12 January - 20 June 2016

Tree nuts, diabetes and metabolic syndrome

13 August 14

Tree nuts may have a positive impact on glycaemic control in diabetes and metabolic syndrome criteria, according to new research at the University of Toronto. Tree nuts include almonds, Brazil nuts, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts.

The researchers performed two meta-analyses, one focusing on metabolic syndrome criteria and one on markers of blood sugar in diabetics. In the first, data from 47 randomised trials including 2200 participants was used; the trials' subjects included healthy individuals, sufferers from dyslipidemia and Type II diabetes, and people fitting the criteria for metabolic syndrome (a person is considered to have metabolic syndrome if he or she has three of the following risk factors: low levels of 'good' cholesterol, high triglycerides, high blood pressure, high blood sugar and extra weight around the waist). Tree nut consumption of 56g/2oz daily was found to have a beneficial effect on two of these markers, decreasing triglycerides by ~0.06 mmol/L and fasting blood glucose - where patients are not allowed to eat or drink anything but water for eight hours before their blood glucose levels are tested - by ~0.08 mmol/L.

In the second meta-analysis, the researchers analysed data from 12 randomised clinical trials including 450 diabetic participants. Pooled analyses showed an overall significant lowering of HbA1c (glycated haemoglobin, which reflects avergae plasma glucose concentration) of -0.07% and fasting glucose of -0.15 mmol/L, at a median tree nut dose of 56 g/d over a median duration of ~8 weeks.

The lead researcher, Dr John Sievenpiper, noted that in both studies the biggest reductions in triglycerides and blood glucose were seen when tree nuts replaced refined carbohydrates rather than saturated fats in the diet, and it was suggested in the second paper's discussion that tree nuts might reduce the glycaemic load of the diet via a carbohydrate displacement mechanism. It was also noted that magnesium and/or monounsaturated fats in the nuts might be contributory to their beneficial effects.

The researchers drew attention to the fact that no weight gain or adverse impact on the other risk factors for metabolic syndrome was observed in participants, even though nuts are high in calories. Nuts also have a high fat content, but this is 'good', or unsaturated fat. They therefore concluded that daily consumption of tree nuts has an overall metabolic benefit, and can form part of a healthy diet supporting the management of glycaemia in Type II diabetes sufferers. [ScienceDaily, Eurekalert]

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