Two new meta-analyses involving tree nuts (almonds, Brazil nuts, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts) were recently published in the online publications, British Medical Journal Open (BMJ Open) and PLOS ONE. The BMJ Open article looked at the effects of tree nuts on metabolic syndrome (MetS) criteria and showed that tree nut consumption resulted in a significant decrease in triglycerides and fasting blood glucose. The PLOS ONE article focused on the effect of tree nuts on glycemic control in diabetes and showed significant decreases in HbA1c and fasting blood glucose levels.
Researchers from the University of Toronto conducted both meta-analyses. In the paper focusing on MetS, the analysis included 47 randomized control trials with 2,200 participants who were otherwise healthy or had MetS criteria, dyslipidemia (elevated levels of blood cholesterol and/or triglycerides), or type 2 diabetes. "We found that tree nut consumption of about two ounces per day was found to decrease triglycerides significantly by ~0.06 mmol/L and to decrease fasting blood glucose significantly by ~0.08 mmol/L over an average follow-up of eight weeks," stated Cyril Kendall, Ph.D., lead researcher of the study.
This is important since MetS is a cluster of risk factors shown to be associated with mortality, a twofold increased risk for cardiovascular disease, and a fivefold increased risk for type 2 diabetes. While the diagnostic criteria can vary, presence of any three of the five following conditions results in a diagnosis of MetS: abdominal obesity, elevated triglycerides, low HDL cholesterol (the good cholesterol), high blood pressure, and hyperglycemia (high blood sugar levels). Based on NHANES data from 2003-2006, an estimated 34.3% of the U.S. population has MetS.
In addition to the effect of nuts on MetS, the researchers also looked at the effect of nuts on glycemic control in those with diabetes. The PLOS ONE analysis included 12 randomized clinical trials with 450 participants and compared the effects of diets emphasizing tree nuts to isocaloric diets without tree nuts on HbA1c (a marker of longer term blood sugar control), fasting blood glucose, fasting insulin and insulin resistance (HOMA-1R). The results showed that diets emphasizing about two ounces of tree nuts per day significantly lowered HbA1c (P=0.0003) and fasting glucose (P=0.03) compared to the control diets. While neither diet showed significant effects on fasting insulin and insulin resistance, the direction of effect favored tree nuts.
According to Dr. Kendall, "Both of our analyses indicate that daily tree nut consumption has an overall metabolic benefit and can improve risk factors for metabolic syndrome, and glycemic control in individuals with type 2 diabetes."
"With MetS and diabetes on the rise worldwide, this is yet another reason to include tree nuts in your diet every day," states Maureen Ternus, M.S., R.D., Executive Director of the International Tree Nut Council Nutrition Research & Education Foundation (INC NREF). "In 2003, FDA (in its qualified health claim for nuts and heart disease) recommended that people eat 1.5 ounces of nuts per day-well above current consumption levels. We need to encourage people-especially those at risk for MetS and those with diabetes-to get their handful of nuts every day."