The authors of a new study believe that eating eggs and foods with cholesterol increases the risk of death. Let's see if it is really reasonable to consider the cholesterol that food contains as dangerous to health.
There is cholesterol, and there is cholesterol
The idea that cholesterol is associated with heart disease, will not seem new to anyone. Almost everyone has heard of the so-called «bad cholesterol» in the blood. However, the question of the harmfulness of cholesterol in our diet is not so simple.
Cholesterol is needed by the body. It is found in animal foods (dietary cholesterol) — eggs, butter, meat, shrimp, lobsters. In addition, the liver can synthesize it in the required amount. In human blood, it moves, joining complexes of proteins and lipids — lipoproteins. The combination of cholesterol with low-density lipoprotein (LDL) is simply called «bad» cholesterol, and with high-density lipoprotein (HDL) — «good». The level of «bad» cholesterol in the blood increases not only because of the use of cholesterol in food.
The role of dietary cholesterol in the development of atherosclerosis and heart disease was first described by our compatriot Nikolai Anichkov. In what has been called one of the most important discoveries of the 20th century, he fed rabbits a cholesterol-rich diet. As a result, the animals developed atherosclerosis of the aorta.
More than 100 years have passed since Anichkov's experiments, but how harmful dietary cholesterol is to human health remains a matter of debate. Critics point out that in nature, rabbits, unlike humans, do not eat cholesterol. In addition, Cholesterol-rich foods usually also contain saturated fats, which can increase the risk of atherosclerosis (eggs and crustaceans are the exception).
It is expected that people's sensitivity to dietary cholesterol may differ. In 1991, scientists described an 88-year-old man who ate 25 eggs a day and showed no signs of atherosclerosis. However, such a reaction can be considered exceptional: after all, dietary cholesterol can increase the level of «bad» cholesterol in the blood.
Not cholesterol, but saturated fats
A high level of «bad» cholesterol in the blood is one of the risk factors for atherosclerosis and, as a result, heart disease and stroke. According to modern concepts, of dietary factors, it is not dietary cholesterol that has a decisive influence on this level, but saturated fats. They are found in many animal products and in coconut oil.
In 1965, Harvard scientists conducted a study that is not ethical by today's standards. In an experiment on mentally ill people, they found that saturated fat had a greater effect on blood cholesterol levels than dietary cholesterol itself. These findings support several more recent and less radical studies.
What research and guidelines say
Scientific evidence about the dangers of cholesterol remains controversial. Data from individual studies may be discouraging for those who love to eat eggs. For example, a 2019 analysis of six studies found that dietary cholesterol is associated with heart disease and the risk of dying from it. However, in general, studies give mixed results, from which it is difficult to draw firm conclusions.
Due to the lack of evidence for the harm of cholesterol and the benefits of limiting its amount in the diet, it was «crossed out» from the list of food hazards in a number of documents. The maximum amount of dietary cholesterol is no longer listed in the American Dietary Guidelines and the American Heart Association guidelines for reducing cardiovascular risk. Earlier (for example, 20 years ago) it was recommended to consume no more than 300 milligrams of cholesterol per day.
Eggs are useful and harmful
Eggs are a good source of quality proteins, vitamins, and other bioactive substances, including carotenoids, choline, and lecithin. Among other protein foods, they are included in the American dietary recommendations. Many people avoid eggs in their diet because, according to some reports, the cholesterol they contain can increase the risk of developing cardiovascular disease.
What the newest study has shown
The newest study, in which data from more than half a million people were processed, showed that eating eggs is associated with health risks. The study participants were followed for about 16 years. They completed detailed questionnaires about their diet every year.
Eating every additional 300 milligrams of cholesterol or every half an egg per day was associated with a 7% increased risk of dying from any cause, including cancer. At the same time, it was not about the effect of egg whites on this indicator.
The authors of the study, published in PLoS Medicine, believe that limiting cholesterol, and specifically egg yolks, in the diet should reduce the risk of death.
How many eggs per day can you eat without health risksEggs are an important source of dietary cholesterol. Scientists have long argued how dangerous it is to eat them and how many eggs a day you can eat.
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Does the question remain unanswered?
In comments to the Science Media Center, a number of experts expressed skepticism about the work.
«The biggest flaw in the study is how the data on egg consumption was collected,» said Ada Garcia, senior lecturer at the University of Glasgow. When people are asked to remember what they ate for a whole year, a large number of errors are possible, she recalled. Such studies cannot provide accurate results.
«We eat food combinations, and one particular aspect of the diet — in this case, eggs — cannot be entirely blamed for the problems,» Garcia said. According to the expert, blaming eggs for an increase in the risk of heart and vascular disease is a simplification, and therefore, according to the expert, “the conclusions of the study are inflated.”
«These studies are inconsistent with what we know about the relatively small impact of eggs and dietary cholesterol on blood cholesterol levels and heart disease, compared to many other risk factors,» said Professor Bruce Griffin, a metabolism specialist. from the University of Surrey.
Griffin points out that it was previously known that eating large amounts of eggs and dietary cholesterol was associated with an unhealthy lifestyle. Therefore, the «effect» of eggs in the diet may be mediated by other factors. Those who eat more eggs are more likely to eat more fatty foods and few healthy foods (vegetables, fruits). They may have lower incomes and lower levels of education.
Despite years of research, the question of eggs in diet and health remains unanswered. A large number of epidemiological studies have produced conflicting results, with some suggesting that eggs in moderation are beneficial, others that they can be harmful. This study, while qualitative, only adds more white noise to the discussion,” said Riyaz Patel of University College London.