While previous studies have shown that walnut supplementation favorably affects cholesterol and other lipids that are signs of cardiovascular risk, this new study is the first to demonstrate that a diet high in walnuts decreases C-reactive protein (CRP), a marker of inflammation strongly associated with heart disease.
Dr. Penny Kris-Etherton, distinguished professor of nutrition who led the study. says, "In a heart healthy diet, you need different unsaturated fatty acids that come from a variety of vegetable sources. Walnuts are a good source of two essential unsaturated fatty acids, alpha-linolenic acid and linoleic acid. They are a source of dietary fiber and a small amount of plant protein and other important vitamins and minerals. This research shows that walnuts, with their unique nutrient profile, can play a role in reducing cardiovascular risk factors as part of eating plans that also control saturated fat, trans fat, dietary cholesterol and calories."
The study is detailed in a paper, Dietary Alpha-Linolenic Acid Reduces Inflammatory and Lipid Cardiovascular Risk Factor in Hypercholesterolemic Men and Women, in the current issue of the Journal of Nutrition. The authors are Guixiang Zhao, former doctoral student in nutritional sciences at Penn State; Dr. Terry D. Etherton, distinguished professor and head of the Department of Dairy and Animal Sciences; Dr. Keith R. Martin, assistant professor of nutritional sciences; Dr. Sheila G. West, assistant professor of biobehavioral health; Dr. Peter J. Gillies, director, Health Science Strategy, DuPont Haskell Laboratory for Health and Environmental Sciences, DuPont; and Kris-Etherton.
The study included 20 men and 3 women, average age about 50, who were overweight, had moderately elevated cholesterol and LDL cholesterol and were representative of individuals at risk for cardiovascular disease. On average their total cholesterol was 225, LDL cholesterol 154, HDL cholesterol 45 and triglycerides 137 mg/dl.
The participants ate three experimental diets that provided about 35 percent of total calories as fat. One diet approximated the average American diet (AAD). Another, the linoleic acid (LA) diet, included an ounce of walnuts and a tablespoon of walnut oil that provided about 12.6 percent of calories from linoleic acid and 3.6 percent of calories from alpha-linolenic acid. The third, the alpha-linolenic acid (ALA) diet, included the walnuts and walnut oil as well as a teaspoon of flaxseed oil to boost the content of alpha-linolenic acid. The fat content was 10.5 percent of calories from linoleic acid and 6.5 percent from alpha-linolenic acid.
The participants consumed each diet for six weeks. Then they took a two-week break before beginning the next diet. At the end of each 6-week diet period, they provided blood samples so that their cardiovascular risk factors could be monitored.
Compared to the average American diet, both the LA and the ALA diets lowered total cholesterol about 11 percent, LDLs about 11 or 12 percent and triglycerides about 18 percent. After six weeks on the diet, CRP declined after both the LA and ALA diets but more so on the ALA diet. Some participants had a dramatic reduction in CRP.
Kris-Etherton notes, "It will be important to determine whether there is a genetic basis for this different CRP response. "