Science of Eggs: How to Hard Cook an Egg
Top 5 health benefits of eggs
Both the egg white and yolk are rich in nutrients, including proteins, vitamins and minerals. The yolk contains fat-soluble vitamins (such as vitamins D and E) and essential fatty acids; while most of the protein is found in the egg white.
Since the domestication of the chicken, people have been enjoying and nourishing themselves with eggs .
Interested in trying our FREE 7-day healthy diet plan? Click here and choose between our meat eaters, vegetarian or vegan meal plans.
Eggs are an important and versatile ingredient for cooking, and their particular chemical make-up is key to many important baking reactions. There are lots of different types of egg, the most common being chicken, while more gourmet choices might include duck, goose and quail.
Discover our full range of health benefit guides or, check out some of our best egg recipes, from our mushroom brunch to our egg and puy lentil salad with tamari and watercress.
Nutritional benefits of eggs
One medium chicken egg (boiled) contains:
84 kcal / 351 KJ
8.3g protein
5.7g fat
1.6g sat fat
18mcg folate
1.89mcg vit D
Top 5 health benefits of eggs
1. Highly nutritious
Whole eggs are nutritionally rich, supplying almost every nutrient you need. They are useful sources of some of the hard to get nutrients like vitamins D and B12 as well as the mineral iodine. Eggs are regarded as a ‘complete’ source of protein as they contain all nine essential amino acids, which we must obtain from our diet.
Furthermore, if you choose brands enriched with omega-3 fatty acids, due to the diet the chickens are fed, you’ll benefit from higher omega-3 fatty acids as well as fat soluble vitamins such as vitamins A and E.
2. May support heart health
Eggs are rich in several nutrients that promote heart health, such as betaine and choline. A study of nearly half a million people in China suggests that eating one egg a day may reduce the risk of heart disease and stroke, although experts stress that eggs need to be consumed as part of a healthy lifestyle in order to be beneficial.
3. Source of choline
Eggs are one of the best dietary sources of choline. This little talked about nutrient is needed by everyone of us for the formation of cell membranes and for brain function, including memory. It’s especially important during pregnancy and breast feeding, when an adequate supply of choline is essential for normal brain development.
4. May support eye health
As we age its normal for our vision to start to deteriorate but there are some useful nutrients, obtained from a balanced diet, which may help support eye health. Eggs are one example of an eye-friendly food. The yolk contains large amounts of carotenes, of particular note are lutein and zeaxanthin, which are important for preventing macular degeneration and cataracts. Eggs are also a source of vitamin A which is key for good eye sight.
5. May support weight management
Eggs are rich in protein, which is more filling than either fat or carbohydrate. As a food choice, eggs score well, being high on the satiety index, a measure of how filling a food is. In fact, studies show that an egg breakfast is more sustaining than the equivalent calorie counted carb breakfast and, what’s more, may help reduce your calorie intake later in the day.
Are eggs safe for everyone?
Salmonella food poisoning has been a concern, especially if eggs are eaten raw or undercooked. However, following changes in production protocols, the Food Standards Agency (FSA) has changed its guidelines.
Current recommendations confirm that infants, children, pregnant women and the elderly may safely eat raw or lightly cooked eggs as long as they are produced under the British Lion Code of Practice. Visit the FSA website for more information.
Another safety concern regarding eggs is that they are a common food allergen, particularly among young children. Although most children outgrow an egg allergy by the time they go to school, some cases do persist into later childhood and sometimes even adulthood.
More like this
See your GP if you have any concerns regarding allergies to eggs.
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This article was last reviewed on 31 August 2021 by Kerry Torrens.
Kerry Torrens BSc. (Hons) PgCert MBANT is a Registered Nutritionist with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.
Jo Lewin is a registered nutritionist (RNutr) with the Association for Nutrition with a specialism in public health. Follow her on Twitter @nutri_jo.
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What Is the Egg Diet?
At Verywell, we believe there is no one-size-fits-all approach to a healthy lifestyle. Successful eating plans need to be individualized and take the whole person into consideration. Prior to starting a new diet plan, consult with your health care provider or a registered dietitian, especially if you have an underlying health condition.
What Is the Egg Diet?
The egg diet is a weight loss program that requires you to build at least one meal each day around the traditional breakfast staple, the chicken egg. It is a low-calorie, low-carbohydrate, high-protein plan designed to help you lose weight quickly without losing muscle mass.
The egg diet is not a formal plan outlined in a book or available for sale. There are different versions of the egg diet, including an egg-only diet or a boiled egg diet. In all variations of the plan, you'll eat three meals a day with no snacks and drink only water or zero-calorie beverages. More flexible forms of the egg diet include foods like grilled chicken, fish, and steamed veggies but eliminate starchy foods and sugar.
What Experts Say "Eggs are little nuggets of nutrition, providing protein, choline, vitamin D, lutein and more, but the egg diet, on the whole, is low in carbs which can leave you hungry. Also, eating the same food over and over (like eggs for breakfast) can get boring for some, which can lead to non-compliance." —Kelly Plowe, MS, RD
The 7-Day Diet Plan
While there are many different versions of the diet, including egg-only diets, here is one example:
Day 1 : Boiled eggs, grapefruit, steamed asparagus; Baked fish, steamed broccoli; Poached chicken breast, steamed mushrooms and spinach.
: Boiled eggs, grapefruit, steamed asparagus; Baked fish, steamed broccoli; Poached chicken breast, steamed mushrooms and spinach. Day 2 : Poached eggs, steamed broccoli; Sirlion steak, steamed spinach and kale; Pork tenderloin, grilled asparagus.
: Poached eggs, steamed broccoli; Sirlion steak, steamed spinach and kale; Pork tenderloin, grilled asparagus. Day 3 : Lean ham, steamed kale; Boiled eggs, spinach, chopped mushrooms; Steamed fish, asparagus.
: Lean ham, steamed kale; Boiled eggs, spinach, chopped mushrooms; Steamed fish, asparagus. Day 4 : Boiled eggs, orange slices; Grilled turkey breast, steamed broccoli; Sirloin steak, grilled mushrooms, steamed kale.
: Boiled eggs, orange slices; Grilled turkey breast, steamed broccoli; Sirloin steak, grilled mushrooms, steamed kale. Day 5 : Mixed berries, lean ham, steamed asparagus; Baked sole, steamed spinach; Pork tenderloin, broccoli.
: Mixed berries, lean ham, steamed asparagus; Baked sole, steamed spinach; Pork tenderloin, broccoli. Day 6 : Poached eggs, steamed spinach, grapefruit; Baked chicken breast, steamed broccoli; Grilled turkey breast, steamed kale, mushrooms.
: Poached eggs, steamed spinach, grapefruit; Baked chicken breast, steamed broccoli; Grilled turkey breast, steamed kale, mushrooms. Day 7: Boiled eggs, berries; Tuna fish, spinach, asparagus; Poached chicken breast, steamed kale, mushrooms.
What You Can Eat
Since there is no one standard egg diet, what you eat will depend on the type you follow. In general, you can expect to eat many eggs, other lean proteins, vegetables, and some fruit. All versions of the egg diet require you to eat primarily egg-based meals. Besides the eggs, here are some examples of foods you might eat on various egg diets.
Lean Protein
Chicken
Fish
Sirloin steak
Lean cuts of pork
Vegetables
Fruit
Grapefruit
Other citrus fruits
Berries
What You Cannot Eat
What you cannot eat on the egg diet depends on the variation of the diet.
Fruit
In one variation of the diet, all fruit other than grapefruit is eliminated. In other variations, other fruits are acceptable.
Starches
Starchy carbohydrates from grains or vegetables are avoided in most versions of the egg diet.
Grains
Bread
Cereal
Pasta
Potatoes
Carrots
Squash
Corn
Non-Nutritive and Processed Foods
Alcohol
Sugar
Sugary foods and beverages
Processed meats
Fried foods
Juice
Dairy
Milk
Cheese
Yogurt
How to Prepare the Egg Diet & Tips
While eggs can be part of a healthy diet, a nutrition plan built almost exclusively on eggs is not. Some variations of the egg diet are better for you than others, but none of them provide balanced nutrition.
14-Day Egg Diet
If you choose this two-week version of the diet program, you’ll consume three meals daily. Snacks are not allowed, nor drink with calories. Each day, eat one meal with eggs. The remaining meals can be built around other sources of lean protein, such as chicken or fish.
You can add low-carbohydrate vegetables such as broccoli or spinach to supplement the protein on your plate. Citrus fruit is sometimes allowed. This diet is sometimes called the “boiled egg diet” and requires you to eat hard-boiled eggs rather than poached, scrambled, or fried eggs.
Egg and Grapefruit Diet
This is a variation of the 14-day egg diet and lasts for the same amount of time. On this version of the diet, you eat half a grapefruit at each meal with your egg or lean protein. No other fruit is allowed.
Egg-Only Diet
This version of the egg diet is a mono diet. Mono diets are extreme, unhealthy weight loss programs where you eat only a single food for an extended period. People on this program eat only hard-boiled eggs and water for two weeks.
As you might imagine, exercise is not recommended on this plan because of the extreme fatigue that you are likely to experience.
“Medical” Egg Diet
This version of the egg diet requires you to eat one egg and one piece of bread thrice daily. You can also eat as many fruits and vegetables as you like. Beverages allowed include water, black coffee, and other zero-calorie drinks. Eggs can be prepared any way you want as long as no calories are added. That means you can’t use butter or oil for cooking your egg.
Some followers believe that this version of the egg diet is used in medical settings to reduce a patient’s weight before surgery, but there is no evidence to support that rumor. While some bariatric physicians put their patients on diets before surgery, it is typically a liquid diet (including meal replacement shakes), and a physician or other medical expert supervises the program.
Keto Egg Diet
Ketogenic diets also called keto diets, require increasing fat intake to put your body into a state of ketosis. The most popular ratio promoted on the internet is one egg to one tablespoon of fat (cheese or butter). This version of the egg diet recommends eating eggs with butter and cheese to get your body to produce ketones.
Pros of the Egg Diet
The egg diet doesn't offer notable health benefits when compared to a more varied and sustainable eating plan. Fast weight loss (not typically a positive effect of a diet due to unsustainability) on the egg diet is more attributable to its low-calorie count than any particular effects of the diet.
Eggs are nutrient-dense : Eggs are a highly nutrient-dense food with plenty of vitamins, minerals, and bioavailable protein. However, this isn't enough to say the egg diet is healthy because of its low calories and reduced variety of foods.
: Eggs are a highly nutrient-dense food with plenty of vitamins, minerals, and bioavailable protein. However, this isn't enough to say the egg diet is healthy because of its low calories and reduced variety of foods. Eliminates processed foods: Although you never have to eliminate processed foods to eat a nutritious diet, the egg diet does take out foods that don't offer nutritive qualities to your eating plan. However, the egg diet is also very restrictive and doesn't offer balance in terms of food choice.
Cons of the Egg Diet
Eggs are a common food allergen, so anyone allergic to eggs should not attempt the egg diet. The limitations of the egg diet can pose risks to bone density, heart health, and digestion, especially if followed for an extended period.
May cause calcium deficiency : The egg diet doesn't provide adequate sources of calcium since dairy isn't included in the plan. Stricter versions of the egg diet don't include high-calcium veggies or fortified foods to help meet your needs. Adults require 1,000 to 1,300 milligrams of calcium per day. One large egg has about 24 milligrams of calcium. A cup of cooked greens or other non-starchy vegetables have under 100 milligrams per serving.
: The egg diet doesn't provide adequate sources of calcium since dairy isn't included in the plan. Stricter versions of the egg diet don't include high-calcium veggies or fortified foods to help meet your needs. Adults require 1,000 to 1,300 milligrams of calcium per day. One large egg has about 24 milligrams of calcium. A cup of cooked greens or other non-starchy vegetables have under 100 milligrams per serving. May reduce bone density : Not getting enough calcium can pose a health risk for individuals with low bone density, especially post-menopausal women who are generally at higher risk. Insufficient calcium intake may also play a role in developing cardiovascular disease and some cancers.
: Not getting enough calcium can pose a health risk for individuals with low bone density, especially post-menopausal women who are generally at higher risk. Insufficient calcium intake may also play a role in developing cardiovascular disease and some cancers. High in cholesterol : Dietary cholesterol and eggs don't have the bad reputation they once did. However, individuals with a high risk of heart disease are still advised to limit their intake to one egg per day.
: Dietary cholesterol and eggs don't have the bad reputation they once did. However, individuals with a high risk of heart disease are still advised to limit their intake to one egg per day. Low in calories : Eggs only have about 78 calories each, so you're unlikely to consume enough to meet your calorie needs each day (since the other foods allowed on the diet are low-calorie as well). You won't have the energy to maintain regular workouts to support your metabolism on such a restrictive plan.
: Eggs only have about 78 calories each, so you're unlikely to consume enough to meet your calorie needs each day (since the other foods allowed on the diet are low-calorie as well). You won't have the energy to maintain regular workouts to support your metabolism on such a restrictive plan. Low in fiber: Fiber is essential for healthy digestion and regularity. Like other animal products, eggs are naturally fiber-free. The Academy of Nutrition and Dietetics recommends at least 25 grams of fiber per day for women and 38 grams for men. Even if you're eating some fruits and vegetables on the egg diet, it would be virtually impossible to reach this level when eggs are your primary food. Beyond just the digestive system, fiber benefits individuals with diabetes and heart disease and helps support weight loss.
Is the Egg Diet a Healthy Choice for You?
Eggs are an excellent source of complete protein. They provide several beneficial vitamins and minerals, including choline and vitamin A. Compared to expensive diets that require special powders and supplements, the egg diet is a whole-food approach to weight loss. However, depending on how strictly you follow it, the egg diet is missing essential nutrients, like fiber.
Current dietary guidelines set forth by the U.S. Department of Agriculture include recommendations and tips for a healthy, balanced diet. The following nutrient-dense foods are recommended as part of a healthy diet:
Beans and legumes (all beans, lentils, peas)
Dairy products (reduced-fat milk, cheese, and yogurt, including fortified soy-based dairy alternatives)
Fruits, especially whole fruits (apples, berries, melon)
Grains, especially whole grains (quinoa, brown rice, oats)
Lean protein (chicken breast, fish, turkey breast, seafood)
Nuts and seeds (walnuts, almonds, sunflower seeds)
Oils (olive oil, avocado oil)
Vegetables of all types and dark, leafy greens (kale, spinach, broccoli, Swiss chard, green beans)
The egg diet does not provide well-rounded nutrition and does not meet USDA dietary guidelines. It is not considered a healthy, long-term diet.
If you're looking to lose weight, nutrition experts advise counting calories to meet your goals. The USDA recommends a reduction of 500 calories per day for weight loss. On a 2,000-calorie diet, that's around 1,500 calories per day, but this can vary based on age, sex, weight, and level of physical activity. If you're interested in determining your calorie guidelines, you can use a calculator.
Although eggs are nutritious, the egg diet doesn't have enough variety or calories to be considered a healthy or sustainable way of eating. With such restriction, weight regain is likely. You'll also miss out on fiber, calcium, and other essential nutrients by sticking to the egg diet for more than a few days.
A Word From Verywell
Although the promise of fast weight loss can be appealing, the egg diet is an overly restrictive fad diet that's unlikely to produce beneficial lasting results. Learning to practice healthy eating habits that include all the food groups will give you the flexibility and variety for building a positive relationship with food.
Remember, following a long-term or short-term diet may not be necessary for you and many diets out there simply don’t work, especially long-term. While we do not endorse fad diet trends or unsustainable weight loss methods, we present the facts so you can make an informed decision that works best for your nutritional needs, genetic blueprint, budget, and goals.
If your goal is weight loss, remember that losing weight isn’t necessarily the same as being your healthiest self, and there are many other ways to pursue health. Exercise, sleep, and other lifestyle factors also play a major role in your overall health. The best diet is always the one that is balanced and fits your lifestyle.
Science of Eggs: How to Hard Cook an Egg
You need an egg, a pot, some water—how complicated can it be? But when we asked members of the Exploratorium staff how to hard cook an egg, every person we asked gave us a slightly different answer.
Even a task as seemingly simple as hard cooking an egg involves making many choices. Here are a few—and the science behind them:
Add salt to the water?
Egg white solidifies more quickly in hot, salty water than it does in fresh. So a little salt in your water can minimize the mess if your egg springs a leak while cooking. The egg white solidifies when it hits the salt water, sealing up the crack so that the egg doesn’t shoot out a streamer of white.
To prick or not to prick?
Some people use a pin to make a small hole in the shell at the large end of the egg before they put the egg in the water. At the large end of each egg is a small air space. When you hard cook an egg, this air heats up, expands, and escapes through pores in the shell—but not before the egg white sets. This leaves the egg with a flattened end. Pricking the egg provides a quick escape route for the air, which gives you an egg with a smoothly rounded end. If you prick an egg, watch for a jet of air shooting from the hole as the egg cooks.
Scientists disagree on the other possible benefits of pricking an egg. Some say that piercing the eggshell with a pin lets water leak between the shell and the egg’s internal membrane, making for an egg that's easier to peel. Others claim that providing a quick way out for expanding gases makes the egg less likely to crack as it cooks, which may be particularly important for older eggs with larger air sacs. Still others say that poking a hole in the shell weakens it, making cracks more likely.
Hot water or cold?
Some people put their eggs in cold water; others heat the water to boiling, then drop in the egg. Both methods have advantages and disadvantages.
When you drop an egg in boiling water, you heat it up quickly. When you start with cold water, you heat it slowly. And the difference in heating makes a difference in the cooked egg white.
An egg white is about 10% protein and 90% water. It’s the proteins that cause the egg white to solidify when you cook it. Egg white proteins are long chains of amino acids. In a raw egg, these proteins are curled and folded to form a compact ball. Weak bonds between amino acids hold the proteins in this shape—until you turn up the heat. When heated, the weak bonds break and the protein unfolds. Then its amino acids form weak bonds with the amino acids of other proteins, a process called coagulation. The resulting network of proteins captures water, making a soft, digestible gel.
If you keep the heat turned up too high or too long when you cook an egg, the proteins in the egg white form more and more bonds, squeezing some of the water out of the protein network and making the egg white rubbery.
Starting with cold water lets you heat the egg more slowly, which keeps the whites from getting rubbery. But this method takes longer and gives you less control over the cooking time. (How long it takes the water to reach boiling depends on the size and shape of your pot, among other things.) Starting with boiling water offers more control over timing but this may cook the whites into a rubbery state. And it has another disadvantage: The egg is more likely to crack because the air in the egg has less time to escape as the egg heats up.
New egg or old?
The age of your egg affects your end result. Very fresh eggs tend to be more difficult to peel. The more acidic the egg’s contents are, the harder the egg is to peel. As an egg ages, carbon dioxide (which is a weak acid) leaks out through pores in the egg’s shell, making the egg white less acidic.
Cold-water plunge?
If you don’t plunge your egg into cold water when you take it off the heat, it goes on cooking . . . and cooking . . . and cooking. The longer you cook the egg, the more likely you are to end up with a rubbery white and a green yolk.
Why does the yolk turn green? The green-gray color (and the whiff of sulfur smell that often accompanies it) comes from the reaction of iron in the egg yolk and sulfur in the egg white. When heated, the two can combine to make green-gray ferrous sulfide and hydrogen sulfide gas. To avoid getting a green yolk, cook your eggs just long enough to reach the desired doneness—no more. And quickly plunge the cooked eggs into cold water to stop the cooking process and minimize the iron-sulfur reaction.
Some people also say that the cold-water plunge makes eggs easier to peel.
