Long-term effects of popular dietary approaches on weight loss and features of insulin resistance

Objective: High-carbohydrate (HC)-high-fibre diets are recommended for weight loss and for treating and preventing diseases such as diabetes and cardiovascular disease. We report a randomised trial comparing high-fat (HF) and high-protein (HP) diets with the conventional approach. Research design and methods: A total of 93 overweight insulin-resistant women received advice following randomisation to HF, HP or HC dietary regimes, to achieve weight loss followed by weight maintenance over 12 months. Weight, body composition and measures of carbohydrate and lipid metabolism were investigated. Results: Retention rates were 93% for HP and 75% for HC and HF. Features of the metabolic syndrome improved in all groups during the first 6 months, to a greater extent on HF and HP than an HC. During the second 6 months the HF group had increases in waist circumference (mean difference 4.4cm (95% CI 3.0, 5.8)), fat mass (2.3 kg (1.5, 3.1)), triglycerides (0.28 mmol/l (0.09, 0.46)) and 2 h glucose (0.70 mmol/l (0.22, 1.18)). Overall there was substantial sustained improvement in waist circumference, triglycerides and insulin in the HP group and sustained but more modest changes on HC. Dietary compliance at 12 months was poor in all groups. Conclusions: HP and HC approaches appear to be appropriate options for insulin-resistant individuals. When recommending HP diets appropriate composition of dietary fat must be ensured. HC diet recommendations must include advice regarding appropriate high-fibre, low glycaemic index foods.