Lecithin is present in all living cells and is a significant constituent of nerve and brain cells.

Commercial lecithin, most of which comes from soya bean oil, which may be Genetically Modified, contains a mixture of phosphoglycerides containing principally lecithin, cephalin and phosphatidyl inositol. Other sources are egg yolk, from where it was originally obtained, and leguminous seeds, including peanuts and maize, which also may be Genetically Modified. Vegetarians should be aware that it can also be obtained from animal fat.

In cells lecithin protects the membranes and the polyunsaturated fats within the cells from oxygen attack.

As an emulsifier it lowers the surface tension of water allowing the better combining of oils, fats and water in such foods as chocolate, ice cream, margarine and mayonnaise. In bread and bakery products it increases volume and also acts as an anti-staling agent thereby extending shelf life.

In margarine it has the added advantage of preventing water leakage, so preventing spitting when frying, and protecting beta-carotene (E160a Vitamin A). In chocolate it allows a reduction in the cocoa butter content, prevents crystals forming and reduces viscosity (see E476). Soya lecithin has the same binding ability as egg yolk lecithin and can be used in place of eggs in many products. It also helps powders mix quickly and easily in milk or water.

Lecithin is also a good synergist to antioxidants in fats and oils so is often used in combination with them.

For a time it was thought that lecithin supplements could help Alzheimer sufferers but this line of research did not lead anywhere.