A Plant-Based High-Carbohydrate, Low-Fat Diet in Overweight Individuals in a 16-Week Randomized Clinical Trial: The Role of Carbohydrates

Abstract

The effects of carbohydrates on body weight and insulin sensitivity are controversial. In this 16-week randomized clinical trial, we tested the role of a low-fat, plant-based diet on body weight, body composition and insulin resistance. As a part of this trial, we investigated the role of changes in carbohydrate intake on body composition and insulin resistance. Participants (n = 75) were randomized to follow a plant-based high-carbohydrate, low-fat (vegan) diet (n = 38) or to maintain their current diet (n = 37). Dual-energy X-ray absorptiometry was used to measure body composition. Insulin resistance was assessed with the Homeostasis Model Assessment (HOMA-IR) index. A repeated measure ANOVA model was used to test the between-group differences from baseline to 16 weeks. A linear regression model was used to test the relationship between carbohydrate intake, and body composition and insulin resistance. Weight decreased significantly in the vegan group (treatment effect -6.5 [95% CI -8.9 to -4.1] kg; Gxt, p < 0.001). Fat mass was reduced in the vegan group (treatment effect -4.3 [95% CI -5.4 to -3.2] kg; Gxt, p < 0.001). HOMA-IR was reduced significantly in the vegan group (treatment effect -1.0 [95% CI -1.2 to -0.8]; Gxt, p = 0.004). Changes in consumption of carbohydrate, as a percentage of energy, correlated negatively with changes in BMI (r = -0.53, p < 0.001), fat mass (r = -0.55, p < 0.001), volume of visceral fat (r = -0.35, p = 0.006), and HOMA (r = -0.27, p = 0.04). These associations remained significant after adjustment for energy intake. Changes in consumption of total and insoluble fiber correlated negatively with changes in BMI (r = -0.43, p < 0.001; and r = -0.46, p < 0.001, respectively), fat mass (r = -0.42, p < 0.001; and r = -0.46, p < 0.001, respectively), and volume of visceral fat (r = -0.29, p = 0.03; and r = -0.32, p = 0.01, respectively). The associations between total and insoluble fiber and changes in BMI and fat mass remained significant even after adjustment for energy intake. Increased carbohydrate and fiber intake, as part of a plant-based high-carbohydrate, low-fat diet, are associated with beneficial effects on weight, body composition, and insulin resistance.

Keywords: carbohydrates; diet; fiber; nutrition; plant-based; vegan.

Figure 1

Enrollment of the Participants and Completion of the Study.

Figure 2

Changes in body weight, fat mass, and insulin resistance in the vegan and control group at baseline and after 16 weeks. (A) Body Weight, Gxt p < 0.001; (B) Fat Mass, Gxt p < 0.001; (C) Visceral Adipose Tissue (VAT) Volume, Gxt p < 0.001; and (D) Homeostatic Model Assessment Insulin Resistance (HOMA-IR), Gxt p = 0.004. Gxt is interaction between group and time from the ANOVA model. *** for p < 0.001. Data are given as means with 95% confidence intervals.

Figure 3

Regression models for changes in carbohydrate intake and changes in body composition, fat mass, and insulin resistance in both groups combined. (A) Total carbohydrate intake and change in BMI: r = −0.36; p = 0.005; (B) Total carbohydrate intake and change in volume of visceral fat: r = −0.45; p < 0.001; (C) % carbohydrate intake from total energy and change in BMI: r = −0.53, p < 0.001; (D) % carbohydrate intake from total energy and change in fat mass: r = −0.55, p < 0.001; (E) % carbohydrate intake from total energy and change in volume of visceral fat: r = −0.35, p = 0.006; (F) % carbohydrate intake from total energy and change in HOMA: r = −0.27, p = 0.04; (G) Total fiber intake and change in BMI: r = −0.43, p < 0.001; (H) Total fiber intake and change in fat mass: r = −0.42; p < 0.001; (I) Total fiber intake and change in volume of visceral fat: r = −0.29; p = 0.003; (J) Intake of insoluble fiber and change in BMI: r = −0.46, p < 0.001; (K) Intake of insoluble fiber and change in fat mass: r = −0.46, p < 0.001; (L) Intake of insoluble fiber and change in volume of visceral fat: r = −0.32, p = 0.01.

Figure 3

Regression models for changes in carbohydrate intake and changes in body composition, fat mass, and insulin resistance in both groups combined. (A) Total carbohydrate intake and change in BMI: r = −0.36; p = 0.005; (B) Total carbohydrate intake and change in volume of visceral fat: r = −0.45; p < 0.001; (C) % carbohydrate intake from total energy and change in BMI: r = −0.53, p < 0.001; (D) % carbohydrate intake from total energy and change in fat mass: r = −0.55, p < 0.001; (E) % carbohydrate intake from total energy and change in volume of visceral fat: r = −0.35, p = 0.006; (F) % carbohydrate intake from total energy and change in HOMA: r = −0.27, p = 0.04; (G) Total fiber intake and change in BMI: r = −0.43, p < 0.001; (H) Total fiber intake and change in fat mass: r = −0.42; p < 0.001; (I) Total fiber intake and change in volume of visceral fat: r = −0.29; p = 0.003; (J) Intake of insoluble fiber and change in BMI: r = −0.46, p < 0.001; (K) Intake of insoluble fiber and change in fat mass: r = −0.46, p < 0.001; (L) Intake of insoluble fiber and change in volume of visceral fat: r = −0.32, p = 0.01.