New study shows fat to be an effective fuel for high-intensity training.
An international team of sports scientists has demonstrated that replacing carbohydrates with fat does not impair high-intensity exercise performance.
The researchers found that restricting daily carbohydrate intake to less than 50 grams, and replacing the majority of those reduced calories with fat, did not reduce the ability to perform high-intensity interval training (HIIT) compared to a control group whose members consumed a typical high-carbohydrate diet.
While previous studies have demonstrated impaired performance when consuming inadequate carbohydrate, the new study allowed participants time to adapt their metabolisms to the very low-carbohydrate diet over a four-week period.
The 18 study subjects were recreational athletes between the ages of 18 and 30. Those consuming the lower intake of carbohydrates were shown to be able to use much more fat and ketones as an alternative energy source.
What may be the first study to examine the effects of long-term reductions in dietary carbohydrate intake on HIIT performance, the four-week study also evaluated cardiorespiratory and metabolic responses in all subjects and found no impairments.
The results challenge the presumed necessity of a high-carbohydrate diet for high-intensity exercise performance. Most athletes, coaches and scientists presume that reduced dietary carbohydrate intake will severely impair these types of workouts, considered as vital components of optimal performance for most sports and general fitness.
However, researchers found no evidence of performance compromise during the HIIT workouts.
The control group consumed a diet that was about 48 percent carbohydrate, 17 percent protein, and 35 percent fat, while the study group followed a very low-carbohydrate diet of about 8 percent carbohydrate, 29 percent protein, and 63 percent fat for the four-week test period.
An important finding was the significant increase in fat oxidation — the increased use of stored body fat for energy. In particular, there was a progressive increase in fat oxidation over the repeated HIIT workouts, which supports the importance of aerobic metabolism for such training.
Traditionally, dietary guidelines have recommended daily carbohydrate intake of 6-10 grams per kilogram of body weight for athletes performing one to three hours of daily moderate- to high-intensity exercise.
The study is titled, “Effects of A 4-Week Very Low-Carbohydrate Diet on High-Intensity Interval Training Responses,” and published this month in the Journal of Sports Science and Medicine. It was performed at the Human Motion Diagnostic Centre & Department of Human Movement Studies, Ostrava University, Czech Republic, and led by Lukas Cipryan. His collaborators included Daniel Plews, Alessandro Ferretti, Philip Maffetone and Paul Laursen.
While traditional nutritional advice is to load up on carbohydrates, science continues to prove that fat is a powerful and healthful fuel alternative for human performance.
To read the full text of the study in the Journal of Sports Science and Medicine, click here.