Many children are engaged in sport and some are very talented young athletes. Nutrition is important especially in growing children but are their needs further increased when in training?
The following article was written by leading exercise physiologist and sports nutritionist Asker Jeukendrup. It can be found in its original form on www.mysportscience.com.
A question I get asked very often is: “do children need sports nutrition”. As always the answer of the scientists is “it depends”… but let’s break down this question into a number of smaller questions:
Is the physiology of children fundamentally (or significantly) different from adults?
Do children have different nutrition requirements?
Should recommendations for children be different from adults?
Once we have answered those questions it should be possible to get to an evidence based judgement.
To start with the short answers:
Is the physiology of children fundamentally (or significantly) different from adults? No.
Do children have different nutrition requirements? Yes, especially protein requirements may be increased.
Should recommendations for children be different from adults? Largely no, the recommendations we have for adults are appropriate for children. Some of the advice is expressed per kilogram body weight and some take into account individual sweat rates and therefore any differences are already taken into account in the current recommendations.
Carbohydrate and fat
There may be differences in substrate use (preference for carbohydrate or fat as a fuel) between children and adults. Young children preferentially use fat as a fuel and the capacity to use carbohydrate tends to be lower. These differences in metabolism diminish throughout adolescence, especially in boys. Therefore, it appears that children may be less carbohydrate dependent, but the differences are probably to impact the practical recommendations. During prolonged exercise in adults, carbohydrate feedings has been shown to improve exercise performance and studies suggest that this is no different in children. The delivery of carbohydrates requires a gastro-intestinal system that can absorb carbohydrate well. During the early years of development, the gastro-intestinal system grows and the capacity to absorb carbohydrate improves. At the age of 5 good absorptive capacity is usually in place. Carbohydrate intake recommendations during exercise are dependent on exercise duration (as well as intensity). Children typically exercise for shorter durations and lower absolute exercise intensities, reducing the need for carbohydrate during exercise.
One of the main ways that children and adults lose heat is through the evaporation of sweat from the skin. As children have a higher ratio of body surface area to body mass (at the age of 8 years it is approximately 50% higher than that of an adult) it has been suggested that exercising children should be able to get rid of heat quicker than adults. On the other hand, sweat glands are less developed and therefore it may be difficult for children to sweat and get rid of heat. In practice, adults and active children seem to experience similar core temperatures, even when exercising at high temperatures.
The current guidelines for adults take into account sweat rate. If sweat losses are high and result in body weight loss that exceeds 2% body weight it is generally recommended to drink. Drinking behaviour should aim to reduce body weight loss to between 0 and 2%. Both weight gain and excessive weight loss should be avoided. There is no reason to change these guidelines for children because the advice is already based on individual sweat rates.
Protein requirements and weight management
Very few studies have investigated protein requirements in young athletes. It is generally believed however, that growing children have slightly elevated protein needs. It is also known, however that athletes who expend more energy will eat more and will automatically increase their protein intake. Therefore, in the vast majority of cases there will be no need to specifically address protein intake in young athletes. This, is of course different in young athletes who are conscious of body weight and may be in negative energy balance. In that case, however, it may be important to address energy balance first, before addressing the protein intake per se. Although in some cases there are clear links to better performance it is important to be aware that there are also risks of energy deficiency, micronutrient deficiencies, menstrual irregularity, poor bone health and eating disorders. It is pertinent to work with a registered dietitian and/or medical supervision when weight loss or changes in body composition are targeted.
Supplement use amongst junior athletes is common. In a study of 32 track and field junior athletes selected for Team Great Britain at the World Junior Championships, it was found that 62% of the sample used supplements. Other studies have reported a prevalence of between 20-70% with the majority of supplements being multivitamin and minerals. In general, however, supplements for younger athletes are not recommended. It is far more important to provide them with a varied and balanced healthy diet and show athletes from an early age what healthy eating means.
The exercise capacity and usually the exercise duration will be shorter in young athletes. Often the absolute exercise intensity is also lower. There are no fundamental differences in metabolism that make it necessary to alter recommendations. With the same guidelines as adults, however, which take into account duration and intensity of exercise, the advice to younger athletes is generally on the lower end of the scale for carbohydrate and fluids. There is no need to use sports drink if children are running around a field for 30 min (but neither is there a need for adult athletes). Although we may note have specific guidelines for children, extra caution should be exercised if issues like weight management are considered in this population and this should not be done without expert advice from a physician and/or sports dietitian. Supplements are generally not recommended for younger athletes and neither are more extreme nutrition practices such as diets, training low, training low etc.