Lecithin was first identified in 1846 by Maurice Gobley, a French chemist. It is the name for a mixture of phospholipids, an important component of food products, occurring both naturally and added as a supplement. The body breaks down lecithin into choline, phosphate, glycerol, and fatty acids.

Lecithin is found naturally in a number of items used for food, including egg yolk, fish, grains, legumes, peanuts, soybeans, wheat germ, and yeast. It is also used in food preparation to create products such as baked goods, chocolate, margarine, and mayonnaise because of its ability to moisturize, preserve, and emulsify. It is a key ingredient in cooking spray—the substance used to replace oils, margarine, and butter in sautéing and baking.

Lecithin is also used in medical practice as well as in other commercial products, such as plastics, pharmaceuticals, pesticides, cosmetics, soap, and paints. For these applications, it is extracted from eggs or soybeans. Lecithin is also sold in powder, grain, liquid, or capsules as a dietary supplement.

As a dietary supplement, lecithin is claimed to have a number of roles, including improving cardiovascular health, relieving the symptoms of arthritis, and improving liver function. But it is primarily offered as a supplement to assist in weight loss and to provide boosts in fat metabolism, despite the fact that these claims are made without the presentation of any scientific evidence to show that lecithin is effective in weight loss and fat metabolism. Additionally, some claims have been made for soy lecithin improving the metabolism of cholesterol, although the studies that supported this have had their methodology called into question.

Despite this, lecithin does have a crucial role in the human body, as evidenced by the fact that approximately 30% of our brain weight and 66% of our liver fat is lecithin. In addition, lecithin is an essential constituent of every human cell. Yet the American Heart Association believes that lecithin is best obtained naturally through foodstuffs, rather than through supplements, and no Recommended Daily Allowance (RDA) has been set by the Food and Drug Administration (FDA).

High doses of lecithin of over 25 grams per day can cause negative side effects, including nausea, stomach upset, diarrhea, and vomiting. Another danger to a very small portion of the population with an extreme soy allergy. Although most people with soy allergy are allergic only to soy protein, and therefore not affected by soy lecithin, people who are extremely allergic to soy may also be sensitive to soy lecithin and experience an allergic reaction