Effects of dietary carbohydrate-to-fat ratio on the gut microbiome following weight loss.

In the Framingham State Food Study (FS(2)) randomized feeding trial, varying carbohydrate-to-fat ratio during 20-week weight-loss maintenance did not change gut microbiome composition, despite diet-induced metabolic context.

• Why it matters: Carbohydrate restriction can improve metabolic health, but its specific effects on the gut microbiome are unclear, especially during post–weight-loss maintenance.
• What they did: Adults with overweight and obesity underwent calorie restriction to lose weight, then were randomized to low-carb (20% carb, 60% fat), moderate-carb (40% carb, 40% fat), or high-carb (60% carb, 20% fat) diets for 20 weeks, with microbiome profiling and dietary confounder control.
• The result: Microbiome shifts occurred after weight loss, but no compositional changes were detected across carbohydrate-to-fat ratios; additionally, Shuttleworthia abundance correlated positively with maintenance of total energy expenditure after weight loss.

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