Athletes and diet

Louise Burke of the Australian Institute of Sport reports from an international meeting of dieticians

A What's the most efficient way to fuel an athlete -- a few large meals or lots of frequent snacks? This is the issue that was considered recently in Paris as part of a workshop on 'Periodicity of Eating and Human Health'. This workshop was endorsed by the American Dietetic Association and European Federation of the Associations of Dieticians, and sponsored by a leading multinational food manufacturer. An international panel of nutrition experts considered the effects of the timing and frequency of our eating on variables such as obesity (excessive body weight), blood glucose (sugar), blood lipids (fats), tooth decay, energy expenditure, mental performance, and sports performance.

B Central to the workshop was the difficulty in measuring how people eat. Our knowledge is confused because of the various ways that researchers have reported 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 gathering and reporting information about the timing and frequency of food and fluid intake was a key point in the workshop summary.

C In reviewing clinical studies and epidemiological literature, the workshop participants noted that the frequency of eating may have a number of physiological and psychological effects, including an immediate temporary impact on blood glucose and blood lipid concentrations. The participants agreed that the impact over a more extended period of time, particularly in the management of diabetes (excessive blood sugar levels) and hyperlipidemias (excessive blood fat levels), needs to be studied in greater depth.

D The participants pointed out that most people typically eat five to six times between morning and evening. For athletes, the timing and frequency of food intake has been studied from a number of angles. It appears that athletes with high energy requirements need to eat frequently: typically six to ten times per day. Participants agreed that it seemed practical for athletes to adopt a way of eating known as 'grazing', that is, consuming small to moderate-size meals and snacks over the day, rather than risk the discomfort of eating a few, very large meals.

E It was accepted that athletes have to fit food intake around their schedules for training and competitions, and the role of energy-releasing carbohydrates -- sugars, and also foods such as bread and pasta -- is key. The goal is to match carbohydrate consumption to the fuel needs of the athlete. Fueling up before the event is essential. Advising people to avoid sugar or other carbohydrates in the hour prior to exercise is now seen to be misguided. This concern followed the over-publicity received by one study, which reported reduced performance during exercise following a glucose feed the hour before. Since then, there have been at least 10 studies showing that, despite alterations in levels of blood glucose and/or insulin at the start of exercise, carbohydrate feedings in the one to four hours before exercise either fail to affect performance or may even improve it.

F Consuming carbohydrate during exercise is an important strategy athletes employ when entering endurance events, such as marathons and long-distance cycling races. The participants agreed that 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 for athletes is to eat sufficient carbohydrate as soon as possible during exercise rather than wait for the onset of fatigue. Early intake is also important in the recovery phase -- which is when exercise has stopped. An immediate intake of carbohydrate will enhance restoration of muscle glycogen (the body's energy reserves stored in the muscles). This is an important consideration when the next period of training or competition is scheduled in less than eight to twelve hours. Participants at the meeting agreed that there are other ways in which timing and frequency of nutrient intake may affect training and performance, and that more research in this area is required.

G By itself, more frequent eating apparently does not increase the risk of obesity or affect the nutritional value of diets. But again, the workshop participants felt that more research is needed before a way to spread intake can be sensibly recommended. It was also noted that even if strong guidelines could be drawn up, it is notoriously difficult to get people to change how they eat. Most of us choose the way we eat to meet a variety of social, emotional, physiological, cultural, and practical needs. We tend to be creatures of habit and inflexible when it comes to long-term modification to those habits.