Carbs are “known” to support endurance exercise; cyclists and runners hold the 4-calories-per-gram carbohydrate as an irreplaceable necessity for athletic performance. But what if this were not true, what if fat, at 9-calories-per-gram, were a better fuel source for many, or most, athletes?

While working on my 2015 book, which describes how to use The Blood Code for athletes, I have pored through research that sells a different story about the preferred dietary energy source. I am from a marathon running family, so the concept of carbs before events is not foreign to me. And I have always assumed that the fats in a pre-race meal would “slow me down”. Let me share three facts that I have learned about supporting athletes without the insulin burden that comes from dietary carbs.

Fact #1: Long-Term Intake of a “high-fat” diet may improve athletic performance

It appears that endurance athletes can adapt to high-fat diets without any detrimental effect on physical capacity. At the very least, it has been clear in a list of studies that utilizing a diet that is higher in fat does not adversely affect exercise performance. In a study comparing athletes eating a high-fat diet (70% of calories from fat and 7% from carbohydrate) and a high-carb diet (74% carbohydrate and 14% fat) peak performance remained unchanged between the groups. But when these athletes maintained 50% of their peak performance for a sustained period, the high-fat group performed better.

It is helpful to note here that “peak performance” is when one exercises at 85-90%. Whereas most of us relate to the 50% peak performance state, the ordinary day with some moderate exercise has the same demands as the athlete at 50% of peak performance.

Fact #2: Short-term Intake of a high fat meal before an endurance event does not adversely affect your performance

In fact, more fat = more endurance: According to a study by the University of Buffalo, a low-fat diet may hamper your endurance. Researchers concluded that a medium or high caloric intake from fat, about 30 to 45 percent of your total caloric intake, is your best bet for improving performance if you run at least 35 miles a week. Some runners and athletes simply need more calories. Also, when your body burns fat for energy, it conserves glycogen, which is always in relatively short supply.

Fact #3: “Eating high fat does not cause you to be fat”

A study, long ago last decade, by researchers in New Zealand found that total body fat, lean tissue mass, and body weight did not change when the athletes ate a high-fat diet vs. a high carbohydrate and low-fat diet. The results of this study send a clear message: When energy requirements are high, athletes should choose to increase dietary fat intake. Remembering that even when you consume most of your fat calories as saturated fats (46% in this study) there was no extra weight gain and/or increased adiposity.
R. Brown, et al. High-carbohydrate versus high-fat diets: effect on body composition in trained cyclists, Med Sci Sports Exerc 2000, 32(3): 690-694.