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This summary is from the IAAF 2nd International Consensus Conference on “Nutrition for Athletics“ held in Monaco from April 18-20, 2007. Copies of the CD and booklet are available from the IAAF website www.iaaf.org.
Physique and Performance in Athletic Events
Presenter: Helen O’Connor (AUS)
People have very different genetics and variations are on a wide continuum from naturally very lean to virtually impossible to achieve weight goals. In some athletics events, success is only likely within a relatively small range of body shapes and sizes and international-level competitors in different events have different physiques. For instance, 400m runners tend to be the tallest of all track runners. Taller people have an advantage in high jumping because they have a higher centre of mass. Other physical characteristics, like power-to-weight ratio, limb length, energy expenditure and heat exchange, all have impact on performance. Some characteristics, like height, cannot be changed while others, like weight and body fat, can be manipulated by diet and training.
Reducing weight in athletes should be done with a high carbohydrate diet, to support training and glycogen recovery. Nutrient density should be high and energy intake should never drop below 30kcal or 125kJ/kg fat free mass. A lower energy density (energy/g food) of the diet is also advised. Reduced carbohydrate diets are very popular in the general population and also in the athlete community. Studies have shown improved weight loss compared to low-fat diets, but these have never included athletes. The well-described advantages of sufficient carbohydrate in athletes will probably negate possible positive effects of low-carbohydrate diet weight loss therefore carbohydrate intake should not be under 5g/kg/day. However, carbohydrate intake advice should be individualised and not be interpreted as a license to eat unlimited amounts of carbohydrate.
Low Glycemic Index diets can have effect for athletes who want to lose weight. A possible negative effect is reduced glycogen resynthesis. Protein is the most satiating of all macronutrients. Protein also induces the highest thermo genesis. Protein needs are higher on an energy restricted diet. Therefore, a relatively high protein intake can have a role in an energy restricted diet. However, if protein intake becomes too high, carbohydrate intake might be compromised.
Dairy intake has effect on body composition. Different mechanisms have been proposed. The calcium forms fatty acid soaps from the triglycerides and some is excreted. Conjugated linolic acid might have a role and other mechanisms have been proposed, but more research needs to be done to elucidate the mechanism.
Athletes should be advised on basic diet and foods. This way, a more accurate diet can be prescribed. Also, the athlete should know how much to consume on rest days, when injured or when in a transition phase. The extra food can be given per hour of exercise.
Surface anthropometry is recommended as the most practical and safe method to assess and track changes in body composition. When measuring skin folds, it is advised to give a confidence interval. This shows the athlete a more realistic figure.
The above summary was written by Peter Res
If you wish to download this handy Grams and Calorie Calculator for Carbohydrate, Protein, and Fat, click here for the Excel spreadsheet.
This is part 5 of 14 in a series from the 2007 2nd IAAF International Consensus Conference “Nutrition for Athletics”