Serum lipid response to the graduated enrichment of a Step I diet with almonds: a randomized feeding trial

Serum lipid response to the graduated enrichment of a Step I diet with almonds: a randomized feeding trial1–3 Joan Sabaté, Ella Haddad, Jay S Tanzman, Pera Jambazian, and Sujatha Rajaram ABSTRACT Background: Frequent consumption of nuts may lower the risk of cardiovascular disease by favorably altering serum lipid and lipoprotein concentrations. Objective: We compared the effects of 2 amounts of almond intake with those of a National Cholesterol Education Program Step I diet on serum lipids, lipoproteins, apolipoproteins, and glucose in healthy and mildly hypercholesterolemic adults. Design: In a randomized crossover design, 25 healthy subjects (14 men, 11 women) with a mean (± SD) age of 41 ± 13 y were fed 3 isoenergetic diets for 4 wk each after being fed a 2-wk runin diet (containing 34% of energy from fat). The experimental diets included a Step I diet, a low-almond diet, and a high-almond diet, in which almonds contributed 0%, 10%, and 20% of total energy, respectively. Results: Inverse relations were observed between the percentage of energy in the diet from almonds and the subject’s total cholesterol (P value for trend < 0.001), LDL-cholesterol (P < 0.001), and apolipoprotein B (P < 0.001) concentrations and the ratios of LDL to HDL cholesterol (P < 0.001) and of apolipoprotein B to apolipoprotein A (P < 0.001). Compared with the Step I diet, the high-almond diet reduced total cholesterol (0.24 mmol/L or 4.4%; P = 0.001), LDL cholesterol (0.26 mmol/L or 7.0%; P < 0.001), and apolipoprotein B (6.6 mg/dL or 6.6%; P < 0.001); increased HDL cholesterol (0.02 mmol/L or 1.7%; P = 0.08); and decreased the ratio of LDL to HDL cholesterol (8.8%; P < 0.001). Conclusions: Isoenergetic incorporation of 68 g of almonds (20% of energy) into an 8368-kJ (2000-kcal) Step I diet markedly improved the serum lipid profile of healthy and mildly hypercholesterolemic adults. Total and LDL-cholesterol concentrations declined with progressively higher intakes of almonds, which suggests a dose-response relation. Am J Clin Nutr 2003;77:1379–84. individuals to reduce or avoid certain foods, which is a challenge to long-term adherence (3). Whereas the National Cholesterol Education Program (NCEP) Step I diet is known to reduce LDL cholesterol by 3–10% (4, 5), that reduction is often accompanied by an increase in triacylglycerol and a decrease in HDL cholesterol, both of which contribute to an increased risk of CVD (6). In addition, high-carbohydrate, low-fat diets produce unfavorable shifts in LDL-cholesterol subclasses, which produces further atherogenic risk (7). Because the NCEP Step I diet falls short of favorably altering a person’s overall lipid profile, alternative diets that will accomplish this goal should be identified. In this context, specific whole foods that not only lower LDL cholesterol but also favorably influence other blood lipids could be used as an adjunct to usual or cholesterol-lowering diets. Increased consumption of foods from the whole-grain and legume families was shown to reduce the risk of CVD (8), possibly by lowering LDL cholesterol. Garlic, soy, and fish were shown to lower LDL cholesterol (9, 10) and to favorably modify other lipids and lipoproteins (11). In fact, the latest edition of the American Heart Association dietary guidelines includes specific food recommendations (12). Epidemiologic studies (13–15) have consistently reported an inverse relation between the incidence of CVD and the frequent consumption of nuts, even after adjustment for confounding variables. Almonds, which are high in monounsaturated fat, are commonly consumed in many parts of the world (16). Almonds are unique in that they have significant amounts of protein and have the highest concentration of -tocopherol of all nuts (17). A cholesterol-lowering effect of almonds compared with typical Western diets in healthy and hypercholesterolemic subjects was reported in 2 field trials (18, 19) and 1 clinical trial (20). Our study furthers this investigation by comparing the effects of almond consumption in 2 amounts on multiple serum lipid values with those of a Step I diet in a well-controlled experimental setting. KEY WORDS Serum cholesterol, LDL cholesterol, HDL cholesterol, apolipoproteins, cardiovascular disease, Step I diet, monounsaturated fatty acids, nuts, almonds, humans SUBJECTS AND METHODS INTRODUCTION Hypercholesterolemia is one of the major risk factors for cardiovascular disease (CVD). A cornerstone of treatment for hypercholesterolemia is dietary modification (1), which has the objective of improving the ratio of LDL to HDL cholesterol. Dietary recommendations for lowering LDL cholesterol have centered on restriction of foods high in saturated fat; modification of visible fats such as butter, margarine, and oils; or both. These diets are low to moderate in total and saturated fat (2), and they require Subject recruitment Potential study subjects were healthy men and women aged 20–60 y. The selection process included the completion of a 1 From the Department of Nutrition, School of Public Health, Loma Linda University, Loma Linda, CA. 2 Supported by a research grant from the Almond Board of California. 3 Address reprint requests to J Sabaté, Department of Nutrition, School of Public Health, Loma Linda University, Loma Linda, CA 92350. E-mail: . Received June 4, 2002. Accepted for publication January 27, 2003. Am J Clin Nutr 2003;77:1379–84. Printed in USA. © 2003 American Society for Clinical Nutrition 1379 1380 SABATÉ ET AL This was a randomized, crossover (3  3 Latin-square), controlled feeding trial. The sample size was computed on the basis of the decreases in serum cholesterol that were due to the consumption of nuts as reported in previous studies (reviewed in 21), and it provided for a 10% dropout rate. A sample size of 24 was determined to provide > 90% power to detect significant differences between treatments at P < 0.05. The Institutional Review Board of Loma Linda University approved the study. All participants gave written informed consent. Participants who successfully completed the study received an incentive of $300. senior investigator; 4) randomly collected diet samples (n = 27) covering all 3 treatment diets were homogenized and analyzed (23) for nutrient composition (Covance Laboratories, Madison, WI); and 5) the fatty acid composition of serum triacylglycerol was analyzed at the end of each diet period at the University of California, Davis, to provide an objective measure of dietary compliance. Before determining the fatty acid composition of serum triacylglycerol, the lipids from serum were extracted by using chloroform:methanol (2:1, by vol), and individual lipid classes within each extract were separated by preparative thin-layer chromatography. Each lipid fraction was scraped from the plate and transesterified in 3 N methanolic HCl in a sealed vial under nitrogen atmosphere (100 C for 45 min). The resulting fatty acid methyl esters (...truncated)