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 com-npared 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 healthnand 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/m2n) werenrandomly assigned to either an energy-restricted (about 6–7MJ, 30% deficit) planned isoenergetic LC or HC diet for 8 weeks. At baseline andnweek 8, 24 h urine and faecal collections were obtained and a bowel function questionnaire was completed. Compared with the HC group, therenwere significant reductions in the LC group for faecal output (21 (SD 145) v. 261 (SD 147) g), defecation frequency, faecal excretion and con-ncentrations of butyrate (20·5 (SD 10·4) v. 23·9 (SD 9·7) mmol/l) and total SCFA (1·4 (SD 40·5) v. 215·8 (SD 43·6) mmol/l) and counts of bifi-ndobacteria (P,0·05 time £ diet interaction, for all). Urinary phenols and p-cresol excretion decreased (P#0·003 for time) with no differencenbetween diets (P$0·25). Faecal form, pH, ammonia concentration and numbers of coliforms and Escherichia coli did not change with eitherndiet. No differences between the diets were evident for incidences of adverse gastrointestinal symptoms, which suggests that both diets werenwell tolerated. Under energy-restricted conditions, a short-term LC diet lowered stool weight and had detrimental effects on the concentrationnand excretion of faecal SCFA compared with an HC diet. This suggests that the long-term consumption of an LC diet may increase the risknof development of gastrointestinal disorders.