Effects of a high-protein, low-carbohydrate v. high-protein, moderate-carbohydrate weight-loss diet on antioxidant status, endothelial markers and plasma indices of the cardiometabolic profile

There are concerns that weight-loss (WL) diets based on very low carbohydrate (LC) intake have a negative impact on antioxidant status and biomarkers of cardiovascular and metabolic health. Obese men (n 16) participated in a randomised, cross-over design diet trial, with food provided daily, at approximately 8.3 MJ/d (approximately 70% of energy maintenance requirements). They were provided with two high-protein diets (30% of energy), each for a 4-week period, involving a LC (4% carbohydrate) and a moderate carbohydrate (MC, 35% carbohydrate) content. Body weight was measured daily, and weekly blood samples were collected. On average, subjects lost 6.75 and 4.32 kg of weight on the LC and MC diets, respectively (P<0.001, SED 0.350). Although the LC and MC diets were associated with a small reduction in plasma concentrations of retinol, vitamin E (alpha-tocopherol) and beta-cryptoxanthin (P<0.005), these were still above the values indicative of deficiency. Interestingly, plasma vitamin C concentrations increased on consumption of the LC diet (P<0.05). Plasma markers of insulin resistance (P<0.001), lipaemia and inflammation (P<0.05, TNF-alpha and IL-10) improved similarly on both diets. There was no change in other cardiovascular markers with WL. The present data suggest that a LC WL diet does not impair plasma indices of cardiometabolic health, at least within 4 weeks, in otherwise healthy obese subjects. In general, improvements in metabolic health associated with WL were similar between the LC and MC diets. Antioxidant supplements may be warranted if LC WL diets are consumed for a prolonged period.