Eggplant ?like beets, celery, lettuce, radish, spinach, and collard and turnip greens ?contains nitrates that convert naturally into nitrites in your stomach, and then react with the amino acids in proteins to form nitrosamines. Although some nitrosamines are known or suspected carcinogens, this natural chemical conversion presents no known problems for a healthy adult. However, when these nitrate-rich vegetables are cooked and left to stand at room temperature, bacterial enzyme action (and perhaps some enzymes in the plants) convert the nitrates to nitrites at a much faster rate than normal. These higer-nitrite foods may be hazardous for infants; several cases of "spinach poisoning" have been reported among children who ate cooked spinach that had been left standing at room temperature.

Monoamine oxidase (MAO) inhibitors are drugs used as antidepressants or antihypertensives. They inhibit the action of enzymes that break down tyramine, a natural by-product of protein metabolism, so that it can be eliminated from the body. Tyramine is a pressor amine, a chemical that constricts blood vessels and raises blood pressure. If you eat a food rich in tyramine while you are taking an MAO inhibitor, the pressor amine cannot be eliminated from your body, and the result may be a hypertensive crisis (sustained elevated blood pressure). Eggplants contain small amounts of tyramine.

Carcinoid tumors (tumors that may arise in tissues of the endocrine and gastrointestinal systems) secrete serotonin, which is excreted in urine. The test for these tumors measures the level of serotonin in your urine. Eating eggplant, which is rich in serotonin, in the 72 hours before a test for a carcinoid tumor might raise the serotonin levels in your urine high enough to cause a false-positive test result. (Other fruits and vegetables rich in serotonin are bananas, tomatoes, plums, pineapple, avocados, and walnuts.)