A group of researchers analyzed the results of 12 randomized controlled dietary trials to determine the effect of tree nuts such as almonds, hazelnuts, Brazil nuts and cashews on four markers HbA1c, fasting glucose, fasting insulin, and/or HOMA-IR in 450 predominantly middle-aged adults in a “first-of-its-kind” systemic review.
They found that daily median intake of 56 g (about 2 ounces) of tree nuts over the course of eight weeks significantly reduces HbA1c and fasting glucose in individuals with type 2 diabetes. Diets with a median dose of 56 g/day of tree nuts significantly lowered HbA1c (MD = −0.07% [95% CI:−0.10, −0.03%]; P = 0.0003) and fasting glucose (MD = −0.15 mmol/L [95% CI: −0.27, −0.02 mmol/L]; P = 0.03) compared with control diets. They didn’t observe significant effects for fasting insulin and HOMA-IR, however the direction of effect favored tree nuts.
Improved glycemic control may relate to carb displacement with tree nuts
The ability of tree nuts to improve glycemic control may relate to a carbohydrate displacement mechanism by which tree nuts reduce the glycemic load of the diet by displacing high glycemic-index carbohydrates, according to the review. Of the three trials that showed a significant lowering in HbA1c, the two trials contributing the greatest amount of weight to the analysis (>80% collectively) investigated the effect of tree nuts as a means of displacing carbohydrate by ≥5% of energy.
Still, the researchers noted that large, longer, higher quality trials “with a specific focus on glycemic endpoints as the primary outcome” are needed to determine the impact of tree nuts on glycemic load when replacing high-glycemic index carbohydrates.
The last two decades have seen a proliferation of evidence linking tree nut consumption with a range of health outcomes. A recent large pooled analysis of two of the Harvard cohorts and a recent meta-analysis of prospective cohort studies tied daily nut consumption to lower all-cause mortality rates (see here). Recent evidence that tree nuts lower LDL cholesterol (see here) also resulted in an FDA-qualified health claim and their inclusion in heart association guidelines for cardiovascular risk reduction. The data for diabetes-related outcomes, however, have not been as consistent.
Source: PLOS One
“Effect of Tree Nuts on Glycemic Control in Diabetes: A Systematic Review and Meta-Analysis of Randomized Controlled Dietary Trials”
Authors: Effie Viguiliouk, Cyril W. C. Kendall, Sonia Blanco Mejia, Adrian I. Cozma, Vanessa Ha, Arash Mirrahimi, Viranda H. Jayalath, Livia S. A. Augustin, Laura Chiavaroli, Lawrence A. Leiter, Russell J. de Souza, David J. A. Jenkins and John L. Sievenpiper