Nuts and grains are high in protein and nutrients, though their fat content (75 to 95 percent of total calories) means you shouldn't eat too many at a time. Macadamia, the gourmet of nuts, is the highest in fat. Walnuts and Brazil nuts are your best bet because they're rich in omega-3 fatty acids.
Of all the nuts, peanuts provide the most complete protein. Other nuts are missing the amino acid lysine. But all are easily complemented by grains. As an alternative protein source, they also provide a good dose of healthy fats, including oleic acid, the healthy fat found in olive oil. Peanuts are rich in antioxidant polyphenols like those found in berries. Studies indicate that roasting actually increases the amount of polyphenol called p-coumaric, making roasted peanuts a true protector of cells.
Research has heartened nut lovers. Studies at Loma Linda University in California found that eating nuts five times a week (about two ounces a day) lowered participants' blood cholesterol levels by 12 percent. Walnuts were used, but similar results have been reported with almonds and peanuts. It appears that replacing saturated fat in the diet with the monounsaturated fat in nuts may be the key. It makes sense, then, to eat nuts instead of other fatty foods, not just to gobble them down on top of your regular fare.
Some nuts, notably walnuts and Brazil nuts, are rich in omega-3 fatty acids, which may contribute further to the fight against heart disease and possibly even arthritis. These healthful nuts also may play a role in weight loss and help you manage your weight better. Also, seeds and some nuts contain significant amounts of vitamin E. As an antioxidant, vitamin E can help prevent the oxidation of LDL cholesterol, which can damage arteries. More heartening news: Seeds are a good source of folic acid. Researchers have found that folic acid helps prevent the buildup of homocysteine. High levels of this amino acid have been linked to heart disease, dementia, and broken bones in people with osteoporosis. Eat plenty of folate to keep your homocysteine levels in check.
Seeds, peanuts, and peanut butter are super sources of niacin. Nuts are chock-full of hard-to-get minerals, such as copper, iron, and zinc. Seeds are among the better plant sources of iron and zinc. Iron helps your blood deliver oxygen to your muscles and brain, while zinc helps boost your immune system. And nuts do their part to keep bones strong by providing magnesium, manganese, and boron.
One caution: Toxicity problems do not usually occur from eating foods, only from taking too much of a vitamin or mineral in supplement form. However, Brazil nuts contain an astonishingly high amount of selenium: about 70 to 90 micrograms per nut. In 2000 the National Academy of Sciences set the tolerable upper limit (UL) for selenium at 400 micrograms per day for adults. So, go easy on Brazil nuts, eating maybe one or two per day since you get selenium from other food sources, too.