Some of its constituents are also needed to make important brain chemicals, as well as support bile and liver function.
It's found in egg yolks, liver, soya beans and peanut butter, and is often added to processed foods as an emulsifier.
Lecithin is a natural source of choline, a B vitamin which is used to make a brain chemical messenger called acetylcholine, important for memory and muscle control, and available as a supplement.
Dr Sarah Brewer says: ‘Lecithin is believed to have several important functions, including the processing of fat, which some believe makes it useful in weight control. It also contains phosphatidylcholine, a source of choline which is needed in the brain to support memory function.’
What does lecithin do?
Lecithin prevents blood fats, including cholesterol and triglycerides, from entering cells by suspending them in the bloodstream. Two other ingredients in lecithin, phosphatidylcholine (which breaks down into choline in the body) and inositol, transport fats in the blood, helping to clear them from the body.
Choline is used to make a brain chemical messenger called acetylcholine, which helps muscle control and memory function, as well as supporting the liver.
Inositol also helps metabolise fat and fatty build-up. Sometimes referred to as vitamin B8, it is found in highest concentrations in the brain, eyes and heart.
There's some evidence that lecithin may help lower blood cholesterol, a waxy substance made in the liver which can contribute to heart disease. A Brazilian study found that levels of total cholesterol and ‘bad’ LDL cholesterol both fell significantly in patients with high cholesterol, during the first month of taking a daily supplement of lecithin and soya oil.
The doctors who carried out the study said lecithin might lower cholesterol by reducing its absorption in the intestine or by the increased secretion of bile acids.
Memory and mood
Because lecithin is a rich source of brain-enhancing choline, it is being investigated by scientists as a possible treatment for Alzheimer's disease and cognitive problems. One study, published in 2014, found improvements in mood, memory and awareness in elderly patients with memory problems who were given a lecithin-derived supplement over a three-month period. Forty-nine per cent of those who took the supplement showed improved mood and functioning, compared with 26.3 per cent of the group given a placebo. The authors said it appeared to have a stabilising effect on daily functioning and emotional state. However, experts say larger studies are needed before any recommendations can be made.
A review of the use of inositol, another ingredient of lecithin, published in the journal European Neuropsychopharmacology concluded it had therapeutic effects in treating depression, panic and obsessive compulsive disorder (OCD); a common mental health condition in which a person has obsessive thoughts and compulsive behaviour.
Lecithin has become popular for weight management because it breaks down fat and stops it from entering cells.
One 2014 study of female Japanese taekwondo and judo athletes, who took choline supplements in the seven days before a competition (to reduce body mass and gain a competitive advantage), showed that taking choline did help them lose weight and body fat. The researchers concluded choline supplements could rapidly reduce body mass without affecting strength.
Getting lecithin from your diet
Lecithin is found in liver, eggs, soya beans, peanuts and wheatgerm, and is considered a rich source of choline. It's often added to processed foods such as chocolate, margarine and salad dressings.
Vegans who consume no meat, milk or eggs may be at risk of choline deficiency, and taking a lecithin supplement might be useful.
Very high doses of choline can cause nausea, diarrhoea, vomiting, body odour and sweating.
No safe upper daily limit has been set, but the Linus Pauling Institute in the US says the upper daily tolerability for choline (one of the ingredients in lecithin) is 3,500mg a day.
There is no recommended daily intake for lecithin. Taking two to four capsules each supplying 1,200mg of lecithin (derived from soya bean) a day is considered a therapeutic dose range.