Phospholipids

Phospholipids are fats that form the double layer of every cell membrane and help fats mix with water. The best-known dietary form is lecithin (phosphatidylcholine), found in egg yolks and soybeans, which is also a source of the nutrient choline.

What is it?

A phospholipid has a phosphate-containing head that attracts water and two fatty acid tails that repel it. This lets them line up in double layers (membranes) and act as emulsifiers. Examples are phosphatidylcholine (lecithin), phosphatidylserine and phosphatidylethanolamine. Most of the phospholipids in the body are made by the body itself.

What it does

1. Form cell membranes and the sheath around nerves
2. Help carry fats and cholesterol in the blood (as part of lipoproteins)
3. Act as emulsifiers in bile and in food (lecithin in chocolate, mayonnaise and spreads)
4. Phosphatidylcholine supplies choline for making the neurotransmitter acetylcholine

Food sources

Egg yolks, soybeans and soy lecithin, liver, peanuts, fish roe, wheat germ, beef, and sunflower and canola lecithin. Krill oil contains phospholipid-bound omega-3.

Singapore food examples

1. Egg yolks — soft-boiled eggs, kaya toast, omelettes
2. Soya beans, tofu and soy milk
3. Peanuts
4. Fish roe and fish
5. Liver in soups and congee, in moderation

How much do I need?

There is no recommended intake for phospholipids themselves, and Singapore's RDA table does not list them. The related nutrient choline has an Adequate Intake of 550 mg a day for men and 425 mg for women in the US, which eggs, meat, fish and soya foods help to provide.

Low intake and deficiency

The body makes phospholipids, so there is no deficiency from diet. Low choline intake can contribute to fatty liver and muscle damage, and is a particular concern in pregnancy.

Too much and safety

Phospholipids from food are safe. High doses of lecithin supplements can cause nausea, loose stools and a fishy body odour (from choline). Large amounts of choline (more than 3.5 g a day) can cause low blood pressure, sweating and a fishy odour. Dietary choline metabolised by gut bacteria has been linked to a compound (TMAO) studied in heart disease, and the research is ongoing.

Absorption and bioavailability

Phospholipids are digested to smaller pieces (lysophospholipids and fatty acids), absorbed with bile salts and reassembled in the gut wall. Dietary choline is absorbed well.

Connection to daily life

1. Brain and nerve health: phospholipids are major components of brain membranes
2. Pregnancy: choline from eggs, fish and soy supports a baby's brain development
3. Healthy ageing: a varied diet supplies enough; lecithin supplements have not been proven to protect memory

Sources: 1. National Academies of Sciences, Engineering, and Medicine — Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005) 2. HealthHub Singapore — Recommended Dietary Allowances: https://www.healthhub.sg/well-being-and-lifestyle/food-diet-and-nutrition/recommended_dietary_allowances 3. Health Promotion Board — Singapore Food Insights Database (SG FoodID): https://www.hpb.gov.sg/healthy-living/food-and-beverage/sgfoodid/ 4. FAO/INFOODS — Food composition tables and databases: https://www.fao.org/food-composition/tables-and-databases/en/