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Myth Busting

Do eggs raise your cholesterol levels?

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Jump to: Clinical trials have shown no impact of eggs on blood cholesterol levels | Dietary cholesterol is poorly absorbed in our gut | Eggs don’t raise your risk of heart disease | Take home points

Myth: “Eggs will raise your cholesterol and increase your risk of heart disease”

Historically, eggs have had a bit of a bad reputation, mainly due to their dietary cholesterol content. As high cholesterol levels were previously believed to cause heart disease, eggs were identified as a ‘bad’ food and one to avoid.

At 400mg per 100g (about two medium eggs), they’re the richest source of dietary cholesterol in our diets. Should this concern you? The short answer is no.

In this guide, we’ll address three lines of evidence busting the myth that eggs raise your cholesterol and increase your risk of heart disease.

1) Clinical trials have shown no impact of eggs on blood cholesterol levels

Despite the consistent dogma around eggs and their cholesterol content, trials as early as the 1960s showed that eggs didn’t raise blood cholesterol levels.

To quote Ancel Keys (the researcher that originally hypothesised that cholesterol was the cause of heart disease):

“It is concluded that in adult men the serum [blood] cholesterol level is essentially independent of the cholesterol intake over the whole range of natural human diets. It is probable that infants, children and women are similar”

In plain English: eating high levels of dietary cholesterol has little impact on blood cholesterol levels. Ancel Keys’ own research in the 1960s showed this, and studies conducted since then continue to support this observation.

Why this was ignored, and people continued to be told to reduce their egg consumption to lower cholesterol levels is unclear.

You might also wonder how eggs can contain so much dietary cholesterol and have little effect on our blood’s cholesterol levels, which we’ll cover in the next section.

Key points:

  • Clinical trials dating back to the 1960s have shown that cholesterol from the diet has little impact on circulating blood cholesterol levels.
  • It’s unclear why the advice to lower egg consumption continued despite this evidence.

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2) Dietary cholesterol is poorly absorbed in our gut

Firstly, a bit of background about cholesterol. Cholesterol is so important to our health that it’s produced by every cell in the human body. Among many functions, it’s required to form cell membranes and acts as precursors to essential hormones.

Cholesterol is a part of a family of ‘sterols’ (of which there are around 40) that have different bodily functions, some of which can harm our health. (More on this later.)

Cholesterol comes in two forms:

  1. Unesterified cholesterol: the free or active form
  2. Cholesterol-ester: the storage ‘non-active’ form

The vast majority (more than 50%) of dietary cholesterol in eggs and other foods rich in cholesterol is in the non-active form (cholesterol ester). Due to the chemical structure of this non-active form, it can’t make its way past our gut lining to be transported into the bloodstream. It’s simply excreted out in our stool.

What about the free form of cholesterol in eggs?

This is where it gets a bit complicated so let’s use an analogy. Imagine the gut is a bouncer to a nightclub, and it has the choice of whether you’re allowed to enter the nightclub or not.

Now, you’ve got cholesterol and all their sterol friends coming to the door; some are good, some are bad (remember, there are around 40 types of sterols). The problem is, they’re all dressed pretty much the same, and the bouncers can’t tell the difference. So they tend to avoid letting any of them in.

This is what’s happening in the gut daily. It can’t decipher between what it should and shouldn’t let through, so it often rejects everything to be sure. The transportation of cholesterol into our body is a very selective process.

Key points:

  • Cholesterol is essential for life, and every cell in the body makes it
  • Cholesterol comes in two forms: the free form and storage form
  • The majority of dietary cholesterol is the storage form which isn’t absorbed by the body
  • The gut provides rarely absorbs other free cholesterol from foods, and the majority is passed out of our stool

3) Eggs don’t raise your risk of heart disease

The theory that eggs could be linked to heart disease is due to the diet-heart hypothesis, which states that increased blood cholesterol levels will lead to more cholesterol in the artery wall, forming plaques and increasing your risk of a potential heart attack.

This argument falls down for a couple of reasons 1) high cholesterol levels have been shown to be a poor indicator of heart disease risk, and 2) eggs don’t raise your blood cholesterol levels, as we’ve discussed above.

Some observational studies suggest that people who consume more eggs are more at risk of heart disease. But the associations in these studies aren’t causal, and people who eat more eggs also tend to smoke more, drink more alcohol, exercise less, and generally live unhealthier lifestyles.

So observational studies are an unreliable way to determine the effect of eggs on heart disease risk. However, human clinical trials measuring other risk factors for heart disease, such as blood glucose levels, blood pressure, and weight, can indicate whether eggs impact individuals’ risk.

A randomised controlled trial involving 128 participants with pre or type 2 diabetes was conducted to measure the effect of a high or low egg diet on their markers of heart disease risk. The high egg group was instructed to consume more than twelve eggs a week, while the low egg group had less than two eggs per week.

The study showed that, unsurprisingly, cholesterol levels in the high egg group were unchanged compared to their baseline levels. Both groups saw improvements in weight, HbA1c (average blood sugar), and waist circumference.

Surprisingly, only the high egg group saw reductions in blood pressure as systolic blood pressure decreased by 4.94mm Hg and diastolic by 1.72mm Hg. Blood pressure is considered one of the major risk factors in the development of heart disease.

Other studies have also shown similar results: when eggs are consumed in line with a balanced diet, they can support improvements in health and, specifically, reductions in heart disease risk factors like blood pressure and HbA1c.

Key points:

  • Observational studies have shown associations between high egg intake and heart disease risk.
  • However, observational research can’t prove causation and is often confounded by other factors like smoking, alcohol consumption, and sedentary lifestyles.
  • Human clinical trials have shown that high-egg diets eaten in a balanced diet can support improvements in health and lower your risk of heart disease.

Take home points

  • Eggs have historically had a bad reputation due to their cholesterol content and the belief they will increase your blood cholesterol levels and heart disease risk.
  • Human clinical trials dating back to the 1960s have shown that eggs don’t impact blood cholesterol levels.
  • Research has also suggested that high blood cholesterol levels are a poor indicator of heart disease risk.
  • Other more reliable markers of heart disease risk, such as blood glucose levels, blood pressure, and weight, have all been shown to improve on high egg diets.
  • You don’t need to fear eggs. They can be included as part of a healthy diet and may help you lose weight and lower your risk of heart disease.

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