Animal protein

Other Names

AlbuminAnimal by-product mealAnimal liver mealAnimal protein hydrolysateAnimal protein isolateAnimal-based proteinAnimal-derived proteinAnimal-sourced proteinBlood mealCaseinCollagen proteinComplete proteinConventional animal proteinDairy proteinDried meat solublesEgg proteinFish mealFish protein concentrateGelatin proteinHigh-quality proteinLivestock proteinMeat and bone mealMeat proteinMilk proteinMuscle proteinMyofibrillar proteinPlasma proteinPoultry by-product mealSarcoplasmic proteinWhey protein

Synopsis

Animal Protein: An Encyclopedic Reference

1. Identity, Nomenclature, and Natural Sources

Animal protein refers to the class of proteins derived from animal-source foods (ASFs), including terrestrial mammals, birds, fish, and other aquatic animals, as well as their derived products such as dairy and eggs. Unlike plant proteins, animal proteins are not defined by a single chemical species but rather by their origin and the shared nutritional characteristics that result from it.

Protein is a macronutrient responsible for multiple functions in the human body and is made up of twenty amino acids. Nine of these are not synthesized in the human body and require dietary ingestion to prevent deficiency. These essential amino acids are easily obtained through animal-based proteins but can be present in limited quantities through plant-based protein sources.

The principal animal-derived protein sources include:

Meat proteins: skeletal muscle proteins from beef, pork, lamb, poultry, and game, consisting primarily of myosin, actin, and connective-tissue proteins such as collagen.
Dairy proteins: Whey protein is a mixture of globulins and caseins contained in whey from cheese production. It is of high quality, being rich in essential branched-chain amino acids and rapidly absorbed.
Egg proteins: egg albumin (ovalbumin) and other egg-white globulins, as well as yolk proteins (lipovitellins and phosvitin).
Fish and seafood proteins: myofibrillar proteins from fish muscle, as well as collagen-rich proteins from fish skin.

Protein supplements are available in different formulations such as powders, gummies, protein bars, and ready-to-drink shakes, and can be categorized based on the source of protein, including whey, casein, egg albumin, and carnivore (beef)-based preparations. The majority of these protein supplements are further classified as concentrate, isolate, and hydrolysate based on the processing and concentration of protein. Another very popular category is the amino-acid supplement, which contains individual amino acids or combinations such as branched-chain amino acids (BCAAs) and essential amino acids.

2. Traditional and Historical Use

The consumption of animal protein is as old as the human species itself, though the precise proportions of animal-to-plant foods consumed by prehistoric populations varied considerably across geography, season, and ecology.

Archaeological findings based on isotopic analysis show no universal dietary regimen in prehistoric times. In Israel, fossil evidence from approximately 800,000 years ago reveals a varied, plant-based diet including seeds, wild fruits and vegetables, nuts, and lesser amounts of meat and fish. Examination of microfossils from Neanderthal dental calculus discovered in modern-day Iraq and Belgium demonstrates the consumption of several plants including date palms, legumes, and seeds, with many of the identified plant starch remains revealing chemical changes consistent with cooking. These archaeological findings challenge the modern-day belief that prehistoric humans relied mainly on animal protein sources and raw foods.

An analysis of 13 known quantitative dietary studies of hunter-gatherer (HG) societies demonstrated that animal food provided the dominant (65%) energy source, while gathered plant foods comprised the remainder (35%). This data is consistent with a more recent, comprehensive review of the entire ethnographic data (n=229 HG societies) that showed the mean subsistence dependence upon gathered plant foods was 32%, whereas it was 68% for animal foods. However, these estimates are subject to significant regional variation.

Other evidence, including isotopic analyses of Paleolithic hominid collagen tissue, reductions in hominid gut size, low activity levels of certain enzymes, and optimal foraging data all point toward a long history of meat-based diets in our species.

The dietary patterns of documented traditional and contemporary hunter-gatherer societies also reflect wide geographic diversity. The Hadza (Tanzania) rely on hunted game, honey, wild fruits, and tubers, shifting seasonally between high-meat and foraged diets. The Inuit (Arctic Circle) thrive on high-fat, high-protein foods such as seal, fish, whale, and caribou — an adaptation to a frozen, plant-scarce landscape. The Maasai (Kenya and Tanzania) traditionally consume milk, meat, and blood from cattle, reflecting a pastoralist culture rooted in livestock stewardship.

About 11,000 years ago, humans made a major shift from hunting and gathering to farming, a change known as the Neolithic Revolution that dramatically altered human diets. As the earliest farmers became dependent on crops, their diets became far less nutritionally diverse than hunter-gatherers' diets. Eating the same domesticated grain every day gave early farmers cavities and periodontal disease rarely found in hunter-gatherers. When farmers began domesticating animals, those cattle, sheep, and goats became sources of milk and meat but also of parasites and new infectious diseases. Farmers suffered from iron deficiency and developmental delays, and they shrank in stature.

In pre-modern medical and culinary traditions across multiple cultures — from ancient China's emphasis on meat broths for convalescence to Galenic medicine in medieval Europe advocating meat as a restorative food for the ill and the weak — animal protein held a central place as a concentrated source of nourishment and vitality. These traditions, however, are documented in historical sources rather than clinical evidence, and their specific therapeutic claims cannot be directly verified in the peer-reviewed literature referenced here.

3. Key Constituents and Mechanisms of Action

3.1 Amino Acid Composition

Dietary protein quality is primarily characterized by indispensable amino acid (IAA) content. IAAs cannot be synthesized by the human body and must be obtained from the diet.

Animal proteins are characterized by a complete indispensable amino acid (IAA) profile, meaning they contain all nine essential amino acids in proportions that closely match human requirements. Animal proteins (whey, egg, casein, fish) typically score highest on the Protein Digestibility-Corrected Amino Acid Score (PDCAAS), ranging from 0.92–1.0; plant proteins score lower due to limiting amino acids (e.g., corn = 0.41, wheat = 0.45).

In a study of amino acid content of 35 protein supplement samples, plant-based proteins such as soy, pea, and corn did not meet the requirements for essential amino acid intake, whereas animal-based proteins such as whey, casein, and egg did.

3.2 Protein Quality Scoring: PDCAAS and DIAAS

Two standardized methods exist for evaluating the nutritional quality of dietary proteins.

PDCAAS (Protein Digestibility-Corrected Amino Acid Score) is the FDA and CFIA regulatory standard for protein quality on nutrition labels. DIAAS (Digestible Indispensable Amino Acid Score) is the newer, more accurate method endorsed by the FAO — it measures amino acid absorption at the small intestine and is not capped at 1.0, making it better at differentiating protein quality.

Among selected protein sources, based on the 0.5- to 3-year-old reference pattern, pork meat, casein, egg, and potato proteins are classified as excellent quality proteins with an average DIAAS above 100. Whey and soy proteins are classified as high-quality proteins with an average DIAAS ≥75.

Animal proteins such as meat and milk have greater DIAAS values than plant proteins, but by complementing plant proteins with low DIAAS values with animal proteins with greater DIAAS values, balanced meals that are adequate in all amino acids can be provided.

In general, PDCAAS undervalues the protein quality of animal-sourced foods and overvalues plant-sourced foods, though the differences between PDCAAS and DIAAS are not always high.

3.3 Digestibility and Absorption Kinetics

Animal proteins are more digestible than plant proteins, resulting in greater amino acid availability and stimulation of muscle protein synthesis.

The digestion rates differ substantially among animal protein types. Whey, being water soluble, is absorbed more rapidly than casein, an insoluble milk protein that forms curds in the stomach, retarding its gastric emptying and absorption for hours.

The capacity of a dietary protein to stimulate post-prandial muscle protein accretion depends on the digestion and absorption kinetics of that protein as well as its amino acid composition. A more rapid rise in circulating essential amino acids (EAAs), with leucine in particular, drives the post-prandial rise in muscle protein synthesis rates.

3.4 Key Signaling Mechanisms

Several studies have shown that leucine is able to stimulate specific intracellular signaling pathways related to mRNA translation and thereby acts as a signal nutrient in the stimulation of protein synthesis.

It is well established that high-protein diets (approximately 25–30% of energy intake from protein) provide benefits for achieving weight loss and subsequent weight maintenance in individuals with obesity, and improve glycemic control in type 2 diabetes. These effects may be attributable to the superior satiating property of protein, at least in part through stimulation of gastrointestinal mechanisms involving GI hormone release and slowing of gastric emptying, as well as post-absorptive mechanisms facilitated by circulating amino acids.

In animal models, linear growth is sensitive to total dietary protein, acting for instance through stimulation of insulin-like growth factor-1 (IGF-1) and its binding proteins.

With respect to the insulin/IGF-1 axis, higher animal protein intake was associated with higher IGF-1 and lower IGFBP-1 and IGFBP-2, whereas higher plant protein intake was associated with higher IGF-1 and IGFBP-1. Additionally, IGF-1 and IGFBPs were estimated to mediate approximately 5–20% of the association between animal protein and type 2 diabetes.

4. Scientific Evidence by Area of Use

4.1 Skeletal Muscle Mass and Strength

Evidence level: Moderate to strong (multiple RCTs and systematic reviews/meta-analyses)

The contemporary literature supports the consensus that animal protein foods, relative to their native plant counterparts, offer greater benefit in terms of digestibility, increasing plasma indispensable amino acid availability, stimulating muscle protein synthesis, and supporting muscle integrity and mitigating risk of frailty and sarcopenia.

A systematic review and meta-analysis of randomized controlled trials (RCTs) comparing animal protein to plant protein on lean mass and muscle strength outcomes provided important nuance. Although animal protein is usually considered to be a more potent stimulator of muscle protein synthesis than plant protein, the effect of protein source on lean mass and muscle strength needs to be systematically reviewed. The study examined potential differences in the effect of animal vs. plant protein on lean mass and muscle strength, and the possible influence of resistance exercise training (RET) and age, with 3,081 articles screened and 18 selected for systematic review, of which 16 were used for meta-analysis. The effect of protein source on muscle strength was found to be inconsistent across different outcome measures, and meta-analyses revealed that protein source did not affect changes in strength outcomes.

A more recent systematic review comparing plant- and animal-based proteins directly on acute muscle protein synthesis rates also found twelve studies directly compared plant- and animal-based proteins, with nine studies (75%) reporting no significant differences in MPS, and three studies (25%) reporting lower MPS with plant-based proteins.

At the level of isolated comparisons between specific proteins, short-term randomized, controlled trials of muscle protein synthesis have demonstrated that whey protein increases synthesis more so than casein or soy isolates. However, while animal proteins are more digestible than plant proteins, resulting in greater amino acid availability and stimulation of muscle protein synthesis, isolated plant proteins, plant protein blends, and modified plant proteins enriched with indispensable amino acids can elicit comparable digestion and absorption kinetics to animal proteins.

Clinical and animal studies have also shown that amino acids from soy proteins were more degraded to urea than amino acids from casein or whey proteins and, consequently, were less available for muscle protein synthesis.

4.2 Sarcopenia Prevention in Older Adults

Evidence level: Moderate (multiple RCTs, consistent directional evidence but insufficient longer-term data)

Sarcopenia is a complex, multifactorial process facilitated by a combination of factors including the adoption of a more sedentary lifestyle and a less than optimal diet. Increasing evidence points to a blunted anabolic response after a mixed nutrient meal as a likely explanation for chronic age-related muscle loss. There is currently insufficient longer-term research with defined health outcomes to specify an optimal value for protein ingestion in elderly individuals; however, there is general agreement that moderately increasing daily protein intake beyond 0.8 g·kg⁻¹·d⁻¹ may enhance muscle protein anabolism and provide a means of reducing the progressive loss of muscle mass with age.

Findings from one RCT indicate that a moderately high-protein diet (1.2 g/kg body weight/day) led to significant improvements in muscle strength, reduced fat accumulation, and enhanced muscle composition compared to the normal-protein intake group (0.8 g/kg body weight/day). These results reinforce the growing evidence that higher protein intake is crucial for maintaining muscle function and preventing sarcopenia-related muscle deterioration. Protein is essential for muscle protein synthesis, particularly in older adults who experience anabolic resistance, necessitating higher protein intake to maintain muscle integrity.

Additional evidence suggests a protective role for protein supplementation in older adults in order to preserve lean body mass and prevent frailty. Protein supplements vary widely in their composition, and small trials of heterogeneous study designs have made it difficult to extrapolate findings to develop data-driven, evidence-based recommendations for protein supplementation in sarcopenia prevention.

Of 82 articles detailing 81 unique studies reviewed for their association between dietary protein intake and risk of bone disease, kidney disease, and sarcopenia, only 13 were assessed with low to moderate risk of bias and synthesized. The overarching evidence was insufficient, largely due to the limited number of low to moderate RoB studies, the diversity of dietary protein interventions, and the broad range of outcomes.

Note that aging is associated with blunted appetite, so the consumption of high quantities of plant proteins in order to stimulate muscle protein synthesis may not be a valid strategy for older individuals.

4.3 Child Growth and Development

Evidence level: Moderate (meta-analyses of RCTs showing consistent effects on weight; more limited effects on height)

For normal growth, sufficient dietary protein during pregnancy and early childhood is critical, in particular from animal-source foods due to their complete amino acid profile, contents and bioavailability of lysine, sulfur amino acids, and threonine, and associated insulin-like growth factors, iron, zinc, and vitamin B₁₂.

Extreme protein deficiency leads to hypoalbuminemic malnutrition, metabolic abnormalities, and delayed development; and animal protein-rich foods and supplements have shown beneficial effects in severely undernourished children. However, the role of animal protein in situations of less extreme protein inadequacy is less well established.

A systematic review and meta-analysis of 62 controlled trials comprising over 30,000 participants across 5 continents found that supplementation of protein from animal-source food generally increased weight and weight-for-length in children, but with more limited effects on other growth outcomes such as attained height.

In a systematic review (14 articles) and a meta-analysis (eight articles), animal-source food supplementation in children aged 6 months to 2 years resulted in a substantial effect size on length-for-age z scores (LAZ, 0.15) and weight-for-age z scores (WAZ, 0.20), in comparison to the control group.

While adequate protein intake is essential for physical and cognitive development in individuals under nineteen, excessive intake may accelerate growth and increase the long-term risks of overweight and obesity. Compared to animal-based proteins, plant-based proteins carry a higher risk of nutrient deficiencies in vulnerable populations due to lower digestibility and incomplete amino acid profiles.

4.4 Cardiovascular Disease Risk

Evidence level: Mixed; observational data show source-dependent associations; RCT evidence is limited

Recent data from large cohorts have confirmed that total and animal proteins are associated with the risk of cardiovascular disease and diabetes, even when fully adjusting for lifestyle and dietary or nutritional factors. However, this signal is heterogeneous and source-dependent.

Protein-based factor analysis in the Adventist Health Study-2 cohort showed that a high contribution of protein from meat increased risk of CVD mortality, whereas a high contribution of protein from nuts and seeds was protective. Plant and animal proteins were heterogeneously associated with CVD mortality.

A large systematic review and dose-response meta-analysis of 32 prospective cohort studies found that during a follow-up period of 3.5 to 32 years, 113,039 deaths occurred among 715,128 participants. Intake of total protein was associated with a lower risk of all-cause mortality. Intake of plant protein was significantly associated with a lower risk of all-cause and cardiovascular disease mortality, but intake of total and animal protein was not significantly associated with risk of cardiovascular disease and cancer mortality.

Contrasting this, an analysis of the NHANES III cohort found that there were no associations between animal protein (HR = 0.99; 95% CI: 0.98–1.01; P = 0.29) or plant protein (HR = 1.02; 95% CI: 0.95–1.10; P = 0.55) intake and all-cause mortality.

An important methodological issue concerns confounding. In the EPIC-Heidelberg cohort, higher intakes of red or processed meats were observed among current heavy smokers, participants with obesity, or heavy alcohol drinkers. Adjusting for age, sex, and total energy intake, risk models showed increased all-cause, cardiovascular, and cancer-related mortality with higher red or processed meat intakes (HR ranging from 1.25 [95% CI: 1.15–1.36] to 1.76 [1.46–2.12] comparing highest to lowest tertiles). However, these findings suggest heavy confounding and provide little support for the hypothesis that animal protein, as a nutrient, is a major determinant of mortality risk.

A pooled analysis of six prospective cohort studies with 29,682 US participants found that substituting eggs, processed meat, unprocessed red meat or poultry with nuts, whole grains, legumes or fish was associated with lower risks of incident CVD and all-cause mortality.

The sources or types of protein in the diet have long been overlooked regarding their link to cardiometabolic health. The picture is complicated by the fact that animal and plant proteins are consumed along with other nutrients and substances which make up the "protein package," so plant and animal protein come with clear nutrient clusters.

4.5 Body Weight and Glycemic Control

Evidence level: Moderate for short-term effects; weaker for long-term maintenance

There is evidence that the beneficial effects of greater protein intake on body weight and glycemia may only be sustained for 6–12 months. While both suboptimal dietary compliance and metabolic adaptation, as well as substantial limitations in the design of longer-term studies are likely to contribute to this contradiction, the source of dietary protein may also play a role.

In a controlled study of 37 participants with type 2 diabetes, researchers compared the effects of animal versus plant protein intake on circulating levels of IGF-1 and IGF-binding proteins over a 6-week period. Participants consumed isocaloric diets composed of either 30% energy animal or plant protein, 30% fat, and 40% carbohydrates for 6 weeks. Both diets induced similar and significant increases of IGF-1, which was unaffected by the different amino acid compositions of plant and animal protein.

Despite improvements of insulin sensitivity and major reductions of liver fat, IGFBP-2 decreased with both diets while IGFBP-1 was not altered. It was concluded that animal and plant protein similarly increase IGF-1 bioavailability while improving metabolic parameters and may be regarded as equivalent in this regard.

4.6 Cancer Risk

Evidence level: Mixed and observational; no definitive mechanistic RCT evidence

Greater consumption of plant protein sources like legumes, nuts, seeds, and whole grains is associated with reduced risks of cardiovascular diseases, some cancers, and mortality, especially compared to red and processed meats. However, evidence is mixed for some health outcomes, and more research is still needed.

The growth hormone/insulin-like growth factor-1 (IGF-1) system is highly interrelated with the insulin signaling pathway. Reduced activation of insulin and IGF-1 pathways has been linked to longevity and a reduction of cancer, but it remains unclear whether this is linked to reduced IGF-1 pathway activity or to improved insulin sensitivity.

5. Body Systems Associated with Animal Protein

Musculoskeletal system: Muscle protein synthesis, lean mass accretion, sarcopenia prevention, and bone matrix support via IGF-1 stimulation and amino acid supply.
Endocrine system: Modulation of IGF-1, insulin secretion, and IGF-binding proteins; anabolic signaling via leucine-sensitive mTORC1 pathway.
Cardiovascular system: Source-dependent associations with CVD risk; red and processed meat linked to elevated risk in observational data; fish and poultry generally neutral or protective.
Renal system: Glomerular filtration rate is influenced by protein intake; contraindicated at high intakes in pre-existing kidney disease.
Growth and development (pediatric): Critical for linear growth, weight gain, and cognitive development in children; particularly important in low- and middle-income settings.
Metabolic health: Impacts on body weight regulation, satiety hormones, glucose homeostasis, and hepatic fat metabolism.

6. Dosage Forms and Reported Dosages

The first official recommendation for daily protein intake was reported in 1936 by the League of Nations at 1.0 g/kg of body weight. This has been subsequently challenged by several joint FAO/WHO expert committees, who established the current recommendation of 0.8 g/kg daily protein intake in healthy adults, accounting for approximately 10–15% of daily energy intake, in 2007.

In pregnancy and lactation, the RDA for protein is increased to 71 g/day. The daily value for protein is 50 g, used on Dietary Food Labels in reference to a standard daily 2,000-calorie diet.

To sustain nitrogen balance, protein intake for strength and power athletes is recommended between 1.4–1.8 g/kg per day, whereas for endurance athletes it is between 1.2–1.4 g/kg per day.

In the context of sarcopenia, one RCT compared a normal-protein (NP) diet containing the RDA of 0.8 g protein·kg⁻¹·day⁻¹ with a moderately high-protein (MHP) diet providing 1.2 g protein·kg⁻¹·day⁻¹, corresponding to approximately 15 and 25% of total energy from protein, respectively.

In the context of acute post-exercise muscle protein synthesis, the consensus of research on protein consumption in the post-exercise window is a dose of 20 grams, with a more specific dosing range of between 0.25 to 0.3 grams per kilogram of body weight.

In the context of type 2 diabetes research, one RCT had 37 participants with type 2 diabetes consume isocaloric diets composed of either 30% energy from animal or plant protein, 30% fat, and 40% carbohydrates for 6 weeks.

For supplementation purposes, protein supplements are available in different formulations such as powders, gummies, protein bars, and ready-to-drink shakes. Protein powders are commercially available and composed of different types of animal- or plant-based proteins. Commonly available protein powders include whey, casein, and pea protein.

7. Safety Considerations and Interactions

7.1 Renal Function

There is little evidence that links high protein intakes to increased risk for impaired kidney function in healthy individuals. However, renal function decreases with age, and high protein intake is contraindicated in individuals with renal disease.

Athletes or exercising populations commonly consume increased amounts of dietary protein, and there is no evidence that this population is at increased risk of renal disease. For example, protein intakes in the range of 1.4–1.9 g/kg/day did not impair renal function in a group of athletes consuming increased amounts of dietary protein, while similar outcomes could be concluded from results of longitudinal studies that have examined the impact of protein supplementation on strength and body composition changes.

In a series of case reports in male bodybuilders, protein intakes ranging from 2.6 to 5.8 g/kg daily over a period of two years had no effect on clinical markers of kidney (BUN, creatinine, and eGFR) and liver function.

Although potential negative consequences of a higher protein intake have been suggested — namely that a diet higher in protein could lead to renal injury and affect bone health — there is currently no scientific foundation for this in human studies. However, renal function does decrease with age, and high protein intake is contraindicated in individuals with renal disease. Assessment of renal function is recommended for older individuals before they adopt a higher-protein diet.

7.2 Bone Health

Sparse literature has addressed the impact of dietary protein intake on bone disease risk in children and adolescents. Only a single study examined the impact of dietary protein intake on bone disease risk in adults, yielding mixed findings. The overall findings on the impact of protein intake on bone disease in adults were mixed, with some studies showing no effect and others indicating benefits.

Higher levels of IGF-1 were associated with improved muscle and bone mass, and higher animal protein intakes were associated with reduced risks of osteoporotic fractures in some epidemiological studies, though mechanistic evidence from controlled trials is limited.

7.3 Contaminants and Co-Constituents in Supplements

Whey protein supplements contribute not only to protein intake but also to dietary exposure to minerals. The labelling present provides the percentage of protein and rarely refers to other components, such as potentially toxic elements including B, Cu, Mo, Zn, and V, which have tolerable upper intake levels set by the European Food Safety Authority.

7.4 Heterogeneity of Animal Protein Sources

Animal and plant proteins are consumed along with other nutrients and substances which make up the "protein package," so plant and animal protein come with clear nutrient clusters. This means that risks associated with high animal protein intake in observational studies may partly reflect co-consumed nutrients (e.g., saturated fat, sodium in processed meats) rather than protein per se.

Evidence for a beneficial effect of plant proteins is mixed. Limited and inconsistent results highlight the probable role of confounding by non-protein dietary components, and possibly also relate to the association between dietary protein sources and diet quality. Dietary proteins are not consumed in isolation but are embedded in complex food matrices as a part of the overall diet.

7.5 Pediatric Considerations

While adequate protein intake is essential for physical and cognitive development in individuals under nineteen, excessive intake may accelerate growth and increase the long-term risks of overweight and obesity.

7.6 Interactions with Exercise

The International Society of Sports Nutrition (ISSN) recommends that healthy, exercising individuals consume protein before and after resistance exercise to stimulate muscle protein synthesis (MPS); in an even distribution across the day; and in whole foods and supplementation to ensure intake of protein quality and quantity. The ISSN also recommends achieving adequate intake of leucine to most effectively stimulate MPS.

References

Health Conditions

Health conditions that Animal protein may help support.

No conditions available.

Body Systems

Body systems that Animal protein may help support.

No body systems available.