Comparative effects of very low-carbohydrate, high-fat and high-carbohydrate, low-fat weight-loss diets on bowel habit and faecal short-chain fatty acids and bacterial populations

Abstract

Very low-carbohydrate diets are often used to promote weight loss, but their effects on bowel health and function are largely unknown. We compared the effects of a very low-carbohydrate, high-fat (LC) diet with a high-carbohydrate, high-fibre, low-fat (HC) diet on indices of bowel health and function. In a parallel study design, ninety-one overweight and obese participants (age 505) years; BMI 332) kg/m2) were randomly assigned to either an energy-restricted (about 6 61 (sd 147) g), defecation frequency, faecal excretion and concentrations of butyrate ( 5 (sd 10 37) mmol/l) and total SCFA (15) v. 8 (sd 4305 time 0 0·25). Faecal form, pH, ammonia concentration and numbers of coliforms and Escherichia coli did not change with either diet. No differences between the diets were evident for incidences of adverse gastrointestinal symptoms, which suggests that both diets were well tolerated. Under energy-restricted conditions, a short-term LC diet lowered stool weight and had detrimental effects on the concentration and excretion of faecal SCFA compared with an HC diet. This suggests that the long-term consumption of an LC diet may increase the risk of development of gastrointestinal disorders.