Long-term effects of increased dietary polyunsaturated fat from walnuts on metabolic parameters in type II diabetes

Abstract

Background/Objectives: Most dietary interventions have metabolic effects in the short term, but long-term effects may require dietary fat changes to influence body composition and insulin action. This study assessed the effect of sustained high polyunsaturated fatty acids (PUFA) intake through walnut consumption on metabolic outcomes in type II diabetes. Subjects/Methods: Fifty overweight adults with non-insulin-treated diabetes (mean age 54±8.7 years) were randomized to receive low-fat dietary advice ± 30 g per day walnuts targeting weight maintenance (around 2000 kcal, 30% fat) for 1 year. Differences between groups were assessed by changes in anthropometric values (body weight, body fat, visceral adipose tissue) and clinical indicators of diabetes over treatment time using the general linear model. Results: The walnut group consumed significantly more PUFA than the control (P ¼ 0.035), an outcome attributed to walnut consumption (contributing 67% dietary PUFA at 12 months). Most of the effects were seen in the first 3 months. Despite being on weight maintenance diets, both groups sustained a 1-2 kg weight loss, with no difference between groups (P ¼ 0.680). Both groups showed improvements in all clinical parameters with significant time effects (Po0.004), bar triacylglycerol levels, but these were just above normal to begin with. The walnut group produced significantly greater reductions in fasting insulin levels (P ¼ 0.046), an effect seen largely in the first 3 months. Conclusions: Dietary fat can be manipulated with whole foods such as walnuts, producing reductions in fasting insulin levels. Long-term effects are also apparent but subject to fluctuations in dietary intake if not of the disease process.

Health Benefits of Nut Consumption

“…Recent well controlled intervention studies with walnuts [71,72,73,74], almonds [75], hazelnuts [76], pistachios [77], macadamias [78], and peanuts [79] showed LDL-cholesterol reductions ranging from 4% to 11% versus comparator diets, confirming the cholesterol-lowering efficacy of various nut types. A Mediterranean diet supplemented with 30 g of mixed nuts (walnuts, almonds and hazelnuts) per day also showed beneficial effects on the lipid profile compared with advice on a low-fat diet in diabetic and non diabetic participants in the PREDIMED study, a randomized trial of dietary intervention for the primary prevention of cardiovascular disease [80].…”

“…Nuts had no discernible effect on fasting or postprandial glucose and hemoglobin A1C in patients with diabetes [73,92,93,94]. Changes in insulin sensitivity in response to nut diets have been inconsistent.…”

“…No effects were seen in feeding studies of healthy subjects [92], hyperlipidemic patients [95], or patients with insulin-resistant states, such as obesity [96] or the metabolic syndrome [97,98]. Two recent small studies, however, found reduced insulin levels in patients with metabolic syndrome [82] and diabetes [73] after nut feeding. The three-month report of the larger PREDIMED study [80] also showed that the Mediterranean diet enriched with nuts was associated with improved insulin sensitivity and fasting glucose levels in non diabetic and diabetic participants, respectively.…”

Nut consumption for vascular health and cognitive function

“…Other studies investigated HbA1c in individuals with type 2 diabetes and found that 28 g walnuts/d and 36 g almonds/d reduced HbA1c by 4 % (62,64) . However, in other individuals, HbA1c did not change with 37 -75 g mixed nuts/d (66) , 30 -50 g walnuts/d (69,70,72) or 57 -112 g almonds/d (for 4 weeks) (65) .…”

Walnut: past and future of genetic improvement

“…Several human clinical studies of coronary heart disease have demonstrated that walnut consumption can lead to lower blood LDL cholesterol concentrations (Feldman and Elaine 2002;Banel and Hu 2009). Moreover, a diet with increased PUFA from walnuts is also linked to longterm beneficial effects on type II diabetes (Tapsell et al 2009). Dietary walnut fingerprinting using HPLC-q-ToF-MS analysis characterized some urinary biomarkers, such as fatty acids metabolites, (Garcia-Aloy et al 2014) and positive effects of walnut consumption on inflammatory processes, vascular reactivity, glycemic control (Ros 2010), and oxidative stress (Zhao et al 2014) were described.…”