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.

摘要

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 50.6 (SD 7.5) years; BMI 33.7 (SD 4.2) kg/m2) were randomly assigned to either an energy-restricted (about 6-7MJ, 30% deficit) planned isoenergetic LC or HC diet for 8 weeks. At baseline and week 8, 24 h urine and faecal collections were obtained and a bowel function questionnaire was completed. Compared with the HC group, there were significant reductions in the LC group for faecal output (21 (SD 145) v. -61 (SD 147) g), defecation frequency, faecal excretion and concentrations of butyrate (-0.5 (SD 10.4) v. -3.9 (SD 9.7) mmol/l) and total SCFA (1.4 (SD 40.5) v. -15.8 (SD 43.6) mmol/l) and counts of bifidobacteria (P<0.05 time x diet interaction, for all). Urinary phenols and p-cresol excretion decreased (P<=0.003 for time) with no difference between diets (P