Onions probably aren’t the first food you think about when you’re planning your daily carbs, but they are a source of natural sugar, complex carbs and fiber. Onions give you a healthy carbohydrate option because, along with the carbs, they supply beneficial phytonutrients, which are plant compounds that promote health. They contain antioxidant flavonoids, as well as the same substance found in garlic that may help prevent gastric and colorectal cancers, according to the Linus Pauling Institute.
One small raw onion, which equals about two large slices, has 6.5 grams of total carbohydrates. The recommended dietary allowance for healthy men and women is 130 grams of total carbohydrates daily, so you'll get 5 percent of your daily carbs from this portion. While you may not fill a large part of your daily intake with onions, when you combine them with other foods such as vegetables, beans, whole grains or lean protein, onions add an extra boost of fat-free and low-calorie carbs.
Fiber for Heart and Health
About half the fiber in an onion is the insoluble type and the other half is soluble fiber. Insoluble fiber keeps your digestive system regular and helps prevent some gastrointestinal problems, such as diverticular disease. Soluble fiber forms a gel-like mass in your digestive tract that makes you feel full and slows down the absorption of sugar into the bloodstream. It also binds with cholesterol and carries it out of your system, which helps prevent heart disease. Women should consume 25 grams of fiber daily, while men need to get 38 grams.
Simple Sugar Boost
The natural simple sugar you’ll get from a small onion -- 3 grams -- is the type of carbohydrate your body prefers to use for energy, especially for working muscles and your brain. The benefit of getting sugar from onions is that the fiber helps prevent a large spike in blood sugar. This is quite different from unhealthy added sugar in beverages, baked goods and candy.
Complex Carbs Endure
Starch is the form of carbohydrate usually referred to as complex carbs. Onions and other plants store the sugar they need in the form of starches. These carbs are similar to simple sugar because they consist of molecules of sugar. The difference is that starches contain many molecules that form complex shapes, while simple sugars only contain a few molecules. As a result, it takes longer for your body to break down and digest starches, and that provides long-term energy. One small onion has approximately 2 grams of starch.