Walnuts are a rich source of polyunsaturated fatty acids, including alpha-linolenic acid and linoleic acid, and contain a greater amount of polyphenolic compounds than wood nuts and other vegetable oils. In a new randomized, controlled trial, researchers at the University of Pennsylvania and the University of Arizona examined the effects of replacing some of the saturated fats in a diet with walnuts. The researchers found that when participants ate whole walnuts combined with lower amounts of saturated fat, they had lower blood pressure.
Central pressure is the pressure exerted on organs such as the heart. This measure, like blood pressure measured in the traditional arm, provides information about a person's risk of developing cardiovascular disease.
"Our research shows that because nuts have reduced major stress among participants, their risk of cardiovascular disease may also decline," said Professor Penny Pennes, professor of research at the University of Texas at Columbia University.
"Walnuts contain alpha-linolenic acid, plant-based omega-3, that can positively affect blood pressure," says Elisa Tindoll, Ph.D. Candidate at Penn State.
"We wanted to see if alpha-linolenic acid was the main contributor to this cardiac benefit, or if it was another active biological component of walnuts, such as polyphenols, we designed the study to see if these components have other benefits."
For the study, the researchers recruited 45 overweight or obese participants between the ages of 30 and 65. Prior to the study, participants were placed on a "running" diet for two weeks.
"Putting everyone on the same diet for two weeks before the start of the study helped put everyone on the same plane starting," said Tindall.
"The desired diet included 12 percent of their calories from saturated fat, mimicking an average American diet," he said, "when the participants started with the diets of the study, we knew for sure that the nuts or other fats had replaced saturated fats."
After the diet, participants were randomized to one of the three diets, all of which included less saturated fat than the diet.
The diets included one that included whole walnuts, one that contained the same amount of alpha-linolenic acid and polyunsaturated fatty acids without walnuts, and one that the alkaline acid partially replaces the same amount of alpha-linolenic acid found in walnuts, without walnuts.
All three diets replaced walnuts or vegetable oils to 5 percent of the saturated fat content of the desired diet, and all participants followed each diet for six weeks with a break between diet periods.
After each diet period, the researchers assessed the participants on a number of cardiovascular risk factors, including central systolic and diastolic blood pressure, hypertension, cholesterol, and arterial stiffness.
They found that while all diets have a positive effect on cardiovascular outcomes, the diet with whole nuts provided the greatest benefits, including lower diastolic blood pressure.
"The results underscore the importance of replacing saturated fat with healthier alternatives," Tindall said.
The findings were published in the May issue of Journal of the American Heart Association.
Elisa M. Tindal et al. 2019. Replacing saturated fat with walnuts or vegetable oils improves central blood pressure and serum lipids in adults at risk of cardiovascular disease: controlled randomized trial. Journal of the American Heart Association 8 (9): e011512; doi: 10.1161 / JAHA.118.011512
This article is based on text provided by Pennsylvania State University.