The efficacy of ad libitum low-fat diets in reducing body weight and fat in overweight and obese adults remains controversial.
We examined the effect of a 12-week low-fat, high–complex carbohydrate diet alone (HI-CHO) and in combination with aerobic exercise training (HI-CHO + EX) on body weight and composition in 34 individuals with impaired glucose tolerance (20 women and 14 men; mean ± SEM age, 66 ± 1 years). Participants were randomly assigned to a control diet (41% fat, 14% protein, 45% carbohydrates, and 7 g of fiber per 1000 kcal), a HI-CHO diet (18% fat, 19% protein, 63% carbohydrates, and 26 g of fiber per 1000 kcal), or a HI-CHO diet plus endurance exercise 4 d/wk, 45 min/d, at 80% peak oxygen consumption (HI-CHO + EX). Participants were provided 150% of estimated energy needs and were instructed to consume food ad libitum. Total food intake, body composition, resting metabolic rate, and substrate oxidation were measured.
There was no significant difference in total food intake among the 3 groups and no change in energy intake over time. The HI-CHO + EX and HI-CHO groups lost more body weight (–4.8 ± 0.9 kg [P = .003] and –3.2 ± 1.2 kg [P = .02]) and a higher percentage of body fat (–3.5% ± 0.7% [P = .01] and –2.2% ± 1.2% [P = .049]) than controls (–0.1 ± 0.6 kg and 0.2% ± 0.6%). In addition, thigh fat area decreased in the HI-CHO (P = .003) and HI-CHO + EX (P<.001) groups compared with controls. High carbohydrate intake and weight loss did not result in a decreased resting metabolic rate or reduced fat oxidation.
A high-carbohydrate diet consumed ad libitum, with no attempt at energy restriction or change in energy intake, results in losses of body weight and body fat in older men and women.