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Walnuts may help lower blood pressure for those at risk of heart disease
In a randomised, controlled trial, researchers examined the
effects of replacing some of the saturated fats in participants’
diets with walnuts. They found that when participants ate
whole walnuts daily in combination with lower overall
amounts of saturated fat, they had lower central blood
pressure.
According to the researchers, central pressure is the
pressure that is exerted on organs such as the heart. This
measure, like blood pressure measured in the arm in the
traditional way, provides information about a person’s risk
of developing cardiovascular disease (CVD).
Dr Penny Kris-Etherton, distinguished professor of
nutrition at Penn State, said the study suggests that because
walnuts lowered central pressure, their risk of CVD may
have also decreased. ‘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,’ Kris-Etherton said. ‘So, it seems like there’s a little
something extra in walnuts that are beneficial – maybe their
bioactive compounds, maybe the fibre, maybe something else
– that you don’t get in the fatty acids alone.”
Alyssa Tindall, recent student in Dr Kris-Etherton’s lab
and a new PhD graduate in nutrition, said the study was one
of the first to try to uncover which parts of the walnuts help
to support heart health.
‘Walnuts contain alpha-linolenic acid (ALA) a plant-
based omega-3 that may positively affect blood pressure,’
Tindall said. ‘We wanted to see if ALA was the major
contributor to these heart-healthy benefits, or if it was
other bioactive component of walnuts, like polyphenols. We
designed the study to test if these components had additive
benefits.’
For the study, the researchers recruited 45 participants
with overweight or obesity who were between the ages of
30 and 65 years. Before the study began, participants were
placed on a ‘run-in’ diet for two weeks.
‘Putting everyone on the same diet for two weeks prior
to the start of the study helped put everyone on the same
starting plane,’ Tindall said. ‘The run-in diet included 12%
of their calories from saturated fat, which mimics an average
US diet. This way, when the participants started on the study
diets, we knew for sure that the walnuts or other oils replaced
saturated fats.’
After the run-in diet, the participants were randomly
assigned to one of three study diets, all of which included
less saturated fat than the run-in diet. The diets included one
that incorporated whole walnuts, one that included the same
amount of ALA and polyunsaturated fatty acids without
walnuts, and one that partially substituted oleic acid for the
same amount of ALA found in walnuts, without any walnuts.
All three diets substituted walnuts or vegetable oils
for 5% of the saturated fat content of the run-in diet. All
participants followed each diet for six weeks, with a break
between diet periods.
Following each diet period, the researchers assessed the
participants for several cardiovascular risk factors, including
central systolic and diastolic blood pressure, brachial
pressure, cholesterol level and arterial stiffness.
The researchers found that while all treatment diets had
a positive effect on cardiovascular outcomes, the diet with
whole walnuts provided the greatest benefits, including lower
central diastolic blood pressure. In contrast to brachial
pressure, which is the pressure moving away from your heart
and measured with an arm cuff in the doctor’s office, central
pressure is the pressure moving toward your heart.
Tindall said that the results underline the importance of
replacing saturated fat with healthier alternatives. ‘An average
American diet has about 12% calories from saturated fat,
and all our treatment diets all had about 7%, using walnuts
or vegetable oils as a replacement,’ Tindall said. ‘So, seeing
the positive benefits from all three diets sends a message
that regardless of whether you replace saturated fats with
unsaturated fats from walnuts or vegetable oils, you should
see cardiovascular benefits.’
Kris-Etherton added that the study supports including
walnuts as part of a heart-healthy diet. ‘Instead of reaching
for fatty red meat or full-fat dairy products for a snack,
consider having some skim milk and walnuts,’ Kris-Etherton
said. ‘I think it boils down to how we can get the most out
of the food we’re eating, specifically, how to get a little more
bang out of your food buck. In that respect, walnuts are a
good substitute for saturated fat.’
Source:
Medical Brief 2019