Are HIIT training and Ketogenic Diets compatible?

Many a fitness enthusiast are ardent proponents of HIIT, while others are of very low carbohydrate high fat diets (VLCHF) more commonly known as ketogenic diets.  Understandably so, as there is a slew of available research to validate the efficacy of HIIT as well as ample evidence to validate the efficacy of ketogenic diets.  However, until recently no studies had examined the effects of long-term reductions in carbohydrate intake on HIIT performance. Carbohydrate availability and muscle glycogen content are primary components of metabolism and exercise performance with skeletal muscle increasingly reliant on carbohydrates as a fuel source as exercise rises in intensity. Thus, it stands to reason that restriction of carbohydrates availability, forcing greater reliance on fat as the primary fuel source, would adversely affect strenuous exercise performance, such as that needed for high-intensity interval training (HIIT) 

In a study conducted by Lukas Cipryan et al out of Ostrava University, participants were asked to alter their habitual mixed Western diet to that of a very low-carbohydrate high-fat diet for 4 weeks in which researchers examined its effect on physiological variables during a graded exercise test and a HIIT bout. While substantial changes in substrate oxidation were found, with heightened levels of fat oxidation and blood lactate concentration in the VLCHF group, no adverse effects of a 4-week VLCHF diet on any aspect of performance during either the GXT or the HIIT bout in these participants.

The key points uncovered at the Ostrava University were:

  • Substantially increased rates of fat oxidation shown during a graded exercise test and high-intensity interval training (HIIT) session.
  • No impairment in performance and cardiorespiratory responses after consuming a VLCHF diet relative to a group consuming their mixed western-based diet.
  • A four-week adaptation period to a VLCHF diet preserved high-intensity exercise performance.

The results support that athletes engaging in HIIT can follow a very low carbohydrate high fat approach without detrimental effects to their performance and training.  While promising this is just one study with limitations therefore additional studies are warranted to further validate the outcomes produced by Cipryan et al.

Journal of Sports Science and Medicine 2018 (17), 259 - 268.