Are eggs good for metabolic health?
Eggs often get conflicting headlines, but research is clear that you don’t need to avoid them for health reasons. Here’s what eggs do for you, and what our experts have to say.
For every bit of research suggesting chicken eggs are bad for your health, another study suggests the opposite. For example, eggs have historically been demonized for their cholesterol content, and while they do contain significant amounts, we now know that isn’t inherently bad. Quality and context are everything.
So are eggs good for you? Eggs are a complex food, with dozens of components and nutrients that can change depending on how they are prepared, where the hen was raised and what she was fed. And context matters beyond the egg itself: Research shows that what you eat with eggs (e.g., bacon, toast) has more influence on your overall health than your daily egg consumption.
> “When it comes to micronutrients, eggs are one of the most diverse foods.”
So while we can’t tell you whether or not to eat eggs, we can tell you they are not inherently a health-damaging food. Eggs, like all foods, deliver information to the body, much of which helps it carry out essential processes. It’s important to know what information they provide, how your body can use it, and how it fits your overall nutritional approach.
First, Four Practical Tips
- **Make eggs part of a healthy breakfast.
**Eating a breakfast of eggs, pancakes, syrup, juice, and sausage will have a much different nutritional profile than, say, a hard-boiled egg on top of a green salad with fresh smoked salmon. Your best bet is to keep eggs as part of a low glycemic meal, without refined carbohydrates and sugars that will likely raise glucose and insulin. - **Choose your cooking method wisely.
**Frying an egg in oil affects the health of that meal. Avoid processed seed oils like canola or safflower oils, which have damaging linoleic acids, and favor minimally processed oils like olive oil, coconut oil, or avocado oil. If you use animal fats like butter or lard, try to use products from grass-fed butter and pasture-raised animals. - **Go for poached or soft boiled.
**Some research suggests that cooking the egg whites while leaving the yolk essentially raw preserves the most nutritional value while still allowing the cooking process to increase the bioavailability of its proteins and kill any pathogenic bacteria. - **Buy quality.
**Pasture-raised hens produce higher-quality, more nutritious eggs and support more sustainable farming and environmental practices.
Four Key Things We Get from Eggs
Cholesterol
Among common foods, egg yolks have one of the highest dietary cholesterol contents ––about 186 milligrams in an average large egg. Nutritional guidelines proposed by the American Heart Association in the 1960s advised people to limit consumption of eggs because of their high cholesterol content, but newer research consistently shows that moderate egg consumption alone does not increase a person’s risk of obesity or heart disease. Instead, a person’s overall diet appears to have a much greater effect.
That’s because it turns out cholesterol is complicated. So-called “good” high-density lipoprotein (HDL) cholesterol at high levels in the blood is linked to a lower risk of heart disease and stroke. In contrast, elevated “bad” low-density lipoprotein (LDL) cholesterol is associated with an increased risk of those conditions. But many now argue that it is much more complicated than that and that the size of LDL particles matters more for cardiovascular risk than their absolute concentration in the blood. Smaller-sized LDL particles (sdLDL) are more dangerous for cardiovascular disease than large particles and are promoted more by foods with refined carbohydrates, not higher fat foods like eggs.
Similarly, cholesterol ratios like triglycerides-to-HDL have been shown to potentially be a better gauge of health risk than LDL cholesterol levels alone. On top of that, only about 25% of blood cholesterol is tied to diet, and the liver and intestines synthesize the rest. It’s also important to remember that though cholesterol is often vilified, the body needs it to build cell membranes and produce vitamin D, testosterone and estrogen, and bile acids.
The old dietary recommendations were based on the now outdated but still oft-heard idea that eating large amounts of dietary cholesterol led to high LDL cholesterol levels in the blood, thus increasing the risk of developing heart disease.
So what does that mean for eggs? In 2015, the U.S. Department of Health and Human Services updated the Dietary Guidelines for Americans to eliminate the previous recommendation to limit consumption of dietary cholesterol to 300 mg per day and included eggs as part of its recommended healthy eating patterns. (Note that the updated guidelines also point out that people should still consume as little dietary cholesterol as possible, partly because foods with high levels of dietary cholesterol also tend to have higher levels of saturated fat, which the guidelines still suggest minimizing.)
In other words, for most people, cholesterol is not a reason to avoid eggs.
Micronutrients
Although macronutrients like carbohydrates, fats, and proteins dominate nutrition discussions, micronutrients, including vitamins and minerals, are essential to metabolic function (more on that here). When it comes to micronutrients, eggs are one of the most diverse foods.
Eggs are incredibly rich in vitamins. A single egg contains every vitamin except vitamin C, though these nutrients are distributed differently between the yolk and the white.
Yolks include high amounts of vitamin A, D, E, K, B1, B2, B5, B6, B9, and B12. Significant amounts of vitamins B1, B2, B3, B5, B6, B8, B9, and B12 are concentrated in egg whites. Eating two eggs can provide 10–30% of the daily recommended amount of many of these vitamins. However, the amount of liposoluble vitamins (those that dissolve in fat) an egg contains—vitamins A, D, E, and K—depends significantly on a hen’s diet. [More on that below.]
Eggs contain high amounts of phosphorus, calcium, and potassium and carry all of the essential trace elements, including copper, iron, magnesium, manganese, selenium, and zinc. Like liposoluble vitamins, the amount of selenium and iodine in an egg is heavily influenced by what a hen eats.
Choline
Eggs are the second-best source, after beef liver, of choline, a water-soluble nutrient often associated with the family of B vitamins. A single hard-boiled egg contains 27% of the recommended daily intake of the nutrient. All living cells need it for structural integrity. It is a source of methyl groups (molecules that contain one carbon atom bonded to three hydrogen atoms), which we require for multiple steps in cellular metabolism. Choline deficiency, though rare among healthy non-pregnant Americans, has been linked to muscle and liver damage as well as nonalcoholic fatty liver disease.
A 2020 study investigating the existence of a link between egg consumption and diabetes hypothesized that choline might be involved. The study of more than 8,500 people living in China found that eating eggs was associated with higher fasting glucose, and therefore higher risk for Type 2 diabetes. The authors suggested that an inflammatory response to choline found in egg yolks may be partially to blame. However, the people in the study who ate the most eggs were also less active, consumed more fat and protein, and had higher serum cholesterol levels than those who ate the least. The authors noted that the overall diet, shifting from a vegetable-heavy Chinese diet to Western cuisine, likely contributed to the association.
Protein
Eggs are mostly water (about 76%), but after that, the most abundant substance is protein. After breast milk, eggs are the best source of high-quality protein for humans.
Roughly 12.6% of an egg is protein, and the egg yolk has about 5% more protein by weight than an egg white. In egg whites, which contain around 150 proteins, the most abundant is ovalbumin (54% of the total).
The recommended dietary allowance for protein is 0.8 grams per kilogram of body weight (that’s about 56 g for the average 70 kg—or 154 lb—human), and a single large egg can provide up to 6.3 grams. In addition to helping maintain muscle mass and bone health, eating protein-rich foods like eggs helps people feel fuller for longer, partly because protein intake is associated with the release of hormones linked to satiety like GLP-1 and peptide YY (PYY). Of all the macronutrients, protein also causes the most significant rise in the thermic effect of food, or diet-induced thermogenesis (DIT), the amount of extra energy the body spends to process certain foods, which may also increase satiety. Protein can raise DIT by 30%, compared to 10% for carbohydrates and 3% for fat.
How Eggs Impact Metabolic Health
Eggs and Cardiovascular Disease
For years, nutrition recommendations flip-flopped on eggs and cardiovascular disease, mainly because eggs are high in dietary cholesterol. But the most recent epidemiological research favors the idea that eggs alone are not bad for heart health.
A 2020 study of more than 37,000 Americans over a median of 7.8 years looked at the health impacts of egg consumption and total cholesterol intake. An earlier meta-analysis of 17 studies found that dietary cholesterol had only a modest association with LDL cholesterol and total blood cholesterol. However, in the new study, people who ate more dietary cholesterol tended to eat more saturated fat and sodium. Not only was the number of eggs a person consumed daily not linked to high cholesterol, but the researchers also found that eating eggs was not associated with all-cause and heart disease mortality. And though high total dietary cholesterol was associated with all-cause mortality, many factors other than eggs appear to play a role.
In a 2019 study of more than 29,600 American adults over a median of 17.5 years, initial analyses appeared to suggest a less favorable view of eggs. They found that consuming higher amounts of dietary cholesterol or eggs was each modestly associated with higher risk of cardiovascular disease and all-cause mortality. That risk increased with the number of eggs a person ate each day. But the adjusted data told a different story: The association between egg consumption and cardiovascular disease was no longer significant after the researchers considered total dietary cholesterol intake. This suggests that overall diet had more effect on cardiovascular disease and mortality risk than daily egg intake alone.
The authors of a 2020 meta-analysis of three large cohorts from the U.S., along with 27 other studies from Europe and Asia, reached a similar conclusion. The analysis, which included more than 1.7 million participants, showed that eating at least one egg per day was not associated with an increased risk of cardiovascular disease in the European and U.S. studies. In the Asian cohorts, this level of egg consumption was associated with potentially lower cardiovascular disease risk, which the authors noted is likely due to differences in local cuisine. People with high egg intake in the cohort from China consumed fewer eggs (0.76, on average) than people with high egg intake in the European and U.S. cohorts. Also, in Western countries, eggs are typically eaten with red and processed meats (like bacon or sausage) and refined grains (white bread), whereas in Asia, they’re incorporated into many different dishes.
Finally, another 2020 meta-analysis on eggs and cardiovascular health, which included 23 studies on almost 1.5 million people, found that eating more than one egg per day did not increase a person’s risk of cardiovascular disease. It was also associated with a significant risk reduction of coronary artery disease compared with people who ate one or no eggs daily. As one explanation for this finding, the researchers pointed to previous research showing that eggs boost absorption of carotenoids (a type of antioxidant), which have been shown to reduce cardiovascular risk by lowering blood pressure and reducing inflammation. Past studies also showed that certain compounds in eggs might improve HDL cholesterol.
The takeaway: What these studies all suggest is that older findings about eggs and heart health likely missed the point: eggs alone don’t negatively affect heart health, but a Western diet high in processed foods and saturated fat does. In addition, the large amounts of sugar and carbohydrates commonly found in the Western diet raise insulin levels, which also contributes to cardiovascular health risks.
Do Eggs Cause Other Health Problems?
Eggs and Obesity
Research on a link between egg consumption and obesity is scarce. One reason may be that eggs promote satiety through their high protein and relatively low-calorie content (when boiled, not fried), and as such, are commonly viewed as a helpful food for weight loss. In a 2019 systematic review of literature linking certain foods with weight gain, researchers found only one study that evaluated the impact of egg consumption on abdominal obesity. The 2016 study, which included almost 2,000 people 40 years or older in rural South Korea, found that people who ate more eggs had lower rates of obesity. But when researchers tracked the health of participants for the next roughly three years, this association disappeared.
The takeaway: There’s not enough evidence to draw a conclusion about eggs and obesity.
Eggs and Other Metabolic Disorders
Research on the metabolic effects of eggs has been mixed, with no solid and high-quality studies demonstrating that eggs increase or decrease diabetes risk. The research on either side has also thus far failed to identify a robust physiological mechanism for its findings. Instead, a common theme is that the more extensive diet of the studied population may be influencing these associations.
On the “eggs increase metabolic risk” side:
- A 2020 study based on surveys of Chinese adults suggested that people who ate one egg per day had a 60% increased risk of diabetes compared to those who ate a quarter egg per day on average. To explain why the authors suggest that choline in the yolks may spur inflammation or that egg white hydrolysate could be interfering with glucose metabolism. But they also note that Chinese diets changed considerably—from a traditional diet rich in grains and vegetables toward one with more meat, oil, and snacks—during the study period (1991-2009) and that other study findings seem correlated to that larger dietary context.
- A 2016 meta-analysis of studies from around the world showed that the association between egg intake and increased risk of diabetes was strongest in the U.S. Since there is no robust biological explanation for this link, the authors noted, habits associated with American egg-eating—including smoking, lower physical activity, and higher red meat consumption—may partially explain the findings.
On the “eggs decrease metabolic risk” side:
- One small randomized controlled trial in humans from 2018 showed that eating one egg a day significantly lowered insulin resistance in overweight and obese people with Type 2 diabetes or prediabetes. To explain this finding, the authors pointed to previous research on egg’s potential to stave off hunger, suggesting that people who ate one egg a day and had lower insulin resistance may have been eating less overall. The researchers also noted that people who ate an egg a day didn’t have any significant change in their total or LDL cholesterol levels after 12 weeks.
- In a review published the same year, researchers in Denmark argued that observational studies linking egg eating and diabetes risk are likely driven by dietary patterns associated with high egg intake as well as physical activity levels and genetics. People can eat an egg a day, they wrote, but those who already have diabetes or cardiovascular disease should maintain a healthy lifestyle if they do so.
Finally, as with many nutritional studies around controversial topics, it’s essential to pay attention to any potential biases, such as the source of funding (say, an egg industry group or cholesterol-lowering drug manufacturer). In a 2017 review of randomized controlled trials, researchers concluded that eating 6 to 12 eggs per week did not have an adverse effect on cardiovascular disease risk factors in people with prediabetes or diabetes. Still, they also noted that they and some of the studies they analyzed had these conflicts of interest.
The takeaway: Potential metabolic consequences are probably not a reason to avoid eggs. The more critical factor to consider is how eggs fit into your overall dietary pattern and lifestyle. Eggs eaten in the context of a sedentary lifestyle, a Western diet high in processed foods, and smoking will likely have different health impacts than those eaten as part of a balanced diet and active, nonsmoking lifestyle.
What Affects the Nutritional Value of Eggs
A Chicken’s Diet
Research shows that a hen’s diet influences the nutritional composition of her eggs. While the amount of lipids and protein in eggs of the same size more or less stays the same no matter what a hen eats, the fatty acid profile of the yolk and the egg’s trace mineral and micronutrient content vary considerably with the hen’s diet. For example, one review of micronutrients in eggs states that selenium content in eggs can increase as much as six-fold with a selenium-rich hen diet from fortified commercial feed.
The types of triglycerides and phospholipids in an egg also depend on the types of fatty acids in a hen’s feed. For example, if a hen’s diet is high in monounsaturated fatty acids, her eggs will be, too. The same is true for unsaturated omega-6 fatty acids, which some recent research suggests are beneficial for the heart. However, other research indicates that the balance of omega-6 fats and omega-3 fats in the body is an essential indicator for cardiovascular health.
> “‘Eggs are actually a superfood. The yolk is the most nutritious part—low in calories, high in protein, and full of vitamins, minerals, antioxidants, choline, and phytonutrients.’”
Pasture-raised eggs are those from hens who are free to roam and eat from outdoor fields. One 2010 study compared pasture-raised eggs with those from caged hens. The pasture-raised hens also ate commercial feed, but the caged hens ate only commercial feed.
Compared to caged eggs, pasture-raised eggs had double the amount of vitamin E and long-chain omega-3 fats, 2.5 times more total omega-3 fatty acids, and less than half the ratio of omega-6 to omega-3 fatty acids. (The study also compared pasture-raised hens who foraged grasses versus those who foraged clover and found the grass-fed eggs had 23% more vitamin E than the clover group.)
It’s usually challenging to determine what’s in a hen’s feed by reading an egg carton. If you’re able to buy pasture-raised eggs from a local farmer, you may have better luck determining the total nutritional value of your eggs based on the types of plants that grow in their pasture and which additional nutrients their supplemental feed contains.
Cooking Methods
Naturally, an egg fried in butter or oil delivers different nutrients (and calories) than a boiled egg. But how one cooks an egg––including whether an egg is consumed cooked or raw––also appears to impact the bioavailability of the egg’s protein, calcium, and some vitamins, including A, D, and E.
Hard-boiling eggs, in particular, may decrease the amount of bioavailable polyunsaturated fatty acids, selenium, and vitamin A. While the amount of protein an egg contains doesn’t change when it’s cooked, the proteins themselves undergo significant conformational changes, which in some cases make them easier to digest. Though some lab studies have shown that cooking makes proteins in egg whites more digestible and may also reveal potential new bioactive peptides, including antioxidants, we don’t know whether these findings transfer to real-world eating.
A meta-analysis of the literature on egg nutrition concluded that cooking egg whites while leaving the yolks mostly raw (i.e., poaching or soft-boiling) yielded the best nutritional value for eggs. Allowing the cooking process to act only on proteins in the egg whites may make them more bioavailable (and inactivate any pathogenic bacteria) while allowing the yolk’s vitamins, lipids, and micronutrients to remain relatively intact.
Are Eggs Good For You? What Our Experts Say
Dr. Mark Hyman, Levels advisor, and functional medicine pioneer, describes the health benefits of eating eggs in the context of the low-starch, low-glycemic diet in his book The Pegan Diet:
> What about eggs? The main concern here is cholesterol, but the misinformation on the effects of dietary cholesterol is finally coming to the surface. We now understand that some of the foods we were told to avoid for years are among the most beneficial. Eggs are actually a superfood. The yolk is the most nutritious part—low in calories, high in protein, and full of vitamins, minerals, antioxidants, choline, and phytonutrients (yes, the yolk has carotenoids like lutein). After all, egg yolks contain all the nutrients needed for creating a whole new life. Ditch those egg white omelets. Whole egg omelets taste better anyway! There is one caveat: Some people are sensitive to eggs. If you have an autoimmune condition or suspect an egg sensitivity, eliminate eggs for three weeks. Add them back in on day 22 and see how your body responds. You might need to stay off eggs for a few months or more.
Dr. Molly Maloof, Levels advisor and physician:
> While there are conflicting studies about the impact of eggs on metabolic health, evidence suggests that in the context of an otherwise healthy diet, eating an egg a day seems to be the healthiest choice.
Dr. Frank Lipman, leading functional-medicine physician:
> Yes, it’s okay to eat the whole egg: whites and yolks, as each delivers unique nutrients; the yolk is an excellent source of choline, which many people are deficient in. Use eggs to help you break out of your breakfast routine by adding one to a plate of leftovers or topping a breakfast salad.
