While previous studies have shown that walnuts favourably affect cholesterol and other lipids, 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.
"Walnuts are a good source of two essential unsaturated fatty acids, alpha-linolenic acid and linoleic acid. 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," said Dr Penny Kris-Etherton, distinguished professor of nutrition who led the study.
Published in this month's issue of the Journal of Nutrition, the study involved 20 overweight men and three women, with moderately elevated cholesterol and LDL cholesterol.
The participants ate three experimental diets that provided about 35 per cent 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 per cent of calories from linoleic acid and 3.6 per cent 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 per cent of calories from linoleic acid and 6.5 per cent 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 six-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 per cent, LDLs about 11 or 12 per cent and triglycerides about 18 per cent. 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.
"It will be important to determine whether there is a genetic basis for this different CRP response," noted Kris-Etherton.