Comparative effects of a low-fat diet and a high-fat, ketogenic diet on body composition and athletic performance in recreationally-active males and females

Athletes often manipulate dietary carbohydrates, and one dietary approach is a low-carbohydrate, high-fat, ketogenic diet (KD). Therefore, the purpose of the present investigation was to compare effects of a KD and a control diet (CD) on body composition and athletic performance in trained males and females. In a parallel-arm, longitudinal, diet- and exercise-controlled design, 39 participants (23 ± 4.4 years; 75.8 ± 15.5 kg; 169.4 ± 8.3 cm) exercised for 9 weeks while consuming either a KD or a CD. Diets were matched for energy intake. Non-protein macronutrients for the KD (percent energy as carbohydrate:fat:protein, 5:72:23) differed from the CD (53:24:23). Pre- and post-testing were conducted during the weeks prior to and following the intervention. A 5-component (5C) model of body composition was calculated using Dual X-ray Absorptiometry (DXA)-determined bone mineral content (BMC) and fat mass (FM), bioelectric impedance spectroscopy (BIS)-determined intra- (ICF) and extracellular fluid (ECF), and scale weight data. Tests of athletic performance included vertical jump (VJ), 1-repetition maximum (1RM) in the back squat and bench press, repeated Wingate sprints, and a 5 km time trial (5k) run. A significant group by time effect for body weight (p = 0.031) was observed for KD (-1.1 ± 1.9 kg) versus CD (+0.3 ± 1.9 kg), and this was associated with a trend (p = 0.075) for greater loss of FM (KD: -3.2 ± 2.8; CD: -1.9 ± 1.6 kg), which was lost with the 5C model (p = 0.260). KD reduced (p = 0.017) ECF compared to CD (KD: -0.3 ± 0.6; CD: +0.3 ± 0.9 L), yet increases in lean soft tissue (LST) were identical between groups (+2.1 ± 1.5 kg). KD tended to reduce (p = 0.054) peak power (PP) output during the first Wingate sprint (KD: -28.1 ± 85.9; CD: +25.1 ± 79.7 W). Recovery of PP between the first and final set was significantly greater (p = 0.042) in KD (+155.9 ± 147.4 W) than CD (+70.0 ± 98.6 W). The present data suggest that overall exercise adaptations are not compromised following 9 weeks of a KD. A KD reduces body weight, predominately as FM.