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new study suggests that eating walnuts might
help people at risk of cardiovascular disease to lower their blood pressure —
that is, if they consume them as part of a diet low in saturated fats.
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.
Walnuts
contain a plant-based omega-3 called
alpha-linolenic acid (ALA), which scientists believe has beneficial effects
on blood pressure.
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 hypertensionguidelines.
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.
Experimental diets
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."
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