They may be small in size, but nuts pack a nutritional punch and have been linked to numerous health benefits. While most nuts are calorically dense and a typical serving can contain over 30% of the recommended daily value of total fat, the majority of that is comprised of polyunsaturated and monounsaturated fats. Nuts also contain dietary fiber and protein that can contribute to increased satiety levels.1 Three new studies suggest that nuts could play an important role in diabetes prevention and management, particularly in reducing the risk of cardiovascular events.
Tree Nuts and Metabolic Syndrome
In 2003, the Food and Drug Administration (FDA) approved the claim that “scientific evidence suggests, but does not prove that eating 1.5 ounces per day of most nuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease” for food labels.4 Since then, studies have found that various tree nuts may have benefits in preventing metabolic syndrome (MetS). The first systematic meta-analysis on the effects of tree nut consumption on at least one criterion of MetS (waist circumference, triglycerides, high-density lipoprotein (HDL) cholesterol, blood pressure (BP), or fasting blood glucose) evaluated 49 randomized controlled trials of ≥3 weeks of 2,226 patients who were otherwise healthy or had dyslipidemia, MetS, or type 2 diabetes.5 The pooled analyses showed that tree nut interventions were associated with lowered triglycerides (MD=−0.06mmol/L (95% CI −0.09–−0.03mmol/L) and fasting blood glucose (MD=−0.08mmol/L (95% CI −0.16–−0.01 mmol/L) vs. control diet interventions. No effects were seen on waist circumference, HDL cholesterol, or BP. A serving of approximately 50g/day of tree nuts for MetS risk reduction is recommended by the study authors, particularly since there was no increase in side effects vs. control diets reported in any of the trials.
Pistachio Nuts and Cardiovascular Risk Factors
Can replacing low-fat or fat-free snacks with pistachios reduce cardiovascular risk factors? Sheila G. West, PhD, from Pennsylvania State University, and colleagues recruited 30 patients with well-controlled type 2 diabetes between 40–74 years of age with a body mass index (BMI) between 18.5–45.0 kg/m2 and C‐reactive protein (CRP) <10.0mg/L. Study participants were managing their blood glucose by either diet and exercise alone or using diabetes medication(s) except for insulin.A two week run-in period to establish baseline values for a typical Western diet was conducted and participants were next randomized to one of the following diets with calories ranging from 1800–3900kcal/day based on the Harris‐Benedict equation and adjustments for weight stability as needed:
- A run‐in diet, a nutritionally adequate diet with total fat based on a typical Western diet (36% total fat, 11.5% saturated fat, and 278mg/day of cholesterol);
- A control diet based on the American Heart Association’s Therapeutic Lifestyle Changes diet with reduced total fat (26.9% of energy), saturated fat (6.7% of energy), and cholesterol (186mg/day);
- A pistachio diet replacing low‐fat or fat‐free carbohydrate snacks (ie, pretzels, string cheese, etc.) in the control diet with pistachios equivalent to 20% of daily energy (range of 59–128g, variable on calorie assignment).
After four weeks, the subjects had a two week washout period and were then randomized to one of the other two remaining diets for four weeks. After a second two week washout period, the participants were then assigned to the last remaining diet. After each diet period, blood pressure (BP), systemic hemodynamics, and heart rate variability at rest and during acute mental stress were assessed, along with 24 hour ambulatory BP in a subset of patients (n=21). The pistachio diet significantly lowered total peripheral resistance (−3.7±2.9%, P=0.004), increased cardiac output (3.1±2.3%, P=0.002), and improved some measures of heart rate variability (all P<0.05). This diet also significantly reduced systolic ambulatory BP by 3.5±2.2mmHg (P=0.046); the greatest reduction was evident during sleep (−5.7±2.6mmHg, P=0.052). Diastolic BP did not differ between the diets and no differences in dipping status (≥10% reduction in systolic BP during sleep) were evident.2