First, some clarification on cholesterol.
We can refer to actual cholesterol in the blood as cholesterol, but some people also falsely refer to the lipoproteins (High density lipoprotein or HDL, the "good" lipoprotein and LDL or Low density Lipoprotein, the "bad" lipoprotein; both terms are simplistic though). This FAQ entry will address all three.
"Does it increase Cholesterol?" Interventions
The answer as to whether it raises these parameters is 'it depends' - it appears to in some people, but not all. Some people are known as 'hyperresponders' and do experience a spike in blood cholesterol, LDL, and HDL when consuming eggs. At least one study that had two trial periods (egg period, no egg period) noted significant differences where one group of healthy persons had a significant increase in cholesterol after consumption of 3 eggs daily for 10 weeks while the other group showed no such spike.
Right off the bat, there appears to be high interindividual differences. What happens to one person may not work for another, and you may experience an increase in cholesterol even if it is not the norm
Studies that found no effect on plasma levels of cholesterol included one with 31% and 46% fat content of the diet for 5 weeks in 24 men with either 193mg or 560mg cholesterol daily with 7.7% protein at 2800kcal, 32 year old healthy men having 2 eggs a day with 41% dietary fat failed to find an influence on circulating cholesterol, adding 3 eggs (563mg cholesterol) to the diet of young men without dietary controls, no difference between 3, 7, and 18 eggs per week in 70 young men on a high fat diet,
Studies that do find a relation of cholesterol on circulating lipoproteins used a 55/30/15 carb/fat/protein diet with 200 or 600mg, finding an increase in LDL and shift towards a worse HDL/LDL ratio with the higher dose, an increase from 97mg to 418mg cholesterol daily in young adult vegetarians increased LDL over 3 weeks when consumed via test foods (rest of diet not controlled), pairing 3 eggs daily with 2g Vitamin C (despite the eggs themselves not increasing lipoproteins), and an 11% increase in LDL (independent of other lipids) possibly via the LDL-receptor downregulation when subject to 1g of cholesterol daily.
No significant defining features for these studies, but a trend towards young men having less influence from cholesterol in the diet on circulating lipoproteins and a higher carbohydrate percentage in the diet leading to greater LDL levels from cholesterol (whether this is due to carbohydrate inclusion or fatty acid/protein exclusion is not confirmed)
In studies specifically targeting unhealthy populations, persons with high cholesterol and high lipids appear to significantly increase LDL in those with high blood lipids but not in those with normal lipids and high cholesterol, an increase in LDL seen in diabetic patients when it did not exist in normal patients,
The answer as to whether it is a concern is 'not likely'. In those who experience spikes in LDL and cholesterol, they also experience spikes in HDL and their risks for cardiac problems does not increase. Although in some unhealthy populations or healthy persons with low baseline fatty acid and cholesterol intake, LDL increases can exceed HDL increases; in this population, an increased risk for heart disease may be inferred but it has not been demonstrated epidemiologically.
Some disease populations such as type II diabetics and hyperlipidemics (those with high blood triglycerides) should exercise caution around eggs, as there is a greater chance for LDL increases in these populations relative to healthy controls
"Does it increase Cholesterol?" Surveys
In survey research, it is common to see a relationship between egg consumption and dietary cholesterol. A meta-analysis of 17 studies noted that although HDL, LDL, and total cholesterol increased in most studies that there was a trend towards a worsening of the HDL:Cholesterol and HDL:LDL ratios. Of these studies, it was split between free living and metabolic ward studies (where diet is controlled) and sample size ranged from 9 to 79. The studies investigated in this meta-analysis were mentioned in the previous section.
When investigating risk of heart disease, there appears to be no epidemiological link between eggs and coronary heart disease although sub-group analysis might suggest a link between egg yolk consumption and diabetics getting a slightly increased risk of heart disease.
Common to see increases in cholesterol levels, although an equal amount of evidence shows a lack of increase in cholesterol levels; no studies have currently shown an increase in risk of coronary heart disease, suggesting that measuring circulating cholesterol levels may be poorly indicative of heart disease from egg intake
When can eggs be bad?
No studies have looked at a very high egg intake (greater than 6 a day), so it is just not known what an intake at this level does. They could be bad, they could be good, they could be inert.
If eggs are consumed and you are a hyperresponder (thus the spike in all cholesterol levels) but the eggs are not combined with a healthy diet, there is a possibility that the bad overall diet can reduce HDL and cause this supposedly inert spike in cholesterol to potentially induce some risk. There is also the problem of the lighter, fluffier LDL particles (LDL-A, or 'normal' LDL) to become more dangerous by being oxidized into LDL-B (the 'small, dense' LDL), but this seems to be independent of egg consumption by itself and needs another factor. As elaborated on in the next section, this is mostly due to having a bad diet alongside egg consumption. It would be prudent to focus on the diet as a whole rather than isolated parts.
Pairing eggs with an obesogenic diet (high carbohydrate with a high glucose AUC, indicative of insulin resistance) and/or an unhealthy body state to start with, is a recipe for eggs to become problematic
What if I'm unique?
If consumed in moderations and in conjunction with an otherwise healthy diet, eggs even fine for people who are not completely healthy. Drops in weight and blood cholesterol have even been seen in persons eating 3-4 eggs a day and starting from a BMI ranging from 35-40 given they adhere to a grain-free diet or otherwise reduced carbohydrates.
In mouse models of those genetically susceptible to increases in cholesterol, eggs still tend to show beneficial trends in blood parameters. With the above information, this suggests that genetics are less of a factor relative to environment when eggs are concerned.
Eggs, when consumed by healthy persons in the range of 1-6 a day (higher levels not really studied), usually do not adversely affect blood lipids. Some studies note no increases, some studies note a benign increase of both LDL and HDL; few note adverse changes in lipoprotein status
In healthy persons, eggs have never been directly associated with an increase in coronary heart disease risk; merely indirectly assumed via increases in circulating cholesterol
Eggs, when consumed by unhealthy persons in the range of 1-4 a day and with a healthy low-grain and low-carb diet, may not negatively affect blood cholesterol and lipoprotein levels and may actually improve them (although the low-grain diet is more likely to be doing this)
Eggs, when consumed by unhealthy persons and with a generally high carbohydrate and obesogenic diet, might worsen or prevent a bettering of blood cholesterol levels and lipoprotein levels