A low-carbohydrate high-fat diet significantly improved reflux symptoms and gastrointestinal-related quality of life in participants with obesity while altering fecal short-chain fatty acid concentrations, according to a recent study.

In the randomized controlled CARBFUNC trial, published in Clinical Nutrition, researchers investigated the effects of varying carbohydrate amounts and qualities on gastrointestinal (GI) symptoms, gastrointestinal-related quality of life (GI-QoL), fatigue, and fecal short-chain fatty acid (SCFA) concentrations in adults with obesity. A total of 193 participants were randomized to one of three isocaloric, iso-proteinic diets: a higher-carbohydrate, lower-fat diet with refined carbohydrates (A-HCLF), a higher-carbohydrate, lower-fat diet with minimally processed carbohydrates (C-HCLF), and a low-carbohydrate, high-fat diet (LCHF). Participants followed these diets for 3 and 12 months, with outcomes assessed through questionnaires and fecal sample analysis.

Weight loss was similar across all groups (5%-7% at 12 months). The LCHF group demonstrated significant improvements in reflux symptoms compared to the A-HCLF group, as measured by the Gastroesophageal Reflux Disease Questionnaire (mean change: −0.62 [95% CI: −1.18, −0.048], p = 0.034 at 3 months; −1.03 [95% CI: −1.88, −0.19], p = 0.017 at 12 months). GI-QoL, assessed by the Short-Form Nepean Dyspepsia Index, also improved in the LCHF group at 3 months (mean change: −1.88 [95% CI: −3.22, −0.52], p = 0.007), though this was not significant at 12 months.

Fecal SCFA concentrations showed marked changes. The LCHF diet significantly reduced acetic acid at 3 months (−6.41 mmol/kg [95% CI: −12.8, −0.047], p = 0.048) and total SCFAs at 12 months (−21.3 mmol/kg [95% CI: −38.0, −4.56], p = 0.013). In comparison, the C-HCLF group significantly increased fecal butyric acid at 3 months (4.97 mmol/kg [95% CI: 1.71, 8.23], p = 0.003), highlighting a differential impact of carbohydrate quality on SCFA production.

No significant between-group differences were observed in irritable bowel syndrome severity or fatigue scores at either 3 or 12 months. These findings suggest that while diet composition significantly influences reflux and GI-QoL, its impact on other GI symptoms and fatigue may be limited.

Study limitations include a high dropout rate and the exploratory nature of secondary outcome analyses, which may affect the generalizability of the findings. 

Conflict of disclosures can be found in the published study.