Vegetarian diet improves insulin resistance and oxidative stress markers more than conventional diet in subjects with Type 2 diabetes

Abstract

Aims: The aim of this study was to compare the effects of calorie-restricted vegetarian and conventional diabetic diets alone and in combination with exercise on insulin resistance, visceral fat and oxidative stress markers in subjects with Type 2 diabetes.

Methods: A 24-week, randomized, open, parallel design was used. Seventy-four patients with Type 2 diabetes were randomly assigned to either the experimental group (n = 37), which received a vegetarian diet, or the control group (n = 37), which received a conventional diabetic diet. Both diets were isocaloric, calorie restricted (-500 kcal/day). All meals during the study were provided. The second 12 weeks of the diet were combined with aerobic exercise. Participants were examined at baseline, 12 weeks and 24 weeks. Primary outcomes were: insulin sensitivity measured by hyperinsulinaemic isoglycaemic clamp; volume of visceral and subcutaneous fat measured by magnetic resonance imaging; and oxidative stress measured by thiobarbituric acid reactive substances. Analyses were by intention to treat.

Results: Forty-three per cent of participants in the experimental group and 5% of participants in the control group reduced diabetes medication (P < 0.001). Body weight decreased more in the experimental group than in the control group [-6.2 kg (95% CI -6.6 to -5.3) vs. -3.2 kg (95% CI -3.7 to -2.5); interaction group × time P = 0.001]. An increase in insulin sensitivity was significantly greater in the experimental group than in the control group [30% (95% CI 24.5-39) vs. 20% (95% CI 14-25), P = 0.04]. A reduction in both visceral and subcutaneous fat was greater in the experimental group than in the control group (P = 0.007 and P = 0.02, respectively). Plasma adiponectin increased (P = 0.02) and leptin decreased (P = 0.02) in the experimental group, with no change in the control group. Vitamin C, superoxide dismutase and reduced glutathione increased in the experimental group (P = 0.002, P < 0.001 and P = 0.02, respectively). Differences between groups were greater after the addition of exercise training. Changes in insulin sensitivity and enzymatic oxidative stress markers correlated with changes in visceral fat.

Conclusions: A calorie-restricted vegetarian diet had greater capacity to improve insulin sensitivity compared with a conventional diabetic diet over 24 weeks. The greater loss of visceral fat and improvements in plasma concentrations of adipokines and oxidative stress markers with this diet may be responsible for the reduction of insulin resistance. The addition of exercise training further augmented the improved outcomes with the vegetarian diet.

Trial registration: ClinicalTrials.gov NCT00883038.

FIGURE 1

Enrollment of the participants and completion of the study. T2DM, Type 2 diabetes mellitus.

FIGURE 2

Anthropometric variables, LDL cholesterol, insulin sensitivity, resting energy expenditure and Beck score during the study. Experimental group: closed circles/solid line; control group: open circles/dashed line. Error bars represent 95% CIs. P-values for interaction between group and time assessed by repeated measures ANOVA are P < 0.001 for weight (a), P < 0.001 for waist circumference (b), P = 0.05 for LDL cholesterol (c), P = 0.02 for subcutaneous fat (d)*, p = 0.007 for visceral fat (e)*, P = 0.04 for metabolic clearance rate of glucose (MCR) (f)†. *Magnetic resonance imaging data were not complete in 15 out of the 74 participants: 8/37 in the experimental group (six because of dropout, two as a result of claustrophobia during the first examination) and 7/37 in the control group (six because of dropout, one as a result of claustrophobia during the first examination). †Data from the hyperinsulinaemic isoglycaemic clamp were not complete in 19 out of the 74 participants: 9/37 in the experimental group (six because of dropout, three as a result of patients’ fragile veins) and 10/37 in the control group (six because of dropout, four as a result of patients’ fragile veins).

FIGURE 3

Plasma levels of oxidative stress markers and adipokines during the study. Experimental group: closed circles/solid line; control group: open circles/dashed line. Error bars represent 95% CIs. P-values for interaction between group and time assessed by repeated measures ANOVA are P = 0.002 for Vitamin C (a), P < 0.001 for superoxide dismutase (b), P < 0.001 for reduced glutathione (c), P < 0.001 for glutathione reductase (d), P = 0.004 for glutathione peroxidase (e), P = 0.003 for glutathione transferase (f), P = 0.02 for adiponectin (g), P = 0.005 for resistin (h) and P = 0.05 for leptin (i). GSH, glutathione; NADPH, nicotinamide adenine dinucleotide phosphate.