More Fats Burned by Male Athletes on Keto Diet but Effect Muted in Women - Study

Researchers from the University of Poznan in western Poland reported on the results of a study, “Effect of a four-week ketogenic diet on exercise metabolism in CrossFit-trained athletes,” published online earlier this month in the Journal of the International Society of Sports Nutrition.    A  ketogenic diet is one in which the majority of calories come from fat, with a lesser fraction of protein and very little in the way of carbohydrates.  The researchers noted that the ketogenic diet was first researched in the 1930s as a potential treatment for epilepsy and more recently has been associated with positive effects on weight loss, insulin resistance, diabetes and high blood pressure.  In addition, one of the major components of many ketogenic diets and products, coconut oil has been associated with neuroprotective effects via its ketone content. 

The theory behind the diet is that, despite the high exogenous fat intake, because of the paucity of glucose circulating in the blood, the body is forced to convert to mainly burning fat, and thus there is less endogenous fat buildup.  The diet also has been postulated to have performance enhancing effect, because of the way the diet shifts the molecular mechanism of cellular signalling. To test this hypothesis the researchers recruited 30 adult CrossFit participants 18-40 years old who were actively training at two clubs in Poznan.  Crossfit is a training regimen which is gaining increasing popularity that features rapid, short busts of activity at high power outputs and includes weight lifting and plyometric exercises. 

After baseline measurements, the participants shifted to the ketogenic style of eating for four weeks.  The ketogenic diets provided about the same caloric intakes as what the subjects had been consuming.  The diets consisted of 15% protein in the form of meats, fish and dairy, and 75% fat in the form of coconut, rapeseed and olive oils,  butter and nuts.  The remaining 5% consisted of carbohydrates.  At the end of the study, only 22 participants remained after eight dropped out for reasons of not being able to adapt well to the diet, drowsiness, irritability, and injurry during the cycling tests.  Among the 22 remaining participants, the researchers found that they all shifted their energy utilization to some degree toward burning more fat.  But only the men showed statistically significant shifts in this direction at all ranges of VO2 max (maximum oxygen uptake), whereas for the women this change was significant only at around 65% of VO2 max, which equates to a moderately hard, but sustainable effort.