Cholesterol is a fat-like substance present in all our cells. It serves many functions, such as providing the raw material for pregnenolone, from which are derived many other hormones: cortisol, DHEA, testosterone …
Cholesterol is shuttled throughout the body by two kinds of carriers made of fat on the inside and protein on the outside: low-density lipoproteins (LDL, often called the “bad cholesterol”) and high-density lipoproteins (HDL, often called the “good cholesterol”).
Some studies report that eating eggs doesn’t increase blood cholesterol in healthy people.
● One 5-month study in 70 young men on a high-fat diet compared the effects on cholesterol of 3, 7, and 14 eggs per week.
● One 5-week study in 24 healthy men compared four 2,800-kcal diets: low fat and low cholesterol; low fat and normal cholesterol; normal fat and low cholesterol; normal fat and normal cholesterol. Protein intake was fixed at 7.7%.
● One 10-day study gave 32 healthy men 2 eggs per day as part of a diet with 42–45% fat.
Some studies report that eating eggs does increase blood cholesterol in healthy people.
● One 10-week study in 40 healthy men gave them daily either 3 eggs, 2 g of ascorbic acid, neither, or both. Only the group who took both saw a statistically significant increase in cholesterol and LDL, but the study reported considerable variability in individual responses.
● One 2-month study gave 6 men and 3 women either 137 or 1,034 mg of cholesterol per day as part of a 45:40:15 carbohydrate:fat:protein diet. Their HDL:LDL ratio worsened with the higher dose.
● One 4-week study gave 10 athletic men either 200 or 600 mg of cholesterol per day as part of a 55:30:15 carbohydrate:fat:protein diet. Their HDL:LDL ratio worsened with the higher dose.
● One 3-week study gave lactovegetarian college students one extra-large egg per day, thus adding 381 mg of cholesterol to their diet.
Some studies report that eating eggs increases blood cholesterol in some healthy people.
The current concensus is that only a minority of “hyperresponders” experience a spike in blood cholesterol, LDL, and HDL when consuming eggs.
Eggs increase cholesterol in only a minority of healthy people. Dietary cholesterol seems to have less effect on young people. Dietary cholesterol seems to increase LDL more when the diet is high in carbohydrate (and thus low in fat).
Healthy people seem to have little to fear, but what about at-risk populations?
● One 18-week study in 161 people reported that 2 eggs per day raised LDL in people with high blood lipids but not in people with normal blood lipids and high cholesterol.
● One 3-week study in 21 men reported that an additional 800 mg per day of cholesterol raised LDL levels in insulin-dependent diabetic men but not in healthy men.
Should people with diabetes or high blood lipids shun eggs entirely? That’s probably unnecessary. Diabetics and hyperlipidemics who experience spikes in LDL also experience spikes in HDL, and the risk for cardiac complications does not increase.
In some unhealthy populations, as in healthy people with low baseline intake of fat and cholesterol, LDL increases can exceed HDL increases; but although an increased risk for cardiovascular disease may be inferred, none has been demonstrated epidemiologically.
In survey research, it is common to see a relationship between egg consumption and dietary cholesterol. A meta-analysis of 17 studies (some of which metabolic ward studies) with sample sizes ranging from 9 to 79 noted that HDL, LDL, and total cholesterol all increased in most studies, and that the HDL:LDL and HDL:cholesterol ratios both tended to worsen. Some of the studies investigated in this meta-analysis were mentioned in the previous section.
Various recent surveys and reviews have shown little to no correlation between egg consumption and risk for cardiovascular disease. Whereas a prospective study of 3,898 men and women reported that egg consumption or dietary cholesterol didn’t seem to increase the risk of incident diabetes, one sub-group analysis might suggest a link between egg consumption and a slightly increased risk of cardiovascular disease in people who are already diabetic.
Some studies link egg consumption to an increase in cholesterol levels; some do not; but no study has shown an increase in risk of cardiovascular disease.
Very high egg intakes (more than 6 eggs per day) have yet to be studied, so their effects (positive or negative) are unknown. If your HDL levels are low to begin with (as can happen with a poor diet) and if you belong to the minority of “hyperresponders” who experience a spike in blood cholesterol, LDL, and HDL when consuming eggs, then your eating eggs may lead to greater LDL oxydation and increased risk of vascular disease.
Even if you aren’t completely healthy, if your diet is, then eating eggs in moderation should be fine. Drops in blood cholesterol and weight (starting from BMI 35–40) have even been seen in people eating 3 or 4 eggs per day if they stuck to a grain-free diet or otherwise reduced their carbohydrate intake.
In mice genetically susceptible to increases in cholesterol, eggs tend to improve blood parameters. This, in addition to the information above, suggests that genetics matter less than environment with regard to the effects of egg consumption.
Full analysis: are eggs healthy or bad for you?
In healthy people, even 6 eggs/day (the highest intake studied) doesn’t seem to adversely affect blood lipids. Some studies note no change in HDL or LDL; some note a benign increase in both; few note adverse changes in lipoprotein status.
In healthy people, eggs have never been directly associated with an increase in cardiovascular risk — such an increase was merely assumed from an increase in circulating cholesterol.
In unhealthy people, 1–4 eggs/day combined with a healthy low-carb diet may actually improve lipoprotein status (an effect likely due to the low-carb diet more than to the eggs).
In unhealthy people with an obesogenic diet (notably one high in carbohydrate), egg consumption might negatively affect blood levels of cholesterol and lipoproteins.