context: Plant foods contain thousands of natural chemicals. These are called phytonutrients or phytochemicals." Phyto" refers to the Greek word for plant. These chemicals help protect plants from germs, fungi, bugs, and other threats. Fruits and vegetables contain phytonutrients. Other plant-based foods also contain phytonutrients, such as: Whole grains Nuts Beans Tea Phytonutrients aren't essential for keeping you alive, unlike the vitamins and minerals that plant foods contain. But when you eat or drink phytonutrients, they may help prevent disease and keep your body working properly. More than 25,000 phytonutrients are found in plant foods. Web MD takes a look at these six important phytonutrients -- and their potential health effects: Carotenoids Ellagic acid Flavonoids Resveratrol Glucosinolates Phytoestrogens More than 600 carotenoids provide yellow, orange, and red colors in fruits and vegetables. Carotenoids act as antioxidants in your body. This means they tackle harmful free radicals that damage tissues throughout your body. The types of carotenoids that may have other health benefits include: Alpha-carotene, beta-carotene, and beta-cryptoxanthin. Your body can convert all of these to vitamin A. This vitamin helps keep your immune system working properly, and it's needed for eye health. Yellow and orange foods like pumpkins and carrots are good sources of alpha- and beta-carotene. These also contain beta-cryptoxanthin, as do sweet red peppers. Lycopene. This gives red or pink color to: Tomatoes Watermelon Pink grapefruit Lycopene has been linked to a lower risk of prostate cancer. Lutein and zeaxanthin. These may help protect you from cataracts and age-related macular degeneration, which are two types of eye problems. Good sources of these phytonutrients are greens such as: Spinach Kale Collards Ellagic acid is found in a number of berries and other plant foods, especially: Strawberries Raspberries Pomegranates Ellagic acid may help protect against cancer several different ways. For example, it may slow the growth of cancer cells. And it may help your liver neutralize cancer-causing chemicals in your system. But studies of this acid have mainly been done in the laboratory, so its benefits for human health is an unknown. A large number of phytonutrients fall into the flavonoid category. They are found in a variety of plant foods. The types of flavonoids include: Catechins. Green tea is an especially good source of catechins. The drink may help prevent certain types of cancer. Hesperidin. Found in citrus fruits, this flavonoid works as an antioxidant reducing inflammation in the body to help prevent chronic disease. Flavonols. Quercetin is a well-studied type of flavonol. It is found in: Apples Berries Kale Onions It might help reduce people's risk of asthma, certain types of cancer, and coronary heart disease. Resveratrol is found in: Grapes Purple grape juice Red wine It acts as an antioxidant and anti-inflammatory. Some research suggests that resveratrol might play a role in reducing the risk of heart disease and certain cancers. And it may help extend life, animal studies have shown. But more human studies are needed to establish a clear relationship. Glucosinolates are found in cruciferous vegetables, including: Brussels sprouts Cabbage Kale Broccoli They give these vegetables their sharp odor and flavor. The glucosinolates turn into other chemicals during the cooking process and while you digest these foods. These chemicals may help hold in check the development and growth of cancer. Because of their structure, phytoestrogens can exert estrogen-like effects. They can also block the effects of your natural supply of estrogen. Soy foods contain isoflavones -- a type of phytoestrogen. Some evidence suggests that soy foods may be linked to: Lower risk of endometrial cancer Lower risk of bone loss in women Your body converts lignans, another type of phytonutrient, into chemicals with some estrogen-like effects. Two especially good sources of lignans are: Flaxseeds Sesame seeds However, research supporting a role for lignans in preventing endometrial cancer or osteoporosis is limited.