eading Performance Nutritionist, James Collins, helps decipher the latest research to help you optimise your training diet, in this case focussing on the importance of balance between energy intake and energy output.
It is widely acknowledged that insufficient energy (calorie) intake during periods of intense training can compromise the immune system and consequently increase susceptibility to infection. Professor Neil Walsh and colleagues at Bangor University and the Ministry of Defence (UK) have recently investigated the effect of insufficient energy intake on immune function, during an 8-week arduous training programme.
The results from the study provide further support for the importance of energy intake during heavy training blocks to preserve immune function and also highlight the benefits of supplementing the habitual diet with energy-dense foods during heavy training.
A higher dietary energy intake (habitual diet + dietary supplementation) was shown to prevent a decrease in immune function, measured by circulating total leucocytes, lymphocytes and monocytes and increased saliva SIgA output, during the 8 weeks of training.
The group that consumed the nutritional supplement in addition to a habitual diet lost less body weight than the group that only consumed a habitual diet.
Thirty male soldiers took part in this study, which involved 8 weeks of arduous military training. Fifteen men were asked to follow a habitual diet providing a daily energy intake of ~14 MJ for weeks 0-6 and ~17.7MJ for weeks 7-8.
The other fifteen men were asked to follow the same habitual diet plus an additional daily supplement. This equated to a daily energy intake of ~19.7MJ and ~21.3MJ for weeks 0-6 and 7-8 respectively. Both the habitual diet and the nutritional supplement provided macronutrients in a ratio of ~45% carbohydrate, ~40% fat and ~15% protein. Blood and saliva samples were taken at weeks 0, 6 and 8, and were analysed for various immune indices. Body composition was assessed at 0 and 8 weeks.
Take home message
Insufficient energy intake during intensive periods of training and competition will reduce body weight, but may also impair exercise performance and immune function.
Performers should carefully plan when to reduce body fat, to avoid placing excess physiological strain on the body, increasing infection risk. Energy-dense sports foods and supplements, such as sports drinks, recovery drinks, and meal replacements, can provide a convenient way to meet increased energy needs at this time.
Diment BC, Fortes MB, Greeves JP, Casey A, Costa RJS, Walters R, Walsh NP (2012) Effect of daily mixed nutritional supplementation on immune indices in soldiers undertaking an 8-week arduous training programme. European Journal of Applied Physiology. 112:1411–1418
James Collins is acknowledged as a leading expert in Sport & Exercise Nutrition. He is Head Nutritionist for Arsenal Football Club, and was also heavily involved in advising Team GB Olympic teams and individuals in the run up to the London 2012 Olympic Games, and now towards Rio 2016.
James regularly collaborates with television, such as BBC on factual documentaries and provides expert comment to CNN and Sky on topical issues. James sits on The Royal Society of Medicines ‘Food and Health’ Council, is a member of the international group PINES (Professionals in Nutrition for Exercise and Sport) and is a Registered Nutritionist.
His Harley Street clinic works with different celebrities from performance industries, focussing on Weight & Metabolism and Performance. James’ unique position allows him to maintain close industry links within Europe and the USA.