Abstract
Adopting low carbohydrate, ketogenic diets remains a controversial issue for individuals who resistance train given that this form of dieting has been speculated to reduce skeletal muscle glycogen levels and stifle muscle anabolism. We sought to characterize the effects of a 12-week ketogenic diet (KD) on body composition, metabolic, and performance parameters in participants who trained recreationally at a local CrossFit facility. Twelve participants (nine males and three females, 31 ± 2 years of age, 80.3 ± 5.1 kg body mass, 22.9 ± 2.3% body fat, 1.37 back squat: body mass ratio) were divided into a control group (CTL; n = 5) and a KD group (n = 7). KD participants were given dietary guidelines to follow over 12 weeks while CTL participants were instructed to continue their normal diet throughout the study, and all participants continued their CrossFit training routine for 12 weeks. Pre, 2.5-week, and 12-week anaerobic performance tests were conducted, and pre- and 12-week tests were performed for body composition using dual X-ray absorptiometry (DXA) and ultrasound, resting energy expenditure (REE), blood-serum health markers, and aerobic capacity. Additionally, blood beta hydroxybutyrate (BHB) levels were measured weekly. Blood BHB levels were 2.8- to 9.5-fold higher in KD versus CTL throughout confirming a state of nutritional ketosis. DXA fat mass decreased by 12.4% in KD (p = 0.053). DXA total lean body mass changes were not different between groups, although DXA dual-leg lean mass decreased in the KD group by 1.4% (p = 0.068), and vastus lateralis thickness values decreased in the KD group by ~8% (p = 0.065). Changes in fasting glucose, HDL cholesterol, and triglycerides were similar between groups, although LDL cholesterol increased ~35% in KD (p = 0.048). Between-group changes in REE, one-repetition maximum (1-RM) back squat, 400 m run times, and VO2peak were similar between groups. While our n-sizes were limited, these preliminary data suggest that adopting a ketogenic diet causes marked reductions in whole-body adiposity while not impacting performance measures in recreationally-trained CrossFit trainees. Whether decrements in dual-leg muscle mass and vastus lateralis thickness in KD participants were due to fluid shifts remain unresolved, and increased LDL-C in these individuals warrants further investigation.
Highlights
Dietary practices that facilitate losses in body fat while maintaining or leading to an accretion of muscle mass have been of interest to individuals who resistance train recreationally
One ketogenic diet (KD) participant presented with a strength: body mass ratio of 0.93, but the investigators decided to include the subject in the analyses due to limited n-sizes
We have demonstrated in rats that six weeks of KD feeding does not adversely affect markers of muscle hypertrophy, and that KD- and Western diet (WD)-fed rats experienced similar increases in hind limb muscle masses and molecular markers suggestive of anabolism when voluntarily trained on resistance-loaded running wheels over a six-week period [5]
Summary
Dietary practices that facilitate losses in body fat while maintaining or leading to an accretion of muscle mass have been of interest to individuals who resistance train recreationally In this regard, there is overwhelming support that higher protein diets are able to improve muscle mass gains while not affecting body fat [1,2,3,4]. Given that the diet is very low in carbohydrates, it has been posited that a KD will reduce skeletal muscle glycogen levels and chronically increase intramuscular AMP-activated protein kinase (AMPK) signaling These findings have been reported in mice [8,9], and have led the authors to speculate that KD feeding may lead to a chronic suppression of mammalian target of rapamycin complex 1 (mTORc1) signaling and muscle protein synthesis, as well as an eventual stagnation in the anabolic response to resistance training and/or a loss in muscle mass in humans
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