Actually, peanuts aren't really nuts, they're legumes, so they're related to peas and dry beans. Real nuts are also called tree nuts, and include almonds, hazelnuts, pecans and walnuts. They're good for your health too; however, peanuts and peanut butter tend to be more affordable than the higher-priced tree nuts and nut butters.
Peanuts and heart health: Peanuts are heart healthy because they're a good source of monounsaturated fatty acids. Eating peanuts may help lower your total cholesterol. The United States Food and Drug Administration allows the following claim to be placed on the packaging of foods that contain whole or chopped peanuts:
Scientific evidence suggests but does not prove that eating 1.5 ounces per day of most nuts such as peanuts as part of a diet low in saturated fat and cholesterol may reduce the risk of heart disease. See nutrition information for fat content.
One and a half ounces of peanuts is equal to about 50 nuts, and would have about 240 calories -- but you can divide that into two different snacks. Or you can use peanuts in your recipes or sprinkle them on a salad.
Peanuts and weight loss: Peanuts are not really a low-calorie food; they're actually quite energy-dense. But as long as you watch your portions, eating them may help you lose weight. Studies indicate that people who eat nuts, including peanuts, tend to have lower body mass indexes.
So how can a food that's actually high in calories per ounce help you lose weight? Part of the reason may be that peanuts are high in good fats, protein and fiber, so just a small serving can satisfy your hunger and keep you feeling fuller longer. The key to eating peanuts and losing weight is to watch your serving sizes closely. Next time you get hungry between meals, eat one ounce of peanuts (about 35 individual nuts). That will add about 160 calories to your daily intake, but may tide you over until your next meal and this may help stop you from overeating when that meal is served.
Peanuts and weight gain: It may seem a little odd that one type of food can be good for both losing weight and gaining weight. Peanuts, in small amounts, may help curb your appetite; however, when eaten in larger amounts, they can provide extra calories and encourage weight gain. If you wan to gain weight, you should do so by increasing your intake of nutritious, energy dense foods, not by eating more junk foods. Since peanuts and peanut butter are higher in calories, but still nutritious, they're a good choice for adding extra calories (try a healthier PB&J sandwiches).
King JC, Blumberg J, Ingwersen L, Jenab M, Tucker KL. "Tree nuts and peanuts as components of a healthy diet." J Nutr. 2008 Sep;138(9):1736S-1740S.
Mattes RD, Kris-Etherton PM, Foster GD. "Impact of peanuts and tree nuts on body weight and healthy weight loss in adults." J Nutr. 2008 Sep;138(9):1741S-1745S.
United States Department of Agriculture. "Peanuts, all types, dry-roasted." Accessed April 4, 2011. http://www.nal.usda.gov/fnic/foodcomp/search/
United States Food and Drug Administration. "FDA Qualified Health Claims." Accessed April 4, 2011. http://www.fda.gov/Food/GuidanceComplianceRegulatoryInformation/GuidanceDocuments/FoodLabelingNutrition/FoodLabelingGuide/ucm064923.htm