Healthy elderly people who ate a walnut-supplemented diet for 2 years showed significant reductions in LDL cholesterol, according to a randomized study that used imaging to evaluate lipid changes.
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“Regularly eating walnuts will lower your LDL cholesterol and improve the quality of LDL particles, rendering them less prone to enter the arterial wall and build up atherosclerosis, and this will occur without unwanted weight gain in spite of the high-fat – healthy vegetable fat, though – content of walnuts,” Emilio Ros, MD, PhD, senior author of the Walnuts and Healthy Aging (WAHA) study, said in an interview.
WAHA is a parallel-group, randomized, controlled trial that followed 636 patients over 2 years at centers in Loma Linda, Calif., and Barcelona. They were randomly assigned to either a walnut-free or walnut-supplemented diet, and every 2 months they were underwent nuclear magnetic resonance spectroscopy and recorded their compliance, toleration, medication changes, and body weight.
The researchers reported “significantly decreased” total cholesterol, LDL cholesterol and intermediate-density lipoprotein cholesterol, along with reductions in total LDL cholesterol particles and small LDL cholesterol particle number in patients on a walnut-supplemented diet, compared with controls. However, triglycerides and HDL cholesterol were unaffected.
Study results
The study reported mean reductions in the following lipid categories among what the researchers called the “walnut group”:
- Total cholesterol, –8.5 mg/dL (95% confidence interval, –11.2 to –5.4), a 4.4% mean reduction.
- LDL-C, –4.3 mg/dL (95% CI, –6.6 to –1.6), a 3.6% reduction.
- Intermediate-density lipoprotein cholesterol, –1.3 mg/dL (95% CI, –1.5 to –1.0] for a 16.8% reduction.
- Total LDL cholesterol particles, a reduction of 4.3%.
- Small LDL cholesterol particle number, a 6.1% decrease.
Dr. Emilio Ros
“WAHA is the largest and longest randomized nut trial to date, which overcomes power limitations of former trials, smaller and of shorter duration,” said Dr. Ros, of the lipid clinic, endocrinology, nutrition service at the Hospital Clinic Villarroel at the University of Barcelona. He noted that studies he has participated in have already shown that the walnut-supplemented diet had beneficial effects on blood pressure, systemic inflammation and endothelial function.
Other strengths of the study, he said, were that it recruited patients from two distinct locations and that it retained 90% of participants over 2 years (the study started out with 708 participants).
Christie Ballantyne, MD, concurred that the size and duration of the study are worth noting. “People always have questions about what they should eat,” said Dr. Ballantyne, chief of cardiology at Baylor College of Medicine and director of cardiovascular disease prevention at Methodist DeBakey Heart Center, both in Houston, said in an interview. “It’s very difficult to do nutritional studies. Most studies are small and short term, so it’s unusual to have study that’s large with 2 years of follow-up. This is a larger-than-usual study.”
Potential study limitations
Dr. Ros did acknowledge some limitations of the study. Participants weren’t blinded, the feeding setting wasn’t controlled, and participants were generally healthy and had average normal lipid profiles because they were taking statins, which may explain the modest lipid improvements in the study. “LDL cholesterol lowering by nuts is related to baseline levels, hence the reduction observed in our study was modest,” he said.
Additionally, because the study group was elderly, the results don’t apply to younger people. “Yet,” Dr. Ros added, “we know from many prior studies that nuts in general and walnuts in particular will lower blood cholesterol regardless of age.”
Dr. Christie Ballantyne
Dr. Ballantyne noted that the use of nuclear magnetic resonance spectroscopy to evaluate lipid levels involves a methodology that isn’t as systematic or as standardized as the typical lipid profile, and that different systems use proprietary software to interpret results. “That’s a little bit of an issue,” he said. “What exactly do the numbers mean?”
Overall, though, Dr. Ballantyne said the study is a significant addition to the literature. “The study is large, well done, and it confirms the benefits of something we’ve been telling patients is a good choice. It’s useful because there’s so much noise. It is important because there’s tremendous confusion and misinformation about what’s really healthy to eat.”
The study was supported by a grant from the California Walnut Commission (CWC), from which Dr. Ros and two coauthors received research funding through their institutions. Dr. Ros also reported receiving compensation from CWC and serves on a CWC advisory council. The other authors have no relationships to disclose. The WAHA study was supported by a grant from the CWC, from which Dr. Ros and some coinvestigators have received research funding through their institutions. Dr. Ballantyne has no relevant relationships to disclose.