When combined with a diet low in saturated fat, eating walnuts may help lower blood pressure in people at risk for cardiovascular disease, according to a new Penn State study.
In a randomized, 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.
Central pressure is the pressure that is exerted on organs like the heart. This measure, like blood pressure measured in the arm the traditional way, provides information about a person's risk of developing cardiovascular disease (CVD).
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, noted the researchers. There may be something extra in walnuts that are beneficial, perhaps bioactive compounds or fibre, that you don't get in the fatty acids alone.
Walnuts contain alpha-linolenic acid (ALA), a plant-based omega-3 that may positively affect blood pressure.
The researchers 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.
About the study
For the study, the researchers recruited 45 participants with overweight or obesity who were between the ages of 30 and 65. Before the study began, participants were placed on a "run-in" diet for two weeks to put everyone on the same starting plane. The run-in diet included 12 percent of their calories from saturated fat, which mimics an average American diet. This way, when the participants started on the study diets, the researchers 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 (another fatty acid) for the same amount of ALA found in walnuts, without any walnuts.
Following each diet period, the researchers assessed several cardiovascular risk factors including central systolic and diastolic blood pressure, brachial pressure, cholesterol 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.
The average American diet has about 12 percent calories from saturated fat; the three study diets had about seven percent, using walnuts or vegetable oils as a replacement.
Source: Journal of the American Heart Association, 2019.
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