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).