- After a 2-year study, participants who consumed about half a cup of walnuts each day had lower levels of low-density lipoprotein (LDL) cholesterol compared with their levels at the beginning of the study.
- These individuals also experienced a reduction in total cholesterol.
- The research was supported by a grant from the California Walnut Commission.
A growing body of scientific research suggests that walnuts, which are high in omega-3 fatty acids, may protect against heart disease.
Over the years, a number of studies have investigated whether consuming walnuts might reduce cardiovascular risk factors.
For instance, a 2019 meta-analysis links higher walnut consumption with a lower cardiovascular disease incidence and mortality, including lower coronary heart disease incidence and mortality and lower atrial fibrillation.
A new study, which appears as a research letter in the American Heart Association journal Circulation, investigates whether the addition of walnuts to the daily diet for 2 years influences cholesterol levels, specifically. Moreover, this study focuses on older adults.
The authors found that including walnuts in the diet decreased the total cholesterol and modestly lowered levels of LDL cholesterol, which people often refer to as “bad” cholesterol.
Additionally, the scientists measured the participants’ subclasses of LDL cholesterol. One of these subclasses — small dense LDL particles — are more often associated with atherosclerosis, which occurs when fatty deposits build up in the arteries.
In their study, they found that daily consumption of walnuts reduced both the number of total LDL particles and small LDL particles.
An optimal composition
Dr. Emilio Ros, senior author of the current study and director of the Lipid Clinic at the Endocrinology and Nutrition Service of the Hospital Clínic of Barcelona in Spain, spoke with Medical News Today. He explained how he and his colleagues have studied the health benefits of walnuts for many years.
“We always obtained good results regarding cholesterol lowering (standard lipid profile), improved endothelial function, reduced blood pressure, and anti-inflammatory effects,” he said.
Dr. Ros does not hesitate to sing the praises of walnuts, which he includes in his own diet. “Walnuts have an optimal composition of nutrients and bioactives, including sizable amounts of alpha-linolenic acid, the vegetable omega-3 fatty acid, the highest polyphenol content of all nuts, and phytomelatonin,” he explained.
In this study, the research indicates, according to Dr. Ros, that “regularly eating walnuts will lower your LDL cholesterol and improve the quality of LDL particles, rendering them less atherogenic (less prone to enter the arterial wall and build up atherosclerosis, the basis of cardiovascular diseases), and this will occur without unwanted weight gain in spite of the high fat (healthy vegetable fat, though) content of walnuts.”
Dr. Ros told MNT he elected to take on this study because no other research had looked at lipoprotein composition, which, he said, “can provide additional insight into the antiatherogenic potential of walnuts.”
Lowered ‘bad’ cholesterol
In total, 636 participants aged 63–79 years completed the study. They all resided in either Barcelona, Spain, or Loma Linda, CA.
Of the participants, 67% were female. The participants were cognitively healthy and had no significant health conditions.
About half of the participants were taking drugs for high blood pressure or hypercholesterolemia, which, according to Dr. Ros, is typical for this older adult population. Of the participants, 32% were taking statins.
The researchers instructed one group of the participants not to eat any walnuts. The other group incorporated half a cup of raw walnuts into their daily meals. Health practitioners monitored the participants, looking for how well they were following their diet and any changes to their weight, every other month.
The researchers tested the participants’ cholesterol levels and analyzed the concentration and size of lipoproteins with nuclear magnetic resonance spectroscopy.
Over the course of the study, the participants who consumed walnuts reduced their LDL cholesterol levels by an average of 4.3 milligrams per deciliter (mg/dl) and their total cholesterol by an average of 8.5 mg/dl. The participants in the walnut group reduced their number of total LDL particles by 4.3% and of small LDL particles by 6.1%.
Among the participants who consumed walnuts, LDL cholesterol changes differed by sex. In males, LDL cholesterol fell by 7.9%. In females, it fell by 2.6%.
A modest benefit
Dr. Sanjiv Patel, an interventional cardiologist at MemorialCare Heart & Vascular Institute at Orange Coast Medical Center in Fountain Valley, CA, told MNT that the study is not a game changer when it comes to adding to what scientists already know about diet and the heart.
“We already knew that nuts are beneficial for your health,” he said.
He did appreciate that the researchers followed participants over a 2-year period. “It wasn’t a few weeks kind of study,” he said.
Dr. Patel pointed out the participants in the study experienced only a modest drop in LDL cholesterol. “There is a reduction in their [cholesterol] profile but not to the level of what you get taking statins,” Dr. Patel said. “So people who are at a significant risk of heart disease or have heart disease already should not substitute statins for nuts. They can, in addition, take the nuts to add to the benefit but not replace it.”
Indeed, Dr. Ros told MNT that in the future, he would like to conduct a study looking at the impact of adding walnuts to the diets of individuals at risk of experiencing cardiovascular disease.
Dr. Patel also cautioned that individuals who read this study should not think it is OK to down bag after bag of walnuts. He advises sticking to no more than a handful per day.
Certain limitations
Dr. Ros also pointed out some limitations to the study when speaking with MNT. For instance, he explained that the study was not “blinded.” In other words, the participants knew that they were in the walnut group.
He also explained that “the study was not conducted in a controlled feeding setting, but in free-living individuals, who could choose their daily foods, hence it was not an isoenergetic intervention, and there was an increase in energy and fat intake in the walnut group, which might have influenced the results.”
Importantly, Dr. Patel also noted that the research was supported by a grant from the California Walnut Commission, which was established to represent the walnut growers and handlers of California. “Obviously, that kind of taints the data a little bit,” he said.
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