Completed Projects

Title: Effects of Walnuts on Endothelial Function in Overweight Adults with at Least One Factor of Metabolic Syndrome
Status: Completed
Topic: Cardiovascular Health / Endothelial Function*
Funding Source: California Walnut Commission
Funding Period: 2010-2011
Study Design: Randomized, Controlled, Cross–Over Trial

To determine if consumption of walnuts improves endothelial function, cholesterol, and triglycerides in overweight adults with at least one indicator of metabolic syndrome (a cluster of conditions that occur together and raise the risk of cardiovascular disease and Type 2 diabetes)

Further Study Details:

Walnuts are a nutrient-dense whole food source of antioxidants and an essential omega-3 fatty acid, and are thought to be beneficial to cardiovascular health. This study examined the effects of daily walnut consumption (2 ounces or 56 grams per day for 8 weeks) among 46 overweight non-diabetic adults (18 men and 28 women) men and women who had at least one risk factor for metabolic syndrome, but who had not been diagnosed with cardiovascular disease. Specifically, it examined whether consuming walnuts had any effect on endothelial function, blood pressure, fasting glucose, total cholesterol, HDL cholesterol, LDL cholesterol, triglycerides, body weight, or waist circumference. Study participants were asked to practice their usual eating habits during an 8-week control phase. They were instructed during another 8-week period to continue their usual eating habits, with one exception - eating 2 ounces of walnuts per day while adjusting for the extra calories from the walnuts so their daily calorie intake would be consistent with the control phase. There was a 4-week washout period between the two dietary phases.

*Cardiovascular health is a research priority at the Yale-Griffin Prevention Research Center. We have a vascular lab where we conduct studies of endothelial function – a measure of blood vessel behavior. Blood flow and blood vessel reactivity are indicators of heart health. When blood vessels dilate (expand) or constrict (shrink) properly, endothelial function is considered to be normal. If they constrict when they should dilate, endothelial function is abnormal. Impaired (or abnormal) endothelial function is associated with an increased risk of heart disease. We measure endothelial functioning with the use of ultrasound imaging of the brachial artery in the arm (called Brachial Artery Reactivity Scan or BARS) – a simple and painless procedure which provides a picture of the blood vessels.


Study participants had an average age of 57 years. Of the 46 enrolled, 40 completed the study. After 8 eight weeks of daily walnut intake, participants’ endothelial function improved significantly compared to the control phase, and their body weight and waist circumference remained stable. They experienced a trend in reduction of systolic blood pressure (the upper number in a blood pressure reading); however, that did not quite reach statistical significance. Participants’ mean measures of fasting glucose, total cholesterol, LDL, HDL and triglycerides while eating walnuts did not differ significantly from baseline as compared to while on the control diet. The study results provide evidence that walnuts can play a role in protecting against diabetes and heart disease in at-risk individuals.


Overweight men and women age 30 to 75 years who were non-smokers with a body mass index (BMI) greater than 25, and who had at least one risk factor for metabolic syndrome (high blood pressure, high fasting serum glucose, high fasting serum triglycerides, and/or low fasting HDL cholesterol).

Changed at: 11/28/2018 7:09 AM Changed by: Lisa Seaberg
Created at: 8/30/2010 10:06 AM Created by: Griffin Hospital