Effects of Nut Consumption on Glycemic Control and Cardio metabolic Outcomes in Adults with Diabetes Mellitus

A Systematic Review and Meta-analysis of Randomized Controlled Trials

Abstract

Background: Dietary modification is an essential part of diabetes mellitus management, and nuts have garnered attention due to their favorable composition of unsaturated fatty acids, dietary fiber, plant protein, minerals, and bioactive compounds. However, evidence of their effects on glycemic control and broader cardiometabolic outcomes in people living with diabetes is heterogeneous.

Objective: To examine the effects of nut consumption on glycemic control and cardiometabolic outcomes in adults living with diabetes mellitus.

Methods: A systematic review and meta-analysis of randomized controlled trials was conducted according to the PRISMA 2020 statement. Electronic searches identified potentially eligible studies evaluating nut consumption in adults with diabetes mellitus. Included trials compared a nut dietary intervention to a control dietary intervention and reported at least one prespecified glycemic or cardiometabolic outcome. The primary outcomes were glycated hemoglobin (HbA1c) and fasting blood glucose. Secondary outcomes included postprandial glucose, lipid parameters, blood pressure, body weight, and body mass index. Risk of bias was assessed using the Cochrane Risk of Bias 2 (RoB 2) tool. Where sufficient comparable data were available, pooled mean differences (MDs) with 95% confidence intervals (CIs) were calculated.

Results: A total of 3,214 records were identified, of which 42 full-text articles were assessed for eligibility. Twenty-seven RCTs were included in the quantitative synthesis. Eighteen RCTs evaluating HbA1c showed a significant reduction associated with nut consumption (MD −0.22%, 95% CI −0.35 to −0.09). Similarly, analysis of 21 RCTs showed a significant reduction in fasting blood glucose (MD −7.8 mg/dL, 95% CI −12.4 to −3.2). Nut consumption was also associated with reductions in total cholesterol (−9.5 mg/dL) and LDL cholesterol (−7.2 mg/dL), while no significant overall effect was observed for HDL cholesterol. Ten RCTs reporting blood pressure demonstrated a reduction in systolic blood pressure (MD −3.1 mmHg, 95% CI −5.6 to −0.6). No significant overall changes in body weight or BMI were observed. Subgroup findings suggested favorable glycemic effects with almonds, improvements in insulin sensitivity and endothelial measures with pistachios, and more consistent lipid benefits with walnuts. Risk-of-bias assessment identified 14 trials at low risk, 9 with some concerns, and 4 at high risk of bias.

Conclusions: Consumption of nuts was associated with modest improvements in glycemic control and selected cardiometabolic risk factors, particularly HbA1c, fasting blood glucose, total cholesterol, LDL cholesterol, and systolic blood pressure, without a significant increase in body weight or BMI. Although the effects varied according to the type of nut consumed and study characteristics, consumption of nuts was associated with improved cardiometabolic risk profiles, including reduced body weight and BMI. Further adequately powered, longer-duration randomized trials using standardized nut doses and well-defined dietary comparators are required to examine the long-term clinical relevance of these effects.