If you’re trying to eat a heart-healthy diet, figuring out what to believe can be overwhelming. The advice we get on everything from eggs to olive oil is often confusing and maddeningly contradictory.
Ironically, this growing confusion comes at a time when scientists who study nutrition know more than ever. Too often, though, we hear about only the latest study (which may be poorly designed) or research that’s cherry-picked to support an agenda. That’s like seeing one or two pieces of a jigsaw puzzle and trying to determine what the entire picture is.
To know what the science really shows, it pays to look at all the evidence, assigning greater weight to studies that are more rigorous. In many cases, this can give us a reliable indication of what’s really good or bad. Based on a thorough review of research, here’s what’s believable — and what’s not — regarding some familiar claims about heart health.
Nuts are good for your heart
True. Once regarded as high-fat nutritional villains to be avoided at all costs, nuts are now touted as a health food that can ward off heart disease. And perhaps rightly so. Several large cohort studies (the type in which people are asked about their dietary habits and then followed for years or decades) have consistently found lower odds of heart disease and heart-related deaths among nut eaters, regardless of sex, age, location or occupation.
These findings are bolstered by results from clinical trials demonstrating that nuts lower LDL cholesterol levels, the kind associated with an increased risk of heart disease. Nuts also appear to decrease inflammation in arteries, which may contribute to heart attacks.
So which nuts are best for you? If you listen to producers of walnuts, almonds or peanuts (which, technically, aren’t nuts but legumes), each will tell you that its nut is superior because of some ingredient it contains. The truth is that it’s impossible to say which is best because no one has done a head-to-head comparison.
All nuts are relatively high in unsaturated fats, which are thought to be good for the heart. And all nuts are relatively high in calories, so it’s important to pay attention to portion sizes. About a handful a day is enough to reap health benefits. It may even promote weight loss by helping you feel full. But going nuts and overindulging can lead to extra pounds.
Oats lower cholesterol
TRUE. Oats contain a type of soluble fiber known as beta-glucan, which is also found in barley. It’s thought to lower cholesterol by binding to bile acids and removing them from the body. Bile acids are made from cholesterol, so when the body has to deploy more of its cholesterol to help replace the eliminated bile acids, there’s less of it in the blood.
The Cochrane Collaboration, an independent group that assesses the evidence for various treatments, conducted an analysis in which it pooled results from eight randomized studies involving people with elevated cholesterol and other risk factors for heart disease. Subjects assigned to eat oat cereal every day lowered their total and LDL cholesterol levels seven or eight points more than those on a diet of refined grains. The studies lasted only four to eight weeks, so we don’t know about long-term effects.
To see a benefit, you need three grams of beta-glucan a day, which you can get from 1.5 cups of cooked oatmeal, three cups of instant oatmeal or three cups of Cheerios. Unfortunately, oatmeal cookies don’t count.
Fish oil protects your heart
True. Decades ago, scientists discovered that Greenland Eskimos rarely died from heart disease despite a diet high in fat from fish. Researchers theorized that the fish fat was somehow protective, an idea that subsequent research has largely supported.
Several cohort studies show that people who regularly eat fish are less likely to die of heart disease than those who don’t eat fish. Randomized trials involving heart attack survivors have found that subjects given fish oil supplements were less likely to die of heart disease than those who didn’t take the capsules. And in a randomized study of people with high cholesterol, participants who took fish oil had fewer heart attacks and deaths from heart disease.
The key ingredients appear to be the omega-3 fatty acids EPA and DHA, which are found in most fish but especially in oily ones such as salmon, mackerel, trout, sardines and tuna. Studies suggest that these fats may help relax blood vessels, reduce blood pressure, prevent abnormal rhythms and lower blood fats known as triglycerides.
While the evidence of benefits is strong for people who have heart disease or are at high risk for it, it’s less clear whether fish oil wards off heart attacks in those at low risk. Still, it seems reasonable to follow the American Heart Association’s recommendation and eat oily fish at least twice a week. People with heart disease are advised to get twice as much, or 1,000 milligrams per day of EPA and DHA combined.