Eating 1 ounce of tree nuts like walnuts a day -- an amount equal to about 14 halves -- may significantly lower your risk of dying from chronic medical conditions like cancer or heart disease. That's the conclusion of a 2013 study published in "The New England Journal of Medicine." Besides being a rich source of dietary fiber, vitamin B-6, copper, manganese and heart-healthy omega-3 fatty acids, walnuts can add protein to the diet of vegans, vegetarians and people limiting their animal product consumption. On their own, however, walnuts cannot fulfill your protein requirement.
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A 1-ounce serving of English walnuts, the most common type of walnut in the United States, contains 4.3 grams of protein. For the average man, this amount would supply around 7.6 percent of his 56-gram recommended intake of protein per day. Women should have approximately 46 grams of protein daily, and eating an ounce of walnuts would fulfill 9 percent her recommended allowance. Walnuts do not contain enough protein per serving to be considered a good source of the nutrient.
Comparison to Other Foods
According to the U.S. Department of Agriculture, walnuts contain about as much protein per ounce as 1 cup of frozen, chopped broccoli, 1 cup of cooked long- or medium-grain white rice and 1 cup of sweet yellow corn kernels. Compared to vegetables like brussels sprouts, winter squash, kale, peas, green beans, beets, potatoes and asparagus, walnuts are a superior source of protein, though they provide far less per serving than poultry, fish, shellfish, beef, pork, dairy products, beans and legumes. When it comes to nuts, walnuts have less protein in an ounce than cashews but more than an ounce of pecans or chestnuts.
Making Complete Protein
Walnuts do not contain all of the amino acids your body requires. While the nuts have a high concentration of amino acids such as tryptophan, valine, leucine and threonine, they lack others like methionine, alanine and proline. Because of this, walnuts are considered an incomplete protein. To complete the protein you receive from walnuts with the amino acids the nuts are missing, you should aim to consume a wide variety of whole grains, beans, legumes and produce throughout the day, says the Centers for Disease Control and Prevention. Add walnuts to your salads, mix them into homemade, low-sugar trail mix or use them as a crunchy topping for pilafs or pasta dishes.
If you fulfill more of your daily protein needs with plant-based sources like walnuts and less with red meats like pork or beef, you may be less likely to die from cancer or heart disease, determined an "Archives of Internal Medicine" study from 2012. Nutrition specialist Dr. Melina Jampolis, however, cautions that you should be careful not to eat too many. Each ounce of walnuts has over 180 calories, 18 grams of total fat and 1.7 grams of saturated fat. Limit your nut consumption to one 1/4-cup serving per day, advises Jampolis.