Walnut Ingestion in Adults at Risk for Diabetes: Effects on Diet Quality, Body Composition, and Cardiac Risk Measures
Complete Project
Title:
Walnut Ingestion in Adults at Risk for Diabetes: Effects on Diet Quality, Body Composition, and Cardiac Risk Measures
Status:
Completed
Topic:
Nutrition / Diet
Funding Source:
California Walnut Commission
Funding Period:
2012-2014
Study Design:
Randomized controlled parallel design with two treatment arms
Purpose:
We examined the effects of 6 months of daily walnut intake on diet quality, body composition, and markers of cardiovascular risk in a group of adults at risk for diabetes. Many people who are at risk for diabetes are also at risk for developing cardiovascular disease. Prior research has confirmed the health benefits of consuming walnuts, which are a rich source of omega-3 fats, other healthful nutrients, and antioxidants. Although walnuts are high in calories, they have not been found to contribute to weight gain in short-term studies, perhaps because they contribute to a feeling of satiety. We wanted to see if the effects would hold true over a longer time, and to compare the effects of adjusting, vs. not adjusting, for calories in the walnuts.
Further Study Details:
The study included a 6-month walnut phase (2 oz walnuts/day), 3-month washout phase, and 6-month control phase (no walnuts). During the walnut phase, each adult was randomly assigned to either a calorie-adjusted or ad libitum diet. We expected to find that a walnut-included diet (with or without advice to adjust for calories from the walnuts), when compared to a walnut-excluded diet, would significantly improve diet quality, body weight, percent body fat, and other measures of risk for diabetes (fasting glucose, hemoglobin A1C) and/or cardiovascular disease (blood lipids, vascular function). We also expected to find that keeping calorie levels constant while adding walnuts to the diet would enhance the beneficial effects of walnuts on diet quality, body composition, and vascular function.
Findings:
Our data suggest that 6 months of a diet including 2 oz. of walnuts per day (whether calorie-adjusted or not) improved diet quality in adults at risk for diabetes. The effects of this diet (whether calorie-adjusted or not) on vascular function, waist circumference, total and LDL cholesterol were inconclusive. Neither version of the diet improved fasting blood glucose, HDL cholesterol, blood pressure, body mass index, percent body fat, percent body water, or visceral fat. Controlling calorie intake did not seem to enhance the beneficial effects of walnuts on diet quality, body composition, or vascular function. More research is needed to clarify the effects of walnuts in adults at risk for diabetes.
Eligibility:
Men and women age 25 to 75 years, who were non-smokers, and at high risk for diabetes based on their weight, fasting blood glucose, and/or other risk factors
Yale-Griffin Prevention Research Center