Are ketogenic diets beneficial to the fitness and fatness of healthy adults?

The late 1970s marked the beginning of the obesity epidemic: U.S. obesity rates went from increasing gradually to exponentially over the course of the next two decades. Coincidentally, this rise was accompanied by recommendations to limit the consumption of total dietary fat to avoid heart disease and other ailments. For a long time the USDA food pyramid dictated that carbohydrates (whole grains) should be dietary staples, the Surgeon General recommended that Americans reduce their consumption of foods high in fat, and the National Institute of Health (NIH, 1984) suggested that Americans cut their saturated fat consumption. The overall consensus amongst the American population was that eating fat made you fat.

In recent years the tables have turned and low carbohydrate diets have become a popularized means to induce weight loss. Support behind ketogenic and low carbohydrate diets have been further strengthened by studies demonstrating that ^[1]carbohydrate restriction can be effective at promoting fat loss^[1]. Additionally, ketogenic diets (<10% calories from carbohydrates and >60% of calories from fat) have been shown to be beneficial for decreasing side effects of diseases like epilepsy, and may show some promise in conditions including polycystic ovary syndrome^[2], neurodegenerative diseases, diabetes^[3], and cancer^[4]. Despite the growing use of ketogenic diets amongst various disease populations, insufficient evidence exists in non-athletes and athletes to support that ketogenic diets do not negatively impact aerobic and physical performance in healthy individuals.

In the reviewed study, the authors set out to address this research gap by determining the impact of an ad libitum (without caloric restriction), 6-week, ketogenic diet on physical performance, body composition, and blood parameters in healthy adults.

For years, the idea that high fat, low carbohydrate, diets could be beneficial was contested. Although data exists suggesting that ketogenic diets are beneficial for weight loss and certain diseases, there is limited evidence elucidating their effects on physical performance and daily activity. In this study, researchers investigated how 6 weeks of a calorically unrestricted ketogenic diet impacted physical performance, body composition, and blood parameters in healthy men and women.