huevo

Egg (Gallus gallus domesticus): A Comprehensive Reference on Nutritional Identity, Bioactive Constituents, and Scientific Evidence

1. Identity and Nomenclature

The hen's egg — the subject of this article — is produced by the domesticated chicken, Gallus gallus domesticus, a subspecies of the red junglefowl native to tropical and subtropical Southeast Asia and the Indian subcontinent. The term "egg" in the dietary and nutritional sciences almost universally refers to the hen's egg unless otherwise specified, though duck, quail, goose, and ostrich eggs are also consumed. In regulatory and nutritional databases, the hen's egg is classified as an animal-source food rather than a botanical ingredient, but it is widely employed as a whole-food dietary supplement, a source of isolated bioactive fractions (egg white protein, egg yolk phospholipids, eggshell membrane, and lecithin), and a vehicle for nutrient enrichment.

Common names: Egg, hen's egg, whole egg, egg white (albumen), egg yolk.

Taxonomic source: Gallus gallus domesticus (Linnaeus, 1758); Family Phasianidae.

Key chemical constituents (discussed in detail in Section 3) include ovalbumin, ovomucoid, ovotransferrin, lysozyme (egg white), phosphatidylcholine, lutein, zeaxanthin, cholesterol, vitamins A, D, E, K, B12, riboflavin, biotin, choline, selenium, iodine, and long-chain polyunsaturated fatty acids.

2. Common Forms and Preparations

Eggs contain ample essential proteins, fats, vitamins, minerals, and bioactive compounds, and their compositions and net amounts can be influenced by strain, age, hen diet, and environmental conditions. They are available in a range of commercial forms:

• Whole shell eggs: The primary food form, consumed boiled (hard or soft), fried, poached, scrambled, or incorporated into preparations.
• Dried/powdered egg white: A concentrated protein supplement used in sports nutrition and clinical nutrition. In studies using egg white as a protein supplement, liquid egg white is not typically used directly due to its unfavorable taste and flavor; therefore, dried egg white is likely to be used.
• Egg white hydrolysate (EWH): Enzymatically hydrolysed egg white protein, used in fatigue and exercise studies. The minimum effective dose of EWH to exert its antifatigue effect has been reported as 5 g.
• Egg yolk phospholipid supplements: Extracts standardised for phosphatidylcholine, used in cognitive-health formulations.
• Enriched/designer eggs: Eggs from hens fed diets supplemented with omega-3 fatty acids, lutein, or DHA, yielding eggs with elevated levels of these specific nutrients.
• Eggshell membrane: A byproduct used as a source of collagen, hyaluronic acid, and chondroitin for joint health formulations. Eggshells and eggshell membranes are currently unutilised by-products of chicken eggs that could be potential nutrient resources.

3. Traditional and Historical Use

The chicken was most likely domesticated for its eggs before 7500 BCE, from jungle fowl native to tropical and subtropical Southeast Asia and the Indian subcontinent. Chickens were brought to Sumer and Egypt by 1500 BCE, and arrived in Greece around 800 BCE, where the quail had been the primary source of eggs.

In Thebes, Egypt, the tomb of Haremhab, dating to approximately 1420 BCE, shows a depiction of a man carrying bowls of ostrich eggs and other large eggs, presumably those of the pelican, as offerings. The domestication of fowl, especially chicken, is thought to have started in China around 6000 BC.

In ancient Rome, eggs were easily obtained and recommended as wholesome food, being consumed hard- or soft-boiled, fried, and poached, and used as a binding agent in cookery. Hard-boiled eggs were regarded as a more substantial food. In ancient Rome, eggs were preserved using a number of methods and meals often started with an egg course. The ancient text De re coquinaria ("On the Subject of Cooking") by the Roman writer Apicius contains nearly 500 popular Roman recipes, including eggy custards, quiches, and omelettes.

Ancient Egyptian bakers used eggs to make breads, early African cultures mixed egg whites into recipes as a thickening agent, and the Romans were fond of turning eggs into tasty cakes and desserts.

The Babylonian Talmud, a Jewish work from late antiquity, states: "A soft-boiled egg is better than six logs of farina," reflecting an early cultural recognition of the egg's nutritive superiority.

A popular Easter tradition in some parts of the world is the decoration of hard-boiled eggs. A similar tradition of egg painting exists in areas of the world influenced by the culture of Persia. Before the spring equinox in the Persian New Year tradition (called Norouz), each family member decorates a hard-boiled egg and they are set together in a bowl.

Eggs have held a prominent place in culinary traditions around the world for centuries. They are often associated with fertility, renewal, and life in various cultures. From ancient Egypt, where they were buried with the dead, to their use in religious ceremonies, eggs symbolise creation and rebirth.

In traditional Chinese medicine and Ayurvedic systems, eggs were used as restorative foods for the elderly and convalescing individuals, though formal pharmacopeial monographs for eggs as a medicinal agent are absent from the major traditions. Their role was primarily nutritive — a concentrated, easily digested source of life-sustaining nutrients rather than a pharmaceutical agent.

4. Key Constituents and Active Compounds

4.1 Macronutrient Composition

According to the 2018 USDA National Nutrient Database, one large egg contains 6.3 g of protein distributed between the yolk and white portions (3.6 g in egg white and 2.7 g in egg yolk). A medium-sized boiled egg (50 g) contains 78 kcal energy, 6.29 g protein, 0.56 g carbohydrate, and 5.3 g total fat, of which 1.6 g is saturated, 2.0 g is monounsaturated, and 0.7 g is polyunsaturated.

The yolk makes up just over one-third of an egg. It provides three-fourths of the calories, all of the fat-soluble vitamins (A, D, E and K), and all of the choline, lutein, and zeaxanthin. The yolk also provides most of the phosphorus, iron, and folate and almost half of the protein and riboflavin. The white (albumen) provides more than half of the total protein and riboflavin.

4.2 Protein Quality and Amino Acid Profile

Egg protein is a remarkably abundant source of protein, with an amino acid score of 100 and the highest net protein utilisation rate. Eggs contain the highest quality protein and are often used as a standard to measure the quality of other protein sources. Eggs also have the highest biological value of any protein, meaning the essential amino acids they provide are used very efficiently by the body.

The protein quality of egg protein is second only to breast milk, and is the protein closest to breast milk in nature; almost 98% of egg protein can be absorbed effectively by the human body. One characteristic of egg white protein is that it contains approximately the same amount of branched-chain amino acids as milk protein.

The dominant egg white proteins are:

• Ovalbumin (Gal d 2): Ovalbumin is a globular phosphoglycoprotein and the most abundant protein in egg white (approximately 54%, w/w), with a molecular weight of 45 kDa.
• Ovotransferrin (Gal d 3): Approximately 12% of egg white protein; possesses antimicrobial and antioxidant properties.
• Ovomucoid (Gal d 1): Ovomucoid's structural characteristics — disulfide bonds, covalent binding with carbohydrate chains, and homology to trypsin inhibitors — may confer resistance to heat and digestive enzymes, allowing immunoreactive epitopes to remain intact after digestion; this is why ovomucoid is considered a major egg allergen.
• Lysozyme (Gal d 4): Approximately 3.5% of egg white protein; well-characterised antimicrobial enzyme.

4.3 Lipids and Phospholipids

Phospholipids are among the bioactive components of eggs. The yolk is particularly rich in phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and sphingomyelin. Egg yolk is a rich source of different choline-containing chemical forms, such as phosphatidylcholine (PC), lysophosphatidylcholine (LPC), and α-glycerophosphocholine (α-GPC). These phospholipids not only serve as structural membrane constituents but act as carriers for choline delivery across the blood-brain barrier. Since ethanolamine, a breakdown product of phosphatidylethanolamine, inhibits the passage of choline through the blood-brain barrier, choline intake as egg yolk phospholipids would be more effective for cognitive function. Moreover, since free choline is readily degraded to trimethylamine by intestinal bacteria in the upper small intestine before absorption compared with PC, administration of choline as phosphatidylcholine is recommended.

Eggs also contain a significant amount of cholesterol, a lipid molecule that has been associated with the development of cardiovascular diseases. One large egg contains approximately 186 mg of dietary cholesterol, located almost entirely in the yolk.

4.4 Carotenoids: Lutein and Zeaxanthin

The carotenoids lutein and zeaxanthin, which are found in eggs, are important in maintaining eye health. Though these nutrients are present only in small amounts in eggs, research shows they may be more bioavailable, or absorbed and utilised by the body, when obtained from egg yolk than from richer sources.

Lutein and zeaxanthin are the only dietary carotenoids that accumulate in the retina, specifically the macula, and are called macular pigments. As de novo synthesis of lutein within the human body is impossible, lutein can only be obtained from diet. It is a natural substance abundant in egg yolk and dark green leafy vegetables. The lipid matrix of egg yolk enhances the bioavailability of these xanthophylls substantially compared with vegetable sources.

4.5 Choline

Choline (approximately 150 mg per egg) is a precursor to acetylcholine, a neurotransmitter involved in memory and learning. Choline is recognised as an essential nutrient for health because of its many functions in growth and development, as well as neurological function and formation of membrane phospholipids, including phosphatidylcholine (PC) and sphingomyelin.

4.6 Vitamins and Minerals

Eggs provide an excellent source of vitamin B12, biotin (B7), iodine, selenium, and choline; a good source of high-quality protein, riboflavin (B2), and pantothenic acid (B5); as well as the carotenoids lutein and zeaxanthin (252 mcg), all for only 70 calories.

Potassium, calcium, iron, iodine, folate, vitamin D, and fibre are highlighted by the European Food Safety Authority (EFSA) as nutrients of concern for the European population. Of these, choline, vitamin D, folate, and iodine are provided by eggs in clinically useful quantities.

Eggs have been identified as the lowest-cost animal-sourced food for protein, vitamin A, iron, vitamin B12, riboflavin, and choline and the second-lowest-cost source for zinc and calcium.

4.7 Other Bioactive Compounds

In addition to covering fundamental functions for the maintenance of cellular structures and functions, the nutrients present in eggs show in vitro antioxidant, antimicrobial, antihypertensive, anti-inflammatory, and immunomodulatory functions, which could be fundamental in protecting against pathologies such as tumours or neurodegenerative diseases.

The essential amino acid tryptophan (approximately 77 mg per egg) crosses the blood-brain barrier for conversion to the neurotransmitter serotonin, which is involved in decision-making and memory.

5. Scientific Evidence by Area of Use

5.1 Protein Quality and Muscle Health

Background and mechanism: It is well established that eggs are one of the best dietary sources of high-quality protein, with all of the essential amino acids, and are recognised for their high biological value. Studies conducted on the characteristics of egg whites, as they are high in pure protein, have reported various health functions, such as increases in muscle mass and strength enhancement, lowering of cholesterol, and visceral fat reduction.

Egg white protein in female athletes (RCT): In an RCT in 30 healthy female collegiate athletes, participants were randomly divided into a protein group (15.0 g egg white protein; 75 kcal) and a carbohydrate group (17.5 g maltodextrin, 78 kcal). Supplements were administered daily in a double-blind manner prior to training during an 8-week period. Fat-free mass and 1RM assessments increased in both groups. Serum urea and serum citrulline levels after the 8-week regimen increased significantly only in the protein group. The findings indicated that compared to the carbohydrate supplement, the protein supplement was associated with some changes in protein metabolites but not with changes in body composition or muscle strength.

Whole egg vs. egg white during resistance training (RCT): A study published in the British Journal of Nutrition compared whole egg vs. egg white ingestion over 12 weeks of resistance training in resistance-trained men. Significant main effects of time were observed for body weight, skeletal muscle mass, fibroblast growth factor-2, and follistatin, which significantly increased, and for fat mass, TGF-β1, activin A, and myostatin, which significantly decreased in both whole egg and egg white groups. The consumption of eggs absent of yolk during chronic resistance training resulted in similar body composition and functional outcomes as whole egg of equal protein value. Egg white or whole egg may be used interchangeably for the dietary support of resistance-training-induced muscular hypertrophy when protein intake is maintained.

Systematic review and meta-analysis (2025/2026): A meta-analysis of 30 RCTs (n = 1,938) found that in dialysis patients, egg white supplementation significantly increased serum albumin (MD: +0.42 g/dL [95% CI: 0.12–0.72]; I² = 82.4%; four RCTs; GRADE: very low). However, longer-term exercise studies collectively suggest that egg white protein supplementation during resistance training does not consistently produce superior gains in muscle mass or strength compared with carbohydrate or control conditions. These findings are consistent with the broader protein supplementation literature, which suggests that protein timing and dose, rather than protein source per se, are the primary determinants of resistance training adaptations.

Evidence strength: Moderate for egg protein's equivalence to other high-quality proteins for supporting muscle protein synthesis. The superiority of egg protein over other complete proteins is not established in the clinical literature. The GRADE certainty for specific clinical end points in dialysis patients is rated very low due to heterogeneity.

5.2 Cognitive Function and Brain Health

Background and mechanism: Eggs are a widely consumed, nutrient-dense food containing choline, phospholipids, tryptophan, and omega-3 fatty acids, which individually support cognitive processes such as memory, attention, and neurogenesis. Choline, as a neurotransmitter acetylcholine precursor, is reportedly associated with cognitive function.

Egg yolk choline RCT (Japan): A 12-week, randomised, double-blind, placebo-controlled, parallel-group study was conducted in 41 middle-aged and elderly males and females (43.9% female) aged ≥ 60 years and ≤ 80 years without dementia. The choline group received a supplement containing egg yolk choline (300 mg/day), and the placebo group received an egg yolk supplement free from choline for 12 weeks. The results showed that there was a significant improvement in the choline group compared with the placebo group in verbal memory ability, a part of the cognitive function. The results suggested that continued 300 mg/day intake of egg yolk choline improved verbal memory, which is a part of cognitive functions. To confirm the observed effects of egg yolk choline, more well-designed and large-scale studies are warranted.

Observational evidence (systematic review, 2025): While individual nutrients in eggs have demonstrated benefits in supplementation studies, the cognitive effects of whole egg consumption are not well established. A systematic review aimed to evaluate the association between whole egg consumption and cognitive function in healthy adults. Dietary choline intake between 187–399 mg per day has consistently been associated with improved cognitive performance across healthy younger and older adults. Although these associations are observational and not always consistent across cognitive domains.

Previous studies revealed that phosphatidylcholine ingestion increases plasma free choline and brain acetylcholine levels. Conversely, low plasma free choline levels are associated with low cognitive function, suggesting that plasma free choline levels and cognitive function are closely related. Ingestion of egg yolk choline also increased plasma free choline levels, suggesting a contribution to the improvement of verbal memory.

Evidence strength: Preliminary to moderate. Evidence from a single small RCT suggests benefit of egg yolk choline (300 mg/day for 12 weeks) on verbal memory in older adults without dementia. Observational evidence is consistent but not definitive. Large-scale, long-term RCTs on whole egg consumption and cognitive outcomes are lacking.

5.3 Eye Health: Lutein, Zeaxanthin, and Age-Related Macular Degeneration

Background and mechanism: Only lutein and zeaxanthin are found in the human eye. Lutein, zeaxanthin, and meso-zeaxanthin accumulate in the retina of the eye and form the retinal macular pigment. It has been shown that supportive therapy with lutein and zeaxanthin can have a beneficial effect in delaying the progression of eye diseases such as age-related macular degeneration (AMD) and cataracts.

Enriched egg RCT (ALGOVUE trial): Ninety-nine healthy volunteers consumed either two standard eggs or two enriched eggs per day for 4 months. Macular pigment optical density (MPOD) was measured at baseline and at follow-up. A slight but significant increase in MPOD was observed for all study participants consuming two eggs per day for 4 months at all eccentricities tested (0.5°, 1°, 2°, and 4°).

12-egg/week AMD trial: In a clinical study examining patients with early AMD consuming 12 eggs per week for 1 year, results showed greater increases in serum lutein (52% vs. 6%) and zeaxanthin (83% vs. 0%) in the intervention compared to control from baseline to 12 months, however only serum zeaxanthin increased significantly.

6-egg/week intervention: Another study showed that consumption of six eggs per week significantly increased the concentration of macular carotenoids (as measured by MPOD) as well as serum zeaxanthin levels; however, serum lutein levels remained unchanged.

Bioavailability evidence: Eggs are a major dietary source of lutein and zeaxanthin, and are believed to possess the highest bioavailability to the pigments. Observational studies have reported that increased dietary intake and higher serum levels of lutein and zeaxanthin are associated with lower risk of age-related macular degeneration, especially late AMD.

Evidence strength: Moderate for raising serum and macular lutein/zeaxanthin levels through egg consumption. Clinical translation to AMD risk reduction specifically via dietary egg intake (as distinct from purified supplement use) requires further study. The AREDS2 evidence base relates to purified lutein/zeaxanthin supplements, not whole eggs.

5.4 Cardiovascular Disease (CVD) Risk

Background and historical context: Epidemiological data in the 1960s and 1970s relied on simple correlation analyses to show associations and did not account for collinearity of nutrients. Eventually, multivariate analysis of dietary lipids and CVD incidence documented that dietary cholesterol was not an independent risk factor. The 2015 US dietary guidelines finally took into consideration the epidemiological information and data from clinical interventions and eliminated an upper limit for dietary cholesterol.

Effects on lipid profiles (RCT meta-analysis): In a meta-analysis of 28 RCTs, high egg consumption increased total cholesterol, LDL, and HDL cholesterol, but not LDL-to-HDL or TC-to-HDL ratios or triglycerides compared with low egg control diets. Overall, current evidence from systematic reviews of randomised clinical trials indicates that higher egg intake may increase serum total cholesterol concentration and the ratio of low-density lipoprotein to high-density lipoprotein cholesterol, but with substantial heterogeneity in the response.

Observational evidence and cardiovascular outcomes: Recent evidence from observational studies does not provide strong support for a detrimental role of moderate egg consumption (up to one egg/day) on the risk of CVD, especially in European studies. The overall evidence from observational studies indicates that egg consumption is not associated with increased risk of mortality or T2D in European study populations.

Mortality meta-analysis (Circulation, 2022): A prospective analysis of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study with 482,316 person-years of follow-up identified 22,035 deaths. Greater dietary cholesterol and egg consumption were associated with increased risk of overall and CVD-related mortality. Hazard ratios for each additional 300 mg cholesterol intake per day were 1.10 and 1.13 for overall and CVD-related mortality, respectively; for each additional 50 g egg consumed daily, hazard ratios were 1.06 and 1.09, respectively, for overall and CVD-related mortality.

Dose-response meta-analysis (Frontiers in Nutrition, 2022): In a systematic review including 55 studies comprising 2,772,486 individuals: little evidence for elevated risks was seen for intakes below 0.5 egg/day or 250 mg/day of dietary cholesterol. The findings should be considered with caution because of small risk estimates and moderate between-study heterogeneity.

Diabetes interaction: The association between eggs and CVD was modified by type 2 diabetes mellitus status. Egg consumption was significantly associated with an increased risk for incident CVD among participants with T2DM; individuals with the highest egg intake (4.2 ± 0.04 eggs/week) had a 2.8 times higher incidence of CVD than those with the lowest egg intake. However, no association was observed among individuals without T2DM.

Umbrella review (2025): Evidence regarding egg consumption has critically low strength. No sufficient quality of evidence is available to discourage egg consumption. Due to the critically low strength of studies, insufficient evidence is available to discourage egg consumption, suggesting eggs can be part of a healthy diet.

Evidence strength: Mixed and controversial. RCTs demonstrate modest increases in total and LDL cholesterol at higher intakes, but the clinical significance with respect to CVD events is unclear. Observational data in European populations do not support an increased CVD risk with moderate egg consumption. Risk may be population-specific and modified by background diet and metabolic status, particularly type 2 diabetes.

5.5 Type 2 Diabetes Risk

Meta-analysis in US versus European populations: Findings in Swedish men do not support an association between egg consumption and risk of type 2 diabetes. In a meta-analysis, frequent egg consumption was associated with a higher risk of type 2 diabetes in US studies only. Egg consumption habits and associated overall dietary patterns may differ between populations and could potentially explain the discrepancies between reported results. Given the inconsistent results, this relationship warrants further study.

The overall evidence from observational studies indicates that egg consumption is not associated with increased risk of mortality or T2D in European study populations.

Evidence strength: Inconsistent. The association between egg consumption and type 2 diabetes risk appears to be population- and diet-dependent, with risk seen primarily in US-based prospective studies and not replicated in European cohorts. Confounding by overall dietary pattern is a recognised limitation across all studies.

5.6 Metabolic Health and Body Composition

Crossover RCT in young healthy adults: Eggs — particularly egg yolks — are a rich source of bioactive nutrients and dietary compounds that influence metabolic health, lipid metabolism, immune function, and hematopoiesis. A 16-week randomised, crossover intervention trial investigated the effects of consuming an egg-free diet, three egg whites per day, and three whole eggs per day for 4 weeks on comprehensive clinical metabolic, immune, and hematologic profiles in young, healthy adults (18–35 y; n = 26).

Average daily macro- and micronutrient intake significantly differed across egg diet periods, including greater intake of choline during the whole egg diet period, which corresponded to increased serum choline and betaine without altering trimethylamine N-oxide. Whole egg intake increased a subset of large HDL particles and decreased the total cholesterol:HDL-cholesterol ratio and percentage monocytes in female participants using combined oral contraceptive medication.

Evidence strength: Preliminary. The crossover design and small sample size limit generalisability. Findings on HDL subfractions and TMAO require replication in larger, longer studies.

5.7 Child Growth and Development

Meta-analysis of intervention trials in children: Seven studies reporting on nine unique interventions in 3,575 male and female participants were included. Participants in the intervention groups experienced significantly greater increases in height/length (by 0.47 [0.13, 0.80] cm, p < 0.01) and weight (by 0.07 [0.01, 0.13] kg, p = 0.03) when compared to those in the control groups. Eggs are an affordable, nutritious option for improving growth in children, though more studies with longer interventions are warranted.

The potential of chicken eggs as a nutritionally complete protein and source of key micronutrients during the first 1,000 days post-conception has been progressively recognised across the globe, particularly in resource-poor settings.

Evidence strength: Moderate, with statistically significant effects on linear growth and weight gain in children demonstrated across multiple RCTs pooled in a meta-analysis. Generalisability may be limited to populations with baseline nutritional deficit.

5.8 Anti-Fatigue Effects

The minimum effective dose of egg white hydrolysate (EWH) to exert its antifatigue effect is 5 g. When athletes were continuously given 5 g of EWH (Peptifine®) per day for two weeks, the psychological fatigue was reduced when compared to the control. It was thus determined that EWH could be used effectively to improve the exercising capacity of humans, as it is a good source of protein and raw materials for muscles due to its amino acid composition, and it is quickly absorbed and improves physical fatigue through its antioxidant effects.

Evidence strength: Preliminary. Evidence is based on small human studies with specific hydrolysate preparations; generalisation to whole egg or standard egg white powder is not yet supported.

5.9 Cancer

There is little support for a role of egg consumption in cancer development, although a weak association with higher risk of certain cancers has been found in some studies, mainly case-control studies. No associations with cancer risk have been observed in European studies. Eggs have been recognised as functional foods due to the presence of bioactive components, which may play a role in the prevention of chronic and infectious diseases. The presence of antimicrobial, antioxidant, anti-cancer, and hypotensive properties are discussed in the literature.

Evidence strength: Weak and inconsistent. No causal evidence from intervention trials. Epidemiological associations are inconsistent across populations and largely confined to case-control designs with high susceptibility to recall and selection bias.

6. Body Systems and Health Areas Associated with Eggs

• Musculoskeletal system: Egg protein supports muscle protein synthesis and skeletal muscle maintenance; eggshell components provide calcium for bone density.
• Nervous system / cognitive function: Choline (precursor to acetylcholine), phosphatidylcholine (membrane integrity), tryptophan (serotonin precursor), and omega-3 fatty acids support neurological function and memory.
• Visual system: Lutein and zeaxanthin accumulate in the macula; dietary egg intake raises macular pigment optical density.
• Cardiovascular system: Egg intake has complex effects: modest LDL-raising from dietary cholesterol, but also HDL-raising and beneficial phospholipid effects; the net clinical effect is population- and dose-dependent.
• Immune system: Eggs are a rich source of bioactive nutrients and dietary compounds that influence immune function and hematopoiesis.
• Endocrine/metabolic system: Variable effects on insulin sensitivity and type 2 diabetes risk across populations; possible TMAO-mediated effects on cardiometabolic risk under investigation.
• Paediatric growth and development: Choline, an essential nutrient, is important for proper brain development in the fetus and newborn and may play a role in memory function throughout life and into old age.

7. Dosage Forms and Reported Dosages

The following dosages appear specifically in the cited clinical and research literature:

• Whole eggs, general consumption: Most intervention studies used between 1–3 whole eggs per day. Moderate egg consumption of up to one egg per day does not provide strong evidence for a detrimental role on CVD risk in European studies.
• Egg white hydrolysate (antifatigue): The minimum effective dose of EWH to exert its antifatigue effect is 5 g, administered daily for two weeks in the reported clinical study.
• Egg yolk choline (cognitive function): A dose of 300 mg egg yolk choline per day was used in a 12-week randomised, double-blind, placebo-controlled, parallel-group study in adults aged ≥ 60 to ≤ 80 years.
• Egg white protein (resistance exercise): A dose of 15.0 g egg white protein (75 kcal) per day was administered prior to exercise in an 8-week double-blind RCT in female athletes.
• Enriched eggs for macular outcomes: Two enriched or standard eggs per day for 4 months were consumed by participants in the ALGOVUE clinical trial.
• Eggs for child growth interventions: The meta-analysis included intervention studies spanning 3,575 children across seven studies; specific egg doses per day varied by study.
• Dietary choline intake associated with cognitive benefit: Dietary choline intake between 187–399 mg per day (equivalent to approximately two eggs) is associated with better cognitive function.

8. Safety Considerations and Interactions

8.1 Egg Allergy

Egg allergy affects around 1.3% of children under 5 years of age in the United States. Egg allergy is common in young children from other countries as well, with reported prevalence ranging from 1.2–2.7% in European countries. Egg allergy is caused by the production of egg-specific immunoglobulin E (IgE), particularly to the main egg allergens ovomucoid (Gal d 1) and ovalbumin (Gal d 2), which are found in the egg white. Egg allergy is more common in younger children, as a significant portion of egg-allergic individuals outgrow their allergy by school age.

Six egg allergens have been reported: four are present in egg white (ovomucoid, ovalbumin, ovotransferrin, and lysozyme) and two are present in egg yolk (alpha-livetin and YGP42), which are known as resistant to digestive enzymes.

Heat stability: Ovomucoid epitopes are conformationally stable with heating, increasing the likelihood that foods containing baked egg will still cause a reaction in patients with IgE recognising ovomucoid proteins. In contrast, ovalbumin is heat-labile, meaning that patients sensitised only to ovalbumin may tolerate thoroughly baked egg products. Regular ingestion of heated egg in egg-allergic children was associated with immunological changes including a reduction in skin prick test wheal diameters to egg white, a reduction in ovalbumin-specific IgE levels, and an increase in ovalbumin-specific and ovomucoid-specific IgG4 levels.

8.2 Dietary Cholesterol and Cardiometabolic Risk in High-Risk Individuals

Egg consumption was significantly associated with an increased risk for incident CVD among participants with type 2 diabetes mellitus; individuals with the highest egg intake (4.2 ± 0.04 eggs/week) had a 2.8 times higher incidence of CVD than those with the lowest intake. This represents a clinically relevant interaction specific to persons with existing T2DM. Future studies will need to better illustrate the underlying mechanisms, take into account individual variation in serum cholesterol response to dietary cholesterol consumption, and determine the association between substituting eggs with other foods in relation to cardiovascular disease risk. Before all these, the debate about the safety of egg or dietary cholesterol consumption in adults will continue.

8.3 TMAO and Gut Microbiota-Mediated Risks

Identified positive associations between egg intake and CVD may be driven by other mechanisms. Eggs are a rich source of dietary choline that can be converted to trimethylamine by gut bacteria, which is further oxidised to trimethylamine-N-oxide (TMAO). However, notably, in the crossover RCT in young adults, greater intake of choline during the whole egg diet period corresponded to increased serum choline and betaine without altering trimethylamine N-oxide.

8.4 Egg Allergy and Influenza Vaccination

Many influenza vaccines are produced in embryonated hen's eggs and may contain trace ovalbumin residues. Current guidance from allergy and immunisation bodies addresses the management of egg-allergic individuals receiving such vaccines; this is a documented drug-food-biologics interaction of practical clinical significance. Severe egg allergy (anaphylaxis to egg) is a recognised precaution for certain egg-grown vaccines.

8.3 Microbiological Safety

Raw and undercooked eggs are a recognised vehicle for Salmonella enteritidis contamination. The organism resides primarily in the yolk, can penetrate an intact shell, and is destroyed by thorough cooking. Immunocompromised individuals, pregnant persons, the elderly, and young children face greater risk from undercooked egg consumption. Washing and refrigeration practices differ internationally, with implications for shell contamination and bloom integrity.

8.4 Avidin and Biotin Depletion (Raw Egg White)

Egg white contains avidin, a glycoprotein that binds dietary biotin (vitamin B7) with very high affinity, preventing its intestinal absorption. Chronic consumption of large quantities of raw egg white can cause biotin deficiency (dermatitis, alopecia, neurological symptoms). This interaction is abolished by cooking, which denatures avidin and releases biotin for normal absorption. This is a well-established nutritional interaction of direct practical relevance to users of raw egg white protein preparations.

8.5 Interactions with Specific Nutrients and Drugs

Egg yolk cholesterol does not interact directly with cholesterol-lowering drug therapy in a pharmacokinetic sense, but it can blunt the LDL-lowering magnitude achieved by statins at higher intake levels in hyper-responders to dietary cholesterol. Whether the increase in egg consumption will lead to elevated cholesterol absorption and disruption of cholesterol homeostasis has been a concern of debate. Individual variation in the serum cholesterol response to dietary cholesterol is substantial — so-called "hyper-responders" exist in a minority of the population and exhibit greater LDL elevations from dietary cholesterol intake than the average.

9. Evidence Quality and Summary

Given the potential nutritional benefits and socioeconomic accessibility of egg intake, the effects of egg consumption on clinical measures of nutritional status, cardiometabolic risk factors, and hematologic profiles have been evaluated in observational and intervention studies; however, the results are often inconsistent and controversial, which may in part be due to differences in study designs, populations, background diets, and individual variability between subjects.

The balance of evidence points to eggs being a nutritious food, suggesting there are broad health benefits from including eggs in the diet at intakes higher than that currently consumed by European populations. Eggs are a significant food source, providing essential nutrients such as high-quality protein, vitamins, minerals, unsaturated fatty acids, choline, and carotenoids, which highlight their potential health benefits in a balanced diet.

The most robustly supported clinical applications of egg-derived fractions are: (1) whole egg and egg white protein as a high-biological-value protein source supporting nitrogen balance, muscle protein synthesis, and growth in children; (2) egg yolk as a delivery vehicle for highly bioavailable lutein, zeaxanthin, and choline; and (3) choline from egg yolk for support of verbal memory in older adults (small RCT, requires replication). The cardiovascular risk question remains genuinely unresolved, with evidence pointing to population heterogeneity, background diet interaction, and metabolic status as key modifiers.

References

• Matsuoka R, et al. Health Functions of Egg Protein. Nutrients. 2022. PMC9368041
• Nutritional Aspects of Eggs for a Healthy and Sustainable Consumption: A Narrative Review. Food Science & Nutrition. 2025. PMC12411868
• Kuang H, et al. The Impact of Egg Nutrient Composition and Its Consumption on Cholesterol Homeostasis. Cholesterol. 2018. PMC6126094
• The Health Benefits of Egg Protein. PMC9316657
• Comparison of the nutrient composition of eggs produced in the Guatemalan highlands. Food Science & Nutrition. 2023. PMC10724625
• Eggs and Health Special Issue. Nutrients. 2016. PMC5188439
• Nakagawa K, et al. Effects of egg yolk choline intake on cognitive functions and plasma choline levels. Lipids in Health and Disease. 2023. PMC10280906
• Egg intake and cognitive function in healthy adults: A systematic review. PMC12538690
• Eggs and Cardiovascular Disease Risk: An Update of Recent Evidence. PMC10285014
• Eggs – a scoping review for Nordic Nutrition Recommendations 2023. Food & Nutrition Research. 2024. PMC10870976
• Darooghegi Mofrad M, et al. Egg and Dietary Cholesterol Intake and Risk of All-Cause, Cardiovascular, and Cancer Mortality. Frontiers in Nutrition. 2022. PMC9195585
• Associations of Dietary Cholesterol, Serum Cholesterol, and Egg Consumption With Overall and Cause-Specific Mortality. Circulation. 2022. PMC9134263
• Formisano E, et al. Effect of egg consumption on health outcomes: An updated umbrella review. Nutrition, Metabolism and Cardiovascular Diseases. 2025.
• Consumption of Different Egg-Based Diets Alters Clinical Metabolic and Hematological Parameters. PMC10490185
• Egg consumption and growth in children: a meta-analysis of interventional trials. PMC10796599
• Eggs: Healthy or Risky? A Review of Evidence from High Quality Studies on Hen's Eggs. PMC10304460
• Eisenhauer B, et al. Lutein and Zeaxanthin — Food Sources, Bioavailability and Dietary Variety in AMD Protection. Nutrients. 2017. PMC5331551
• The ALGOVUE Clinical Trial: Effects of Daily Consumption of Eggs Enriched with Lutein and DHA. PMC8541434
• Mares J. Lutein and Zeaxanthin Isomers in Eye Health and Disease. Annual Review of Nutrition. 2017. PMC5611842
• Lutein and Zeaxanthin and Their Roles in Age-Related Macular Degeneration. PMC8874683
• Lutein Supplementation for Eye Diseases. PMC7352796
• The Egg Xanthophyll Intervention clinical Trial (EXIT). PMC5297582
• Matsakas A, et al. Effects of Egg White Protein Supplementation on Muscle Strength. Nutrients. 2012. PMC3497008
• Oral Egg-Derived Protein and Peptide Supplementation for Health Outcomes in Adults: Systematic Review and Meta-Analysis. PMC13074808
• Comparison of whole egg v. egg white ingestion during 12 weeks of resistance training. British Journal of Nutrition. 2020.
• Wallin A, et al. Egg consumption and risk of type 2 diabetes: a prospective study and dose–response meta-analysis. Diabetologia. 2016. PMC4861752
• Longitudinal association between egg consumption and the risk of CVD: interaction with T2DM. PMC5916923
• The Fifty Year Rehabilitation of the Egg. PMC4632449
• Eggs, dietary cholesterol, and cardiovascular disease: the debate continues. PMC6790443
• Novel food processing technologies to reduce egg allergenicity. PMC12995051
• Tolerance to heated egg in egg allergy. PMC10734553
• Unscrambling Egg Allergy: Diagnostic Value of Specific IgE for Ovomucoid. PMC3658811
• Eggs as food — Wikipedia (historical and cultural sections).
• Food Timeline: History Notes — Eggs. FoodTimeline.org
• Humans Have Been Eating Eggs for Millions of Years. History.com