Folsom, Calif., (February 9, 2016) – A new study published in the Journal of the American Heart Association found that a diet containing unsaturated fats, such as those found in walnuts and olive oil, has similar weight loss effects as a lower fat, higher-carbohydrate diet.1 The research, led by Dr. Cheryl Rock of the University of California, San Diego School of Medicine, also showed that a diet containing walnuts, which are primarily comprised of polyunsaturated fats, positively impacts heart health markers, such as cholesterol.
"One of the surprising findings of this study was that even though walnuts are higher in fat and calories, the walnut-rich diet was associated with the same degree of weight loss as a lower fat diet," said Dr. Rock. "Considering the results of this study, as well as previous walnut research on heart health and weight, there's something to be said for eating a handful of walnuts a day."
To reach their findings, the research team studied 245 overweight and obese women (22-72 years old) enrolled in a one-year behavioral weight loss intervention. Participants were randomly assigned to three different diets: 1) a lower fat and higher carbohydrate diet, 2) a lower carbohydrate and higher fat diet, or 3) a walnut-rich, higher fat and lower carbohydrate diet. Those prescribed a walnut-rich diet consumed 1.5 ounces per day. Looking at data from the first six months of the intervention, this study found that the average weight loss was nearly eight percent of initial weight for all groups.
The walnut-rich diet participants saw comparable weight loss to the other study groups; however, they exhibited the most improvement in lipid levels, especially in those who are insulin-resistant. In addition to a significant decrease in LDL cholesterol, the walnut participants achieved a greater increase in HDL cholesterol as compared to the other diet groups.
Whereas the lower carbohydrate and higher fat diet participants were encouraged to consume foods higher in monounsaturated fats, the walnut-rich diet provided more polyunsaturated fats. Walnuts are the only nut in which the fat is primarily polyunsaturated fat (13g/oz), including a significant amount of alpha-linolenic acid (ALA), the plant-derived form of omega-3 fatty acids (2.5g/oz).
Recent research from Harvard also shows health benefits of consuming polyunsaturated fats.2 The study suggested that people who replace saturated fats with polyunsaturated fats may live longer and have a lower risk of heart disease. Additionally, the 2015-2020 Dietary Guidelines recommend consumption of polyunsaturated fats as a replacement for saturated fats.3
There are some study limitations that should be considered. The sample only included women, so these results may not be generalizable to men. Although 245 participants were enrolled, the sample sizes for comparisons were reduced because the participants were divided into subgroups. In addition, there is a lack of detailed information about dietary intake and adherence to the diets. Considering the weight loss that was seen in participants, it seems that most were adhering to a reduced calorie diet.
"In addition to these findings, we hope to explore the effect of walnuts on satiety, as we believe satiety is a critical factor for maintaining weight loss," said Dr. Rock.
Additional study co-authors include Tran Le, Shirley W. Flatt, Loki Natarajan, Bilge Pakiz, Elizabeth L. Quintana, Dennis D. Heath, and Brinda K. Rana.
This research was funded, in part, by the National Institutes of Health (CA155435) and the California Walnut Commission.
1 Le T, Flatt SW, Rock CL, et al. Effects of Diet Composition and Insulin Resistance Status on Plasma Lipid Levels in a Weight Loss Intervention in Women [published online ahead of print January 25, 2016]. J Am Heart Assoc. doi: 10.1161/JAHA.115.002771.
2 Li Y, Hruby A, Bernstein AM, Hu FB, et al. Saturated fat as compared to unsaturated fats and sources of carbohydrates in relation to risk of coronary heart disease: A prospective cohort study. J Am Coll Cardiol. 2015;66(14):1538-1548. doi: 10.1016/j.jacc.2015.07.055.
3 U.S. Department of Health and Human Services and U.S. Department of Agriculture. 2015 – 2020 Dietary Guidelines for Americans. 8th Edition. December 2015. Available at http://health.gov/dietaryguidelines/2015/guidelines/