Tree Nuts Improve Glycemic Control in Type 2 Diabetes

Miriam E. Tucker

August 06, 2014

A couple handfuls of tree nuts a day may improve glycemic control in patients with type 2 diabetes, a new systematic review and meta-analysis suggests.

The findings, from a total 450 patients in 11 randomized trials in 5 countries, were published online July 30, 2014 in PLOS One by Effie Viguiliouk, of the Clinical Nutrition and Risk Factor Modification Center, St. Michael's Hospital, Toronto, Ontario, and colleagues.

"Nuts may provide a variety of cardiometabolic health benefits, including improving blood glucose control, lowering LDL and triglycerides, raising HDL, and lowering blood pressure, [all of] which have been found in some clinical and cohort studies," study coauthor Cyril W. C. Kendall, PhD, of the department of nutritional sciences at the University of Toronto and St. Michael's, told Medscape Medical News.

This review specifically looked at studies of tree nuts, which include almonds, Brazil nuts, cashews, hazelnuts, macadamia nuts, pecans, pine nuts, pistachios, and walnuts (but not peanuts, which are legumes).

Nut Research: An Emerging Science

The pooled analyses showed an overall significant 0.07-percentage-point reduction in HbA1c and a fasting glucose drop of 0.15 mmol/L (2.7 mg/dL) with a median dose of 56 g/day of tree nuts (a quarter cup is about 30 g) over a median of 8 weeks. Results for fasting insulin and homeostasis model assessment of insulin resistance were not significant but trended in favor of tree nuts.

Of the 3 trials showing a significant lowering of HbA1c with daily tree-nut consumption, the 2 contributing the greatest weight to the results investigated the effect of tree nuts as a dietary replacement for carbohydrates (rather than fats or proteins).

"Nuts should displace other foods in the diet, ideally those that are less healthy, such as highly refined carbohydrates and animal protein sources," Dr. Kendall told Medscape Medical News.

In addition to displacing carbohydrates, other potential mechanisms for glucose-lowering with tree nuts could relate to their relatively high content of magnesium and monounsaturated fat, both of which have been linked to improved insulin sensitivity.

And although nuts are high in calories, they contain a number of healthful components, such as unsaturated fatty acids, plant protein, fiber, minerals, vitamins, and antioxidants, Dr. Kendall explained.

The authors do point out a limitation, however: there was a high degree of between-study heterogeneity, and "the majority of trials were of short duration and poor quality."

Dr. Kendall told Medscape Medical News that the research on the health benefits of nuts is still an emerging science, most of which has taken place over the past 15 years.

This study was supported by the International Tree Nut Council Nutrition Research & Education Foundation and the Canadian Institutes of Health Research. Ms. Viguiliouk has no disclosures. Dr. Kendall has received research support from the Advanced Foods and Material Network, Agrifoods and Agriculture Canada, the Almond Board of California, the American Pistachio Growers, Barilla, the California Strawberry Commission, the Calorie Control Council, CIHR, the Canola Council of Canada, Coca-Cola (investigator-initiated, unrestricted grant), Hain Celestial, the International Tree Nut Council Nutrition Research and Education Foundation, Kellogg, Kraft, Loblaw, Orafti, Pulse Canada, Saskatchewan Pulse Growers, Solae, and Unilever. He has received travel funding, consultant fees, and/or honoraria from Abbott Laboratories, the Almond Board of California, the American Peanut Council, the American Pistachio Growers, Barilla, Bayer, the Canola Council of Canada, Coca-Cola, Danone, General Mills, the International Tree Nut Council Nutrition Research and Education Foundation, Kellogg, Loblaw, the Nutrition Foundation of Italy, Oldways Preservation Trust, Orafti, Paramount Farms, the Peanut Institute, PepsiCo, Pulse Canada, Sabra Dipping, Saskatchewan Pulse Growers, Solae, Sun-Maid, Tate and Lyle, and Unilever. He is on the dietary guidelines committee for the diabetes nutrition study group of the European Association for the Study of Diabetes and has served on the scientific advisory board for the Almond Board of California, the International Tree Nut Council, Oldways Preservation Trust, Paramount Farms, and Pulse Canada. Disclosures for the coauthors are listed in the article.

PLOS One. Published online July 30, 2014. Article

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