The effects of a ketogenic diet on exercise metabolism and physical performance in off-road cyclists.

Adam Zajac,Miłosz Czuba,Małgorzata Michalczyk,Adam Maszczyk,Grzegorz Zydek,Stanisław Poprzecki

doi:10.3390/nu6072493

Adam Zajac, Miłosz Czuba + Show 4 more

Open Access

https://doi.org/10.3390/nu6072493

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Abstract

The main objective of this research was to determine the effects of a long-term ketogenic diet, rich in polyunsaturated fatty acids, on aerobic performance and exercise metabolism in off-road cyclists. Additionally, the effects of this diet on body mass and body composition were evaluated, as well as those that occurred in the lipid and lipoprotein profiles due to the dietary intervention. The research material included eight male subjects, aged 28.3 ± 3.9 years, with at least five years of training experience that competed in off-road cycling. Each cyclist performed a continuous exercise protocol on a cycloergometer with varied intensity, after a mixed and ketogenic diet in a crossover design. The ketogenic diet stimulated favorable changes in body mass and body composition, as well as in the lipid and lipoprotein profiles. Important findings of the present study include a significant increase in the relative values of maximal oxygen uptake (VO2max) and oxygen uptake at lactate threshold (VO2 LT) after the ketogenic diet, which can be explained by reductions in body mass and fat mass and/or the greater oxygen uptake necessary to obtain the same energy yield as on a mixed diet, due to increased fat oxidation or by enhanced sympathetic activation. The max work load and the work load at lactate threshold were significantly higher after the mixed diet. The values of the respiratory exchange ratio (RER) were significantly lower at rest and during particular stages of the exercise protocol following the ketogenic diet. The heart rate (HR) and oxygen uptake were significantly higher at rest and during the first three stages of exercise after the ketogenic diet, while the reverse was true during the last stage of the exercise protocol conducted with maximal intensity. Creatine kinase (CK) and lactate dehydrogenase (LDH) activity were significantly lower at rest and during particular stages of the 105-min exercise protocol following the low carbohydrate ketogenic diet. The alterations in insulin and cortisol concentrations due to the dietary intervention confirm the concept that the glucostatic mechanism controls the hormonal and metabolic responses to exercise.

Highlights

An interaction between exercise-induced responses and nutrient availability has long been recognized [1]
Compared to a high carbohydrate diet, or a mixed diet with 50%–70% of energy coming from carbohydrate (CHO), a high fat diet with 70% of the calories derived from fat significantly increased the contribution of free fatty acid (FFA) to the total energy expenditure during moderate intensity exercise
Our research showed improvements in VO2max and VO2LT, yet the power output during work at maximal intensity was compromised on the ketogenic diet, which can be explained by lower muscle glycogen stores and the reduced activity of glycolytic enzymes due to the four-week diet intervention [19,40]

Summary

Introduction

An interaction between exercise-induced responses and nutrient availability has long been recognized [1]. High carbohydrate diets increase muscle and liver glycogen stores, improving endurance performance, yet at the same time, they increase the rate of carbohydrate utilization during exercise Having this in mind, scientists and athletes have begun experimenting with dietary procedures that would decrease the rate of carbohydrate utilization, while increasing fat metabolism during prolonged physical work [7,8,9]. Scientists and athletes have begun experimenting with dietary procedures that would decrease the rate of carbohydrate utilization, while increasing fat metabolism during prolonged physical work [7,8,9] It seems that such an alternative in exercise metabolism can be induced by a high fat, low carbohydrate diet. Very low carbohydrate ketogenic diets have been used for years in fighting obesity and different common and rare disease states [10]

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