The Effects of a Ketogenic Diet on Exercise Metabolism and Physical Performance in Off-Road Cyclists

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.

Exercise and Regulation of Lipid Metabolism

“…6 Indeed, several studies indicate that acute provision of excess lipid prior to or during exercise results in use of FAs as the primary metabolic fuel during moderate-intensity exhaustive exercise, whereas carbohydrate use is slowed. [106][107][108][109][110][111][112][113] However, it is important to note that exercise performance in response to short-term exposure to a ketogenic diet (<6 days) often declines, despite substantially enhancing fat oxidation. [108][109][110][111] Alternatively, mounting evidence indicates that prolonged (>4 weeks) consumption of a low-carbohydrate, ketogenic diet not only enhances fat utilization but can either maintain or improve exercise performance.…”

“…[108][109][110][111] Alternatively, mounting evidence indicates that prolonged (>4 weeks) consumption of a low-carbohydrate, ketogenic diet not only enhances fat utilization but can either maintain or improve exercise performance. [113][114][115][116] One such study performed by Zajac et al 113 compared the effects of a 4-week ketogenic diet (70% fat, 15% protein, and 15% carbohydrate) versus a mixed meal diet (30% fat, 20% protein, and 50% carbohydrate) on endurance exercise cycling performance. The authors found that the ketogenic diet increased energy expenditure (higher VO 2 ) and fat utilization (reduced RER and greater clearance of plasma lipid) during moderateintensity exercise.…”

“…These data suggest that the metabolic adaptations in response to a ketogenic diet are sufficient to at least maintain endurance capacity during exhaustive submaximal exercise, while simultaneously maximizing lipid utilization. Equally interesting are findings indicating keto-adapted individuals exhibit reduced inflammatory markers and muscle damage after an exercise bout, 113,114,117,118 indicating ketogenic diets may significantly facilitate postexercise recovery.…”

Optimal Nutrition for Endurance Exercise: A Systematic Review

“…Fat adaptation has become popular among competitive endurance athletes [29]. By improving fat oxidation, it is hypothesized that one may rely less on muscle glycogen and thus improve performance [30].…”

Verificação do dano muscular através da avaliação da concentração de creatina quinase em indivíduos não atletas após prova de ciclismo não competitivo

“…Outros estudos que também avaliaram os níveis de CK em ciclistas obtiveram resultados similares. Um estudo recente com oito ciclistas competitivos avaliou diversos parâmetros bioquímicos, incluindo os níveis de CK; houve elevação nos níveis sérios de CK, contudo não foi encontrada diferença significativa após esforço máximo por 105 minutos no cicloergô-metro [22]. Outro estudo avaliou as concentrações séricas de CK em 10 atletas de iromann, verificando um aumento significativo imediatamente após a prova e ainda quatro dias depois.…”