Many of us have been taught to avoid cholesterol and saturated fats like the plague. The very mention of these words stirs up images of blocked arteries and heart attacks. As a result, whole food groups have been demonised. And the supermarket shelves are packed full of low-fat options.
Egg yolks are an example of a food that’s avoided because of high cholesterol and saturated fat content. So, should we be tossing the yolks and going for the ‘healthy’ egg white omelette instead? Are egg yolks linked to high cholesterol and heart disease? Let’s take a look at what the research has to say. But first, we need to understand cholesterol and its function in the body (it'll be a quick and painless explanation. I promise!).
What Is Cholesterol?
Cholesterol is a fat-like substance made in the liver and found in the blood and all cells of the body. You can also get cholesterol from eating foods from animals such as egg yolks, meat, and whole-milk dairy products. Cholesterol keeps you healthy. It has vital functions such as making cell walls, tissues, hormones, vitamin D, and bile acid.
Cholesterol is transported throughout the body by low-density lipoproteins (LDL, often called the ‘bad cholesterol’) and high-density lipoproteins (HDL, often called the ‘good cholesterol’). LDL and HDL are two kinds of carriers made of fat on the inside and protein on the outside.
How the Body Regulates Cholesterol Levels
Because cholesterol is essential to good health, it’s produced by the body in the liver. When we eat cholesterol-rich foods, the liver produces less. This means that total cholesterol in the body does not change significantly, it’s just coming from the diet instead of the liver. Chris Masterjohn, a PhD in nutritional science, explains:
But I’ve Been Taught That Cholesterol Is Going to Kill Me?!
You were also taught that Santa and the Easter bunny existed.
Dietary fat and cholesterol have been made out to be villains since the 1950s thanks to the infamous research of Ancel Keys. As Gary Taubes explains in Good Calories, Bad Calories:
Keys insisted that a low-fat diet was needed to "lower our cholesterol and our weight and forestall a premature death". His research became dietary dogma and many of us still turn down high-fat foods like egg yolks as a result. If Keys was right, US obesity rates should have decreased when the American Heart Association (the AHA) endorsed his work. But as you can see in the below figure, obesity rates rose steadily in the US starting around 1978, which is when the AHA starting pushing a low-fat diet to Americans.
We need to be careful when interpreting graphs like this, as correlation does not equal causation. But when fat was reduced in our diets, it had to be replaced with something. That something was usually sugar or processed ingredients.
For a complete review of this nutritional debacle and Keys' story, I highly recommend reading Gary Taubes’ book Good Calories, Bad Calories.
But since you probably don’t want to geek out on the history of the dietary fat and heart disease hypothesis, here’s a quick video. This is an oversimplification of the Keys' story, but it touches on some of the issues.
Eggs and Cholesterol Levels
Eggs and cholesterol levels have been widely studied. Research has found that eating eggs has little to no impact on cholesterol levels for most healthy people. For example:
- A 5-month study of young men on a high-fat diet were split into groups consuming either 3, 7, or 14 eggs per week. No significant increase in cholesterol levels was found in any group.
- A 5-week study found no significant increase in cholesterol levels when comparing four different diet groups: low fat and low cholesterol; low-fat and normal cholesterol; normal fat and low cholesterol; normal fat and normal cholesterol.
- In several studies, HDL (‘good cholesterol’) actually goes up.
While studies show that eating egg yolks doesn’t raise total or LDL cholesterol for the majority of healthy people, there are some exceptions.
Studies have found that some people (termed hyper-responders) have slightly elevated cholesterol levels in response to eggs. But eggs can change the LDL particles from small, dense LDL to large LDL. Large LDL are not associated with heart disease.
For the majority of healthy individuals, eating 2-3 eggs per day doesn't appear to increase cholesterol levels. Some studies have found that cholesterol levels may actually improve when eggs are consumed.
Eggs and Heart Disease
- A large-scale study of 3,898 men and women did not find a link between egg consumption or dietary cholesterol and increased risk of diabetes.
- The epidemiological literature does not support the idea that egg consumption is a risk factor for coronary disease.
- A study found that egg and cholesterol intake was not associated with an increased risk of coronary artery disease even when people had a gene that made them highly susceptible to heart disease.
The government is finally starting to catch up with the research. The most recent AHA guidelines have dropped their recommendation to reduce egg intake.
So, regardless of changes in cholesterol levels, the research does not link egg consumption in healthy individuals to an increased risk of heart disease. In fact, some studies actually show a reduced risk.
You Are an N=1 Experiment
I work hard to bring you quality information backed up by relevant science. But at the end of the day, you need to question everything and test things for yourself. This is because we’re all unique. How I respond to eggs could be totally different to your response. Science gives you direction and averages. But no scientist, government panel, nutritionist, etc. will ever know how you’ll react to a specific food.
If you’re concerned about your cholesterol levels, don’t just cut out foods based on what you’ve been told. Visit a reliable doctor and get a test done. It’s quick and easy. And if you do have high cholesterol, focus on whole foods and lifestyle changes. Then re-test to see if levels improve.
Summing up - Key Points
- Cholesterol is found in the blood and in all cells of the body. Cholesterol keeps you healthy.
- Total cholesterol in the body does not change significantly. The body will produce or decrease cholesterol depending on your dietary intake.
- Dietary fat and cholesterol were incorrectly linked to heart disease in the 1950s thanks to the infamous research of Ancel Keys.
- For the majority of healthy individuals, eating 2-3 eggs per day will not increase cholesterol levels.
- Research does not link egg consumption in healthy individuals to an increased risk of heart disease.
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