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If there was a perfect food, the eggs would be a suitor. They are easily available, easy to cook, affordable and packed with protein.
"The egg is supposed to contain all the ingredients necessary for the growth of an organism. It's so dense in nutrients, "says Christopher Blesso, associate professor of nutrition science at the University of Connecticut in the United States.
Eating eggs alongside other foods can help our body absorb more vitamins. For example, one study found that adding an egg to salad can increase the amount of vitamin E that we get from salad.
But for decades, egg consumption has also been controversial because of its high cholesterol content, which some studies have associated with an increased risk of heart disease. An egg yolk contains about 185 milligrams of cholesterol, which is more than half the daily amount of 300 mg of cholesterol recommended by American dietary guidelines until recently.
Does this mean that eggs, rather than an ideal food, could hurt us?
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Cholesterol, a yellowish fat produced in the liver and intestines, is found in every cell of our body. We normally think that it is "bad". But cholesterol is a crucial building block of our cell membranes. It is also necessary for the body to produce vitamin D, as well as hormones, testosterone and estrogen.
We produce all the cholesterol we need, but it is also found in the animal products we eat, including beef, shrimp and eggs, as well as in cheese and butter.
Cholesterol is transported into our body by the lipoprotein molecules in the blood. Each person has a different combination of different types of lipoproteins, and our individual composition plays a role in determining our risk of developing heart disease.
Low-density lipoprotein (LDL) cholesterol – called "bad" cholesterol – is transported from the liver to arteries and body tissues. Researchers say this can lead to cholesterol build up in the blood vessels and increase the risk of cardiovascular disease.
However, researchers have not yet established a link between cholesterol consumption and an increased risk of cardiovascular disease. As a result, US dietary guidelines no longer provide for cholesterol restriction; nor the United Kingdom. The focus is on limiting the amount of saturated fats we consume, which can increase the risk of developing cardiovascular disease. Foods containing trans fatty acids, in particular, increase our LDL levels. Although some trans fats are naturally present in animal products, most are artificially manufactured and are found at higher levels in margarines, snacks and some fried and baked foods, such as pastries, donuts and cakes.
Meanwhile, with shrimp, eggs are the only food that is high in cholesterol and low in saturated fats.
"While cholesterol in eggs is much higher than in meat and other animal products, saturated fats increase blood cholesterol. Maria Luz Fernandez, a professor of nutrition science at the University of Connecticut in the United States, has shown that many studies have shown that there is no relationship between the consumption of alcohol and alcohol. eggs and an increased risk of cardiovascular disease.
The discussion of the effects of eggs on health has shifted in part because our body can compensate for the cholesterol we consume.
"There are systems in place that, for most people, dietary cholesterol is not a problem," says Elizabeth Johnson, associate professor of nutrition research at Tufts University in Boston, USA .
In 2015, as part of a review of 40 studies, Johnson and a team of researchers found no conclusive evidence of the relationship between dietary cholesterol and heart disease.
"Humans have good regulation when they consume dietary cholesterol and produce less of it themselves," she says.
And for eggs, cholesterol can be a health risk even less important. Cholesterol is more harmful when it is oxidized in our arteries, but the cholesterol found in eggs does not oxidize, says Blesso.
"When cholesterol is oxidized, it can become more inflammatory, and eggs contain all kinds of antioxidants that protect it from oxidations," he says.
In addition, some of the cholesterol can be beneficial for us. High density lipoprotein (HDL) cholesterol travels to the liver, where it is broken down and removed from the body. HDLs are thought to have a protective effect against cardiovascular disease by preventing cholesterol from accumulating in the blood.
"People should be worried about the cholesterol circulating in their blood, that is, the one that causes heart disease," says Fernandez.
What matters is the HDL / LDL ratio in our body because high levels of HDL neutralize the effects of LDL.
However, while most of us are able to buffer the cholesterol we consume with the cholesterol we synthesize in our liver, Blesso says that about a third of us will experience an increase in 10 to 15% of his cholesterol level in the blood.
The trials showed that lean and healthy people are more likely to see an increase in LDL after eating eggs. Those who are overweight, obese or diabetic will see a lower increase in LDL and more HDL molecules, says Blesso. So, if you're healthier to start with, eggs could potentially have a more negative effect than if you're overweight – but if you're healthier, you're also more likely to have more weight. good levels of HDL, so an increase in LDL is probably not very harmful.
Research published earlier this year, however, calls into question the recent consensus that eggs are not harmful to health. The researchers examined data from 30,000 adults followed for an average of 17 years and found that each additional half-egg per day was significantly associated with a higher risk of heart disease and death. (They controlled people's eating habits, general health, and physical activity to try to isolate the effects of the eggs.)
"We found that for each additional person consuming 300 mg of cholesterol, regardless of their food, the risk of cardiovascular disease was increased by 17% and the risk of all-cause mortality by 17%," says Norrina Allen, one of The authors of the study and Associate Professor of Preventive Medicine at Northwestern University in Illinois, United States.
"We also found that every half egg per day resulted in a 6% increase in the risk of heart disease and 8% in the risk of death."
Although the study was one of the largest of its kind to address this specific relationship between eggs and heart disease, it was an observation, giving no indication of cause and effect. It was also based on a single set of self-reported data – participants were asked what they had eaten in the previous month or year, and then tracked their health outcomes for up to a year. at 31 years old. This means that the researchers received only one snapshot of what the participants ate, although our diet may change over time.
And the study is in conflict with past results. Many studies suggest that eggs are good for heart health. A previous analysis of half a million adults in China, published in 2018, had even shown exactly the opposite: egg consumption was associated with a lower risk of heart disease. Those who ate eggs daily had 18% less risk of death from heart disease and 28% less risk of stroke deaths than those who did not eat them.
As in the previous study, they were also observations, that is, it was impossible to determine the causes and effects. (In China, do healthier adults simply eat more eggs or make them healthier?). This can, of course, be a big part of the confusion.
Good egg
Although these studies have revived the debate about the impact of cholesterol in eggs on our health, we know some of the ways in which eggs could affect our risk of disease.
One of the ways is to use a compound in eggs called choline, which could protect us from Alzheimer's disease. It also protects the liver.
But it can also have negative effects. The intestinal microbiota metabolizes choline into a molecule called TMO, which is then absorbed by the liver and converted into TMAO, a molecule associated with an increased risk of cardiovascular disease. Blasso asked if eating a lot of choline in eggs could lead to a rise in the TMAO: he discovered studies where it was observed that people had high levels of TMAO until 12 hours after ate eggs.
Research on egg consumption and the TMAO have so far only revealed transient increases in TMAO. However, TMAO is measured as a marker of heart disease only at a baseline level, which can be detected when people are fasting. Blasso compares this to how our blood glucose levels rise temporarily after carbohydrate consumption, but high blood glucose is only associated with diabetes when the blood glucose level is continuous.
It may be because when we eat eggs, we only get the beneficial effects of choline, he says.
"The problem is that instead of being absorbed into the blood, choline continues in the large intestine, where it can become TMA then TMAO," Fernandez explains.
"But in the eggs, choline is absorbed and does not go into the large intestine, so it does not increase the risk of heart disease."
Meanwhile, scientists are beginning to understand the other benefits of eggs for health. Egg yolks are one of the best sources of lutein, a pigment that has been associated with better vision and a lower risk of eye disease, for example.
"There are two types of lutein in the retina of the eye. It can protect the retina from damage caused by light by acting as a filter for blue light because exposure to light damages eyesight, "says Johnson.
Although researchers are still far from understanding why eggs affect us differently, the vast majority of recent research suggests that they pose no risk to our health and are much more likely to be beneficial to health.
However, having eggs for breakfast every day is probably not a healthier option, at least since it is recommended to follow a varied diet … rather than putting all our eggs in one basket.
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