Most fruits and vegetables contribute only modestly to our intake of proteins and calories, but they’re our major source for several vitamins. They provide nearly all of our vitamin C, much of our folic acid, and half of our vitamin A. Each of these plays a number of roles in the metabolism of our cells. For example, vitamin C refreshes the chemical state of metal components in many enzymes, and helps with the synthesis of connective-tissue collagen. Vitamin A, which our bodies make from a precursor molecule in plants called beta-carotene, helps regulate the growth of several different kinds of cells, and helps our eyes detect light. Folic acid, named from the Latin word for “leaf,” converts a byproduct of our cells’ metabolism, homocysteine, into the amino acid methionine. This prevents homocysteine levels from rising, causing damage to blood vessels, and possibly contributing to heart disease and stroke.