Replacing saturated fat with walnuts, vegetable oils lowers blood pressure, study says
When combined with a diet low in saturated fats, eating walnuts may help lower blood pressure in people at risk for cardiovascular disease, according to a new study by researchers at Pennsylvania State University in Centre County, and published in the Journal of the American Heart Association.
In a randomized, controlled trial, researchers examined the effects of replacing some of the saturated fats in participants' diets with walnuts. Walnuts contain alpha-linolenic acid, a plant-based omega-3 fatty acid that may positively affect blood pressure. The researchers wanted to see if alpha-linolenic acid was the major contributor to the heart-healthy benefits, or if it were other bioactive component of walnuts, such as polyphenols. The researchers found that when participants ate whole walnuts daily in combination with lower overall amounts of saturated fat, they had lower central blood pressure.
For the study, the research team recruited 45 participants with overweight or obesity who were between the ages of 30 and 65 years old. Before the study began, participants were placed on a run-in standard American diet for two weeks.
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 typically found in 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, according to the study abstract. Following each diet period, the researchers assessed the participants for several cardiovascular risk factors including central systolic and diastolic blood pressure, brachial pressure, cholesterol, and arterial stiffness.
The researchers found that while all the diets had a positive effect on cardiovascular outcomes, the diet with whole walnuts provided the greatest benefits, including lower central diastolic blood pressure. Additionally, because walnuts lowered central pressure, their risk of cardiovascular disease may have also decreased, researchers say.
An average American diet has about 12 percent calories from saturated fat, according to the Centers for Disease Control’s National Health and Nutrition Examination Survey. The treatment diets had about seven percent, replacing saturated fats with walnuts and vegetable oils when possible.
The researchers say the results underline the importance of replacing saturated fat with healthier alternatives. In addition, walnuts can easily be included as part of a heart-healthy diet.