High-protein/high red meat and high-carbohydrate weight-loss diets do not differ in their effect on faecal water genotoxicity tested by use of the WIL2-NS cell line and with other biomarkers of bowel health.

The impact of popular weight-loss diets with different macronutrient profiles on bowel health in humans has not been previously assessed. The aim of this study was to investigate whether a high-protein/high red meat (HP) diet influences faecal water genotoxicity and other standard biomarkers of bowel health differently compared with a high-carbohydrate (HC) diet. Thirty-three male subjects were randomly assigned to a HP (35% protein, 40% carbohydrate) or HC (17% protein, 58% carbohydrate) isocaloric energy-restricted dietary intervention consisting of 12 weeks intensive weight loss followed by weight maintenance for up to 52 weeks. Faecal samples were collected at 0, 12 and 52 weeks. Faecal water genotoxicity was assessed in the WIL2-NS human B lymphoblastoid cell line by means of the cytokinesis-block micronucleus cytome assay. Average weight loss after 12 weeks was 9.3 ± 0.7kg for both diets, with no further change in weight at 52 weeks. Two-way ANOVA showed a significant effect with time (P<0.001) but not diet for total DNA damage, with a reduction in genotoxicity after 12 weeks intensive weight loss, and a subsequent increase after 9 months weight maintenance to levels not significantly different from baseline. There was no significant effect for time or diet on faecal pH, short-chain fatty acid excretion, phenol or p-cresol. Results suggest that HP and HC weight-loss diets may modify the carcinogenic profile of the bowel contents such that weight loss may exert a beneficial effect by reducing genotoxic load in the short term; however, these results require verification against a non-weight-loss control.