The authors of the current study note that while fish-oil supplements have been demonstrated to reduce the oxidative stability of plasma LDL cholesterol, increased dietary intake of fish may lower the risk of developing type 2 diabetes. Meanwhile, nuts have been shown to have no significant effect on glucose homeostasis and weight. However, a low-fat diet supplemented with nuts can reduce total and LDL cholesterol compared with a low-fat diet alone.

Given this information, the authors of the current study compared two low-fat diets with regular intake of fish with a low-fat diet that included both fish and walnuts. Walnuts have high concentrations of polyunsaturated fats along with antioxidants, and since these qualities may be particularly important in patients with the metabolic syndrome, the authors focused their study on patients with type 2 diabete

"Walnuts are distinguished from other nuts by virtue of their higher polyunsaturated fat content (and importantly their a-linolenic acid [ALA] content) combined with antioxidants in the form of ?-tocopherol," write Linda C. Tapsell, PhD, from the National Centre of Excellence in Functional Foods, University of Wollongong in New South Wales, Australia, and colleagues. "There are mechanistic explanations for the influence of dietary polyunsaturated fatty acid (PUFA) on insulin action and energy metabolism, and cohort studies of women in the U.S. have demonstrated a reduced risk of developing type 2 diabetes with dietary PUFA replacing trans or saturated fatty acids (SFAs)."

58 adults with type 2 diabetes were randomized to one of three dietary advice groups, each with 30% energy as fat: low fat, modified low fat, and modified low fat inclusive of 30 g of walnuts per day.

Patients received dietary advice at baseline, with monthly follow-up and telephone calls bimonthly for support. All groups were advised to consume fish and five daily portions of fruits and vegetables. Body weight, percent body fat, blood lipids, A1c, total antioxidant capacity, and erythrocyte fatty acid levels were measured at baseline and at three and six months.

Erythrocyte biomarkers of dietary intake confirmed higher dietary polyunsaturated fat-to-saturated fat ratio and intakes of ?-3 fatty acids in the walnut group. The walnut group had a significantly greater increase in HDL cholesterol-to-total cholesterol ratio and in HDL The walnut group also had a 10% reduction in LDL cholesterol, reflecting a significant effect by group.

The three groups were similar in changes in body weight, percent body fat, total antioxidant capacity, and HbA1c levels.

All subjects received dietary advice to limit fat intake to less than 30% of total daily energy. This was accomplished via a traditional low-fat diet, a modified low-fat diet based on exchange lists for fatty acids, and a modified low-fat diet using exchanges and accompanied by a daily intake of 30 g of walnuts. Each participant was advised to eat 2 fish meals per week, regardless of dietary group assignment.

Dietary assessment revealed that all groups had good adherence to their diet plans. Total energy intake was within 10% of the recommended value in all assessments, and biomarker analyses confirmed appropriate fatty acid intake. The modified low-fat diet with walnuts group consumed higher levels of PUFAs and ALA.

Body weight remained stable in all 3 groups throughout the trial, but the modified low-fat with walnuts diet was superior to the traditional low-fat diet in body fat analysis at 3 months.

In univariate analysis, LDL cholesterol decreased in the modified low-fat diet with walnuts cohort but remained stable in the two other diet groups.

HDL cholesterol increased in all diet groups, signifying a time effect. However, the modified low-fat diet with walnuts group experienced a more significant increase in HDL than the other diet groups for the last 3 months of the trial..

"Structured 'whole of diet' advice that included 30 g of walnuts/day delivering substantial amounts of polyunsaturated fatty acid improved the lipid profile of patients with type 2 diabetes," the authors conclude.

Source: Diabetes In Control.com: Diabetes Care, Dec 2004.