Editorial

Aim: Compare the long-term effects of an energy-restricted very low-carbohydrate, high-fat (LC) diet with an isocaloric high-carbohydrate, low-fat (HC) diet on exercise tolerance and capacity in overweight and obese adults.

Methods: Seventy-six adults (25 males; age 49.2 ± 1.1 years; BMI 33.6 ± 0.5 kg/m²) were randomized to either a hypocaloric (6–7 MJ/day) LC diet (35% protein, 4% carbohydrate, 61% fat) or isocaloric HC diet (24% protein, 46% carbohydrate, 30% fat) for 52 weeks. Pre- and postintervention, participants’ body weight and composition, handgrip, and isometric knee extensor strength were assessed and participants performed an incremental exercise test to exhaustion.

Results: Forty-three participants completed the study (LC = 23; HC = 20). Overall, peak relative oxygen uptake increased (+11.3%) and reductions occurred in body weight (?14.6%), body fat percentage (?6.9% absolute]), isometric knee extensor strength (?12.4%), handgrip strength (?4.5%), and absolute peak oxygen uptake (?5.2%; p ≤ 0.02 time for all) with no diet effect (p ≥ 0.18). During submaximal exercise, rating of perceived exertion did not change in either group (p = 0.16 time, p = 0.59 Time × Group). Compared to the HC diet, the LC diet had greater reductions in respiratory exchange ratio (LC ?0.04 ± 0.01, HC ?0.00 ± 0.01; p = 0.03), and increased fat oxidation (LC 15.0 ± 5.3% of energy expenditure], HC 0.5 ± 3.9%; p = 0.04).

Conclusion: In overweight and obese patients, an LC diet promoted greater fat utilization during submaximal exercise. Both an LC diet and an HC diet had similar effects on aerobic capacity and muscle strength, suggesting that long-term consumption of an LC weight loss diet does not adversely affect physical function or the ability to perform exercise.