We have already heard that consuming nuts is one of the key factors in improving brain health
. Now, a new study has found that consuming walnuts is beneficial for people who are at risk of heart disease and helps them lower their blood pressure.
The study was conducted by a research team from Penn State University led by Prof Penny Kris-Etherton and was published in Journal of the American Heart Association. Researchers reported that when participants’ combined a diet low in saturated fats with eating walnuts, it lowered blood pressure in people at risk of cardiovascular disease.
For the study, the researchers examined effects of replacing some of the saturated fats in participants’ diets with walnuts, in a randomised and controlled trial. A total of 45 participants, who were either overweight or obese and between the ages of 30 and 65, were recruited. Before the study began, they were placed on a ‘run-in’ diet for a period of 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 plain,” said Dr Alyssa Tindall, one of the other researchers working in Prof. Kris-Etherton’s lab. This initial run-in diet included 12% of their calories from saturated fat, in order to mimic an average American diet. This way, when the participants started on the study diets, researchers could know with certainty that the walnuts or other oils had replaced saturated fats.
Dr Tindall said that the study was one of the first to try to uncover which parts of the walnuts help support heart health. “Walnuts contain alpha-linolenic acid - ALA - a plant-based omega-3 that may positively affect blood pressure,” she 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.”
After the run-in diet, participants were randomly assigned to one of three study diets, all of which included less saturated fat than the run-in diet. One of the study diets incorporated whole walnuts, another included the same amount of ALA and polyunsaturated fatty acids without walnuts, and the third diet had partially substituted oleic acid (another fatty 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, and all participants followed each diet for six weeks, with a break between diet periods. Following each diet period, the researchers assessed participants for several cardiovascular risk factors including central systolic and diastolic blood pressure, brachial pressure, cholesterol and arterial stiffness.
They found that when participants ate whole walnuts daily in combination with lower overall amounts of saturated fat, they had lower central blood pressure—the pressure moving towards your heart. It provides information about a person’s risk of developing cardiovascular disease (CVD).
Since the study suggests that walnuts were the cause of lower central pressure, Prof Kris-Etherton believes that 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,” she explained. “So it seems like there’s a little something extra in walnuts that are beneficial -- maybe their bioactive compounds, maybe the fiber, maybe something else—that you don’t get in the fatty acids alone.”
The research team was able to conclude 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.
Dr Tindall said that the results underline the importance of replacing saturated fat with healthier alternatives. “An average American diet has about 12 percent calories from saturated fat and all our treatment diets all had about seven percent, using walnuts or vegetable oils as a replacement,” Dr 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.”
Prof 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,” she 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.”