Tomatoes are certainly nutritious — a good source of the antioxidants lycopene and beta-carotene. But consider this: if you eat a tomato without adding a little fat — say a drizzle of olive oil — your body is unlikely to absorb all these nutrients. . . . [P]eople who had eaten fat-free or low-fat dressings didn't absorb the beneficial carotenoids from . . . salad. Only when they had eaten the oil-based dressing did they get the nutrients.
Carotenoids are the pigments responsible for red-, yellow- and orange-colored fruits and vegetables. And carotenoids are also found in dark green vegetables such as spinach. The compounds convert to Vitamin A in the body, and studies have found that carotenoids have anti-oxidant activity which may help protect cells from damage caused by free radicals. Human studies have linked high consumption of fruits and vegetables to reduced risk of cancer. . . .
There are other ways to help maximize the absorption of carotenoid nutrients. Chopping or grating breaks down the plant material. "The finer the particle size ... the better the absorption of beta-carotene," . . . many people have heard that raw vegetables are best. But if you're eating carrots, it may be helpful to cook them gently. The heat can soften the food allowing more nutrients to be released. . . . some cooking methods may be better than others. . . . microwaving helped maintain the antioxidants, whereas boiling and pressure cooking led to the greatest losses.
Green beans, beets and garlic all did well with heat — maintaining beneficial phytonutrients after most kinds of cooking. The antioxidant value in carrots actually increased after cooking.
Experts explain that boiling may allow nutrients to leach into the pan water that people end up tossing out, especially with water-soluble nutrients such as Vitamin C and the B Vitamins. . . . many experts say it's best not to fixate too much on how food is prepared. Instead, focus on eating more plant foods — of all colors.