March 26, 2012 -- Of all the nutritious snack options available, new research suggests that raisins and soy may pack some of the biggest wallop when it comes to being heart healthy.
At the American College of Cardiology's annual meeting this past weekend, researchers presented results of separate studies that evaluated the effects of raisins and soy on blood pressure. The studies found that both foods lowered blood pressure when consumed regularly.
Experts weighed in on these and a few other snacks that offer heart-healthy benefits. ABCNews.com compiled a list of the top five.
It's long been believed that raisins have a positive effect on blood pressure, and a study by doctors at the Louisville Metabolic and Atherosclerosis research Center (L-MARC) now offers some proof to that claim.
In their study, Dr. Harold Bays and his colleagues randomly assigned 46 men and women who had borderline high blood pressure to consume either about 60 raisins or a pre-packaged snack three times a day.
"We monitored blood pressure, and when we did that and looked at the final result, we found that compared to the snack group, the raisin group showed a significant decrease in systolic blood pressure," said Bays, who is medical director and president of L-MARC.
Bays believes the potassium in the raisins brought about the decrease in blood pressure.
"Prior studies had already supported that if you give people potassium, blood pressure would go down," he said.
What is also significant about his study, Bays added, is that it is one of the only studies to evaluate the relationship between raisins and blood pressure.
Soy products are protein-rich dietary staples found to have positive cardiovascular effects, including lowering blood pressure.
Researchers led by Safiya Richardson, a fourth-year medical student at Columbia University's College of Physicians and Surgeons studied the relationship between isoflavones, compounds found in soy, and blood pressure among subjects participating in the nationwide Coronary Artery Risk Development in Young Adults (CARDIA) study.
They found that consuming only 2.5 milligrams of isoflavones a day (by comparison, an 8-ounce glass of soy milk has 22 milligrams) lowered blood pressure by about 5 points. The effect was especially strong among African-Americans.
"Studies have shown that one particular isoflavone, genistein, has been found to have cause blood vessels to dilate, which is why it can lower blood pressure," Richardson said. Genistein was one of three isoflavones examined in the study.
While experts generally consider nuts to be heart smart because they contain healthier monounsaturated and polyunsaturated fats, walnuts are a particularly healthy choice.
"Nuts are among the foods that have the types of fats that reduce the levels of LDL -- the 'bad' cholesterol -- and increase the levels of the good HDL cholesterol in our blood," said Dr. Philip Ragno, director of cardiovascular health and wellness at Winthrop University Hospital.
"With walnuts, you are getting alpha-linoleic acid, which converts to an omega-3 fatty acid, which can help prevent cardiovascular disease," said Allison Stowell, dietitian at Guiding Stars, a food rating system based in grocery stores around the country.
Omega-3 fatty acids are also abundant in fish, and according to the American Heart Association, they can lower the risk of developing abnormal heart rhythms and can also decrease the levels of triglycerides in the blood.
A recent study found that walnuts also have about twice the amount of antioxidants as other nuts. Eating foods rich in antioxidants can help reduce the risk of heart disease, according to the Cleveland Clinic.
"Avocados are a super-fruit that has lots of monounsaturated fat," said Stowell.
Avocados also have a lot of vitamins, fiber and potassium. According to the U.S. Centers for Disease Control and Prevention, avocados have 60 percent more potassium than bananas.
One of the healthiest nutrients in avocados and other heart-friendly foods is fiber.
"Fiber helps cleanse the digestive tract of potentially dangerous fats," said Ragno. "Snacks that are high in fiber include oats, grains, beans, fruits and vegetables."
Fiber also helps lower cholesterol, which can help lower the risk of cardiovascular disease.
Dietary guidelines say women should consume 25 grams of fiber per day and men should consume 38 grams, according to the Academy of Nutrition and Dietetics, formerly the American Dietetic Association.