Like garlic, onions come from the lily family and there are many different types of onions from all over the world. The most common varieties are white, yellow, red, and green onions, but they come in a number of sizes, colors, and tastes. However, there are only two main types of onions—spring/summer onions and storage onions. Spring/summer onions are grown in warmer climates and have a more mild and sweet flavor. They include the Walla Walla, Vidalia, and Maui Sweet onions. Storage onions on the other hand are grown in colder climates and after they are harvested, they are dried out for several months, in which time the skins of the onion dry out. Storage onions typically have a stronger flavor and include white, yellow, and red onions. Smaller onions also come in many varieties, such as green onions, scallions, chives, and leeks.
Some of the main health benefits of consuming onions can be found in their high sulfur content. Some of those benefits include the ability to decrease cholesterol levels while raising the high density lipoproteins (HDL), or healthy cholesterol levels, which helps to prevent plaque from sticking to artery walls. Onions also have flavonoids and other chemical compounds that work together to boost our health. Flavonoids act as antioxidants in the body and help to prevent blood clots and protect against heart disease and cancer; they also have anti-inflammatory effects on the body. Studies have shown that onions help to lower blood lipid levels and lower blood pressure. Onions also have antibacterial effects which make this vegetable a great food to consume to help minimize nasal congestion during a cold.
Onions have also been shown to significantly help lower blood sugar. In fact, its ability to lower blood sugar is so strong that it is comparable to medication drugs given to diabetics. Scientists believe that the component of onions responsible for this is a compound called allyl propyl disulfide (APDS). Scientists believe that APDS helps to lower blood sugar by competing with insulin for breakdown sites on the liver; this action of APDS helps to increase the life, or action, of insulin.
Onions have also been used to help treat asthma due to their ability to stop the production of the compounds that cause the bronchial muscle to spasm and then to help the muscle to relax. Onions have also been shown to destroy tumor cells; onion extract is of particular benefit because it is particularly non-toxic, which means that very large doses of it can be given without any adverse effects. Furthermore, onions have a particular compound, called diallyl sulphide, that is not only responsible for the strong smell of onions, but also helps to prevent cancer by blocking the effects of cancer-causing particles in the body.
Onions are also a good source of vitamins B1, B6, C, and K, as well as biotin, chromium, folic acid, and fiber.