Miriam E. Tucker
August 26, 2014
Daily consumption of pistachios may improve the metabolic risk profiles for people with prediabetes, a new study finds.
Mònica Bulló, PhD, professor in the Human Nutrition Unit, Department of Biochemistry and Biotechnology, Institut d’Investigació Sanitària Pere Virgili, Universitat Rovira i Virgili, Reus, Spain, and colleagues published the results of their randomized crossover trial online August 14 in Diabetes Care.
“The results of our study suggest the regular consumption of pistachios [is beneficial] in prediabetes,” Dr. Bulló told Medscape Medical News.
Nuts in general have been associated with cardiovascular benefit, but pistachios appear to hold special properties. They contain more lutein, β-carotene, and γ-tocopherol than do other nuts, and they also appear to hold particular anti-inflammatory properties.
“We choose pistachios because they are less [caloric], have a specific fatty acid profile, and also other bioactive compounds compared to other nuts, with a potential effect on glucose and insulin metabolism,” Dr. Bulló said.
Fifty-four adults with impaired fasting glucose (fasting plasma glucose, 100 – 125 mg/dL) enrolled in the study. All of them had a body mass index less than 35 kg/m2. Five dropped out during the study.
The investigators randomly assigned the participants to start with either a diet including 2 ounces (57 grams) per day of roasted pistachios or a calorie-matched control diet in which other fatty foods (mostly olive oil) compensated for the pistachio calories. The diets were approximately 50% carbohydrate, 35% fat, and 15% protein. After 4 months and a 2-week washout, the participants were switched to the other diet for an additional 4 months.
Fasting plasma glucose dropped by 5.17 mg/dL from baseline with the pistachio diet in the intent-to-treat analysis, whereas it rose by 6.72 mg/dL after the control diet, resulting in a significant difference between the 2 diets (P < .001). Fasting plasma insulin levels dropped by 2.04 mU/mL from baseline with the pistachio diet and rose by 2.52 mU/mL in the control diet, which was also a significant difference (P < .001).
Homeostatic model assessment of insulin resistance decreased with the pistachio diet compared with the control diet, with a drop of 0.69 from baseline vs a rise of 0.97, respectively (P < .001). However, no significant changes were seen in homeostatic model assessment-β cell function or hemoglobin A1c levels.
Although lipid profiles did not change significantly after the diets, mean low-density lipoprotein cholesterol did drop by 4.00 mg/dL during the pistachio diet and increased on the control diet by 1.20 mg/dL (P = .16).
The per protocol results were similar to the intent-to-treat analysis, the authors note.
Other significant changes in cardiometabolic risk factors seen with the pistachio diet but not the control diet include decreases in cellular glucose transport in lymphocytes, fibrinogen, and platelet factor 4. Oxidized low-density lipoprotein levels decreased significantly with the pistachio diet in the per protocol analysis but not the intent-to-treat analysis.
The effect of pistachios on insulin metabolism was explained at least in part by an increase in glucagonlike peptide 1 levels: 4.09 pg/mL in the pistachio group versus a drop of 0.59 pg/mL with the control diet (P = .01).
Although several previous studies have found a beneficial effect of nut intake on glycemia and insulin levels, few have focused on pistachios in particular, and none have studied people in the prediabetes phase in particular. There are no studies of pistachios in people with diabetes, so it is not known to what degree these results can be extrapolated, Dr. Bulló told Medscape Medical News.
This study was funded by the Western Pistachios Association, now known as American Pistachio Growers (U.S.), and Paramount Farms. The authors have disclosed no relevant financial relationships.
Diabetes Care. Published online August 14, 2014. Abstract