Are eggs good or bad for you? The truth may be somewhere in between
Posted February 9, 2021 2:00 p.m. EST
CNN — Forget which comes first, the chicken or the egg. The more important question is: Are eggs good or bad for your health?
Unfortunately, science can't seem to settle on a definitive answer to that either.
Just last year, a large Harvard analysis of 215,000 people found that eating one egg per day was not associated with an increased risk of cardiovascular disease.
Now, a new study of over 500,000 people has found eating even a portion of a whole egg -- with its cholesterol-laden yellow yoke -- increases the risk of dying from all causes, including cardiovascular disease and cancer.
In fact, the overall risk of death went up by 7% for each additional half a whole egg eaten per day, according to the study published Tuesday in PLOS Medicine.
Experts were skeptical.
"Despite many years of research this question about eggs and health has not been answered, with multiple observational studies over the last few decades showing conflicting results -- some suggesting moderate egg intake is good, while others suggesting it may be bad," said Riyaz Patel, a consultant cardiologist at University College London.
"This study, although well conducted, unfortunately only adds more noise to the discussion," Patel said in a statement.
The study results are problematic because they only asked people once about their egg consumption, then followed them for many years without checking to see if their diet had changed, said Dr. Walter Willett, a professor of epidemiology and nutrition at Harvard T.H. Chan School of Public Health.
"They're only getting a snapshot in time," said Willett, who is also a professor of medicine at Harvard Medical School.
"The conclusions of this study are overblown," said Ada Garcia, a senior lecturer in public health nutrition at the University of Glasgow, Scotland, in a statement. "Blaming eggs alone for an increased risk of cardiovascular disease is a simplistic and reductionist approach to the concept of diet and disease prevention."
What do eggs replace?
The poultry industry has long touted the "incredible, edible egg." For a mere 75 calories, they say, an egg delivers 7 grams of high-quality protein, 5 grams of fat and 1.6 grams of saturated fat, along with iron, vitamins, minerals and disease-fighting nutrients like lutein and zeaxanthin.
Eggs are affordable, making them a cheap nutritional powerhouse for families with limited food budgets. Many people on popular low-carb diets such as keto also rely heavily on eggs in their meal plans.
The problem, of course, is the level of cholesterol in the yellow yolk of eggs: One large egg yolk can deliver about 185 milligrams of cholesterol.
Cholesterol is not a bogeyman. Made by the liver, cholesterol is in every cell in the body and is used to make hormones, vitamin D, digestive compounds and more. Sometimes a person's body can make too much cholesterol, leading to a buildup of waxy plaque in blood vessels and later cardiovascular disease.
There is a role played by cholesterol in our diet, but it's more complicated than we used to think, said Willett, who has spent over 40 years studying the effects of diet on the occurrence of major diseases.
Nutritional guidelines used to recommend an upper limit of 300 milligrams of cholesterol a day. Today guidelines suggest eating as little as possible by keeping saturated fats to less than 10% of daily calories.
The key, Willett said, is to look at the overall nutritional pros and cons of the food, as well as what the food is replacing in the diet.
Take fish, for example. Fish contain cholesterol, but also provide essential omega-3 fatty acids critical to optimal health.
And saturated fats from butter, whole dairy and fatty cuts of meat have a much more profound impact on raising levels of LDL (low-density lipoproteins) in the blood than sources of dietary cholesterol such as eggs.
"If someone replaces eggs with doughnuts, other refined starches and sugar or saturated fats, I'd rather they eat eggs," Willett said.
"But for someone who really wants to be in optimal health. putting the emphasis on plant-based protein sources like steel-cut oatmeal and nuts would be a better way to go."
Certain populations may want to watch their intake of eggs, however.
"Someone who's having a difficult time having to use medication for their blood cholesterol levels probably would be better off keeping eggs on the low side," Willett said. "Eggs don't have to be totally eliminated, but I think the old recommendation of not more than two eggs per week for most people is actually still a good recommendation."
People with Type 2 diabetes should be wary as well. The 2020 Harvard study found a higher intake of eggs by people with Type 2 diabetes was associated with increased cardiovascular risk, a link that has been duplicated in previous studies.
What about egg whites?
Can eggs yolks be safely replaced with egg whites? The new PLOS study found replacing half a whole egg with an equivalent amount of egg whites or egg substitutes reduced death from cardiovascular disease by 3%.
"In my view the recommendation made by the authors to replace whole eggs with egg whites/substitutes is not supported by the entirety of evidence available," said UCL's Patel.
"Most studies have not looked at eggs without yolks," Willett said, "mostly because consumption of egg whites is pretty low in the general population. The lowest risk is replacing eggs with nuts and plant-based sources of protein."
Patel added: "I do not think this study changes the general advice, that for most people, eggs can be eaten in moderation as part of a balanced diet, unless they have been advised not to for a specific medical or dietary reason."