Background:
Ketogenic diets (KDs) that elevate
beta-hydroxybutyrate (BHB) promote weight and fat loss. Exogenous
ketones, such as
ketone salts (KS), 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. Purpose: 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. Methods:
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; n = 12) or placebo (KD + PL; n = 13). A matched comparison group (n = 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. Results: The KD induced nutritional
ketosis (>1.0 mM capillary BHB) throughout the study (p < 0.001), with higher fasting concentrations observed in KD + KS than KD + PL for the first 2 weeks (p < 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 (p < 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 (p < 0.01) and trended higher in KD + PL compared to KD + KS (p = 0.076), whereas the
nitrogen excretion during KD + KS was similar to LFD (p > 0.05). Conclusion: 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.