Nuts and fish are great sources of polyunsaturated fatty acids (PUFAs), and monounsaturated fatty acids (MUFAs). Numerous studies have demonstrated that replacing foods, like red meats that are high in saturated fats (SFA), with nuts and fish that are high in PUFAs and MUFAs, has a favorable outcome in cholesterol and triglyceride serum levels. Omega 3 fatty acids are the most widely recognized member of PUFAs found in nuts and fish. The findings of the walnut diet are in agreement with previous findings from several other studies investigating the benefits of nuts on cholesterol fractions. 

Researchers from Pennsylvania State University and the University of Guelph reported last year reported that replacing foods full of saturated fats, with more nut and nut-containing foods into the diet such as walnuts, macadamia and almond nuts, could reduce cholesterol levels in individuals with mildly elevated cholesterol fractions. 

The Pennsylvania State University and the University of Guelph study compared a Macadamia nut rich diet, high in monosaturated fats (MUFA), and half the saturated fat (7% SFA, 18% MUFA), to the average American diet (13% SFA, 11% MUFA). Both diets contained the same amount of total fat. The results of the present study showed that the inclusion of 1.5 ounces/day (5 weeks) of macadamia nuts reduced Total Cholesterol, and LDL-Cholesterol concentrations in men and women with mildly elevated cholesterol, when substituted for SFA in the diet.(2) 

Similarly, a study that substiuted Pistachios for foods higher in saturated fats in a controlled study of dietary intake, demonstrated a lowering of LDL cholesterol of 9 to 12% with a daily serving to two servings (32 to 63 g/d, and from 63 to 126 g/d) of Pistachio nuts. (3) A lower-fat diet control group without Pistachio nuts included, did not derive any cholesterol lowering benefits.(3) 

Apo B, a sub-class of cholesterol, and a marker for cardiovascular disease risk, was also lower in the diet that included Pistachio nuts. Besides being an excellent source of PUFAs, Pistachios are rich in phytosterols, which also have cholesterol lowering benefits. 

 * Cholesterol and triglycerides are the main types of lipids measured in routine blood chemistry tests 

 1. Walnuts and fatty fish influence different serum lipid fractions in normal to mildly hyperlipidemic individuals: a randomized controlled study 

Authors: S. Rajaram, E.H. Haddad, A. Mejia, J. Sabat American Journal of Clinical Nutrition May 2009, Volume 89, Number 5, Pages 1657S-1663S 

 2. A Macadamia Nut-Rich Diet Reduces Total and LDL-Cholesterol in Mildly Hypercholesterolemic Men and Women 

Amy E. Griel, Yumei Cao, Deborah D. Bagshaw, Amy M. Cifelli, Bruce Holub, and Penny M. Kris-Etherton 

J Nutr. 2008 Apr;138(4):761-7. 

 3. Effects of pistachios on cardiovascular disease risk factors and potential mechanisms of action: a dose-response study 

Sarah K Gebaue1, Sheila G West, Colin D Kay, Petar Alaupovic, Deborah Bagshaw and Penny M Kris-Etherton 

American Journal of Clinical Nutrition, Vol. 88, No. 3, 651-659, September 2008