Definition: "An ergogenic aid is any substance or phenomenon that enhances performance "

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Animal study: endurance athletes perform better on a little more fat

With their animal study, published in Sciences & Sports, these Tunisian biologists managed to dismantle a holy cow of the endurance sports world. Their tests showed that a diet containing a little more fat is better for the amount of glycogen in the muscles than a carbohydrate-rich diet.

The role of carbohydrates in endurance sports is similar to that of proteins in strength sports. Carbohydrates are holy in endurance sports, and the industry likes the situation the way it is. Proteins are relatively expensive compared to cheap carbohydrates. That means the companies that focus on endurance sports have higher profit margins than the companies focusing on power sports - and that's why you're unlikely to come across a study like the Tunisian one in the industry-dominated endurance sports media.

The researchers carried out a study on young rats. They were given a normal diet, a diet with slightly raised levels of fat, or slightly raised levels of carbohydrate for a period of four weeks. The table below shows weight percentages, not energy percentages.
















So the Tunisian test was not an experiment about extreme eating patterns. It was about a little more fat, or a little more carbohydrates. And about training: the researchers got their test animals to swim for an hour five times a week. The animals in the control groups got no exercise. The researchers had a total of six groups of rats: "the normal diet control (NC), the high-fat diet control (FC), the high-carbohydrate diet control (CC), normal diet with exercise (NE), high-fat diet with exercise (FE), and high-carbohydrate diet with exercise (CE)".

At the end of the four weeks the researchers measured the amount of glycogen in the muscles of the test animals. To their surprise they discovered that the animals that had eaten more fat [FC and FE] had a considerably higher glycogen level than the animals in the other diet groups.

Animal study: endurance athletes perform better on a little more fat

Animal study: endurance athletes perform better on a little more fat

The insulin level of the animals that had been given more fat was also higher than that of the other animals.

Animal study: endurance athletes perform better on a little more fat

More fat, more insulin and more muscle glycogens. How come?

The researchers suspect that there's a simple mechanism at work here. Mice that eat more fats burn fewer carbohydrates. Their metabolism changes. As a result their bodies have more carbs available for conversion into glycogen, and their insulin level is therefore higher.

The researchers have a clear message for endurance athletes. A diet with a slightly higher level of fats probably leads to better performance than a carb-stuffed diet.

Science & Sports Volume 22, Issue 6, December 2007, Pages 286-288.