Oatmeal is a high-fiber hot cereal made from whole oats. It is very high in soluble fiber, which is why it has been touted for its cholesterol-lowering properties. Soluble fiber also aids weight loss, improves blood-sugar control in individuals with diabetes, and helps stabilize mood. Folate and vitamins B6 and B12 in oatmeal help maintain healthy hair. Oatmeal is also a good source of manganese, which may help reduce PMS symptoms. If you have celiac disease, look for brands of oatmeal that are certified to be gluten-free. Note to IBS sufferers: Oatmeal is rich in fiber, which may cause gastrointestinal upset if you h...

Okra is a pod-shaped green vegetable and a mainstay of Southern cuisine. Like other nonstarchy vegetables, okra is low in calories and has a high water and fiber content, making it a great choice for people who are trying to lose weight or prevent or manage heart disease.

Olive oil is a terrific source of "good" monounsaturated fats and contains antioxidants called polyphenols that protect the body against inflammation. Using olive oil in moderation (in place of butter) helps prevent arthritis-related inflammation and migraines, can reduce bad cholesterol, and is essential to an overall healthy diet.

Olives are a great source of monounsaturated fats, which have been shown to lower cholesterol levels, reduce high blood pressure, and lower the risk for type 2 diabetes. But because olives are often packaged in brine, they are high in sodium, which can raise your blood pressure — so enjoy them in moderation

Onion powder is a spice made from ground dehydrated onions. It isn't as pungent or sharp as fresh onions, but it's a great way to add flavor without adding salt and is a big time-saver in the kitchen. Just make sure not to confuse onion powder with onion salt, which is high in sodium and can increase the risk of high blood pressure.

While Allium vegetables like onions, shallots, leeks, and scallions don't contain significant amounts of vitamins or minerals, they are a good source of allyl sulfides, which are compounds that may help lower blood pressure and hinder tumor growth. They also contain saponins, which may prevent tumors and reduce cholesterol. A particularly important nutrient in Allium vegetables is quercetin. This anti-inflammatory antioxidant may benefit people with inflammatory conditions such as arthritis. People who have arthritis, especially rheumatoid arthritis, have fluid between their joints that contains a significant amoun...

Orange juice is a good source of vitamin C, an antioxidant that helps prevent and manage arthritis, cataracts, macular degeneration, and maintains healthy hair and skin. If fortified with calcium, orange juice may also help to maintain strong bones, reduce blood pressure, and alleviate PMS symptoms. If you have type 2 diabetes, it is best to avoid orange juice and other fruit juices because of the high sugar concentration. Because orange juice and other citrus juices are possible triggers for IBS and migraine headaches, avoid them if they are problematic for you.

Oranges are a popular citrus fruit with a high water content and a good amount of fiber, making them a great choice for people who are trying to lose weight or prevent or manage heart disease or type 2 diabetes. They are also a good source of vitamin C, an antioxidant found in many fruits that helps prevent arthritis, cataracts, and macular degeneration, and maintain healthy hair and skin. Folate in oranges may also help slow memory decline. Because oranges and other citrus fruits are possible triggers for IBS and migraine headaches avoid them if they are problematic for you.

Oregano is an herb often used in Mediterranean and Latin American cooking and can be found fresh and dried. Dried oregano tends to be more pungent than fresh because it is more concentrated. Like other herbs, oregano adds flavor to food without adding sodium, calories, and fat.