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Should Athletes Nibble or Gorge?

Louise Burke, Australian Institute of Sport, Canberra, Australia

This is the question that was pondered recently in Paris as part of a consensus meeting on "Periodicity of Eating and Human Health." The meeting was endorsed by the American Dietetic Association and European Federation of the Associations of Dietitians, and sponsored by Mars Inc. An international panel of nutrition experts considered the effects of the timing and frequency of our eating occasions on things like blood glucose, blood lipids, tooth decay, obesity and energy expenditure, mental performance, and sports performance.

Central to the discussion was the difficulty in measuring how people eat. Our knowledge is confused because of the various ways that researchers have reported the occurrences of food and fluid intake. It was noted that dietary survey work is fraught with errors. For example, people tend to under-report intakes, particularly when they want to appear to eat "better" than they really do. The call for standardization in collecting and reporting information about the timing and frequency of food and fluid intake was a key point in the workshop summary.

In reviewing clinical studies and epidemiological literature, the workshop participants concluded that the frequency of eating may have a number of physiological and psychological effects, including short-term effects on blood glucose and blood lipid concentrations. The long term effects, particularly in the management of diabetes and hyperlipidemias, need to be studied in greater depth.

For athletes (at last, what you’ve all been waiting for!), the timing and frequency of food intake has been studied from a number of angles. Firstly, it appears that athletes with high energy intakes eat frequently: typically 6-10 times per day. It seems practical to adopt a pattern of "grazing" small- to moderate-size meals and snacks over the day, rather than risk the discomfort of gorging on a few very large meals per day.

Of course, athletes have to fit their eating around their training and competition schedules. The timing of carbohydrate intake before, during and after sessions of prolonged high-intensity exercise is also important. The goal is to match carbohydrate supplies to the fuel needs of exercise and recovery. Fueling up before the event is important. Previous advice about avoiding sugar or other carbohydrates in the hour before exercise is now seen to be misplaced. The concern followed the (over) publicity received by one study, which reported reduced performance during exercise following a glucose feed the hour before. The publicity popularized the idea of rebound hypoglycemia and earlier onset of muscle glycogen depletion due to increased insulin in the blood. Since then, there have been at least 10 studies showing that, despite alterations in blood glucose and/or insulin levels at the start of exercise, carbohydrate feedings in the 1-4 hours before exercise either fail to affect or may even improve performance.

Consuming carbohydrate during exercise is an important strategy for endurance events. The timing may be an issue of opportunity provided by the sport (e.g. at aid stations, or at scheduled breaks), rather than a scientific ideal. The main advice is to eat sufficient carbohydrate early in exercise rather than wait for the onset of fatigue. Early intake is also important in the recovery phase. An immediate intake of carbohydrate will enhance restoration of muscle glycogen—an important consideration when the next bout of training or competition is scheduled in less than 8-12 hours. There are other ways in which timing and frequency of nutrient intake may affect training and performance. More research is needed here.

The bottom line of the workshop was that despite the perceived wisdom of the value of "3 square meals" a day, most people eat more often: typically 5-6 times a day. By itself, more frequent eating apparently does not increase the risk of obesity or affect the nutritional value of our diets. But again, more research is needed before we can recommend a way to spread our intake.

It should be noted that even if we could make strong guidelines, it is notoriously difficult to get people to change how they eat. We choose the way we eat to meet a variety of social, emotional, physiological, cultural, and practical needs. Despite any benefits, we tend to be creatures of habit and resist long-term change.

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