What it is

Egg white is mostly water and protein; the yolk holds nearly all the fat, cholesterol, choline and yellow pigments 1.

Per 100 g, whole raw egg contains 372 mg cholesterol, 294 mg choline and 503 µg lutein plus zeaxanthin; the white contains no cholesterol, lutein or zeaxanthin 1. A large egg weighs 50 g and supplies 186 mg cholesterol and 147 mg choline 1. EFSA’s Adequate Intake of choline for adults is 400 mg a day 2.

In the body

Gut cells take up egg cholesterol through a transporter; blood cholesterol rises more in some people than others 34.

NPC1L1, an apical enterocyte protein with a sterol-sensing domain, is critical for cholesterol uptake 35.

Absorption and hepatic uptake of dietary cholesterolIntestinal lumen and enterocyte, then lymph, plasma and hepatocyte
  1. Cholesterol in mixed micelles
  2. NPC1-like intracellular cholesterol transporter 1 (NPC1L1)EzetimibeApical membrane; the ABCG5-ABCG8 pump returns part of it to the lumen
  3. Enterocyte cholesterol
  4. Sterol O-acyltransferase 2 (SOAT2)Long-chain fatty acyl-CoAEndoplasmic reticulum; expressed in enterocytes and hepatocytes
  5. Cholesteryl ester
  6. several stepsAssembly with apoB-48 requires MTTP; chylomicrons are secreted into lymph
  7. Chylomicron
  8. Lipoprotein lipase (LPL)APOC2 (coactivator)Bound to GPIHBP1 on capillary endothelium; hydrolyses triacylglycerol
  9. Chylomicron remnant
  10. several stepsAPOE binds LDLR and LRP1; lysosomal acid lipase (LIPA) frees cholesterol
  11. Hepatocyte cholesterol

When egg yolk raised Dutch volunteers’ cholesterol intake from 129 to 989 mg a day, serum cholesterol rose by 0.82 mmol/L in 17 previously selected hyper-responders and 0.47 mmol/L in 15 hypo-responders 4. The differences were reproducible but modest: responses were unimodal, with a between-person standard deviation of 0.29 mmol/L 4.

Choline is a component of phospholipids and a precursor of acetylcholine and betaine, a methyl donor for homocysteine remethylation; dietary deficiency can cause fatty liver 2. Lutein and zeaxanthin travel in chylomicrons, then partly in HDL, and colour the macula lutea 6.

What studies show

Egg cholesterol raises blood cholesterol modestly; long-term studies of large groups disagree on heart disease 789.

In 17 controlled trials (556 participants, at least 14 days), each extra 100 mg cholesterol a day raised total cholesterol by 0.056 mmol/L (95% CI 0.046 to 0.065) and HDL cholesterol by 0.008 mmol/L 7. One extra egg a day, taken as 200 mg, was predicted to raise LDL cholesterol by 0.100 mmol/L 7.

A review by a group promoting plant-based diets found egg- or poultry-industry funding in 0 of 9 studies from the 1950s and 25 of 42 from 2010–2019 10. Most intervention studies reported net cholesterol rises, which conclusions called favourable in 49% of industry-funded and 13% of other studies 10.