Associations of Dietary Intake with the Intestinal Microbiota and Short-Chain Fatty Acids Among Young Adults with Type 1 Diabetes and Overweight or Obesity

Abstract

Background: Diet, a key component of type 1 diabetes (T1D) management, modulates the intestinal microbiota and its metabolically active byproducts-including SCFA-through fermentation of dietary carbohydrates such as fiber. However, the diet-microbiome relationship remains largely unexplored in longstanding T1D.

Objectives: We evaluated whether increased carbohydrate intake, including fiber, is associated with increased SCFA-producing gut microbes, SCFA, and intestinal microbial diversity among young adults with longstanding T1D and overweight or obesity.

Methods: Young adult men and women with T1D for ≥1 y, aged 19-30 y, and BMI of 27.0-39.9 kg/m² at baseline provided stool samples at baseline and 3, 6, and 9 mo of a randomized dietary weight loss trial. Diet was assessed by 1-2 24-h recalls. The abundance of SCFA-producing microbes was measured using 16S rRNA gene sequencing. GC-MS measured fecal SCFA (acetate, butyrate, propionate, and total) concentrations. Adjusted and Bonferroni-corrected generalized estimating equations modeled associations of dietary fiber (total, soluble, and pectins) and carbohydrate (available carbohydrate, and fructose) with microbiome-related outcomes. Primary analyses were restricted to data collected before COVID-19 interruptions.

Results: Fiber (total and soluble) and carbohydrates (available and fructose) were positively associated with total SCFA and acetate concentrations (n = 40 participants, 52 visits). Each 10 g/d of total and soluble fiber intake was associated with an additional 8.8 μmol/g (95% CI: 4.5, 12.8 μmol/g; P = 0.006) and 24.0 μmol/g (95% CI: 12.9, 35.1 μmol/g; P = 0.003) of fecal acetate, respectively. Available carbohydrate intake was positively associated with SCFA producers Roseburia and Ruminococcus gnavus. All diet variables except pectin were inversely associated with normalized abundance of Bacteroides and Alistipes. Fructose was inversely associated with Akkermansia abundance.

Conclusions: In young adults with longstanding T1D, fiber and carbohydrate intake were associated positively with fecal SCFA but had variable associations with SCFA-producing gut microbes. Controlled feeding studies should determine whether gut microbes and SCFA can be directly manipulated in T1D.

Keywords: fiber; gut microbiome; obesity; short-chain fatty acids; type 1 diabetes.

FIGURE 1

Associations of diet with SCFA-producing gut microbes, fecal SCFA, and intestinal microbial diversity among ACT1ON participants (n = 40). The heatmaps show standardized β estimates from crude (A) and covariate-adjusted (B) GEE models with a repeated statement to consider multiple measurements within participants over time, for the primary pre–COVID-19 analysis. P values were Bonferroni-corrected and statistically significant at P < 0.1 (asterisks). Results are from 40 participants (52 visits) for SCFA and from 40 participants (48 visits) for abundance of intestinal microbes and intestinal microbial diversity. ACT1ON, Advancing Care for Type 1 Diabetes and Obesity Network; avail., available; GEE, generalized estimating equation; sol., soluble; tot., total.

FIGURE 2

Raw visualizations of dietary intake in association with fecal SCFA among ACT1ON participants (n = 40). Scatterplots of raw pre–COVID-19 data show associations of total fiber, soluble fiber, available carbohydrate, and fructose intake (all g/d) with fecal acetate (A, B, C, D) and total fecal SCFA (E, F, G, H, both μmol/g), respectively. All associations were statistically significant after Bonferroni correction of crude or adjusted modeled results (P < 0.1), except for the associations of soluble fiber and fructose intake with total fecal SCFA (F, G, P = 0.1). Data are from 40 participants (52 visits) and were modeled using generalized estimating equations, which included a repeated statement to account for multiple measurements within participants over time. ACT1ON, Advancing Care for Type 1 Diabetes and Obesity Network.