A study led by Dr. Michael C. Falk of the Life Sciences Research Organization and published in the American Journal of Clinical Nutrition, uncovered some interesting results regarding the positive effects of consuming tree nuts.
The results support a growing body of research on tree nuts’ beneficial role relating to cardiovascular disease risk factors. After conducting a systematic review and meta-analysis of 61 controlled trials, researchers, led by Dr. Michael Falk, PhD, Life Sciences Research Organization, conclude that tree nut intake lowers total cholesterol (-4.7 mg/dL; 95% CI: -5.3, -4.0 mg/dL), LDL cholesterol (-4.8 mg/dL; 95% CI; -5.5, -4.2 mg/dL), ApoB (-3.7 mg/dL; 95% CI: -5.2, -2.3 mg/dL), and triglycerides (-2.2 mg/dL; 95% CI: -3.8, -0.5 mg/dL), with no statistically significant effects on other outcomes. Walnuts were investigated in 21 of the 61 trials, more than any other nut reviewed in this study.
No significant effects of tree nut consumption were identified for HDL cholesterol, apolipoprotein A1, apolipoprotein B100, systolic or diastolic blood pressure, or C-reactive protein.
As stated in the paper, potential limitations should be considered. Compliance was often assessed by self-report, and low compliance would cause underestimation of effects. Greater effect sizes were observed in lower quality, nonrandomized trials, yet significant effects on total cholesterol, LDL cholesterol, and ApoB were still seen in high-quality, randomized trials. The relatively few trials in some subgroups examined in heterogeneity analyses limited statistical power to detect potential interaction.
“Our study results further support the growing body of research that tree nuts, such as walnuts, may reduce the risk of cardiovascular disease2 when consumed as part of a healthy diet low in cholesterol and low in saturated fat,” said Dr. Falk. “Tree nuts contain important nutrients such as unsaturated fats, protein (2-6 grams per ounce, depending on the nut), vitamins and minerals. Walnuts are the only nut that provides a significant amount (2.5 grams per serving) of alpha-linolenic acid (ALA), the plant-based form of omega-3s.
Of 1,301 articles surveyed, 61 trials met eligibility criteria for the meta-analysis, totaling 2,582 unique participants. The amount of nuts consumed varied from 5 to 100 g/d (median: 56 g/d), and the duration of intervention was from 3 to 26 weeks (median: 4 week).
Eligibility Criteria:
- Included all published controlled trials that reported the effect of tree nut consumption on blood lipids, lipoproteins, blood pressure, or inflammation. Trials had to be controlled but could be randomized or nonrandomized (with plans to evaluate only randomized trials and all trials combined) and provided mean levels of the outcome in each group with an accompanying measure of statistical uncertainty (e.g., 95% CI, SE) or other data to calculate variance.
- Did not include body weight or adiposity as outcomes
- Excluded trials testing nonnut parts of the plant, nut oils, nuts other than tree nuts (e.g., areca, betel), or legumes (e.g., peanuts) and trials testing mixed dietary interventions for which the specific effect of nuts could not be evaluated. We also excluded trials among children (less than 18 years), participants with known CVD, and participants receiving medication treatment of diabetes, obesity, metabolic syndrome, hypertension, or hyperlipidemia. For crossover trials without a washout period, we excluded trials with an intervention period less than 3 weeks to minimize carryover effects. Trials with 20% dropout rates or having imbalanced dropout between intervention and control groups were also excluded, and articles presenting only observational data, editorials/commentaries, letters, and reviews were not eligible.
This latest research provides insights into the ways walnuts may affect cardiovascular disease risk factors for the study participants. More than two decades of research have shown the role of walnuts and heart health and results continue to provide important information to health professionals, researchers and consumers.
Co-authors with Dr. Falk are Liana C. Del Gobbo, PhD, Robin Feldman, MBA, Kara Lewis, PhD and Dariush Mozaffarian, MD PhD.
This study was supported in part by funds from The International Tree Nut Council Nutrition Research and Education Foundation.
Resources:
- Del Gobbo, L., Falk, M.C., Feldman, R., Lewis, K., Mozaffarian, D. Effects of tree nuts on blood lipids, apolipoproteins, and blood pressure: systematic review, meta-analysis and dose-response of 61 controlled intervention trials. [Published online ahead of print November 11 2015]. Am J Clin Nutr. 2015. doi: 10.3945/ajcn.115.110965.
- Supportive but not conclusive research shows that eating 1.5 ounces of walnuts per day, as part of a low saturated fat and low cholesterol diet, and not resulting in increased caloric intake may reduce the risk of coronary heart disease (FDA). One ounce of walnuts provides 18g of total fat, 2.5g of monounsaturated fat, 13g of polyunsaturated fat, including 2.5g of alpha-linolenic acid, the plant-based omega-3.
- Kris-Etherton P. Walnuts decrease risk of cardiovascular disease: a summary of efficacy and biologic mechanisms. J Nutr. April 2014; 144(4): 547S-554S.