They're good for us, but which nut is the best?
Health-conscious people are mad about nuts these days. The enthusiasm comes from a steady drumbeat of studies over the past decade showing that they're genuine health food. Their most salient effect seems to be heart attack prevention. Some studies suggest they give you some protection against diabetes, too.
True, nuts are high in calories: Just an ounce of most varieties has more than the 140 or so calories contained in 12 ounces of many brands of soda. Ideally, you should incorporate them into regular meals as a protein source. About 80% of the calories come from fat. Much of the fat, though, is "good" monounsaturated and polyunsaturated fat, not the "bad" saturated variety in meat and dairy products — or worse yet, dreaded trans fat. In research studies, cholesterol-lowering diets that contain nuts reduce "bad" LDL cholesterol by 9%–20%, regardless of the amount of fat or nuts.
Other healthful ingredients in nuts include copper, fiber, folate, and vitamin E. They have lots of arginine, an amino acid that the body uses to make nitric oxide. Nitric oxide relaxes blood vessels so blood flows easily. An ounce of most varieties of nuts has about 10%–20% of the recommended daily intake of magnesium. Studies have shown that many Americans don't get enough of the mineral, with average intake falling about 100 milligrams shy of daily recommendations (420 mg for men, 320 mg for women). Magnesium is important to maintaining the proper proportion of calcium to potassium. Also, low levels of magnesium in the diet may contribute to heart attacks and hypertension.
Which nut comes out on top? Almonds, peanuts, walnuts — each has its own association or board, primarily composed of growers and related companies. Of course health claims are a major selling point. So the associations sponsor studies of their particular nut's boon effects on cholesterol levels, blood vessels, and other cardiovascular factors. Competing studies are difficult to compare. But the United States Department of Agriculture has a database of the nutrient content of individual foods that sheds a little light on the subject. Almonds have slightly more vitamin E than walnuts, and much more magnesium. Walnuts, stand out as the only nut with an appreciable amount of alpha-linolenic acid, the only type of omega-3 fat you'll find in a plant-based food. Peanuts (which technically are legumes) lead in the folate category. Cashews have even more magnesium than almonds (83 milligrams per ounce vs. 73) but they lag behind in vitamin E. If it's selenium you're after — as many men are, because the mineral might protect against prostate cancer — then look to Brazil nuts: One ounce has almost 10 times the Recommended Dietary Allowance (RDA) of 55 micrograms. When it comes to taste, macadamia nuts are hard to beat. But they're also high in saturated fat (3.4 grams per ounce) compared with other nuts.
Nobody has done a comprehensive side-by-side comparison of the cholesterol-lowering effect of nuts. But citing individual studies, the authors of an almond study published in Circulation a couple of years ago said that, ounce for ounce, walnuts, peanuts, and pistachios are equally effective. Almonds are a close second, they said. Pecans and macadamia nuts, which are a bit higher in calories, lagged far behind.So far, no nut is the clear hands-down winner. But there is always the noncompetitive approach: mixed nuts. Unsalted, of course.
October 2004 Update