in the generalized acceptance, preference, or choice of sweetened foods or beverages, in humans aged >6 mo. Results Twenty-one studies met our inclusion criteria, comprising 7 population cohort studies involving 2320 children and 14 controlled trials involving 1113 individuals. These studies were heterogeneous in study design, population, exposure, and outcomes measured, and few were explicitly designed to address our research question. The findings from these were inconsistent. We found equivocal evidence from population cohort studies. The evidence from controlled studies suggests that a higher sweet taste exposure tends to lead to reduced preferences for sweetness in the shorter term, but very limited effects were found in the longer term. Conclusions A small and heterogeneous body of research currently has considered the impact of varying exposure to sweet taste on subsequent generalized sweet taste preferences, and this evidence is equivocal regarding the presence and possible direction of a relation. Future work should focus on adequately powered studies with well-characterized exposures of sufficient duration. This review was registered with PROSPERO as CRD42016051840, 24 November 2016.
    Multi-objective decision-making for dietary assessment and advice
    Lemmen - Gerdessen, J.C. van - \ 2017
    Wageningen University. Promotor(en): J.G.A.J. Vorst; P. van 't Veer, co-promotor(en): G.D.H. Claassen. - Wageningen : Wageningen University - ISBN 9789463437073 - 136
    questionnaires - food - fractionation - modeling - diet - food intake - decision making - diet counseling - vragenlijsten - voedsel - fractionering - modelleren - dieet - voedselopname - besluitvorming - dieetadvisering

    Unhealthy diets contribute substantially to the worldwide burden of non-communicable diseases, such as cardiovascular diseases, cancers, and diabetes. Globally, non-communicable diseases are the leading cause of death, and numbers are still rising, which makes healthy diets a global priority. In Nutrition Research, two fields are particularly relevant for formulating healthier diets: dietary assessment, which assesses food and nutrient intake in order to investigate the relation between diet and disease, and dietary advice, which translates food and nutrient recommendations into realistic food choices. Both fields face complex decision problems: which foods to include in dietary assessment or advice in order to pursue the multiple objectives of the researcher or fulfil the requirements of the consumer. This thesis connects the disciplines of Nutrition Research and Operations Research in order to contribute to formulating healthier diets.

    In the context of dietary assessment, the thesis proposes a MILP model for the selection of food items for food frequency questionnaires (a crucial tool in dietary assessment) that speeds up the selection process and increases standardisation, transparency, and reproducibility. An extension of this model gives rise to a 0-1 fractional programming problem with more than 200 fractional terms, of which in every feasible solution only a subset is actually defined. The thesis shows how this problem can be reformulated in order to eliminate the undefined fractional terms. The resulting MILP model can solved with standard software.

    In the context of dietary advice, the thesis proposes a diet model in which food and nutrient requirements are formulated via fuzzy sets. With this model, the impact of various achievement functions is demonstrated. The preference structures modelled via these achievement functions represent various ways in which multiple nutritional characteristics of a diet can be aggregated into an overall indicator for diet quality. Furthermore, for Operations Research the thesis provides new insights into a novel preference structure from literature, that combines equity and utilitarianism in a single model.

    Finally, the thesis presents conclusions of the research and a general discussion, which discusses, amongst others, the main modelling choices encountered when using MODM methods for optimising diet quality.

    Summarising, this thesis explores the use of MODM approaches to improve decision-making for dietary assessment and advice. It provides opportunities for better decision-making in research on dietary assessment and advice, and it contributes to model building and solving in Operations Research. Considering the added value for Nutrition Research and the new models and solutions generated, we conclude that the combination of both fields has resulted in synergy between Nutrition Research and Operations Research.

    “Everything tastes different” : The impact of changes in chemosensory perception on food preferences, food intake and quality of life during chemotherapy in cancer patients
    Vries, Yfke Carlijn de - \ 2017
    Wageningen University. Promotor(en): Kees de Graaf; H.W.M. van Laarhoven, co-promotor(en): R.M. Winkels; Sanne Boesveldt. - Wageningen : Wageningen University - ISBN 9789463436090 - 169
    perception - sensory evaluation - food intake - quality of life - food preferences - neoplasms - taste - macronutrients - drug therapy - breast cancer - perceptie - sensorische evaluatie - voedselopname - kwaliteit van het leven - voedselvoorkeuren - neoplasma - smaak - macronutriënten - geneesmiddelenbehandeling - borstkanker

    Taste and smell changes are common side effects during chemotherapy in cancer patient and may have an impact on food preferences, food intake and quality of life. However, these relations have hardly been studied systematically in specific cancer populations. The overall aim of this thesis was to assess how the sense of taste and smell change upon treatment with chemotherapy in breast cancer and oesophagogastric cancer patients, and to investigate their consequences in terms of food preferences, food intake and quality of life.

    To measure food preferences for both macronutrients and tastes, the Macronutrient and Taste Preference Ranking Task (MTPRT) was developed. in chapter 2, it was shown that by inducing sensory specific satiety for a standardized sweet and savoury meal, it is possible to detect shifts in preferences for both tastes and macronutrients with the MTPRT, and that these results are reproducible.

    In Chapter 3 we studied objective and subjective taste and smell perception and food preferences in advanced oesophagogastric cancer patients undergoing palliative chemotherapy. The result showed that only objective taste function decreases during chemotherapy, but other chemosensory measures were unchanged. A lower subjective taste perception was related to a lower preference for high-protein products. Therefore it is important to consider patients’ taste perception, when providing dietary advice to OGC patients

    Chapter 4 describes a study with similar outcome measures as chapter 3, but in breast cancer patients at several time points during and after chemotherapy, and compared to a healthy control group. The study showed that breast cancer patients like high-protein, high-fat, sweet and savoury products less during chemotherapy, thus showing altered preferences for macronutrients, but not for tastes. Furthermore, results showed a temporary decrease in taste and smell perception during chemotherapy. These findings show that patients should be informed prior to treatment on chemosensory changes, and that these changes should be monitored during treatment due to the consequences for nutritional intake and quality of life

    In chapter 5 we assessed the dietary intake of breast cancer patients before and during chemotherapy compared to a healthy control group, and associations with experienced symptoms during chemotherapy. It was shown that symptoms induced by chemotherapy were associated with lower total energy, protein and fat intake, which was manifested by a lower intake of specific food groups. Therefore, to ensure an optimal dietary intake during chemotherapy, it is important to monitor nutritional status and symptom burden during chemotherapy in breast cancer patients.

    To better understand the impact of chemosensory changes during chemotherapy on daily life, 13 advanced oesophagogastric cancer patients were interviewed (see chapter 6). Patients described a substantial impact of chemosensory and food-related changes on daily life (by changing daily routines), social life (eating being less sociable) and roles in the household (changing roles in cooking and grocery shopping).

    Finally, in chapter 7, we assessed the association between self-reported taste and smell perception and quality of life in breast cancer patients. A worse taste and smell perception was associated with a worse global quality of life, role, social and emotional functioning shortly after chemotherapy. In patients treated with trastuzumab, a worse taste and smell perception was still associated with quality of life, social and role functioning half a year after chemotherapy had ended.

    From the studies in this thesis we can conclude that chemotherapy mainly affects the sense of taste. The subjective perception of taste was associated with a lower preference for food products and lower energy intake. This indicates that it is not necessarily an actual change in the sense of taste or smell that has an impact on patients, but flavour perception as a whole and potentially a lower enjoyment of food. Moreover, these perceived changes in taste and smell can have a substantial impact on cancer patients’ lives, in a practical way by changing daily patterns of eating, but also socially and in roles in the household. A changed chemosensory perception during chemotherapy may lead to a worsened nutritional status, and could thereby negatively impact the response to chemotherapy. Therefore chemosensory perception should be monitored during chemotherapy. Future studies should further investigate the mechanisms behind chemosensory changes, factors that contribute to subjective taste perception and possible interventions to alleviate chemosensory changes during chemotherapy.

    Understanding heterogeneity in decision-making among elderly consumers: the case of functional foods
    Zanden, Lotte D.T. van der - \ 2017
    Wageningen University. Promotor(en): J.C.M. van Trijp, co-promotor(en): P.W. Kleef; R.A. de Wijk. - Wageningen : Wageningen University - ISBN 9789463431439 - 161
    voedselopname - ouderen - voedselsamenstellingtabellen - voedselverrijking - ouderenvoeding - leeftijdsgroepen - marketing - marketing van voedingsmiddelen - ziekenhuisdiëten - besluitvorming - consumenten - voedselconsumptie - food intake - elderly - food composition tables - food enrichment - elderly nutrition - age groups - marketing - food marketing - hospital diets - decision making - consumers - food consumption

    The population of elderly has grown considerably over the past few decades, due to reduced birth rates and increased life expectancy. Old age is, however, still associated with a higher incidence of various health conditions that pose a threat to quality of life and result in high healthcare costs. Various products and services could help elderly to stay active and healthy for longer if they were adopted, such as mobility aids, home modifications and functional foods. A key challenge is to position products and services like these on the market in such a way that elderly can see their value and will start using them. In doing this, it is crucial to know what elderly need and to understand how they make decisions. This thesis therefore aims to provide a deeper understanding of decision-making among elderly consumers. It does so using functional foods as an example, and concentrates on answering the following research questions: 1) Which types of wants, inferences and intentions characterize the elderly consumer population? 2) What are relevant ways to distinguish between elderly consumers? and 3) How can elderly consumers be motivated to form consumption intentions for products and services aimed at promoting their wellbeing?

    An experience-sampling paradigm shows that there are age-related differences in both desires (i.e. wants), such as the desire for food, and goals, such as the goal to work (i.e. intentions), but not in the way these wants and intentions interact with each other (Chapter 2). Young and old consumers experience the same types of conflict between their wants and intentions. The extent of conflict does change with age however, such that older adults experience conflict less often and less strongly than younger adults. This age-related difference can be partly explained by the way in which consumers perceive the time they have left in their lives. Those who perceive time as limited, experience more conflict. Zooming in on product-specific decision-making, a series of focus groups indicates that elderly consumers overall want to use healthy products that they use frequently as a basis for enrichment with protein (Chapter 3). Most elderly do not display intentions to purchase and use such products, however, either because they do not feel the need to use functional foods or because they hold various negative inferences regarding functional foods, such as a high price or bad taste. Importantly, elderly consumers differ strongly in their wants, inferences and intentions, suggesting that segmentation of this population is warranted.

    A narrative review reveals that there are various ways to segment the elderly consumer population, for example based on age, future time perspective or purchase behaviour, and every approach has its strengths and weaknesses (Chapter 4). Based on the objectives of a segmentation approach one can, however, make an informed decision regarding which segmentation base to use. In the functional food market, elderly consumers may best be segmented using a segmentation base on the food or product level (i.e. rather than the person level) that results in segments in which consumers have similar needs and wants, for example the attributes benefits that consumers seek. A segmentation study shows that using such a segmentation base results in segments that provide concrete instructions for the development of functional foods (Chapter 5). The resulting segments of elderly have unique preferences that do not necessarily reflect those of the average elderly consumer and thereby provide useful insights that can help increase our understanding of elderly consumers.

    Segmentation also provides a basis for tailoring products to the needs and wants of elderly consumers. A segmentation study illustrates that such tailoring can increase elderly consumers’ willingness to try protein-enriched foods for the first time (i.e. trial purchase), as well as their willingness to use such products on a more regular basis (i.e. repeat purchase) (Chapter 5). For a small group of elderly, tailoring proves to be ineffective, however, as they categorically reject all types of protein-enriched foods presented to them. These elderly are relatively uninterested in the concept of functional foods, which may be due to negative inferences surrounding such products. Overcoming the activation of such negative inferences may be useful in motivating elderly consumers to use protein-enriched foods. A field study in a hospital setting shows that the implementation of a verbal prompt intervention that motivates consumers to make decisions without much can increase the consumption of protein (Chapter 6). By understanding and capitalizing on cognitive biases in human decision-making, interventions like these can motivate consumers to form consumption intentions even when they hold negative inferences about products or services.

    Overall, this thesis shows that although elderly consumers share an age bracket they are strongly heterogeneous in their wants, inferences and intentions. This heterogeneity is robust, as it can even be observed when zooming in on decision-making regarding a specific product category (i.e. protein-enriched foods). Our understanding of the elderly consumer population increases by studying this heterogeneity, as it provides insights beyond those that apply to the group of elderly that reflect the average. In studying heterogeneity, it pays off to focus on bases that are predictive of behaviour while demographic characteristics like age provide only few insights. Industry and health institutions can also benefit from an increased understanding of the composition of the elderly population and how they make decisions. Such understanding may provide them with concrete instructions for the development and commercialization of products and services for this growing group of consumers.

    External cues challenging the internal appetite control system—Overview and practical implications
    Bilman, Els ; Kleef, Ellen van; Trijp, Hans van - \ 2017
    Critical Reviews in Food Science and Nutrition 57 (2017)13. - ISSN 1040-8398 - p. 2825 - 2834.
    Food environment - food intake - obesity - satiation - satiety
    Inadequate regulation of food intake plays an important role in the development of overweight and obesity, and is under the influence of both the internal appetite control system and external environmental cues. Especially in environments where food is overly available, external cues seem to override and/or undermine internal signals, which put severe challenges on the accurate regulation of food intake. By structuring these external cues around five different phases in the food consumption process this paper aims to provide an overview of the wide range of external cues that potentially facilitate or hamper internal signals and with that influence food intake. For each of the five phases of the food consumption process, meal initiation, meal planning, consumption phase, end of eating episode and time till next meal, the most relevant internal signals are discussed and it is explained how specific external cues exert their influence.
    Evaluation of dietary intake and nutritional supplement use of elite and sub-elite Dutch athletes : Dutch Sport Nutrition and Supplement Study
    Wardenaar, Floris C. - \ 2017
    Wageningen University. Promotor(en): Renger Witkamp, co-promotor(en): Marco Mensink; Jeanne de Vries. - Wageningen : Wageningen University - ISBN 9789463430326 - 189
    food intake - food supplements - athletes - nutrition - sport - dietary guidelines - netherlands - voedselopname - voedselsupplementen - atleten - voeding - sport - dieetrichtlijnen - nederland

    Background: Well-trained elite athletes differ from the general population in being considerably more physically active and by other lifestyle characteristics including intensive training routines and periodisation of their training programs. Hence, adequate intake of energy and nutrients is of great importance to this population to ensure optimal performance and recovery during training or competition and also to minimize health risks. A consistent dietary intake pattern, in line with the sport-specific recommendations can be difficult to achieve for this group. The specific recommendations are formulated for nutritional intake during and after training or within competition. However, a large variation is seen in dietary intake by athletes. Therefore, the question arises as to what extent athletes meet recommendations and use nutritional supplements in an optimal manner.

    Aims: First, to investigate dietary intake and nutritional supplement use by well-trained Dutch athletes and compare these intakes with recommendations both for the general population and sport nutrition recommendations, which are based on expert consensus. Second, to provide an up-to-date overview of nutrient intake levels in a diverse and relatively large group of Dutch elite and sub-elite athletes practicing sports at the highest competitive level.

    Methods: As part of this thesis 24-hour recalls and questionnaires were used to gain insight into dietary intake and nutritional supplement use (n=553). To validate our methods, 24-hour nitrogen urine excretions were obtained in a subsample of our athletic population (n=47). A questionnaire was used to 1) investigate the prevalence of nutritional supplement use in a large sample of the athletic population (n=778) and 2) investigate the prevalence of nutritional supplement use in a large sample of the Dutch general population (n=1544). Finally, food intake during an ultramarathon was monitored (n=4) and questioned using a food frequency questionnaire (n=41).

    Results: Our validation study showed that 24-hour recalls and accompanying questionnaires underestimated protein intake in young elite athletes to the same extent as reported for non- athlete populations. Notwithstanding this, the method was considered suitable for ranking athletes according to their protein intake as needed in epidemiological studies. It was found that most athletes were able to meet the estimated average requirement (EAR) for carbohydrate and protein. Regarding sport nutrition recommendations, most of the athletes met protein (1.2 g/kg) but not carbohydrate recommendations (5 g/kg). No major differences in carbohydrate and protein intake were seen between sports categories (i.e. endurance, team and strength athletes). Athletes were at risk of too low intake levels of several micronutrients, especially when they did not use dietary supplements (i.e. vitamin D, vitamin A, vitamin B1 and B2 in men and women, and iron in women), whereas users of supplements showed a slightly elevated risk of intake levels exceeding the upper intake level (UL). This was in particular the case for vitamin B3. Our investigations in ultramarathon runners showed that these athletes did not reach sports nutrition recommendations from their habitual diet. In men and women, habitual mean carbohydrate (CHO) intake was lower than recommended, as was mean protein intake by women. CHO intake during the race was <60 g/h in 75% of the athletes. A large variation in nutrient and fluid intake was seen. This may be related to a high incidence of GI distress (82% of the runners reported GI complaints, but severe GI distress was low). Use of dietary supplements and sport nutrition products in the general population was reported by two-thirds of all respondents. Thirty-three percent reported the use of sport nutrition products. One could question whether the use of these energy containing sport nutrition products fits all respondents’ physical activity needs. Furthermore, it was shown that almost all athletes (97%) have used nutritional supplements some time during their athletic careers. Additionally, receiving dietary counselling seems to result in better choices with respect to nutritional supplement use.

    Conclusion: On a population level and with respect to the existing sport nutrition recommendations, nutritional intake in well-trained Dutch competitive athletes was low to moderate for carbohydrate intake and sufficient for protein intake. Suboptimal consumption of micronutrients was reported based on comparison with the estimated average requirement (EAR) for several micronutrients, especially for vitamin D. The use of dietary supplements adds to dietary intake. However, not all athletes consume these types of products, and day to day compliance in supplement users is low. Athletes are advised to focus on the selection of whole food carbohydrate-rich products with a high nutrient density and to consume a large variety of products containing both fat-soluble and water-soluble vitamins. When athletes experience difficulties in following these recommendations, the advice could be to use a low dose multivitamin (50-100% RDA).

    Cadmium in soil, crops and resultant dietary exposure
    Rietra, R.P.J.J. ; Mol, G. ; Rietjens, I.M.C.M. ; Römkens, P.F.A.M. - \ 2017
    Wageningen : Wageningen Environmental Research (Wageningen Environmental Research rapport 2784) - 39
    cadmium - soil - food intake - crops - exposure - fertilizers - food safety - toxicology - cadmium - bodem - voedselopname - gewassen - blootstelling - kunstmeststoffen - voedselveiligheid - toxicologie
    White root tips supply plants with oxygen, water and nutrients : healthy roots are fundamental for a healthy plant
    Heuvelink, E. ; Kierkels, T. - \ 2016
    In Greenhouses : the international magazine for greenhouse growers 5 (2016)3. - ISSN 2215-0633 - p. 44 - 45.
    tuinbouw - glastuinbouw - worteloppervlak - wortelharen - wortels - wateropname (planten) - voedselopname - opname (uptake) - calcium - tomaten - pythium - plantenontwikkeling - horticulture - greenhouse horticulture - rhizoplane - root hairs - roots - water uptake - food intake - uptake - calcium - tomatoes - pythium - plant development
    The main, most important function of roots belonging to horticultural crops is the uptake of water and nutrients. Healthy roots are essential for a healthy plant. After all, if the uptake of water and nutrients is not functioning properly, then other aspects also leave a lot to be desired
    The potential of peer social norms to shape food intake in adolescents and young adults : a systematic review of effects and moderators
    Stok, Marijn F. ; Vet, Emely de; Ridder, Denise T.D. de; Wit, John B.F. de - \ 2016
    Health Psychology Review 10 (2016)3. - ISSN 1743-7199 - p. 326 - 340.
    adolescents - food intake - implications for interventions - Social norms - systematic review - young adults

    This systematic review aims to assess the role that peer social norms play in shaping young people's food intake, focusing on the important questions of for whom and when peer social norms are related to how much young people eat. Thirty-three eligible studies were reviewed (17 correlational, 16 experimental). All but one correlational studies found significant associations between norms and food intake. All experimental studies found effects of norm manipulations on food intake, and some evidence was found of behavioural spillover effects of norms. Four moderators were distilled from our literature synthesis that stipulate for whom and when peer social norms are related to food intake: identification with the norm referent group and eating-related habit strength were found to moderate the effects of social norms on food intake; forceful injunctive norms were found not to be related to food intake; and the influence of norms seemed restricted to types of foods typically consumed in the presence of peers. The findings from this literature synthesis have important implications for research, and moderators are discussed in light of psychological theory. Where applicable, potential implications for the development of social norm-based interventions to improve young people's food intake are also highlighted.

    Small intestinal targets involved in food intake regulation : 'from nutrient to satiety signal'
    Ripken, D. - \ 2016
    Wageningen University. Promotor(en): Renger Witkamp; H.F.J. Hendriks. - Wageningen : Wageningen University - ISBN 9789462576438 - 180
    obesity - preventive nutrition - small intestine - ileum - duodenum - jejunum - satiety - appetite control - food intake - safflower oil - vagus nerve - casein - stevia rebaudiana - sucrose - macronutrients - serotonin - animal models - human feeding - obesitas - preventieve voeding - dunne darm - ileum - duodenum - jejunum - verzadigdheid - eetlustcontrole - voedselopname - saffloerolie - nervus vagus - caseïne - stevia rebaudiana - sucrose - macronutriënten - serotonine - diermodellen - humane voeding

    Background and aim: The worldwide increasing prevalence of overweight and obesity raises concerns for health. There is a clear need for preventive strategies, because current preventative interventions have proven to be unsuccessful in the long term. New strategies may be developed based on targets in the small intestine by activating satiety signals. The thesis aimed to investigate small intestinal targets contributing to food intake regulation. These targets included serotonin, the vagal nerve and the intestinal brake mechanism.

    Methods: The effects of ileal stimulation with safflower oil (lipid mixture), casein (protein), sucrose (carbohydrate) and rebaudioside A (non-caloric sweetener) on GLP-1 and PYY release were investigated by applying an porcine ex vivo intestinal segment model. The same model was also used to investigate if serotonin is involved in (non-)nutritional-induced GLP-1 and PYY release.

    The contribution to satiation of GLP-1 and CCK receptors at the vagal nerve, was studied by investigating the effects of GLP-1 and CCK receptor antagonists on ad libitum food intake in a pig model of subdiaphragmatic vagotomy.

    Two placebo controlled randomized crossover studies were performed in healthy volunteers to investigate the effects of small intestinal macronutrient delivery on ad libitum food intake and satiety signals. The first study compared the effects of duodenal, jejunal and ileal casein delivery on ad libitum food intake and satiety signals. The second study investigated if ileal delivery of all three macronutrients results in activation of satiety signals and reduction in ad libitum food intake. In addition, it was investigated if ileal delivery of native casein is efficiently digested and absorbed and does not result in adverse effects. In both studies the nutrients were delivered to the small intestine by inserting a nasointestinal feeding tube in healthy volunteers.

    Results: All macronutrients and rebaudioside A stimulated GLP-1 and PYY release from ileal tissue segments. Protein and fat stimulated serotonin release. Inhibiting the reuptake of serotonin resulted in enhanced nutrient induced GLP-1, PYY and CCK release. Serotonin stimulated GLP-1 release from enteroendocrine cells via a serotonin receptor mediated process.

    Results of the in vivo pig study showed that antagonism of the CCK receptor increased food intake in both vagotomized and sham operated pigs. Blocking the GLP-1 receptor did not affect food intake in both groups.

    The human studies showed that ileal protein delivery inhibited food intake and activated satiety signals as compared to duodenal or jejunal protein delivery. Also, ileal delivery of small quantities (51.7 kcal) of each macronutrient decreased food intake and activated satiety signals. In addition, it was shown that ileal delivery of native casein resulted in a time and concentration depended increase in plasma concentrations of amino acids and did not result in activation of immune responses nor in gastrointestinal complaints.

    Conclusions: The data presented in this thesis show that ileal delivery of all macronutrients results in activation of satiety signals and reduction of food intake. Stimulation of the ileum resulted in the strongest activation of satiety signals and inhibition of food intake compared to duodenal and jejunal stimulation. Besides direct nutrient-receptor interaction, the ileum senses (non-)nutritional stimuli via serotonin mediated processes resulting in GLP-1 release. In conclusion, these results demonstrate that targeting the ileum with small amounts of macronutrients is safe and has potential as a weight management strategy.

    Measurement errors in dietary assessment using duplicate portions as reference method
    Trijsburg, L.E. - \ 2016
    Wageningen University. Promotor(en): Pieter van 't Veer; Anouk Geelen; Jeanne de Vries. - Wageningen : Wageningen University - ISBN 9789462576421 - 128
    diet studies - nutritional assessment - questionnaires - reference standards - correction factors - validity - body mass index - regression analysis - food intake - food - protein - potassium - sodium - energy intake - methodology - dieetstudies - voedingstoestandbepaling - vragenlijsten - referentienormen - correctiefactoren - geldigheid - quetelet index - regressieanalyse - voedselopname - voedsel - eiwit - kalium - natrium - energieopname - methodologie

    Measurement errors in dietary assessment using duplicate portions as reference method

    Laura Trijsburg

    Background: As Food Frequency Questionnaires (FFQs) are subject to measurement error, associations between self-reported intake by FFQ and outcome measures should be corrected for measurement error with data from a reference method. Whether the correction is adequate depends on the characteristics of the reference method used in the validation study. The duplicate portion method (DP), compared to the often used 24h recall (24hR), seems a promising reference method as correlated errors between FFQ and DP, such as memory bias, errors in portion size estimations and food composition databases, are not expected.

    Aim: This thesis aimed to determine the validity of the DP compared to the 24hR as a reference method for FFQ validation. The second aim was to explore the validity of nutrient densities for DP, 24hR and FFQ. The third aim was to determine the factors associated with misreporting of energy, protein and potassium as estimated by DP, 24hR and FFQ.

    Methods: Within the DuPLO-study, a Dutch validation study which is part of the NQplus study, two DPs, two FFQs, two blood and urinary biomarkers and one to fifteen 24hRs (web-based and/or telephone-based) were collected in 198 subjects, within 1.5 years. Also, one or two doubly labelled water measurements were available for 69 participants. Multivariate measurement error models were used to assess proportional scaling bias, error correlations with the FFQ, validity coefficients and attenuation factors. Furthermore linear regression analysis was used to determine the association between misreporting and various factors.

    Results: The DP was less influenced by proportional scaling bias, had lower correlated errors with the FFQ and showed higher attenuation factors than the 24hR for potassium, sodium and protein. Also, the DP seemed a better reference method than the 24hR for the assessment of validity coefficients for the FFQ for various fatty acids. The attenuation factors for the FFQ, using either the DP or 24hR as reference method, agreed reasonably well. Furthermore, the DP showed, when using plasma fatty acids as reference, slightly better ranking of participants according to their intake of n-3 fatty acids (0.33) and the n‑3/LA ratio (0.34) than the 24hR (0.22 and 0.24, respectively). Less group level bias was observed for protein and sodium densities compared to their absolute intakes for FFQ, 24hR and DP, but not for potassium. Overall the validity coefficients and attenuation factors for DP, 24hR and FFQ did not improve for nutrient densities compared to absolute intakes, except for the attenuation factor for sodium density. Lastly, BMI proved to be the most consistent determinant associated with misreporting (group level bias) of energy, protein and potassium for DP, 24hR and FFQ. Men tended to underreport protein by the DP, FFQ and 24hR and persons of older age underreported potassium but only by the 24hR and FFQ. Other explorative determinants did not show a consistent association with misreporting of energy or nutrients by the different dietary assessment methods.

    Conclusion: With respect to error correlations and attenuation factors the DP performed slightly better than the 24hR as a reference method for validating FFQs in epidemiological research. Furthermore, the use of nutrient densities does not necessarily improve the validity of the dietary intake estimates from DP, 24hR and FFQ. Moreover, it was shown that BMI is an important determinant of misreporting of energy, protein and potassium for these three assessment methods.

    Hypothalamic regulation of food intake during cancer
    Dwarkasing, J.T. - \ 2015
    Wageningen University. Promotor(en): Renger Witkamp, co-promotor(en): Klaske van Norren; Mark Boekschoten. - Wageningen : Wageningen University - ISBN 9789462575486 - 147
    hypothalamische regulatie - anorexia - eetlustcontrole - voedselopname - cancer - chronische ziekten - diermodellen - muizen - serotonine - hypothalamic regulation - anorexia - appetite control - food intake - cancer - chronic diseases - animal models - mice - serotonin

    Appetite is often reduced in patients with chronic illness, including cancer.

    Cancer anorexia, loss of appetite, frequently co-exists with cachexia, and the combined clinical picture is known as anorexia-cachexia syndrome. In patients suffering from this syndrome, anorexia considerably contributes to the progression of cachexia, and strongly impinges on quality of life. Inflammatory processes in the hypothalamus are considered to play a crucial role in the development of disease-related anorexia.

    The main aim of this thesis was to further elucidate crucial processes involved in the pathogenesis of anorexia in cancer. To investigate mechanisms specifically involved in cancer anorexia, we used two tumour mouse models with opposing food intake behaviours: a C26-colon adenocarcinoma model with increased food intake and a Lewis lung carcinoma model with decreased food intake. In both models, tumour-induced cachexia (body wasting) was strongly present. The contrast in food intake behaviour between tumour-bearing (TB) mice in response to growth of the two different tumours was used to distinguish processes involved in cachexia from those specifically involved in anorexia.

    The hypothalamus was used for transcriptomic analysis (Affymetrix chips). We found expression of genes involved in serotonin signalling in the hypothalamus to be differentially regulated between the two tumour models. Furthermore, transcriptional activity of genes involved in serotonin signalling were inversely associated with food intake behaviour. Surprisingly, we also found a strong increase in gene expression of NPY and AgRP, potent orexigenic neuropeptides, in both models, meaning that their expression did not reflect food intake behaviour. However, NPY has also been described to regulate energy storage. Therefore, we hypothesized that this upregulation of NPY/AgRP corresponded to weight loss, which was severe in both tumour models.

    Using hypothalamic cell lines we further explored how serotonin might act on food intake regulatory pathways. We showed that serotonin was able to inhibit neuronal NPY secretion, while not affecting gene expression. Inflammatory markers IL-6 and TNFα were also measured in plasma and it was found that C26 TB mice had a lower inflammatory response than LL TB mice. These differences in inflammatory response could be implicated in the differences in feeding behaviour and serotonin signalling between C26 and LL TB mice. We therefore investigated the direct influence of inflammation on hypothalamic serotonin turnover and its contribution to the development of anorexia. To this end, different doses of TNF and IL-6 were administered by injection to healthy mice, inducing an acute inflammatory response. The injected cytokine doses were estimated from their corresponding plasma levels measured in tumour bearing (TB) mice. Also in this cytokine induced-anorexia model, where anorexia was exclusively induced by an inflammatory response, serotonin metabolism in the hypothalamus was affected. Both TNF and IL-6 increased hypothalamic serotonin turnover while also inducing anorectic behaviour. Furthermore, the effect of cytokines on increasing serotonin turnover was supported by in vitro experiments with hypothalamic neuronal cell lines.

    In conclusion, we identified hypothalamic serotonin signalling to play a major role in the decrease in food intake during cancer. Serotonin signalling itself is modulated by inflammatory mediators. Therefore, hypothalamic inflammation is an important trigger in the failure of hypothalamic food-intake regulation, probably by affecting serotonergic signalling, which acts as an upstream modulator of various orexigenic and anorexigenic systems.

    Children and vegetables: strategies to increase children’s liking and intake of vegetables
    Wild, V.W.T. de - \ 2015
    Wageningen University. Promotor(en): Kees de Graaf, co-promotor(en): Gerry Jager. - Wageningen : Wageningen University - ISBN 9789462574953 - 157
    kinderen - kindervoeding - groenten - voedselvoorkeuren - peuters en kleuters - voedselopname - borstvoeding - children - child nutrition - vegetables - food preferences - preschool children - food intake - breast feeding

    Background and aim

    Children’s vegetable intake is far below that recommended. Despite increased awareness of the importance of vegetable consumption for health, it remains challenging to improve children’s vegetable intake. Since food preferences are central to food intake, it is important to understand how they are shaped and which factors play a role in this. So far, research on the formation of vegetable preferences has focused mainly on infants and school age children but is not elaborately investigated in toddlers/pre-schoolers. Therefore the aim of this thesis was to investigate the underlying mechanisms and modifying factors that play a role in developing 2–5-year-old children’s acceptance of vegetables. Effects of different learning mechanisms, strategies, and modifying factors were explored by diverse studies, including four intervention studies in ecological settings (day-care centres and at home). In another study, we compared 10 intervention studies across Europe.


    We conducted a series of day-care and in-home interventions. Healthy toddlers and pre-school children participated in the studies. Vegetable liking was measured by relative preference, and consumption was measured by (ad libitum) intake. First, we studied the underlying mechanisms – flavour–nutrient learning, flavour–flavour learning, and repeated exposure – involved in the development toddlers’ food preferences in the short and long term. Novel products like green vegetable soups and vegetable crisps were used as test products, using within-subject designs. The soups differed in energy density to test flavour–nutrient learning (n=28), and the crisps were offered with different dips to test flavour–flavour learning (n=39). Next, we investigated the efficacy of other strategies like taste modification (n=103) and choice-offering (n=70) on 2–5-year-old children’s vegetable liking and intake, using between-subjects designs. Children consumed different vegetable products at home at dinnertime and therefore we used more familiar vegetables as test products. Finally, we combined the results of 10 intervention studies across Europe to explore the influence of individual child characteristics such as breastfeeding history and breastfeeding duration, age, gender, and food neophobia on 2– 6-year-old children’s (n=750) actual vegetable intake.


    We found a clear and persistent effect of repeatedly offering novel and/or disliked vegetables on 2–5-year-old children’s intake. Results for preferences were inconsistent across the studies. We found no strong evidence that strategies such as flavour–flavour learning, flavour–nutrient learning, diluting/hiding a vegetable were more effective in changing vegetable preference than repeated exposure alone. We observed a small positive effect of choice-offering; this strategy could possibly be effective in somewhat older children who already like vegetables, to increase their consumption volume. Factors like breastfeeding duration, vegetable liking, and food neophobia were important for children’s vegetable intake. Children who were more reluctant to try novel food had lower vegetable intake and were not responsive to strategies like repeated exposure, blending, mixing, or hiding vegetables. Longer breastfeeding duration was positively associated with a higher vegetable intake by 2–6-year-old children across three European countries. Gender and age had no influence.


    This thesis demonstrates that repeatedly offering a novel or disliked vegetable in a trusted positive environment is highly effective in promoting toddlers’ and pre-school children’s vegetable intake. Repeated exposure seems to be the way to teach young children to accept novel or disliked foods. Other strategies such as flavouring, adding energy, or taste modification may be helpful in promoting young children’s willingness to try and taste vegetables. Additional strategies such as choice-offering are needed to promote intake of already liked/familiar vegetables when children get older. Individual differences in child characteristics such as food neophobia, breastfeeding duration, and age play a role in shaping food preferences and therefore should get more attention in strategies to promote children’s vegetable acceptance. These results can be used by parents, caregivers, and public health organizations to stimulate children’s vegetable consumption to maintain a more balanced diet.

    'Mum, can I have Brussels sprouts again?’ : development of vegetable preferences during the first 2 years of life
    Barends, C. - \ 2015
    Wageningen University. Promotor(en): Kees de Graaf, co-promotor(en): Jeanne de Vries; Jos Mojet. - Wageningen : Wageningen University - ISBN 9789462573505 - 187
    voedselvoorkeuren - voedselopname - zuigelingen - spenen - eten - smaakgevoeligheid - groenten - food preferences - food intake - infants - weaning - eating - taste sensitivity - vegetables


    Background and aim

    Most children do not eat the recommended amount of vegetables. Their low vegetable intake may be attributed to their low preference for vegetables. Since the first years of life is a sensitive period in the development of taste preferences, and since taste preferences track over time, we started a longitudinal intervention study to investigate the effect of starting weaning with repeated exposure to vegetable purées on vegetable intake and liking during the first 2 years of life. The primary aim of this thesis was to investigate whether starting weaning with vegetables compared to weaning with fruit had an effect on the intake and liking of vegetables on the short and on the long term. The secondary aim was to investigate whether starting weaning with vegetables compared to weaning with fruit, influenced the preferences for sweet taste and daily intake of sugar.


    First, we conducted an intervention study (n = 101) that investigated the effects of repeated exposure to either vegetable purées (vegetable groups) or fruit purées (fruit groups) on infants’ acceptance of vegetable or fruit purées during the first 18 days of weaning. Intake of the purées and mothers’ rated liking were measured in the lab. From a subsample (n = 60), we also measured liking by analysing the infants’ facial expressions and behaviour after consuming green beans purée in the lab. In two follow-up studies, when the infants were 12 (n = 84) and 23 months of age (n = 81), the long-term effect of the intervention was measured on intake and mothers’ rated liking of the purées in the lab. Additionally, infants’ daily vegetable intake was assessed with 3-day food records at both follow-ups. At the second follow-up, also the influence of starting with vegetables or fruits on children’s preferences for sweet and salty tastes (n = 81), were measured with sweetened and salted water solution and by calculating their daily mono- and disaccharides intake from the 3-day food records. Additionally, a systematic review investigated the current status of knowledge about effective strategies to increase vegetable intake in children younger than 3 y.


    The studies showed that the group of children who were repeatedly exposed to vegetables increased their vegetable intake from 24 ± 28 g to 45 ± 44g (p < 0.001), while the children who were repeatedly exposed to fruit increased their fruit intake from 46 ± 40 g to 66 ± 42 g (p < 0.05) . Interestingly, the first vegetable intake in the fruit group, which was directly after the 18 days of exposure to fruit purées, was as low as the first vegetable intake of the children in the vegetable group at day 1. This indicates that the repeated exposure to fruit did not influence the children’s vegetable intake. These results were confirmed by the results of the facial expressions, showing a decrease in negative facial expressions after repeated exposure to green beans.

    At the follow-ups, when the infants were 12 and 23 months of age, no differences between the vegetable and fruit groups in green beans or apple purée were found in the lab. Daily intake of vegetables at 12 months of age, was 38% higher (p = 0.02) in the vegetable group (75 ± 43 g) than in the fruit group (54 ± 29 g). At 23 months of age, no significant difference in daily vegetable intake was found between the groups. Also the 23 month olds’ preference for sweet water solutions and their daily mono- and disaccharides intake did not differ between groups.

    Finally, the systematic review of literature showed that counselling of the parents on healthy eating and nutrition did have a positive long-term effect on their children’s’ vegetable intake, although the effect was relatively small. The review further showed that repeated exposure was the most studied and also the most effective strategy, since all studies reported an increase in intake after repeated exposure to a vegetable. Also exposure to a variety of vegetables showed to have a positive effect on the intake of a new vegetable.


    Weaning with repeated exposure to vegetables has a positive influence on vegetable intake until at least 12 months of age.

    Claiming satiety: consumer perception, interpretation & subsequent food
    Bilman, E.M. - \ 2014
    Wageningen University. Promotor(en): Hans van Trijp, co-promotor(en): Ellen van Kleef. - Wageningen : Wageningen University - ISBN 9789461738660 - 172
    verzadigdheid - voedselopname - voedselconsumptie - voedselvoorkeuren - voedselverpakking - consumenteninformatie - consumenten - consumentengedrag - satiety - food intake - food consumption - food preferences - food packaging - consumer information - consumers - consumer behaviour

    For many people, food intake management is a challenging process, as food is always in abundance and the appetite control system is challenged and potentially overpowered by habits, routines and cues in the external environment. The present thesis focuses on satiation and satiety expectations and inferences as a guide for food intake, both within and across consumption episodes. More specifically, the role of physiological cues, claims on food packages and packaging design in the development of satiation/ satiety expectations and their effect on food intake is studied. This thesis takes as a starting point that feedback from previous consumption experiences is important for the development of satiety and satiation expectations. In addition, it is expected that satiation and satiety expectations also can be inferred ‘on the spot’, either explicitly (as from satiety claims), but potential also implicitly and more intuitively (as from packaging design and other factors in the eating context).

    Relying on satiety cues in food consumption : studies on the role of social context, appearance focus, and mindfulness
    Veer, E. van de - \ 2013
    Wageningen University. Promotor(en): Hans van Trijp, co-promotor(en): Erica van Herpen. - S.l. : s.n. - ISBN 9789461736895 - 240
    voedselconsumptie - sociale psychologie - consumenten - voedselopname - verzadigdheid - eetlust - eetlustcontrole - honger - fysiologie - bewustzijn (consciousness) - eten - maaltijden - snacks - food consumption - social psychology - consumers - food intake - satiety - appetite - appetite control - hunger - physiology - consciousness - eating - meals - snacks
    Consumers eat at various sequential occasions throughout the day. The current thesis addresses the question of how one consumption episode can affect the amount of consumption at a subsequent episode. The thesis focuses specifically on how the social context during a consumption episode affects subsequent consumption, and on when consumers rely on hunger and satiety cues in sequential consumption episodes.
    Do distant foods decrease intake? The effect of food accessibility on consumption
    Maas, Josje ; Ridder, Denise T.D. de; Vet, Emely de; Wit, John B.F. de - \ 2012
    Psychology and Health 27 (2012)SUPPL. 2. - ISSN 0887-0446 - p. 59 - 73.
    distance - food accessibility - food intake - obesogenic environment

    Objective: Two studies examined the hypothesis that making snacks less accessible contributes to the regulation of food intake. Study 1 examined whether decreasing the accessibility of snacks reduces probability and amount of snack intake. The aim of Study 2 was to replicate the results and explore the underlying mechanism in terms of perceived effort to obtain the snack and perceived salience of the snack.Methods: In Study 1 (N = 77) and Study 2 (N = 54) distance to a bowl of snacks was randomly varied at 20, 70 or 140 cm in an experimental between-subjects design. Main outcome measures were the number of people who ate any snacks (probability of snack intake), the amount of snacks consumed and risk of compensatory behaviour as measured by food craving. In Study 2, self-report ratings of salience and effort were examined to explore potential underlying mechanisms.Results: Study 1 showed lower probability and amount of intake in either of more distant conditions (70 and 140 cm) compared to the proximal condition (20 cm), with no unintended effects in terms of increased craving. Study 2 replicated the results of Study 1 and showed that distance affected perceived effort but not salience.Conclusions: Making snacks less accessible by putting them further away is a potentially effective strategy to decrease snack intake, without risk of compensatory behaviour.

    The role of oral exposure to taste on meal termination
    Bolhuis, D.P. - \ 2012
    Wageningen University. Promotor(en): Kees de Graaf; Catriona Lakemond; Rene de Wijk. - [S.l.] : s.n. - ISBN 9789461733870 - 164
    smaak - voedselopname - eetlust - eetsnelheden - verzadigdheid - mond - overeten - taste - food intake - appetite - eating rates - satiety - mouth - overeating

    Background and aim
    The rise in obesity over the last decades is considered to be related to changes in the food environment. Our current diet exists of foods that facilitate fast intake of energy and minimal oral processing. Various studies showed that higher eating rate leads to higher food intake, and therefore promote energy overconsumption. When consuming at a high eating rate, the food spends less time in the oral cavity, resulting in less sensory exposure per gram food. The exposure to the taste of the food in the oral cavity is potentially important in controlling food intake. The studies in this thesis investigated the principle mechanisms through which orosensory exposure affects satiation. The factors that were studied were taste intensity, oral residence duration and bite size. The impact of these factors and their relative contributions to satiation will provide tools for designing new foods to prevent overconsumption.
    We conducted five studies. The subjects that participated in the studies were healthy young normal weight adults. Satiation was measured by ad libitum intake and subjective ratings of hunger and fullness. Tomato soup was used as test product in all studies. We started by investigating the effect of taste intensity on ad libitum intake (n=48). Salt was used to vary the taste intensity in soup. We selected two salt concentrations for low-salt and high-salt soup that were similar in pleasantness on an individual basis. In the next study, salt taste intensity in soup was investigated again, but this time we changed the state of hunger (a preload was offered) and the meal composition (subjects were served a second course after the soup) (n=43). In the third study, the impact of taste intensity versus the duration of orosensory exposure (manipulated by changing the bite size) on satiation was investigated, by using peristaltic pumps to control the bites (n=55). The fourth study focussed on the underlying mechanisms of bite size on food intake (n=56). Therefore, separate effects of oral residence duration per gram food and number of bites per gram food on ad libitum intake were assessed. Finally, we investigated if bite size affects the perceived food intake. Subjects estimated the amount consumed after intake with small or large bites, in both focussed and a distracted states (n=53). In addition, effects of distraction on bite size were investigated.
    Taste intensity did not affect ad libitum intake when the soup was presented as single lunch-item in a hungry state. However, higher taste intensity reduced ad libitum intake by ~8%, when the soup was presented after a preload or as a starter followed by a second meal. Smaller bite sizes decreased ad libitum intake by ~25% and did not interact with taste intensity. That smaller bites are more satiating than larger bites was confirmed by hunger and fullness ratings. Hunger decreased faster per consumed gram food when consuming with small bites compared to large bites. A similar effect was found for the increase in fullness. Ad libitum intake was separately reduced by longer oral residence duration and higher number of bites per gram food, there was no interaction between the two variables. Time-intensity measurements showed that both higher number of bites and longer oral residence duration increase the total magnitude of orosensory exposure to the taste of the food. Consumption with large bites resulted in underestimations of the amount consumed, whereas consumption with small bites did not. Distraction increased ad libitum intake. Distraction led to a higher number of bites over the meal but did not affect bite size.
    This thesis demonstrates that consuming foods with smaller bite sizes, longer oral residence durations and higher taste intensities lowers food intake. These effects are possibly explained through their enhancement of the orosensory exposure to the taste of the foods. Consumption with large bites leads to underestimation of the amount that is consumed. An underestimation of the amount consumed is a risk factor for overconsumption. These results could be used by the food industry to enhance the satiating capacity of foods in order to prevent overconsumption and decrease the prevalence of obesity.

    A European tool for usual intake distribution estimation in relation to data collection by EFSA
    Klaveren, J.D. van; Goedhart, P.W. ; Wapperom, D. ; Voet, H. van der - \ 2012
    Parma : EFSA (Supporting Publications 2012: EN-300) - 42
    voedselopname - populaties - variantie - food intake - populations - variance
    The present document has been produced and adopted by the bodies identified above as author(s). In accordance with Article 36 of Regulation (EC) No 178/2002, this task has been carried out exclusively by the author(s) in the context of a grant agreement between the European Food Safety Authority and the author(s). The present document is published complying with the transparency principle to which the Authority is subject. It cannot be considered as an output adopted by the Authority. The European Food Safety Authority reserves its rights, view and position as regards the issues addressed and the conclusions reached in the present document, without prejudice to the rights of the authors.
    Effect of variations in concentration of algae and silt on filtration and growth of the razor clam (Ensis directus, Conrad)
    Kamermans, P. ; Dedert, M. - \ 2012
    Yerseke : IMARES (Report / IMARES Wageningen UR C017/11) - 69
    ensis - voedselopname - algen - silt - groeitempo - filtratie - kustwateren - noordzee - ensis - food intake - algae - silt - growth rate - filtration - coastal water - north sea
    As part of a collaboration between the research programme Knowledge for Primary Processes Silt of Rijkswaterstaat Waterdienst NWOB (department of Infrastructure and Environment, MinIenM, RWS) and the Monitoring programme Sand extraction RWS and the LaMER Foundation, RWS-WD NWOB requested further research into the relation between food availability and Ensis production. The aim is to better understand the effect of different algae and silt concentrations on filtration and growth rates and improve prediction of effects. Laboratory experiments were carried out with Ensis directus to estimate food intake rate and growth rate as a function of food density and clam size. Growth experiments carried out in 2010 showed that the species seems to be very fragile as shown by the low growth rates and high mortality rates. Improvements designed to optimize the experimental conditions, survival rates and experimental set-up were implemented in 2011. These were: experimental animals were collected with a box corer instead of a suction dredge; animals were kept in cylinders without sediment, but their shells were closed with elastic bands during the filtration experiments; circular tanks were used with increased water movement; the diet during the growth experiment consisted of two species of algae. Two food levels were tested: low food availability (6.5 μg Chla/l) and high food availability (16.5 μg Chla/l) at four silt concentrations (0, 50, 150 and 300 mg/l). Only the highest silt concentration induced a reduction in filtration rate. Food level did not influence filtration rate of Ensis, but intake rate is higher at the high food concentration, because more algal cells are present in a certain volume of water. Longterm (10 weeks) exposure to silt concentrations of 300 mg/l showed significantly higher growth than the 150 mg/l treatment indicating that exposure to a high silt concentration did not induce a reduction in growth. Long-term (10 weeks) exposure to a food level of 6.5 ug chla per liter reduced shell growth of Ensis compared to growth at 16.5 ug chla per liter. The filtration and growth rate results are used in a modelling study on growth and condition of Ensis during sand extraction 2013-2017 (Schellekens, in prep). The conclusions of this study give more notion of the effects of sand extraction in the coastal zone of the North Sea on the viability of the razor clam Ensis directus. Sand extraction always goes together with an increase of silt concentration in the water column. This reduces the light conditions for algal growth which reduces the food availability for Ensis. The laboratory experiments suggest that Ensis is more sensitive to a reduction in algal concentration than to an increase in silt concentration. Some discussion is given on the implications of the results for the management of sand extraction.
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