Researchers at Stanford University performed a systematic review and meta-analysis of controlled trials to investigate the effects of tree nuts (almonds, Brazil nuts, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts) on blood lipids, lipoproteins, blood pressure and inflammation in adults 18 years and older without prevalent cardiovascular disease (CVD). Tree nut consumption was shown to lower total cholesterol, triglycerides, Low Density Lipoprotein (LDL) cholesterol and its primary apolipoprotein, ApoB.
Of the 1,301 potentially eligible studies, 61 crossover and parallel trials met eligibility criteria with a total of 2,582 individuals. Interventions ranged from 3-26 weeks (median 4 weeks). Nuts were provided in all of the trials, rather than relying only on dietary advice. The amount of nuts varied from 5 to 100 grams per day (median 56 grams/day or approximately 2 ounces). Compared with the control groups, consumption of tree nuts (per serving/day) significantly lowered total cholesterol (-4.7mg/dL; 95% CI-5.3,-4.0), LDL cholesterol, ApoB (-3.7mg/dL; 95% CI -5.2,-2.3) and triglycerides (-2.2mg/dL; 95% CI-3.8,-0.5).
"Accumulating evidence suggests that nut intake lowers the risk of cardiovascular disease. Our findings, showing that nut intake lowers LDL cholesterol, ApoB and triglycerides in clinical trials, provide mechanistic evidence to support this relationship," said lead author Liana Del Gobbo, PhD, currently a researcher in Cardiovascular Medicine at Stanford University. She conducted the study as a research fellow at the Friedman School of Nutrition Science and Policy at Tufts. Interestingly, stronger effects for ApoB were observed in populations with type-2 diabetes (-11.5mg/dL; 95% CI-16.2,-6.8) than among healthy populations (-2.5mg/dL; 95% CI-4.7,-0.3) (p-heterogeneity=0.015).
Nuts contain important nutrients such as unsaturated fats, high quality protein, vitamins (i.e., vitamin E, folate and niacin), minerals (i.e., magnesium, calcium and potassium) and phytochemicals--all of which may offer cardioprotective properties, prompting the U.S. Food and Drug Administration to announce a qualified health claim for nuts and heart disease in 2003. The claim states, "Scientific evidence suggests, but does not prove, that eating 1.5 ounces per day of most nuts, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease."
"This new analysis provides further support that nuts can and should be part of a heart-healthy diet," states Maureen Ternus, M.S., R.D., Executive Director of the International Tree Nut Council Nutrition Research & Education Foundation (INC NREF). "Just 1.5 ounces of nuts per day (about 1/3 cup) can provide many of the important vitamins, minerals and energy we need throughout the day."
The study is published in the American Journal of Clinical Nutrition.