TRANS-FATTY ACIDS—fatty acids that have been altered by food processing and take on abnormal shapes not normally useful to the body.

TESTOSTERONE—a hormone made by the testicles and adrenal glands, and also in various cells of the body, that promotes masculine traits.

SYNAPSE—a connection between two neurons.

STEROID—a large family of chemical substances which includes hormones and drugs that have a chemical structure comprised of a few rings attached to each other. Most steroids contain twenty-seven or more carbon atoms.

STEROL—a steroid of twenty-seven or more carbon atoms with one OH (alcohol) group.

SEROTONIN—a brain chemical (neurotransmitter) that relays messages between brain cells (neurons). It is one of the primary mood-regulating neurotransmitters. It is derived from the amino acid tryptophan. Serotonin can also be converted to melatonin.

RETINA—the back of the eye where light falls and visual input is perceived and later transmitted to the brain for interpretation. The retina contains a large amount of the fatty acid DHA.

RDA (RECOMMENDED DAILY ALLOWANCE)—a nutritional guideline proposed by the government on the appropriate doses of different vitamins and minerals required for good health. Some scientists think that ingesting more than the RDA for certain nutrients may provide additional health benefits. PDV, or percent daily value, is a number similar to the RDA.

PRECURSOR—a substance that precedes, and is the source, of another substance; for instance, 5-HTP is the precursor to serotonin.