Base Nutrition for Sport

Base Nutrition - High Fat Diets and Endurance Exercise

Fat

Fat is an important energy source for muscular work. Fat becomes a particularly important fuel during prolonged exercise. Other functions of dietary fat are for the production of hormones (eg. Testosterone), sources of fat soluble vitamins and some minerals. Some athletes restrict their fat intakes to extremely low levels. In most instances this seems unnecessarily restrictive. Some fat in the diet is essential, and following the New Zealand guidelines for healthy eating should result in an appropriate fat intake.

Some fats are better than others in terms of their effects on heart health. The best types  are monounsaturated and polyunsaturated fat. Good sources of these are:

Background and Theory

Highly trained individuals oxidise proportionally more fat and less carbohydrate during exercise compared to their untrained counterparts. It has been reported that fat-metabolising enzymes within the muscle rise in response to a high-fat, low-carbohydrate diet. Research which has combined the effects of endurance training and fat-rich diets have shown a greater reliance on fat oxidation during physical exercise in animals and humans.

There are an increasing number of gruelling events that are challenging the limits of human endurance. Traditionally high carbohydrate diets have been recommended for endurance athletes because of the relationship between high carbohydrate intakes, increased muscle glycogen and delayed onset of fatigue. However recent research has shown that when individuals adapt to a high fat diet, the relationship between muscle glycogen and performance times does not exist. There are suggestions that a high carbohydrate diet is not optimal for some events. Many athletes find it difficult to consume sufficient calories when a carbohydrate-rich diet is consumed because of the bulky nature of the diet. Because fat contains twice as much energy per gram as carbohydrate, diets with a high fat content are less bulky. Also, in situations where food intake needs to be transported, fat provides an advantage in terms of weight savings.

Research

There has been a wide range of studies looking at the efficacy of high fat diets. Studies from the Human Nutrition Department have conducted studies looking at the effect of high fat diets on physical performance, blood cholesterol levels and body composition in groups of endurance-trained athletes.

One concern with high fat diets is the potential negative effects on blood cholesterol levels. Our research has shown that the consumption of a high fat diet by athletes taking part in high volumes of exercise has no negative effects on the cholesterol levels of these individuals. In addition, these athletes remained lean, with no deposition of body fat and their physical performance was not adversely affected.

In short the research has indicated that endurance athletes taking part in large volumes of exercise could increase their intake of fat without adverse consequences. This increase in fat content would allow athletes to consume more calories without having to consume the huge volumes of food often needed when current dietary recommendations are adhered to.

Practical Implications

Today there are many sporting events that challenge the limits of human endurance. Such events require athletes to exercise for many hours over several days or weeks. This highlights some important nutritional considerations, including recovery and the provision of sufficient energy to maintain lean body mass. Further, if athletes are required to transport their own food supply, there must be careful consideration regarding the supply of sufficient calories for the least weight.

We recently designed the nutritional plan for a group of four rowers taking part in the 2001 Trans-Atlantic rowing race. This event is an unassisted, 2900-mile race across the Atlantic Ocean consisting of teams of two rowers. Competitors were required to transport their food for the entire race, which may last approximately 40-90 days. This highlights the challenge of supplying adequate food to cover the large energy demands of such an event, while at the same time minimising the weight of food to be transported. We designed the diets to be relatively high in fat and therefore energy dense. High fat variations of foods were chosen, which resulted in significant weight savings. The weight loss of our crews was markedly less than other competitors and the performance results spoke for themselves. Our men's team won the race and our female crew (the only all-female crew) finished an amazing fourth.

The use of a diet relatively high in fat can be utilized for other sporting pursuits. A high fat diet may be most beneficial in sports where energy expenditure is high and time for recovery is limited. This includes sporting events which last several days or weeks, and events where athletes are required to carry their food intake. eg. Antarctic Exploration, Endurance Yacht Racing, Endurance Multi-Sport etc. A higher fat content in the diets of these athletes is likely to minimise the high rates of weight loss commonly observed in these events.