Which came first — the egg or controversy about its healthfulness? Few foods in Western culture have come under such scrutiny. One day, nutritionists are saying they’re healthy, and the next they’re saying they’re terrible.

The controversy mostly comes down to the cholesterol in eggs, about which the research is mixed. The American Heart Association recommends healthy adults consume no more than 300 milligrams of cholesterol per day. One large egg has 186 mg of cholesterol and a small one has 141 mg, according to the USDA. But in recent years, scientists have begun to question if the cholesterol in eggs is as bad for you as previously thought. For example, a 2013 meta-analysis published in journal BMJ found that eating one egg per day was not associated with increased risk of heart attack or stroke among healthy people.

Aside from the cholesterol question, eggs are an extremely healthy food. “Eggs are an excellent source of choline . . . and a good source of high-quality protein, vitamin B12, phosphorus and riboflavin,” said Dr. Mitch Kanter, executive director of the Egg Nutrition Center, the research arm of the American Egg Board.

Every single B vitamin is found in eggs, as is a complete range of amino acids, making eggs a complete protein. “High-quality protein helps build muscles and allows people to feel full longer and stay energized, which can help them maintain a healthy weight,” Kanter said.

Eggs are a good source of several minerals that can be hard to get in other foods, such as iodine and selenium. “Eggs are also one of the few foods that are naturally a good source of vitamin D., which helps build strong bones with the help of calcium,” Kanter said. But, he added, eating only egg whites doesn’t give you all the good stuff. “Nutrients found exclusively in the yolk include choline, vitamin B12, vitamin D and iron among others,” he said. Many nutritionists believe that, for healthy people, eggs’ excellent nutrition profile mitigates its cholesterol content.

For as many nutrients as they have, eggs are a relatively low-calorie food. There are just 71 calories in a large egg. There are no carbohydrates or sugars, and only 5 grams of fat (7 percent of your daily recommended intake).

Here are the nutrition facts for eggs, according to the U.S. Food and Drug Administration, which regulates food labeling through the Nutritional Labeling and Education Act:

Nutrition Facts Egg, whole, raw, fresh Serving size: 1 large (50 g) Calories 71 Calories from Fat 45 *Percent Daily Values (%DV) are based on a 2,000 calorie diet. Amt per Serving %DV* Amt per Serving %DV* Total Fat 5g 8% Total Carbohydrate 0g 0% Cholesterol 211mg 70% Dietary Fiber 0g 0% Sodium 70mg 3% Sugars 0g Protein 6g Vitamin A 5% Calcium 3% Vitamin C 0% Iron 5%

“According to the 2015 Dietary Guidelines Advisory Committee report, including eggs at breakfast helps make it the most nutrient-dense of Americans’ eating occasions,” Kanter said. “Eggs can also be a healthy option at other meals, as well as snacks, which are often poor in vitamin and mineral content . . . Because eggs are low in calories and saturated fat, they can serve as a perfect pairing for consuming other nutrient-dense foods — especially those lacking in Americans’ diets, such as fruits, vegetables and whole grains.”

The cholesterol question

At the turn of the 20th century, a scientist named Nikolai Anichkov fed rabbits a diet of pure cholesterol. Their arteries clogged, and the concept that cholesterol causes heart disease was born. Later, in the 1950s, Ancel Keys published a well-known study that concluded that people from cultures that ate the most animal fat were most likely to develop heart disease (his analysis has since been called into question). These two studies proved highly influential and the presupposition that cholesterol and animal fat are bad for the heart became the basis for the American Heart Association’s recommendation that you should not consume more than 300 mg of cholesterol per day. Since a whole small egg contains 47 percent of the daily cholesterol allowance and a large egg contains 62 percent of it, it’s no wonder they’re often considered bad for your heart.

An article in Today’s Dietitian listed eating eggs with abandon as one of the most common heart-health related myths that nutritionists need to expel. Some researchers who are skeptical of eggs point to a 1984 study in the Lancet, in which Harvard researchers had 17 lactovegetarian students add a jumbo egg to their diet for three weeks. This increased their daily cholesterol intake from 97 to 418 mg, and after three weeks their LDL (bad) cholesterol levels had risen 12 percent. Their blood cholesterol levels had also increased. A more recent study, published in 2006 in The Journal of Nutrition, found that eating whole eggs increased LDL and blood cholesterol levels. In the study, a group of young Brazilian men were fed three egg whites per day while another group was fed three whole eggs per day. The rest of their diets were the same, and rather healthful, consisting mainly of fruits, vegetables, chicken, fish and beans. Those who ate whole eggs saw their LDL cholesterol rise more than 30 percent, compared to those who ate the egg whites.

In more recent years, however, whole eggs have made something of a comeback. A 2008 study published in the Upsala Journal of Medical Sciences looked at a group of 19 middle-age, healthy participants who ate a whole egg every day for one month. Researchers found no difference in the participants' cholesterol levels at all.

While the findings on eggs’ ability to raise cholesterol are mixed, a stronger case for eggs comes down to the impact of cholesterol from food on the individual body.

According to the Harvard School of Public Health, “A solid body of research shows that for most people, cholesterol in food has a much smaller effect on blood levels of total cholesterol and harmful LDL cholesterol than does the mix of fats in the diet.” The importance of individual health came up again in an article published in Clinical Opinion in Clinical Nutrition and Metabolic Care, which looked at egg consumption in healthy populations and concluded that, while eggs may increase LDL cholesterol, there is no clearly established link between that and increased risk of heart disease.

A large-scale study of 37,851 middle-age to elderly men and 80,082 middle-age women published in JAMA found “no evidence of an overall significant association between egg consumption and risk of CHD [coronary heart disease] or stroke in either men or women.” The study, which followed participants for 14 years, concluded that eating one egg per day was likely fine for healthy adults. A Circulation study — widely known as the Physicians’ Health Study — looking at egg consumption and heart failure over a 20-year period led to similar conclusions, and suggested that eating six eggs per week did not increase the risk of heart failure.

In fact, a 2013 study published in the journal Lipids showed that eating whole eggs actually increased levels of HDL (good) cholesterol, and allowed the HDL molecules to function more effectively. HDL cholesterol encourages removal of LDL (bad) cholesterol, so the more of it you have, the better, according to the Mayo Clinic. A 2010 article in the Journal of Nutritional Biochemistry produced similar findings, plus noted that the increased HDL levels in the egg-eating participants helped increase the participants’ lutein and zeaxanthin levels. Lutein and zeaxanthin are valuable nutrients that are especially good for your eyes.

Thanks to all these studies and more, in February of 2015 the U.S. government's Dietary Guidelines Advisory Committee eased the longstanding recommendations for cholesterol. (The advisory committee’s report is sent to the Department of Health and Human Services and the Department of Agriculture, who actually issue guidelines for Americans every five years.) “For many years, the cholesterol recommendation has been carried forward, but the data just doesn’t support it,” Alice H. Lichtenstein told The New York Times. People such as those in the Brazilian study and the 1984 Harvard study are now understood as hyper-responders — people who have a greater increase in blood cholesterol when they eat eggs. However, hyper-responders are not representative of the larger population. According to a Nutrition & Metabolism article, about one-third of the population are hyper-responders, but even for them, eggs might not be all bad. It turns out that their increased cholesterol from eggs tends to be large LDL cholesterol, which is considered benign (unlike small LDL cholesterol).

Considering all the conflicting research around eggs, the Mayo Clinic asserts that it is probably fine to eat about six or seven whole eggs per week if you are healthy. In a 2013 column for Live Science, nutritionist Katherine Tallmadge suggested that it’s probably fine to eat an egg a day if you don’t eat a lot of other saturated fats.

Diabetes concerns

The case is likely different for people with diabetes. The Mayo Clinic states that diabetics who eat seven eggs per week “significantly” increase their risk of heart disease. A 2010 analysis published in the Canadian Journal of Cardiology stated that participants in the Physicians’ Health Study who became diabetic during the course of the 20-year study were twice as likely to develop cardiovascular disease if they ate one egg per day.

Health benefits

Protein

Whole eggs are a complete protein, meaning they contain all the necessary amino acids. They’re so good for you, in fact, that the World Health Organization uses egg protein as a standard for evaluating protein in other foods.

“Eggs are all-natural and provide one of the highest quality proteins of any food available,” Kanter said. “One egg provides more than six grams of protein, or 13 percent of the recommended Daily Value (DV), and nearly half is found in the yolk.”

Protein is good for you for myriad reasons, ranging from weight loss to heart health. “Although we often think of protein’s function in building and maintaining muscle, newer research suggests other benefits of protein,” Kanter said. “For example, numerous studies since 2010 have found that protein-rich breakfasts, including those containing eggs, result in blunted postprandial glucose and insulin responses, greater satiety and lower energy intake at a subsequent meal, suggesting a positive role of eggs for hunger and weight management.” One study published in the American Journal of Clinical Nutrition looked at protein-rich breakfasts in overweight or obese adolescent girls and found that high-protein breakfasts were associated with less evening snacking, as well as positive changes in “appetitive, hormonal and neural signals that control food intake regulation.”

“Additionally,” Kanter continued, “diets higher in protein have been linked with lower risk of developing hypertension.” Recently, the American Journal of Hypertension published a study that had followed middle-age adults for more than 11 years. It found that greater consumption of protein was associated with lower long-term risks of high blood pressure.

Furthermore, in an animal study announced by the American Chemical Society, scientists at Clemson University discovered that a peptide called RVPSL (a component of protein) found in egg whites “reduces blood pressure about as much as a low dose of Captopril, a high-blood-pressure drug.” It blocks angiotensin-converting enzymes, which are produced by the body and increase blood pressure.

Eyesight

“Lutein and zeaxanthin are two antioxidants found in egg yolks that may help prevent macular degeneration, a leading cause of age-related blindness,” Kanter said. “The two nutrients are part of the carotenoid family (like beta-carotene in carrots).” The American Optometric Association notes the presence of these anti-oxidants in eggs.

In a study published in The American Journal of Clinical Nutrition, 11 men and women supplemented their diets with 1.3 egg yolks per day for 4.5 weeks. Participants’ levels of lutein increased by 28-50 percent, and their levels of zeaxanthin increased by 114-142 percent.

Choline

“Eggs are one of the richest sources of choline in the diets of Americans,” Kanter said. One whole large egg can provide 35 percent of your daily choline needs — which is good news, because according to a study published in The Journal of the Federation of American Societies for Experimental Biology, 90 percent of Americans do not get enough of it.

“Choline is an essential nutrient that is particularly important for pregnant and breastfeeding women as it contributes to brain and memory development,” Kanter said. One animal study published in The American Journal of Clinical Nutrition emphasized the importance of choline on memory in infants. When rat pups were given choline supplements in utero or in the first two weeks of life, “their brain function changed, resulting in the lifelong memory enhancement.”

According to the University of Rochester Medical Center, research has shown that consuming choline during pregnancy and through lactation may increase a child’s immunity to stress-related illnesses and chronic issues, like hypertension, in the future. This is because increased amounts of choline changed the gene expressions for releasing cortisol — a hormone associated with stress-related and metabolic disorders — in the fetus.

Kanter added that choline “may help prevent neural tube birth defects.” One influential study published in the American Journal of Epidemiology looked at more than 800 mothers — about half of whom had had babies with neural tube birth defects — and found that women at or below the 25th percentile for choline intake had four times the risk of birthing a child with a neural tube defect compared to women in the 75th percentile. The findings extended to all neural tube defects, including spina bifida and anencephaly. Furthermore, an animal study published in Teratologyfound that pregnant mice whose choline was inhibited were much more likely to have offspring with neural tube and facial defects.

Fetuses want choline. A study published in 2013 in The American Journal of Clinical Nutrition demonstrated the demand for choline in pregnant women. Both third-trimester pregnant women and non-pregnant women were randomly assigned to increase their choline content by either 100 or 550 mg per day, and the pregnant women showed increased demand for choline, which was transferred to the fetus. Because fetuses consume so much choline (they need six to seven times as much as adults, according to an article in the Archives of Physiology and Biochemistry), pregnant or nursing mothers’ stores of it are quickly depleted.

Choline isn’t just good for babies. Recently, scientists have been looking at the possibility of adult brains benefitting from choline. A study published in the American Journal of Clinical Nutrition looked at 1,391 volunteers between the ages of 36 and 83 and found that increased dietary choline was associated with improved cognitive function, including visual and verbal memory. Additionally, a British Journal of Nutrition study of more than 2,000 adults in their 70s found positive associations between increased choline and better performances on cognitive tests of perception speed, cognition, sensory motor speed and executive function.

Research has shown that choline is imperative to maintaining healthy organ function in older adults, especially postmenopausal women. According to a study published in The American Journal of Clinical Nutrition, of 57 adults who were deprived of dietary choline, 77 percent of men and 80 percent of postmenopausal women developed signs of fatty liver of muscle damage. Only 44 percent of perimenopausal women developed these signs.

An overview of choline published in Nutrition Reviews noted that choline might also be helpful in preventing heart disease, inflammation and breast cancer.

Weight loss

A relatively low-calorie food, eggs can be an excellent option for dieters. “Because of their satiating properties (the ability to make you feel full longer), eating eggs for breakfast may promote a healthy body weight and reduce the risk for obesity,” Kanter said.

A study of 30 overweight or obese women published in the Journal of the American College of Nutrition found that those who ate egg-based breakfasts instead of bagel-based breakfasts ate less during lunch, for the remainder of the day and for the next 36 hours. A study published in the International Journal of Obesity also demonstrated the effectiveness of egg-based breakfasts on dieters. A group of overweight men and women were divided into four groups: those eating egg breakfasts and put on calorie-restricted diets, those eating egg breakfasts but on no diet, those eating bagel breakfasts and on calorie-restricted diets and those eating bagel breakfasts but on no diet. The only group that showed significant results was the group who ate eggs and was on a diet. Compared to the other groups, this group showed a 61 percent greater reduction in BMI, 65 percent more weight loss, 34 percent greater reduction in waist circumference, and 16 percent greater reduction in body fat. It’s also worth noting that no groups saw a difference in their cholesterol levels.

Risks of eating eggs

As previously mentioned, people with diabetes and possibly high cholesterol or hypertension should watch their egg intake. A Canadian Journal of Cardiology analysis showed that diabetics who ate one egg a day were more likely to develop cardiovascular disease. Eating egg whites instead of whole eggs may be a good option for diabetics.

The Harvard School of Public Health also notes that everyone should pay attention to the trimmings that come with eggs. Cheese, ham, bacon, white toast and other favorites can add lots of calories and saturated fats.

A study published in The American Journal of Clinical Nutrition in 2002 caused a stir when it found that raw egg whites interfere with absorption of biotin. Biotin is a B vitamin that is important to fat and sugar metabolism and blood sugar regulation, according to World’s Healthiest Foods. Egg whites contain a glycoprotein called avidin, which binds to biotin and makes it absorbable by the digestive tract. This problem is solved by cooking egg whites. In fact, whole eggs are actually a good source of biotin, with about 27 percent of your daily-recommended intake.

When raw, eggs can present a risk of infecting eaters with salmonella. The CDC recommends cooking all types of eggs until both the white and yolk are firm.

It is possible to have an egg allergy. According to the American College of Allergy, Asthma and Immunology, up to 2 percent of children develop egg allergies, though most outgrow it by age 16 or 17. Those with egg allergies may experience skin rashes or hives, trouble breathing or stomach pain after eating eggs. Anaphylactic shock can also occur, but is quite uncommon.

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