Studies have consistently linked all kinds of nuts to a reduced risk of heart disease, largely because nuts have a favorable effect on blood cholesterol. Nuts may also help keep blood vessels healthy and have other cardiovascular benefits. Back in 2002, a major study found that women who ate nuts (an ounce at least five times a week) had a lower risk of type 2 diabetes. It’s a myth that nuts increase the risk of complications of diverticulosis (small pouches in the intestinal wall that can become infected). Studies have even linked nut consumption to increased longevity.
At least three-quarters of the calories in nuts come from fat, which is mostly unsaturated (monounsaturated or polyunsaturated), the kind that can improve blood cholesterol levels. Other healthful substances in nuts include potassium, copper, magnesium, fiber (much of it soluble), arginine (an amino acid that helps relax blood vessels), sterols (which also help lower cholesterol), and various antioxidant compounds.
People who eat nuts regularly tend to weigh less than those who don’t—or at least they don’t weigh more, studies show. The protein, fat, and fiber in nuts help make you feel full longer, so you are less hungry—and presumably eat less—later. Some studies also suggest that nuts may slightly increase calorie burning, while other research has found that some of the fat and protein in nuts is not absorbed by the body because it passes through the intestines undigested (unless the nuts are ground into butter).
Peanuts are technically legumes (like dried beans) but are classified with nuts because of their shared nutritional (and physical) qualities. They contain resveratrol (a potentially bendeficial compound also found in grapes and red wine), are richest in arginine, and have the most protein of all nuts. Studies have found that peanuts, like tree nuts, are associated with a range of health benefits.
But some commercial nut butters may still contain trans fat because of the partially hydrogenated vegetable oil added to keep the nut oil from separating. Even though the amount of trans fat is tiny, no amount is healthy. Many nut butters also have added sugar and salt. Check the ingredients.
Though you’re not likely to get much, the skin contains antioxidant compounds and fiber. Almond skins, for example, are rich in flavonoids, including catechins. A paper from the USDA (and the Almond Board of California) found that these compounds in the skin interact with vitamin E in the nuts to protect LDL (“bad”) cholesterol against oxidation. Oxidized LDL is more damaging to arteries.
Brazil nuts are the single best dietary source of selenium. Just one nut provides more than the daily requirement, which is 55 micrograms. But don’t eat too many—a safe upper limit for selenium is only 400 micrograms a day for adults. Doses of more than 1,000 micrograms a day can cause nausea, vomiting, hair loss, and other problems.
Studies have generally found benefits in people eating 1 to 3 ounces of nuts a day. For example, an analysis of 25 studies, in the Archives of Internal Medicine in 2010, found that people who ate about 2 ounces of nuts a day had a 7 percent decrease in LDL cholesterol. The FDA allows nut labels to display a “qualified” health claim saying that eating 1½ ounces of nuts a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. A handful of nuts is about an ounce. This web page will tell you how many nuts are in an ounce and how they stack up in terms of nutrients.