Metabolic phenotypes and the gut microbiota in response to dietary resistant starch type 2 in normal-weight subjects: a randomized crossover trial

Randomized, double-blind, crossover trial in 19 healthy Chinese adults aged 18 to 55 years with BMI < 24 kg/m2. Participants completed both study periods while maintaining stable physical activity and consuming a controlled diet.

Participants received oral HAM-RS2 (resistant starch type 2) at a dose providing 40 g/day of resistant starch for 4 weeks, taken daily with three identical meals per day. The active regimen was compared with a matched control starch providing 0 g/day resistant starch in a randomized crossover design under controlled dietary conditions.

Resistant starch type 2 had beneficial effects on abdominal adiposity and several metabolic and gut-related outcomes. Visceral fat area fell from 26.43 ± 2.63 cm2 to 21.70 ± 1.78 cm2 (p < 0.001) and subcutaneous fat area from 135.81 ± 10.57 cm2 to 127.33 ± 10.66 cm2 (p = 0.031). The intervention also increased 30 min insulin, 30 min C-peptide, active GLP-1, and serum acetate, while LDL-C decreased from 2.62 ± 0.11 to 2.57 ± 0.14; no adverse events were reported. The gut microbiota shifted, including an increase in Ruminococcaceae_UCG-005 and decreases in multiple other genera, supporting a microbiome-linked effect of RS2 on abdominal adiposity and glucose metabolism.

The trial was small, with only 19 completers, which limits precision and subgroup inference. The intervention was short at 4 weeks and enrolled only healthy normal-weight Chinese adults, so generalizability to other populations is limited. The controlled feeding design improves internal validity but may reduce real-world applicability.