Walnuts are a rich source of polyunsaturated fatty acids, including alpha-linolenic acid and the linoleic acid, and contain a proportionally greater quantity of polyphenolic compounds compared with other tree nuts and vegetable oils. In a new randomized, controlled trial, a team of researchers from the Pennsylvania State University and the University of Arizona examined the effects of replacing some of the saturated fats in participants’ diets with walnuts. The team found that when participants ate whole walnuts daily in combination with lower overall amounts of saturated fat, they had lower central blood pressure.
Replacing saturated fatty acids with 57 to 99 g/day of walnuts for 6 weeks reduced central diastolic blood pressure compared with a diet similarly low in saturated fatty acids but with lower alpha-linolenic acid content. Image credit: He Lee.
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.
“Our study suggests that because walnuts lowered central pressure in participants, their risk of cardiovascular disease may have also decreased,” said Penn State Professor Penny Kris-Etherton, senior author of the study.
“Walnuts contain alpha-linolenic acid, a plant-based omega-3 that may positively affect blood pressure,” added Alyssa Tindall, Ph.D. candidate at Penn State.
“We wanted to see if alpha-linolenic acid 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. 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 American 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 alpha-linolenic acid and polyunsaturated fatty acids without walnuts, and one that partially substituted oleic acid for the same amount of alpha-linolenic acid found in walnuts, without any walnuts.
All three diets substituted walnuts or vegetable oils for five percent of the saturated fat content of the run-in diet, and all participants followed each diet for six weeks, with a break between diet periods.
Following each diet period, the scientists assessed the participants for several cardiovascular risk factors including central systolic and diastolic blood pressure, brachial pressure, cholesterol, and arterial stiffness.
They 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.
“The results underline the importance of replacing saturated fat with healthier alternatives,” Tindall said.
The findings were published in the May 7 issue of the Journal of the American Heart Association.
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Alyssa M. Tindall et al. 2019. Replacing Saturated Fat With Walnuts or Vegetable Oils Improves Central Blood Pressure and Serum Lipids in Adults at Risk for Cardiovascular Disease: A Randomized Controlled-Feeding Trial. Journal of the American Heart Association 8 (9): e011512; doi: 10.1161/JAHA.118.011512
This article is based on text provided by the Pennsylvania State University.
