SOFIA, Bulgaria — Eating nuts could help protect against the development of type 2 diabetes in individuals who are already at high risk for the disease, 2 new studies suggest.
Researchers from Spain and the United States reported on the potential benefits of pistachio nuts and almonds, so-called "tree nuts," here at the 2014 European Congress on Obesity.
Mònica Bulló, MD, of the human nutrition unit at Virgili University, Reus, Spain, and senior author on the pistachio study, told Medscape Medical News: "I would advise people to eat a handful of nuts whenever they can."
Her study, conducted in 49 overweight or obese prediabetic subjects, showed that 57 g of pistachios daily for 4 months significantly reduced fasting glucose, insulin, and insulin resistance. Importantly, there was no change in body weight after eating the nuts.
The other trial, presented in a poster by Sze Yen Tan, PhD, of department of nutrition science, Purdue University, West Lafayette, Indiana, reported on 137 adults at elevated risk for diabetes who were randomized to consume 43 g of almonds per day — either with meals or as a snack — or to no almonds, for 4 weeks.
Those who ate the nuts felt less hungry and fuller than those who didn't, and they had lower postprandial blood glucose levels, without experiencing any weight gain.
Dr. Bulló added that nuts in general have been found to be associated with a reduced risk for coronary heart disease through moderation of LDL cholesterol, triglycerides, and circulating glucose concentrations. And in studies in type 2 diabetes, they have been shown to reduce postmeal glucose and insulin levels, although she admitted findings have been "mixed" in this patient population.
But nuts are, she noted, "a rich, dense food with a healthy lipid profile," and pistachios in particular are rich in antioxidant carotenoids, she added.
However, Dr. Richard Elliott, research communications officer at Diabetes UK, told Medscape Medical News that until full reports of these studies have been published, "We would not be able to make a definitive judgement….We are not aware of any strong evidence that eating nuts reduces the risk of type 2 diabetes."
Potential Protective Role of Pistachios
Despite the prior work on nuts, no previous study has evaluated the effect of nuts in prediabetes, which Dr. Bulló told a press briefing here is "a silent disease," indicating blood glucose levels in the range of 100 to 125 mg/dL, associated comorbidities, and an increased mortality risk.
In the study, reported at the meeting by her colleague Pablo Hernández-Alonso, MD, also of Virgili University, 54 overweight or obese prediabetic people were randomly assigned to a control diet or a pistachios diet (57 g daily, around a "handful" of nuts, said Dr. Bulló) for 4 months. They then had a 2-week washout period before crossing over to the alternative diet for another 4 months, so the individuals effectively acted as their own controls.
The diets were designed to be isocaloric and modified according to each individual's weight: the amount of calories varied from 1900 to 2500 per day, depending on the weight of the person.
Both diets were Mediterranean in nature, and the control diet used olive oil in place of pistachios — the diets did not differ in the amount of saturated fatty acids and cholesterol content. At baseline and then monthly, anthropometric measurements were taken, blood pressure was measured, and physical activity was assessed. Blood samples were also collected at the beginning and end of each intervention period to look at hemostatic, inflammatory, oxidative, and related metabolic risk markers.
There were no statistically significant changes in body mass index (BMI) between intervention periods, but fasting glucose, insulin, and insulin-resistance markers decreased significantly after the pistachio diet compared with the control diet (P < .001).
There were nonsignificant decreases in HbA1c and serum-LDL cholesterol levels; the latter became significant when 5 participants who dropped out for personal reasons were excluded from the analysis.
Other metabolic risk markers such as fibrinogen, glucagonlike peptide-1 (GLP-1), oxidized LDL, and platelet factor-4 all showed a statistically significant decrease after the pistachio diet compared with control diet (P < .05).
"Regular consumption of pistachios could decrease insulin resistance, thus suggesting a potential protective role for pistachio consumption against development of type 2 diabetes," Dr. Bulló concluded.
Almonds Get in on the Action Too, but Are Best as a Snack
Meanwhile, in the almond study, 137 adults at elevated risk of diabetes (BMI 27–35 or normal weight with a family history of diabetes) were randomized to 1 of 3 groups: 43 g per day of almonds (approximately 250 calories) with breakfast or lunch; 43 g of almonds alone as a morning or afternoon snack; or no almonds; for 4 weeks.
Those who ate the almonds felt less hungry and fuller than those who did not consume them; these effects were most noticeable when the almonds were eaten as a snack. Similarly, although almond consumption led to lower blood glucose, this reduction was significant only among those who ate the nuts as a snack.
Adding almonds to the usual diet for 4 weeks did not alter body weight or any other anthropometric measures compared with the control group. The lipid profile of those who consumed the nuts did not improve, however, "possibly because participants were generally healthy and normal-cholesterolemic," said Dr. Tan.
Dr. Tan noted that the US Department of Agriculture recommends the inclusion of about 43 g of nuts per day as part of a healthy diet.
"Overall," he concluded, "inclusion of 43 g of almonds into a daily diet, especially as snacks, may help to moderate glycemia without promoting weight gain."
Dr. Bulló's study was funded by the Western Pistachios Association (United States) and Paramount Farms, but none of the funding sources played a role in the design, collection, analysis, or interpretation of the data, and she said neither she nor her colleagues receive any honoraria from these sources. Dr. Tan's study was funded by the Almond Board of California.
2014 European Congress on Obesity. Abstract T5:OS2.3, presented May 31, 2014.