Nutrition Facts Fruit and Vegetables Onion Nutrition Facts and Health Benefits By Barbie Cervoni MS, RD, CDCES, CDN facebook twitter linkedin instagram Barbie Cervoni MS, RD, CDCES, CDN, is a registered dietitian and certified diabetes care and education specialist. Learn about our editorial process Barbie Cervoni MS, RD, CDCES, CDN Reviewed by Reviewed by Marisa Moore, RDN, MBA on September 30, 2020 pinterest instagram Marisa Moore is a registered dietitian nutritionist with a BS in nutrition science and MBA in marketing. She is also the founder of Marisa Moore Nutrition. Learn about our Review Board Marisa Moore, RDN, MBA Updated on September 30, 2020 Print Verywell / Alexandra Shytsman Table of Contents View All Table of Contents Nutrition Facts Health Benefits Allergies Adverse Effects Varieties When It's Best Storage and Food Safety How to Prepare Recipes Members of the lily family, onions are a highly aromatic vegetable used in cuisines around the world. You may have heard rumors that onions become toxic after they're cut, or that onions are too starchy for those on low-carbohydrate eating plans. However, these rumors are quickly dispelled after reviewing the research on onions. Onion Nutrition Facts The following nutrition information is provided by the USDA for one medium raw onion (110g) measuring approximately 2 1/2 inches in diameter. Calories: 44 Fat: 0.1g Sodium: 4.4mg Carbohydrates: 10g Fiber: 1.9g Sugars: 4.7g Protein: 1.2g Carbs One medium onion contains 10 grams of carbohydrates. Of these, 4.7 grams are sugar and 1.9 grams are fiber. Onions have a low glycemic index between 10–15. Fats On their own, onions contain minimal fat. Onions are often prepared with added fat, however, either sautéed in oil or butter, covered in salad dressing, or breaded and deep-fried. Protein Onions are not high-protein food with just a little over 1 gram of protein per serving. Vitamins and Minerals Onions provide vitamin C, folate, and manganese. Onions also contain some calcium and potassium. Health Benefits Onions contain numerous health-boosting phytochemicals to help ward off disease. Along with sulfur-based compounds, onions are rich in quercetin, a powerful antioxidant. Fights Heart Disease Onions contain powerful compounds, called allyl sulfides, that help prevent heart disease. The vitamin C in onions also acts as a powerful antioxidant that is beneficial for cardiovascular health. Finally, onions possess an impressive flavonoid, called quercetin, that reduces blood pressure and inflammation. All of these factors, combined with their natural fiber and potassium content, make onions a clear choice for anyone hoping to improve heart health. May Prevent Cancer The allyl sulfides in onions are also protective against cancer. Specifically, diallyl trisulfide is responsible for regulating several pathways associated with cancer development. These include arresting the cell cycle, preventing the migration of cancer cells, and inducing apoptosis (programmed cell death). Reduces Obesity Risk Lab studies suggest multiple mechanisms by which onions might inhibit excess fat storage. Onion extracts block the generation of new fat cells and increase energy expenditure through thermogenesis. Quercetin is thought to be effective at transforming white fat cells into brown fat cells, which are more metabolically active. Note, however, that these studies were not performed on humans, so more evidence is needed to know if this benefit is relevant. Supports Male Fertility Onions show promise in the treatment of male infertility. The quercetin in onions is beneficial for both sperm motility and viability. Onion peel extract has been shown to enhance the activity of the Hv1 channel, which plays a crucial role in sperm function. Studies suggest that the effects of onion peel are so powerful, they could lead to the development of infertility medications. Improves Memory Onions contain inulin, a type of soluble, prebiotic fiber that feeds healthy bacteria in the gut. It is believed that a gut-brain axis exists, connecting messages from the digestive system with brain activity. A double-blind, placebo-controlled study tested the impact of inulin on mood and cognitive performance. The ingestion of inulin was associated with improvements in the participants' short-term recall and recognition. Although more studies are needed to determine cause and effect, the inulin in onions may be beneficial for cognitive functioning. Allergies Allergy symptoms, like asthma, skin rash, and runny nose, are more often seen as the result of handling onions rather than ingesting them. Nonetheless, anaphylaxis due to an IgE-mediate response (as with a typical food allergy) has been observed following the intake of cooked onions. It is possible to experience allergy symptoms from touching onions or eating them, either immediately after exposure or several hours later. If you believe you have an onion allergy, speak to your doctor for a full evaluation. Adverse Effects Onions can irritate the eyes due to sulfuric acid, which is produced and released during the cutting process. When you cut an onion you break cells, releasing their contents. Enzymes that were kept separate mix with the sulfenic acids to produce propanethial S-oxide, a sulfur compound that wafts upward toward your eyes, making them burn and tear. To reduce irritation, try wearing goggles or chilling the onion before slicing. Onions contain sulfurous compounds that can be absorbed into the bloodstream when ingested and can escape from our pores when sweating. Therefore, some people may "smell like onions" after eating them. Onions, particularly raw onions, can sometimes make your breath smell. To get rid of onion breath, try eating some parsley. Onions also contain fructans. Anyone following a low FODMAP diet for irritable bowel syndrome should be aware that onions may cause abdominal pain, bloating, and gas. When onions are eaten as a whole food ingredient (rather than taken in a supplement form) they are generally considered safe. Taking high doses of onion supplements, however, could potentially interact with some medications, so let your doctor know about any supplements you take. Varieties Onion bulbs come in three colors: red, yellow, or white. Depending on how much daylight is required for onion bulb formation, onions are classified by farmers as short-day (under 12 hours), medium-day, or long-day (14 hours or more). Onion varieties are tested based on their sweetness and pungency. Onion bulbs of the same color may vary in taste based on their chemical composition. Disease-resistance also varies among the different types of onions. You can buy fresh onions or purchase dehydrated onions or onion powder to add flavor when cooking. In addition to typical bulb onions, green onions or scallions are smaller and more mild-tasting. These leafy varieties are actually just immature onion bulbs that were picked before reaching maturity. When It's Best Onions can be found in supermarkets at any time of the year. Choose onions that are free of bruises and cuts. Onions should be firm, not squishy. Avoid pre-cut onions that appear dried out or slimy. Always use pre-cut onions by the expiration date listed on the package. Storage and Food Safety Use fresh onions within 2–4 weeks or purchasing. Store in a dry, well-ventilated area at room temperature. Wash onions under running water before cutting into them. Once you slice an onion, it can be stored in the refrigerator for up to 7 days but should be discarded if you notice any signs of mold. To preserve onions in the freezer, chop into 1/4 to 1/2 inch sections or into a small dice. Onions that are peeled, washed, and sliced don't need to be blanched prior to freezing. Freeze them flat on a baking sheet and then place them into airtight containers. This lets you remove pieces of frozen onion as needed, rather than the pieces sticking together. Onions can also be pureed into a paste before freezing. Onions will keep in the freezer for up to a year. How to Prepare Use onions to flavor sauces, stews, chili, or soup. Top sandwiches, wraps, or burgers with a slice of onion. Dice raw, grilled, or sautéed onions and put them in your salads, side dishes, or eggs. Recipes Healthy Onion Recipes to Try Crock Pot Ropa Vieja (Beef, Peppers, Onions) Harissa Chickpea and Chicken Soup Tomato Fennel Stew With Cod Lightened Up Zucchini Casserole Was this page helpful? Thanks for your feedback! Get nutrition tips and advice to make healthy eating easier. Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Fit uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Onions, raw. FoodData Central. U.S. Department of Agriculture. Published April 1, 2019. Anderson GH, Soeandy CD, Smith CE. White vegetables: Glycemia and satiety. Adv Nutr. 2013;4(3):356S-67S. doi:10.3945/an.112.003509 Exploring aromatics. Academy of Nutrition and Dietetics. Updated 2020. Dabeek WM, Marra MV. Dietary quercetin and kaempferol: Bioavailability and potential cardiovascular-related bioactivity in humans. Nutrients. 2019;11(10). doi:10.3390/nu11102288 Puccinelli MT, Stan SD. Dietary bioactive diallyl trisulfide in cancer prevention and treatment. 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