For years, exercise specialists and sports dietitians have suggested that a high-carbohydrate, low-fat diet would best support an endurance-training athlete. However, some research may support the adoption of a high-fat, low-carbohydrate diet to increase athletic performance. The mass media has also climbed aboard with claims that this eating regimen may also promote weight loss. But is this diet really good for you?

A Bit about Carbs

Carbohydrates are essential for energy - when a carbohydrate is broken down into its simplest form, glucose is left. Glucose produces the energy necessary to run, swim, lift, and perform every other physical activity you can think of. Glucose has become well-known to endurance athletes because they need to accumulate glucose stores in order to be able to participate in competitions. 

Can High Fat Diets be Beneficial?

The word “fat” has gained a negative connotation in popular culture and is often avoided. However, the dietary guidelines suggest that a healthy diet should include 20-35% of one’s daily calories from healthy fats (for more information on healthy fats, see our article on Nuts here: http://the-sage.org/articles/why-were-nuts-about-nuts). Studies are now suggesting that endurance athletes may be able to healthily consume 60-75% of their daily calories from fat. This process, called “fat adaptation,”
recommends that trained endurance athletes consume a high-fat diet for a short period of time (1-3 weeks) while continuing their normal training, then restore their carbohydrate stores with a high-carbohydrate diet while tapering their training in the 1-3 days before a competition.

Enhancement to Performance

Endurance athletes who participated in short-term, high-fat diets experienced several enhancements to their performance. First, these athletes were able to travel the same distance in a shorter amount
of time. Additionally, these athletes experienced a lower heart rate and did not significantly increase their work of breathing compared to those not on a performance-related high fat diet.

Fat Burning and Blood Glucose

During these short-term, high-fat diets, it has been found that higher rates of fat burning occur while the stored glucose is spared from being burned during exercise. The spared glucose will then be expended during competition for optimum performance at the end of the high-fat diet. Furthermore, blood glucose levels stayed within the average range and did not drop due to the high-fat diet.

Chronic Disease Risk

Large amounts of fat are commonly known to cause many health problems; however, these endurance athletes may be in the clear. According to one study, the liver functions of the participants remained normal throughout the high-fat diet and carbohydrate restoration.  Triglycerides, which are a type of fat in the bloodstream, increased during the high-fat diet as well as during a high-carbohydrate diet. There was not a significant difference in cholesterol levels, but it is unclear whether healthy HDL and unhealthy LDL levels were affected. However, because of the short duration, the high-fat diet does not appear to cause any chronic health problems.

Who Is It For?

Although a high-fat diet can sound enticing to some, it is not recommended for the population at large nor for weight loss purposes. This specific high-fat, carbohydrate reloading diet is suggested for trained endurance and ultra-endurance athletes only. This diet is not recommended for those who
are mostly sedentary or considered leisure athletes. Furthermore, a two-week, high-fat diet appears to be the optimum amount of time with the best results. Little to no results were found for any duration over this two-week period and a high-fat diet was found to have the same or less of an effect as a typical high-carbohydrate diet. It is suggested that endurance athletes focus on their traditional
nutritional diets for the majority of the year and adopt a high-fat diet approximately two weeks before a major competition.

Here at The Sage we support all kinds of athletes and want to promote their performance using nutrition. At the same time, not every diet is right for every person. Our goal is to educate people on the specific diets out there to help you decide which ones best benefit your own lifestyle and activity levels.

Happy Eating!

Jamie Pepper, Nutrition Intern