Background: Diabetes is a chronic, potentially debilitating, and often fatal disease. Dietary strategies to reduce postprandial glycemia are important in the prevention and treatment of diabetes. Nuts are rich in mono- and polyunsaturated fatty acids, which may reduce hyperglycemia and improve metabolism.

Objectives: To evaluate the effectiveness of pistachio nut supplementation on glycemic and inflammatory measures in patients with type 2 diabetes.

Methods: In this double-blind, randomized, placebo-controlled, crossover trial, 48 diabetic patients were equally assigned to groups A and B. Patients in group A received a snack of 25 g pistachio nuts twice a day for 12 weeks and group B received a control meal without nuts. After 12 weeks of intervention, the patients had an 8-week washout. Then the groups were displaced, and group B received the same amount of pistachios for 12 weeks.

Results: With respect to the total change in variables over both phases, there was a marked decrease in HbA1c (-0.4%) and fasting blood glucose (FBG) concentrations (-16 mg/dl) in the pistachio group compared with the control group (p ≤ 0.001 for both). There was no overall significant change in BMI, blood pressure, HOMA-IR, and C-reactive protein (CRP) concentrations. Analysis of the two phases separately showed a decrease in FBG by 14 mg/dl and in HbA1c by 0.45% in the treatment group (A) after 12 weeks, while no significant differences were seen in group B (control group). In the second phase, FBG decreased from 151.36 ± 39.22 to 137.28 ± 28.65 mg/dl (-14 mg/dl) and HbA1c decreased from 7.42 ± 0.97 to 7.15 ± 0.68 mg/dl (-0.28%, p = 0.013 and p = 0.033, respectively) in the pistachio group (B). Pistachio consumption reduced systolic blood pressure (p = 0.007), BMI (p = 0.011), and CRP (p = 0.002) in patients from the treatment groups, but not insulin resistance.

Conclusions: Dietary consumption of pistachio nuts as a snack has beneficial effects on glycemic control, blood pressure, obesity, and inflammation markers in diabetic patients.