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Why Go Nuts

Many people avoid nuts, thinking they are "too fattening." But research now suggests that nuts can, in fact, help with weight control. Here’s the latest on this, plus other news about nuts.

The weight of evidence

With the exception of chestnuts, nuts contain a lot of calories—160 to 200 an ounce, most from healthy unsaturated fats. But in general, people who eat nuts regularly tend to weigh less than those who don’t—or at least they don’t weigh more, population studies show. For instance, a Spanish study of nearly 9,000 people, reported in Obesity last year, found that those who ate nuts at least twice a week were less likely to gain weight over 28 months than those who never or rarely ate nuts.

Even when people add nuts to their usual diets, they don’t seem to gain much, if any, weight. In a small study from Purdue University last year, women who added 344 calories worth of almonds a day to their diets—without purposefully cutting back on calories elsewhere or exercising more—did not gain weight after 10 weeks. Similar findings have been reported with walnuts and peanuts. Fewer studies have looked at whether nuts can actually help you lose weight, but one found that a low-calorie diet that included almonds led to more weight loss than a same-calorie, nut-free diet.

A 2007 review from Australia sums it up: When added freely to a diet, nuts cause less weight gain than would be predicted—and when added to a calorie-controlled diet, they don’t cause weight gain and may sometimes make weight loss easier.

What is it about nuts? The fiber and protein in nuts help make you feel full longer, so you are less hungry—and presumably eat less—later. And some (but not all) studies suggest that nuts may slightly increase calorie burning. Interestingly, some research has also found that not all the fat in whole nuts is absorbed—from 4% to 17% passes out of the body undigested.

Good for your heart

Studies have consistently linked nuts to a markedly reduced risk of heart disease, largely because they have a favorable effect on blood cholesterol. According to a review of studies in the Journal of Nutrition in 2005, eating about 2 to 3 ounces of nuts most days of the week—in particular almonds, pecans, peanuts, and walnuts—may significantly lower total and LDL ("bad") cholesterol. In some cases nuts have been shown to increase HDL ("good") cholesterol. In recent studies walnuts also improved blood vessel health, while pistachio and macadamia nuts favorably altered risk factors for heart disease in other ways. A study several years ago linked nuts to a reduced risk of Type 2 diabetes.

A heart-healthy explanation: The unsaturated fats in nuts can improve blood cholesterol levels, especially when substituted for foods high in saturated fat, such as meat and cheese. Other nutrients and substances in nuts also have heart-health benefits, including B vitamins, potassium, copper, magnesium, vitamin E, fiber (much of it soluble), arginine (an amino acid that helps relax blood vessels), sterols (which help lower cholesterol), and a range of other phytochemicals. The FDA allows most nuts to carry a "qualified" health claim—that is, one hedged with qualifiers—stating that 1.5 ounces a day may help reduce the risk of heart disease.

Not so nutty advice

• Though nuts are healthful and may help you control your weight, don’t go overboard—limit yourself to an ounce or two a day. One small handful is about an ounce.

• Nut butters, including almond, cashew, and, of course, peanut butter, have the same nutritional advantages as the nuts themselves and are a healthier sandwich filling than cheese and most meats.

• Watch out for the sodium in packaged nuts. Unsalted varieties are widely available.

• For people who don’t eat meat or want to consume less, nuts are one of the best plant sources of protein. The USDA counts nuts in the "meat and bean" group of its food pyramid.

 

UC Berkeley Wellness Letter, May 2008