Whole grain products, fish and bilberries alter glucose and lipid metabolism in a randomized, controlled trial: the Sysdimet study

Abstract

Background: Due to the growing prevalence of type 2 diabetes, new dietary solutions are needed to help improve glucose and lipid metabolism in persons at high risk of developing the disease. Herein we investigated the effects of low-insulin-response grain products, fatty fish, and berries on glucose metabolism and plasma lipidomic profiles in persons with impaired glucose metabolism.

Methodology/principal findings: Altogether 106 men and women with impaired glucose metabolism and with at least two other features of the metabolic syndrome were included in a 12-week parallel dietary intervention. The participants were randomized into three diet intervention groups: (1) whole grain and low postprandial insulin response grain products, fatty fish three times a week, and bilberries three portions per day (HealthyDiet group), (2) Whole grain enriched diet (WGED) group, which includes principally the same grain products as group (1), but with no change in fish or berry consumption, and (3) refined wheat breads (Control). Oral glucose tolerance, plasma fatty acids and lipidomic profiles were measured before and after the intervention. Self-reported compliance with the diets was good and the body weight remained constant. Within the HealthyDiet group two hour glucose concentration and area-under-the-curve for glucose decreased and plasma proportion of (n-3) long-chain PUFAs increased (False Discovery Rate p-values <0.05). Increases in eicosapentaenoic acid and docosahexaenoic acid associated curvilinearly with the improved insulin secretion and glucose disposal. Among the 364 characterized lipids, 25 changed significantly in the HealthyDiet group, including multiple triglycerides incorporating the long chain (n-3) PUFA.

Conclusions/significance: The results suggest that the diet rich in whole grain and low insulin response grain products, bilberries, and fatty fish improve glucose metabolism and alter the lipidomic profile. Therefore, such a diet may have a beneficial effect in the efforts to prevent type 2 diabetes in high risk persons.

Trial registration: ClinicalTrials.gov NCT00573781.

Figure 1. Flow diagram of the study.

Figure 2. Changes in dietary intake during the 12-week intervention in the HealthyDiet (n = 36), Whole grain enriched diet (WGED) (n = 34) and Control (n = 35) groups.

Bars represent mean of absolute changes ± SD. Means without a common letter differ in mixed model comparison, FDR p<0.05.

Figure 3. Bar charts of glucose metabolism parameters in each group before and after the intervention.

A) plasma 2 hour glucose, B) area under the curve (AUC) for glucose, C) Insulinogenic index (IGI) and D) Disposition index (DI) in OGTT. Values are means ± SEM, n = 37, 34 and 35 in the HealthyDiet, Whole grain enriched diet (WGED) and Control groups, respectively, except for IGI and DI, n = 36 before and n = 35 after the intervention in the HealthyDiet group, and n = 32 before and after the intervention in the WGED group.

Figure 4. Associations between glucose metabolism and plasma EPA and DHA content.

Changes in insulinogenic index (IGI) (A and B) and disposition index (DI) (C and D) during the intervention period (95% Confidence interval) according to quartiles of changes in plasma EPA (A and C) and DHA (B and D) content (%). * p<0.01 in Kruskal-Wallis test. All groups combined, n = 99. Ranges of changes in EPA quartiles: 1 = −2.3–0.4% units; 2 = −0.3−0.1% units; 3 = 0.1−0.6% units; 4 = 0.6−4.2% units, and in DHA quartiles: 1 = −2.4–0.6% units; 2 = −0.6–0.1% units; 3 = −0.04−0.7% units; 4 = 0.7−3.0% units.