Can eating walnuts reduce cardiovascular risk?
The scientists, at Pennsylvania State University in State College, explain that their study is one of the first to investigate how the properties of walnuts may affect heart health.
The results of the research, which the California Walnut Commission part funded, now appear in the Journal of the American Heart Association.
The researchers wanted to find out if the ALA content of walnuts contributes to improvements in heart health or if some other components of walnuts, such as polyphenols, might help control blood pressure among people at risk of cardiovascular disease.
Biggest killer of US adults
Cardiovascular disease causes the most deaths among adults in the United States. A 2019 study by the American Heart Association (AHA) reported that 840,000 people in the U.S. died from cardiovascular disease in 2016 alone.
That study also found that almost half of all U.S. adults have some form of cardiovascular disease.
The AHA suggest that the increase in the number of people that doctors say have high blood pressure has driven these high levels of cardiovascular disease.
However, the AHA acknowledge that part of this rise in the number of people with high blood pressure is a result of the 2017 change to the AHA/American College of Cardiology hypertension guidelines. The amended version redefined high blood pressure as a reading of 130/80 millimeters of mercury (mm Hg), rather than the previous 140/90 mm Hg.
The scientists recruited 45 participants, aged 30–65, who were either overweight or obese to their study. All participants followed a "run-in" diet for 2 weeks before the start of the study.
The run-in diet mimicked an average U.S. diet by including a 12% calorie content from saturated fat. This was to ensure that all participants were starting the study from a similar position.
The scientists then randomly assigned the participants into three different diet groups, all of which were low in saturated fats; they followed these diets for 6 weeks before moving onto the next. All participants followed all diets at some point. The diets were:
- a diet that included whole walnuts
- a diet that did not include walnuts but which incorporated the same amount of ALA and polyunsaturated fatty acids
- a diet that did not include walnuts and which partially substituted the same amount of ALA present in walnuts with another fatty acid called oleic acid
Walnuts linked with lower blood pressure
The team assessed all the participants for cardiovascular risk factors at the end of each diet period. From these data, the researchers found that the heart health of participants from all three groups improved to some extent.
They say that this finding indicates that replacing saturated fats with unsaturated fats, be it from walnuts or vegetable oils, should lead to cardiovascular benefits.
However, the researchers also found that the participants who ate the whole walnut diet had lower central blood pressure than those who ate the other diets.
Central blood pressure is the pressure moving toward the heart, and scientists consider it to be a reliable indicator of a person's cardiovascular risk.
"When participants ate whole walnuts, they saw greater benefits than when they consumed a diet with a similar fatty acid profile as walnuts without eating the nut itself," explains lead study author Prof. Penny Kris-Etherton, at Pennsylvania State University.
"So it seems like there's a little something extra in walnuts that [is] beneficial — maybe their bioactive compounds, maybe the fiber, maybe something else — that you don't get in the fatty acids alone."
Prof. Penny Kris-Etherton
Walnuts and skim milk beat meat and dairy
The researchers think that lowering central blood pressure with the walnut diet may also decrease overall cardiovascular disease risk among the participants on this diet.
However, it is worth noting that the study only included 45 participants. So, larger studies will be needed to firm up the conclusions.
The take-home message is that for people at risk of cardiovascular disease, Prof. Kris-Etherton suggests "instead of reaching for fatty red meat or full-fat dairy products for a snack, consider having some skim milk and walnuts."