Although consumption of as little as 5 ounces of nuts per week has been shown to reduce cardiovascular (CVD) risk by 30-50%, most studies have not differentiated the effects of specific types of nuts. Walnuts are unique as a rich source of n-3 and n-6 polyunsaturated fatty acids (PUFAs). In a study of older subjects, Almario et al. demonstrated that walnuts added to the diet have a dual effect of lowering both total cholesterol and low-density lipoprotein (LDL) cholesterol.
The 5 men and 13 postmenopausal women in the study averaged 60 years of age and had high serum cholesterol levels. Over a 5-1/2 month period, they consumed four diets in sequence: their habitual diet (HD), HD + walnuts , a low-fat diet (LFD), and a LFD + walnuts. Walnuts were provided at 48 grams per 1850 dietary calories per day. Compared with both the HD and LFD, the LFD + walnuts significantly reduced total cholesterol and LDL-cholesterol concentrations. Compared to the diets without walnuts, the proportion of small particle LDL decreased by 27% with the HD + walnuts and 7% with the LFD + walnuts. Small particle LDL is considered to be a promoter of CVD. None of the subjects gained weight during the walnut diets, even though their energy intakes increased.
The authors conclude that the metabolic effect of walnuts is favorable, and that walnuts affect lipid metabolism differently than other food sources of n-3 and n-6 fatty acids, such as fish oil and soybean products.