Functional foods are designer foods with effects that extend beyond basic nutrition. They can serve to prevent certain illnesses, strengthen the immune system, or promote good digestion. Such health effects are achieved by adding certain active substances. Another term for such a food can be "nutraceutical" (nutrition and pharmaceutical).

So far, there is no binding definition of functional foods. If a health benefit can be scientifically proven, the term functional food can be used for marketing.

In principle, it is possible to genetically modify plants to produce substances beneficial to human health. Such plants could produce substances previously not found in the plant, or in quantities that were otherwise not possible.