Red, yellow, and orange bell peppers are simply riper versions of green ones, and their longer maturing time increases their overall nutrient content.
All bell peppers, especially red ones, contain high levels of the antioxidants vitamin C, beta-carotene (vitamin A), vitamin E, and zinc, so they fight off free radicals and protect against heart disease, strokes, and some cancers. These same nutrients are vital for a strong immune system and for energy production
Storing and serving: Choose firm, unwrinkled peppers and store in the fridge. All colors can be eaten raw or cooked and can even be juiced.
Onions are a good source of many powerful antioxidants, which neutralize the cell-damaging free radicals in the body, helping to reduce the risk of strokes, heart disease, cancer, Alzheimer's disease and the other degenerative diseases of aging. Chief among these is quercetin, which is plentiful in red onions and protects against heart disease by preventing furred arteries and blood clots from forming.
The sulfurous compounds in onions -- the ones that cause tears when you slice onions -- when eaten daily will help reduce high blood pressure and high cholesterol levels and may help protect against asthma and some inflammatory disorders, such as rheumatoid arthritis. These compounds, also found in garlic, are thought to fight cancer and stimulate the liver's own natural detoxification process.
Storing and serving: Onions can be stored for several weeks at room temperature in a dry, well ventilated basket or vegetable rack out of direct sunlight. Keep scallions in the fridge.
Nutrient-rich avocados are often shunned because of their high-fat content. However, much of this fat is the monounsaturated variety and is easily digested, with none of the artery-clogging effects of saturated fat.
Avocados are rich in the antioxidants vitamins (A, C, and E) that protect cells from the damage inflicted by free radicals and are useful for preventing conditions such as heart disease. The vitamin E content also means that avocado helps maintain healthy skin and circulation. Not only does eating avocado provide its own antioxidants, it also improves the absorption of antioxidants from other fruits and vegetables eaten at the same time.
Storing and serving: Most avocados reach the supermarket in an unripened form. As they ripen, they start to lose important antioxidant nutrients, especially vitamin C, so eat as soon as they are ripe.