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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    Dietary protein intake and kidney function decline after myocardial infarction: the Alpha Omega Cohort
    Esmeijer, Kevin ; Geleijnse, Johanna M. ; Fijter, Johan W. de; Kromhout, Daan ; Hoogeveen, Ellen K. - \ 2020
    Nephrology Dialysis Transplantation 35 (2020)1. - ISSN 0931-0509 - p. 106 - 115.
    diet - kidney function decline - myocardial infarction - protein intake

    BACKGROUND: Post-myocardial infarction (MI) patients have a doubled rate of kidney function decline compared with the general population. We investigated the extent to which high intake of total, animal and plant protein are risk factors for accelerated kidney function decline in older stable post-MI patients. METHODS: We analysed 2255 post-MI patients (aged 60-80 years, 80% men) of the Alpha Omega Cohort. Dietary data were collected with a biomarker-validated 203-item food frequency questionnaire. At baseline and 41 months, we estimated glomerular filtration rate based on the Chronic Kidney Disease Epidemiology Collaboration equations for serum cystatin C [estimated glomerular filtration rate (eGFRcysC)] alone and both creatinine and cystatin C (eGFRcr-cysC). RESULTS: Mean [standard deviation (SD)] baseline eGFRcysC and eGFRcr-cysC were 82 (20) and 79 (19) mL/min/1.73 m2. Of all patients, 16% were current smokers and 19% had diabetes. Mean (SD) total protein intake was 71 (19) g/day, of which two-thirds was animal and one-third plant protein. After multivariable adjustment, including age, sex, total energy intake, smoking, diabetes, systolic blood pressure, renin-angiotensin system blocking drugs and fat intake, each incremental total daily protein intake of 0.1 g/kg ideal body weight was associated with an additional annual eGFRcysC decline of -0.12 (95% confidence interval -0.19 to -0.04) mL/min/1.73 m2, and was similar for animal and plant protein. Patients with a daily total protein intake of ≥1.20 compared with <0.80 g/kg ideal body weight had a 2-fold faster annual eGFRcysC decline of -1.60 versus -0.84 mL/min/1.73 m2. Taking eGFRcr-cysC as outcome showed similar results. Strong linear associations were confirmed by restricted cubic spline analyses. CONCLUSION: A higher protein intake was significantly associated with a more rapid kidney function decline in post-MI patients.

    Dose, timing, and source of protein intake of young people with spastic cerebral palsy
    Anker–van der Wel, Ieke ; Smorenburg, Ana R.P. ; Roos, Nicole M. de; Verschuren, Olaf - \ 2020
    Disability & Rehabilitation 42 (2020)15. - ISSN 0963-8288 - p. 2192 - 2197.
    Cerebral palsy - children - disability - muscle - nutrition - protein intake

    Purpose: Since the dose, timing and source of dietary protein intake are important for muscle growth and development, the aim of this study was to examine the dose, timing and source of protein intake of young people with cerebral palsy. Materials and methods: Dietary intake was assessed in 19 children with spastic cerebral palsy (Gross Motor Function Classification System levels I–V; Eating and Drinking Classification System levels I–V; 10 males, 9 females; mean [SD] age 11 years 2 months [3 years 3 months]) using a 3-day food diary. The data were analyzed for three age categories (4–8, 9–13, and 14–17 years). Results: Average 3-day protein intake (62.1 g [27.9 g]) was within the recommended boundaries with a minimum of 1.0 g/kg body weight/day and a maximum of 4.1 g/kg body weight/day. However, dinner was the only mealtime that provided at least 25 g of protein, which is needed for optimal muscle maintenance. The main food groups that contributed to protein intake were ‘milk and milk products’, ‘meat, meat products and poultry’, and ‘bread’. Conclusions: These observations suggest timing of protein intake can be improved with higher intakes during breakfast and lunch to better support skeletal muscle growth and development.IMPLICATIONS FOR REHABILITATION Recent studies have shown that smaller muscles and early atrophy are already present at young age in individuals with cerebral palsy. Besides physical training, adequate protein intake (with optimal dose, timing and source of protein) may be a key factor in the prevention and treatment of loss of muscle mass in children with cerebral palsy. In a relatively small sample this study shows that overall protein intake (dose) was in line with recommendations and also that the source of the protein seemed sufficient to contain all essential amino acids. Improvement of the timing of protein intake throughout the day, with higher intakes during breakfast and lunch, seems important to better support skeletal muscle growth and development.

    Associations among High-Quality Protein and Energy Intake, Serum Transthyretin, Serum Amino Acids and Linear Growth of Children in Ethiopia
    Tessema, Masresha ; Gunaratna, Nilupa S. ; Brouwer, Inge D. ; Donato, Katherine ; Cohen, Jessica L. ; McConnell, Margaret ; Belachew, Tefera ; Belayneh, Demissie ; Groote, Hugo De - \ 2018
    Nutrients 10 (2018)11. - ISSN 2072-6643
    energy intake - Ethiopia - inflammation - linear growth - protein intake - protein quality - serum IGF-1 - serum transthyretin

    Limited evidence is available on the associations of high-quality protein and energy intake, serum transthyretin (TTR), serum amino acids and serum insulin-like growth factor-1 (IGF-1) with linear growth of young children. Data collected during the baseline of a randomized control trial involving rural Ethiopian children aged 6⁻35 months (n = 873) were analyzed to evaluate the associations among height/length-for-age z-scores, dietary intakes, and these biomarkers (i.e., serum level of TTR, IGF-1, tryptophan and lysine, and inflammation). The prevalence of stunting was higher for children >23 months (38%) than ≤23 months (25%). The prevalence of inflammation was 35% and of intestinal parasites 48%. Three-quarters of the children were energy deficient, and stunted children had lower daily energy intake that non-stunted children (p < 0.05). Intakes of tryptophan, protein, and energy, and serum levels of tryptophan and IGF-1 were positively correlated with the linear growth of children. Controlling for inflammation, intestinal parasites, and sociodemographic characteristics, daily tryptophan (b = 0.01, p = 0.001), protein (b = 0.01, p = 0.01) and energy (b = 0.0003, p = 0.04) intakes and serum TTR (b = 2.58, p = 0.04) and IGF-1 (b = 0.01, p = 0.003) were positively associated with linear growth of children. Linear growth failure in Ethiopian children is likely associated with low quality protein intake and inadequate energy intake. Nutrition programs that emphasize improved protein quantity and quality and energy intake may enhance the linear growth of young children and need to be further investigated in longitudinal and interventional studies.

    Nutritional interventions to preserve skeletal muscle mass
    Backx, Evelien M.P. - \ 2016
    Wageningen University. Promotor(en): Lisette de Groot; L.J.C. van Loon. - Wageningen : Wageningen University - ISBN 9789462579149 - 158
    musculoskeletal system - nutritional intervention - skeletal muscle - vitamin d - creatine - leucine - nandrolone - protein intake - young adults - elderly - overweight - athletes - preservation - skeletspierstelsel - maatregel op voedingsgebied - skeletspier - vitamine d - creatine - leucine - nandrolon - eiwitinname - jongvolwassenen - ouderen - overgewicht - atleten - behoud

    Muscle mass is the main predictor for muscle strength and physical function. The amount of muscle mass can decline rapidly during periods of reduced physical activity or during periods of energy intake restriction. For athletes, it is important to maintain muscle mass, since the loss of muscle is associated with decreased muscle strength, decreased physical performance and a longer recovery period. In the older and more clinically compromised populations, the consequences of muscle loss can substantially impact metabolic health, physical functioning, quality of life and mortality rates. In this thesis, the effects of different nutritional interventions on the preservation of muscle mass are being evaluated.

    Vitamin D deficiency (serum 25-hydroxyvitamin D or 25(OH)D) has been associated with increased muscle loss and reduced muscle strength. In chapter 2, we identified seasonal changes in 25(OH)D concentration in elite athletes. We observed that 25(OH)D concentrations were highest at the end of summer (113±26 nmol/L), and lowest at the end of winter (78±30 nmol/L). Athletes that had a sufficient 25(OH)D concentration (>75 nmol/L) at the start of the study, still had a high risk (20%) of being deficient (<50 nmol/L) in late winter. Thus, a sufficient 25(OH)D concentration in summer does not guarantee a sufficient status in winter. In chapter 3, we assessed 25(OH)D concentrations in 128 highly-trained athletes and found that 70% had a deficient or insufficient 25(OH)D concentration at the end of the winter season. Supplementation with 2200 IU/d vitamin D resulted in a sufficient 25(OH)D concentration in 80% of the athletes after 12 months and was therefore a better dosage to improve 25(OH)D concentration than 400 or 1100 IU/d.

    In the following chapters, we assessed the effects of creatine supplementation (chapter 4), leucine supplementation (chapter 5) and nandrolone administration (chapter 6) on the preservation of muscle mass during a short period of muscle disuse. For all of these compounds there is prior evidence for their efficacy in augmenting muscle mass and strength gains in combination with resistance-type exercise training and all have been suggested to attenuate the loss of muscle mass during a period of muscle disuse. During 7 days of single-leg immobilization, muscle mass decreased by ~6% and muscle strength decreased by ~8%. Surprisingly, none of the tested compounds attenuated the loss of muscle mass during 7 days of single-leg immobilization in healthy, young men.

    In chapter 7, we performed a fully controlled dietary intervention to assess the impact of a high protein intake on the preservation of lean body mass during 12 weeks of energy intake restriction. Sixty-one overweight and obese men and women were randomly assigned to either a high protein diet (1.7 g/kg/d) or a normal protein diet (0.9 g/kg/d) during 12 weeks of 25% energy intake restriction. During the dietary intervention, subjects lost 9±3 kg body weight with a concomitant 2±2 kg decline in lean body mass with no differences between the two intervention groups. Thus, increasing protein intake above habitual intake levels (0.9 g/kg/d) did not preserve lean body mass during a period of energy intake restriction.

    Finally, in chapter 8 we reflected on the main findings described in this thesis. In this chapter, we point out that the populations studied were all healthy and well-nourished. We conclude that in these populations, additional creatine, leucine and protein beyond habitual intakes did not preserve muscle mass. Older and/or malnourished individuals might be more responsive to these nutritional interventions. Future research could also focus on the combined effects of two or more nutritional compounds during disuse that are known to affect different mechanisms. Moreover, we speculate that the tested nutritional compounds could be effective in accelerating the regain of muscle mass and strength after a period of muscle loss. However, it should be noted that muscle loss during disuse occurs at a rate that is several-fold greater than muscle (re)gain during resistance type exercise training. Therefore, it is imperative that we continue our endeavors to identify nutritional or pharmaceutical compounds or exercise mimetics that may help to prevent or attenuate disuse atrophy.

    Cater with Care : impact of protein-enriched foods and drinks for elderly people
    Beelen, J. - \ 2016
    Wageningen University. Promotor(en): Lisette de Groot; Frans Kok, co-promotor(en): Nicole de Roos. - Wageningen : Wageningen University - ISBN 9789462578814 - 142
    undernutrition - hospital catering - hospitals - protein - elderly - protein intake - food - beverages - diet studies - dietetics - dietitians - randomized controlled trials - ondervoeding - ziekenhuiscatering - ziekenhuizen - eiwit - ouderen - eiwitinname - voedsel - dranken - dieetstudies - diëtetiek - diëtisten - gestuurd experiment met verloting

    Protein undernutrition is a major health concern for older adults, especially for those who are ill. There is growing consensus for a protein intake target of 1.2 - 1.5 gram per kg bodyweight per day (g/kg/d) for these older adults. However, this target is not reached by the majority of older adults. Therefore, more effective and novel strategies to increase protein intake are warranted, including the use of protein-enriched foods and drinks. This thesis evaluated the impact of the developed protein-enriched foods and drinks on protein intake and physical performance among older adults. The studies in this thesis were done as part of the Cater with Care® project; a collaboration between the university, care organizations, and partners from the food industry. The industrial partners developed the products, focusing each on different product categories: Carezzo Nutrition developed bread, pastry, and fresh juices and soups; The Kraft Heinz Company focused on long shelf-life and convenience foods; and the Veal Promotion Foundation produced veal meat.

    To fit the products to the needs of the target group, interviews with undernourished older adults (at home or hospitalized) and with dietitians were conducted (chapter 2). These interviews showed that undernutrition awareness is low among older adults. To treat undernutrition by changing their eating habits, older adults need to be aware of their health problem, they need to be willing to change, and they need to be able to understand and implement the dietitian’s advices. This process takes time while undernutrition should be treated immediately. For immediate treatment, enriched products could be used, without first creating awareness. According to the interviewees, enriched products should fit within older adults’ eating habits, and have small portion sizes.

    To gain insights in food choices of hospitalized older adults (65 years and older) an observational study was conducted. In this study, energy and protein intakes of 80 hospitalized older patients at low and high risk of undernutrition were assessed (chapter 3). Patients who received an energy- and protein-rich menu, because of their risk of undernutrition, were better able to reach the protein and energy targets than patients with a low risk of undernutrition receiving a standard menu. Based on these results we proposed that all hospitalized older adults – both at low and high risk of undernutrition – should receive an energy- and protein-rich menu.

    Subsequently, a pilot study was done in a care home and a rehabilitation center with the aim to explore the potential of the developed protein-enriched products to increase protein intake (chapter 4). Participants did not compensate their consumption of regular protein-rich foods (e.g. dairy, cheese) upon the introduction of protein-enriched foods and drinks. The 22 institutionalized elderly (mean age 83 years) consumed 12 gram protein per day more than they did before the intervention. Consequently, more people met the protein target of 1.2 g/kg/d than before the intervention. We concluded that protein-enriched products enabled institutionalized elderly to reach protein intake targets. Furthermore, we gained valuable feedback to improve the assortment of protein-enriched products for the effectiveness study.

    In the final study, effects of the protein-enriched products on protein intake and physical performance were studied in a randomized controlled trial during hospitalization and subsequent recovery at home. During the hospital period in which 147 older patients participated, patients that received protein-enriched products increased their protein intake compared to the control group that already received a protein-rich hospital menu (chapter 5). As a result, 79% of the intervention group reached a protein intake of 1.2 g/kg/d, compared to 48% of the control group. Finally, effects of the protein-enriched products were tested at home, for a longer period (chapter 6). Half of the hospital phase participants (n = 75) continued the intervention at home for 12 weeks. The protein-enriched products were successfully implemented in the daily menu of the older adults: the intervention group had a higher average protein intake (1.5 ± 0.6 g/kg/d) than the control group (1.0 ± 0.4 g/kg/d) during the 12-week intervention period. Seventy-two percent of the intervention group reached a protein intake of 1.2 g/kg/d during the 12-week intervention, compared to 31% of the control group. Protein intake of the intervention group was mainly increased by the following protein-enriched products: bread, dairy drinks, dairy desserts, soups, and fruit juices. However, despite the successful improvement of protein intake, we found no added value on physical performance in the first 6 months after hospitalization.

    It was concluded that with the protein-enriched familiar foods and drinks, we have a feasible, acceptable, and appetizing long-term strategy to increase protein intake of older adults in various settings. We envisage a beneficial role of these protein-enriched products in combination with physical activity in older adults with lower protein intakes.

    Dietary proteins and aspects of the metabolic syndrome : evidence from observational studies and short-term interventions
    Nielen, M. van - \ 2015
    Wageningen University. Promotor(en): Edith Feskens, co-promotor(en): Marco Mensink. - Wageningen : Wageningen University - ISBN 9789462574793 - 131
    metabool syndroom - diabetes mellitus - stofwisselingsstoornissen - diabetes type 2 - hart- en vaatziekten - sojaeiwit - arginine - eiwitinname - ziekte-incidentie - ontsteking - cohortstudies - metabolic syndrome - diabetes mellitus - metabolic disorders - type 2 diabetes - cardiovascular diseases - soya protein - arginine - protein intake - disease incidence - inflammation - cohort studies

    Background Type 2 diabetes (T2D) and cardiovascular diseases (CVD) are important causes of morbidity and mortality worldwide. The metabolic syndrome (MetS) identifies people at elevated risk of T2D and CVD by its mutual risk factors, such as abdominal obesity, atherogenic dyslipidemia, raised blood pressure and impaired glucose tolerance. Improvements in individual aspects of MetS could be risk-reducing for T2D and CVD and could thus be clinically relevant. Besides by using drug therapy, this can be achieved by lifestyle changes, such as weight loss, increasing physical activity and changes in dietary composition. In addition to general dietary recommendations, such as diets rich in fiber, fruits and vegetables and low in refined grains and saturated fatty acids, increasing dietary protein and soy intake seem promising approaches to prevent MetS. Short-term trials report positive effects of dietary protein intake on weight loss and weight maintenance after weight loss. The postprandial and short-term effect of protein and soy consumption on insulin resistance, glucose homeostasis, and other aspects of MetS are not frequently studied in humans in energy balance. Also, the long-term association between dietary protein intake and T2D incidence is uncertain, it even seemed risk-increasing in prior research.

    Objectives We evaluated the impact of dietary protein intake on T2D incidence, aspects of MetS and other cardio-metabolic risk factors, by observational studies (long-term) and interventions (short-term). We studied not only total protein intake, but also specific protein types, more specifically soy protein and arginine-rich protein. We explored the long-term association between total, animal, and plant protein intake and the incidence of T2D. We further investigated the effects of a 4-week strictly controlled weight-maintaining moderate-high-protein diet rich in soy on insulin sensitivity and other cardio-metabolic risk factors. Next, we investigated if inflammatory markers were also changed as a possible pathway through which dietary protein affects cardio-metabolic risk factors. Lastly, we examined whether protein, and more specific arginine-rich protein, added to a high fat meal improved postprandial metabolism and cardiovascular risk factors.

    Methods The association between dietary protein intake and T2D incidence was studied in the EPIC-InterAct case-cohort study (nincident cases= 12,403; nsubcohort=16,154).

    In a randomized crossover trial of 2 4-week periods diets with a moderate-high-protein content, i.e. 22 energy percent (En%) protein, 27En% fat, and 50En% carbohydrate, were studied (n=15). In a diet with protein from mixed sources (HPmix) we partly replaced meat products with soy products (HPsoy) to investigate the effect of soy protein intake on insulin resistance, glucose homeostasis, and other aspects of MetS.

    A high-fat challenge test was used to study postprandial metabolic markers, inflammatory markers and arterial stiffness (n=18). We compared the postprandial response after a high-fat liquid control meal (95g fat) without protein with meals with 30g added protein.

    Results Intake of total protein (per 10 g: HR 1.06 [95% CI 1.02–1.09], Ptrend < 0.001) and animal protein (per 10 g: HR 1.05 [95% CI 1.02–1.08], Ptrend < 0.001) was associated with higher incidence of T2D, after adjustment for main confounders including other dietary factors.

    Partly replacing meat with soy in a moderate-high-protein diet resulted in greater insulin sensitivity (FSIGT: SI:34 ± 29 vs. 22 ± 17 (mU/L)-1min-1, P=0.048; disposition index:4974 ± 2543 vs. 2899 ± 1878, P=0.038). After HPsoy total cholesterol was 4% lower than after HPmix (4.9 ± 0.7 vs. 5.1 ± 0.6 mmol/L, P=0.001) and LDL cholesterol was 9% lower (2.9 ± 0.7 vs. 3.2 ± 0.6 mmol/L, P=0.004). The summary score for inflammation was lower after HPsoy compared with HPmix (ɀ-score: -0.2 ± 0.3 vs. -0.1 ± 0.2, P=0.04), after excluding participants with CRP>6mg/L and extreme outliers. Individual inflammatory markers were not significantly different.

    Adding protein to a high-fat meal increased the postprandial insulin response. No differences between arginine-rich and protein low in arginine on postprandial responses were seen. Intact proteins and hydrolysates resulted in similar responses.

    Conclusion High total and animal protein intake was associated with modestly elevated T2D incidence in a large cohort of European adults. In contrast, a moderate-high-protein diet for 4 weeks improved many cardio-metabolic risk factors. Partly replacing meat with soy in this moderate-high-protein diet had clear advantages regarding insulin sensitivity and total and LDL cholesterol, and it improved the overall inflammatory state, although not showing clear benefits at individual inflammation markers. We hypothesized to see an origin of these short-term health effects in postprandial properties of arginine-rich protein. However, arginine-rich protein was not superior to a protein low in arginine added to a high-fat meal, regarding postprandial excursions in glucose, insulin, lipids and inflammatory markers.

    In view of the rapidly increasing prevalence of MetS and T2D, limiting iso-energetic diets high in dietary proteins, particularly from animal sources, should be considered as on the long-term protein intake seems to increase T2D and CVD risk. However, at the short-term partly replacing meat with soy in a moderate high-protein diet could be preventive for several aspects of MetS, such as improvements in insulin sensitivity, total and LDL cholesterol and possibly a reduced inflammatory state.

    Effect of dietary protein on lipid and glucose metabolism: implications for metabolic health
    Rietman, A. - \ 2015
    Wageningen University. Promotor(en): Frans Kok; D. Tomé, co-promotor(en): Marco Mensink. - Wageningen : Wageningen University - ISBN 9789462573482 - 160
    voeding en gezondheid - stofwisselingsstoornissen - eiwitinname - dieet - metabolisme - lipiden - glucose - macronutriënten - nutrition and health - metabolic disorders - protein intake - diet - metabolism - lipids - glucose - macronutrients

    Abstract

    Background: Diet is an important factor in the development of the Metabolic Syndrome (Mets) and type 2 Diabetes Mellitus. Accumulation of intra hepatic lipid (IHL) can result in non-alcoholic fatty liver disease (NAFLD), which is sometimes considered the hepatic manifestation of Mets. Manipulation of the dietary macronutrient composition – altering either fat or simple carbohydrates – has the potential to change lipid storage in the liver. Protein also has this ability, however human data is scarce. Moreover, high dietary protein intake is linked with an increased type 2 Diabetes risk. Therefore, it is essential to study the metabolic consequences of changes in macronutrient composition focussing on altering dietary protein quantity.

    Objective: In this thesis the effects of dietary protein on metabolic health focusing on lipid and glucose metabolism were investigated in both observational studies as well as in a human dietary intervention trial.

    Methods: In an observational study (n=1283), Fatty Liver Index (FLI) was calculated and related to macronutrient consumption from dietary assessment data. In a controlled dietary intervention, participants (n=27) were assigned to either a control-diet for 4 weeks, or a high-fat, hypercaloric diet, with either a high-protein or a normal-protein content for two weeks, and vice versa. Measurements of IHL (1H-MRS) and blood plasma glucose and lipid concentrations were performed, both in the fasting state and following a meal.

    Results: In the observational study, the prevalence of fatty liver as indicated by an FLI>60, was 22.0%. Compared to persons with a normal FLI score of <30, protein intake was positively related with high FLI score >60 (OR: 1.26 per 1 en%, 95%CI 1.16-1.37). This was in particular the case for protein intake from animal sources. In the dietary intervention study, the high-protein diet compared to the normal-protein diet resulted in lower IHL and plasma TG concentrations (IHL: 0.35 ± 0.04 % vs. 0.51 ± 0.08 %; p=0.08; TG: 0.65 ± 0.03 vs. 0.77 ± 0.05 mmol/L; p=0.07). Furthermore, after the meal challenge the free fatty acids (FFA) response was significant different between all three intervention diets (p=0.03). Moreover, the postprandial glucose response was significantly lower after adaptation to NP compared with HP (p=0.03), without differences in the postprandial insulin responses (p=0.37).

    Conclusions: From data of the intervention study and observational studies reported in this thesis, it can be concluded that dietary protein intake is associated with alterations in metabolic profile, with both favourable and potential unfavorable health outcomes. On the short term increasing dietary protein in healthy subjects improved lipid metabolism, as seen by lower TG and IHL levels, but not glucose metabolism. On the long term, however, a high-protein intake was related to a fatty liver, and associated to insulin resistance.

    Dietary protein and blood pressure : epidemiological studies
    Altorf-van der Kuil, W. - \ 2012
    Wageningen University. Promotor(en): Pieter van 't Veer, co-promotor(en): Marianne Geleijnse; Marielle Engberink. - S.l. : s.n. - ISBN 9789461733078 - 203
    voedingseiwit - bloeddruk - epidemiologische onderzoeken - eiwitinname - dieet - dietary protein - blood pressure - epidemiological surveys - protein intake - diet


    Background
    Elevated blood pressure is a major risk factor for cardiovascular diseases. Diet and lifestyle have a substantial impact on blood pressure, but the role of protein intake is not yet clear. This thesis focuses on total dietary protein, types of protein (i.e. plant and animal), protein from specific sources (i.e. dairy, meat, and grain), and specific amino acids in relation to blood pressure levels and incident hypertension.

    Methods
    The associations of dietary protein, protein types, and protein from specific sources with population blood pressure levels were cross sectionally examined in 20,820 Dutch adults aged 25 to 65 y (MORGEN Study). The relation with risk of hypertension was examined in 3,588 of these adults with 15 years of follow-up (Doetinchem Study) and in 2,241 older Dutch adults (≥55y) with 6 years of follow-up (Rotterdam Study). In the latter cohort we also examined the relation of specific amino acids (i.e. glutamic acid, arginine, lysine, cysteine, tyrosine, and essential amino acids) with blood pressure levels and risk of hypertension. As an ancillary Study, a fully controlled randomized cross over trial with different protein-rich diets was conducted to obtain objective biomarkers for dietary protein types that may be used in future epidemiological studies. Finally, we performed several meta-analyses to summarize our findings for dietary protein and protein types in relation to blood pressure and incident hypertension, combined with data from the literature.

    Results
    The epidemiological studies presented in this thesis and a meta analysis of observational studies showed no associations of total protein and animal protein with blood pressure or incident hypertension. A meta analysis of 14 randomized controlled trials, however, showed a pooled blood pressure effect of protein supplementation (weighed mean contrast in intake of 41 g/d) of 2.1 mmHg systolic (95%-CI: 2.9 to 1.4) when compared to carbohydrate intake. In the epidemiological studies in this thesis plant protein was significantly inversely associated to blood pressure levels ( 1.8/ 1.0 mmHg with 14 grams higher energy adjusted intake), but not with incident hypertension (all HR per SD ~1.00). Meta-analyses of cross sectional studies showed a small differential association of plant and animal protein with blood pressure (-0.52 mmHg per SD of dietary plant protein versus +0.03 mmHg per SD of animal protein), but this association was not present in meta-analyses of prospective studies and trials. The epidemiological analyses on meat protein and dairy protein in this thesis revealed no consistent associations with blood pressure or incident hypertension. Grain protein was inversely associated with diastolic (but not systolic) blood pressure, and with borderline significant lower risk of hypertension in a general Dutch population (HR: 0.75, 95% CI: 0.73 to 1.00), but this association was absent in older adults. No associations with blood pressure or incident hypertension were found for amino acid intakes. Finally, we identified a combination of 3 urinary amino acids as a potential biomarker for meat protein intake and a combination of 7 plasma amino acids as a potential biomarker for grain protein intake

    Conclusion
    Results from this thesis suggest a small beneficial effect of protein on blood pressure if consumed instead of carbohydrates. Plant protein, e.g. from grain, may be more beneficial to blood pressure than animal protein but data are too limited to draw firm conclusions. After validation, future epidemiological studies could make use of biomarkers as more robust estimates for protein from specific sources and amino acid intakes. Randomized controlled trials are warranted to examine the blood pressure effect of specific types of protein, reflecting habitual intakes in western societies, compared to different types of carbohydrate. At present, a prudent diet for the prevention of hypertension with adequate amounts of dietary protein, preferable from plant sources, is recommended.

    Patterns of nitrogen and energy intake and their relation to the control of voluntary feed consumption in ruminants and monogastric animals
    Ketelaars, J.J.M.H. - \ 1984
    Wageningen : Centre for Agrobiological Research - 176
    herkauwers - voeropname - voedingsfysiologie - spijsvertering - energieopname - eiwitinname - verteerbaarheid - spijsverteringsstelsel - systeemanalyse - modellen - voedersystemen - ruminants - feed intake - nutrition physiology - digestion - energy intake - protein intake - digestibility - digestive system - systems analysis - models - feeding systems
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