The Effects of a 6-Week Controlled, Hypocaloric Ketogenic Diet, With and Without Exogenous Ketone Salts, on Body Composition Responses

Abstract

<b>Background:</b> Ketogenic diets (<b>KDs</b>) that elevate beta-hydroxybutyrate (<b>BHB</b>) promote weight and fat loss. Exogenous ketones, such as ketone salts (<b>KS</b>), also elevate BHB concentrations with the potential to protect against muscle loss during caloric restriction. Whether augmenting ketosis with KS impacts body composition responses to a well-formulated KD remains unknown. <b>Purpose:</b> To explore the effects of energy-matched, hypocaloric KD feeding (<50 g carbohydrates/day; 1.5 g/kg/day protein), with and without the inclusion of KS, on weight loss and body composition responses. <b>Methods:</b> Overweight and obese adults were provided a precisely defined hypocaloric KD (~75% of energy expenditure) for 6 weeks. In a double-blind manner, subjects were randomly assigned to receive ~24 g/day of a racemic BHB-salt (KD + KS; <i>n</i> = 12) or placebo (KD + PL; <i>n</i> = 13). A matched comparison group (<i>n</i> = 12) was separately assigned to an isoenergetic/isonitrogenous low-fat diet (LFD). Body composition parameters were assessed by dual x-ray absorptiometry and magnetic resonance imaging. <b>Results:</b> The KD induced nutritional ketosis (>1.0 mM capillary BHB) throughout the study (<i>p</i> < 0.001), with higher fasting concentrations observed in KD + KS than KD + PL for the first 2 weeks (<i>p</i> < 0.05). There were decreases in body mass, whole body fat and lean mass, mid-thigh muscle cross-sectional area, and both visceral and subcutaneous adipose tissues (<i>p</i> < 0.001), but no group differences between the two KDs or with the LFD. Urine nitrogen excretion was significantly higher in KD + PL than LFD (<i>p</i> < 0.01) and trended higher in KD + PL compared to KD + KS (<i>p</i> = 0.076), whereas the nitrogen excretion during KD + KS was similar to LFD (<i>p</i> > 0.05). <b>Conclusion:</b> Energy-matched hypocaloric ketogenic diets favorably affected body composition but were not further impacted by administration of an exogenous BHB-salt that augmented ketosis. The trend for less nitrogen loss with the BHB-salt, if manifested over a longer period of time, may contribute to preserved lean mass.