Human health

Animal-sourced foods make it easier to meet protein targets

Is our protein intake excessive? And are we relying too much on animal sources, as the ‘protein transition’ argument suggests? For some people this may hold true, but this viewpoint fails to recognize the distinct nutritional needs of various populations. While minimum protein recommendations are designed to prevent deficiencies, higher intakes are more effective in supporting optimal health. Animal-derived proteins generally offer higher quality than plant-based options and are rich in essential micronutrients that are already scarce globally. Additionally, they provide these nutrients with lower energy and carbohydrate content, benefitting those with higher physiological demands.

Protein as the cornerstone of a nourishing diet
Recommendations may be too low for many
Optimal protein intake varies per population
Adequate protein as a percentage of energy intake
Protein sources differ in nutritional value

Protein as the cornerstone of a nourishing diet

Protein-rich foods form the cornerstone of a nourishing diet, supporting both overall nutritional adequacy and physical development. High-quality protein sources, such as dairy, meat, fish, and eggs, are associated with better micronutrient intake, increased adult height, and a lower risk of childhood stunting. Protein also plays an important role in cardiometabolic health, with high-protein diets linked to reduced mortality. Clinical studies further show improved outcomes for hypertensive or obese individuals, including better glucose control in type-2 diabetes patients.

Criticisms of excessive protein intake in Western diets, particularly claims of harm to kidney or bone health, lack scientific support and ignore the evolutionary adaptations of humans to high intake levels of protein. Instead of focusing narrowly on quantity, emphasis in dietary policies may have to shift to protein quality instead. Even in high-income countries, many individuals still fail to meet optimal levels of high-quality protein. Additionally, the anabolic response to protein intake post-exercise is more sustained than previously believed, challenging the idea of a strict upper limit for protein benefits.

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Protein correlates with dietary adequacy and physical development

Sufficient protein intake is the cornerstone of a healthy diet. Both the protein-to-carbohydrate ratio [Wabo et al. 2022] and intake levels of high-quality protein [de la O et al. 2022] are associated with a more adequate supply of micronutrients in general, thus serving as markers for dietary adequacy. The quality of protein serves as an outstanding predictor for physical development and adult height, being positively associated with the consumption of dairy, pork, eggs, beef, and potatoes, and negatively correlated with cereals and legumes [Grasgruber & Hrazdíra 2008]. Low amounts of meat in the diet also correlate with higher stunting incidence during the first few years of childhood [Adesogan et al. 2020].

Protein correlates with better cardiometabolic health

In general, a lower all-cause mortality risk has been associated with a higher dietary protein-to-carbohydrate ratio of a diet [Wabo et al. 2022] and, in the case of Japanese older adults, with higher protein intake levels (paralleling higher levels of animal protein) [Kurata et al. 2023]. Moreover, supplementation of high-quality protein during intervention trials was shown to improve markers for cardiometabolic health in hypertensive or overweight/obese individuals [Zhou et al. 2024]. High-protein diets are also effective to reduce hyperglycemia in patients with type-2 diabetes [Flores-Hernández et al. 2024].

The myth of “too much” protein in the Western diet

High-quality protein from animal source foods is more readily available in high-income countries (60% or more of dietary proteins) than in low- and middle-income countries (15-30% of dietary protein) [Tome et al. 2024; see also elsewhere]. In the EU, for instance, protein from animal sources covers 60% of the total, consisting mostly of meat (52%) and dairy (34%), followed by eggs (7%) and seafood (7%). Cereals and cereal products usually offer the largest share of plant proteins in Western diets [e.g., Lin et al. 2010]. These overall protein levels are said to be too high (about 70% higher than the 50 g/d recommendation for an adult of by the World Health Organization) [Westhoek et al. 2016]. Yet, when considering protein quality, intake levels may even be too low for many individuals within high-income countries [Wolfe et al. 2024].

In contrast to what some other authors claim [see, for instance, Mariotti & Gardner 2019], we argue that this contention overlooks that recommendations are (1) not met by substantial parts of the population, (2) not necessarily optimal, and (3) do not pay sufficient attention to protein quality. Moreover, claims that higher intake levels may harm bone and kidney health are unfounded [see elsewhere] and overlook that humans are evolutionary adapted to elevated protein levels [see elsewhere]. As a matter of fact, humans prioritize protein. In contrast to the widespread belief that the anabolic response to protein feeding during postexercise recovery has an upper limit, which would be leading to the oxidation of excess amino acids, the magnitude and duration of this anabolic response is not restricted and has been underestimated [Trommelen et al. 2023].

Recommendations may be too low for many

The recommended dietary allowance (RDA) for protein is conventionally set at 0.83 g per kg of body weight, at population level. This is a minimum value to prevent loss of lean body mass in healthy adults, not an optimal one, and not even one reached by everyone.

Re-analysis of nitrogen balance data and other evidence suggests that this target may be too low to begin with, as some of the evidence suggests that consuming below 1.3 g/kg/d could lead to muscle mass loss. Many individuals may benefit from even higher protein intake, as outlined below.

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The estimated average requirement (EAR) of protein is estimated at 0.66 g per kg body weight per day, or 0.83 g/kg/d as a recommended daily allowance (RDA) at population level, when taking variation into account [Richter et al. 2019; Tome et al. 2024]. This should be seen as a minimum value to avoid deficiency and loss of lean body mass in young adults specifically. However, re-analysis of nitrogen balance data and other new lines of evidence indicate that this recommendation may be too low and should be revised [Weiler et al. 2023]. Most adults benefit from higher protein intake for optimal health, at 1.2-1.6 g/kg/d [Layman, 2009; Phillips 2016, 2020], while eating below 1.3 g/kg/d may even lead to loss of muscle mass [Tagawa et al. 2021]. During short term weight loss, for instance, doubling the current recommendation protects against muscle loss while promoting the loss of body fat [Pasiakos et al. 2013]. Critically, the proposed level for nitrogen balance is not necessarily an optimal one for the entire population. Moreover, dietary guidelines fail to consider protein quality [Wolfe et al. 2024], as will be discussed below.

Optimal protein intake varies per population

Based on current scientific evidence, the recommended daily protein allowance for the general population should be revised upwards, increasing from 0.83 g/kg to over 1.0 g/kg of body weight. Specific groups—such as active individuals, children, pregnant women, and older adults—require even higher amounts, typically ranging from 1.2 to 2.2 g/kg/d, depending on their unique needs.

For weight loss, combining resistance training with 1.6 g/kg of protein helps preserve muscle mass and optimize fat loss, while at least 1.2 g/kg prevents muscle breakdown during caloric restriction. Optimal muscle building requires 1.6–2.2 g/kg, with certain cases benefiting from even higher intakes.

Older adults at risk of sarcopenia experience reduced efficiency in muscle protein synthesis and benefit from daily protein intakes of 1.0–1.5 g/kg , ideally from high-quality protein sources and combined with physical activity. Despite these recommendations, many older adults, particularly those in nursing homes, fail to meet these targets, increasing their risk of muscle loss and frailty.

In medical contexts, intakes of up to 2.0 g/kg or higher support recovery, improve nutritional status, and enhance outcomes in critical illness, wound healing, and chronic diseases. A meta-analysis of intervention trials looking into patients undergoing cancer therapies has shown that high-protein supplementation mitigates weight loss, improves muscle strength, and lowers hospitalization rates. Paleo-style diets and other diets rich in branched-chain amino acids, particularly leucine, have shown improvements in glucose control for type-2 diabetes patients at protein intake levels above 1.0 g/kg.

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The need to revise the protein recommendations for specific groups

Whereas the suggested intake of protein may have to be revised to at least 1.0 g/kg/d in general, this may even be higher for specific groups [Phillips et al. 2016; Weiler et al. 2023]. Optimal muscle building, for instance, requires 1.6 g/kg/d with an upper limit for benefit at 2.2 g/kg/d [Iraki et al. 2019; Bagheri et al. 2023], or higher [up to 3.5 g/kg/d; Tagawa et al. 2021].

A recent method (IAAO) suggests a similar range of increased RDA values: 1.6 g/kg in active, trained adult males [Packer, 2015]; 1.6 g/kg in children older than three, 1.6-2.0 g/kg in pregnant women, and 1.2-1.3 g/kg in older adults [Tang et al., 2014; Arentzon-Lantz et al, 2015; Weiler et al. 2023]; 1.8 g/kg for endurance athletes [Kato et al., 2016]; 1.7-2.2 g/kg for young bodybuilders [Bandegan et al., 2017]; 1.8 and 1.5 g/kg for active male and female adolescents [Brooks et al., 2017], and 1.7-1.9g/kg for lactating women [Rasmussen et al. 2020].

Protein recommendations for weight loss

An intervention trial has shown that a low-calorie high-protein diet (35% of kcal) weight and waist circumference, while also optimizing risk markers [Rodrigo-Carbó et al. 2024]. People trying to achieve weight loss while preserving muscle mass are advised to combine a hypocaloric diet with resistance training and a protein intake of 1.6 g/kg/d [Cava et al. 2017]. Consumption of a diet containing 2.4 g/kg/d was more effective than 1.2 g/kg/d in promoting increases in lean body mass and losses of fat mass when combined with a high volume of exercise [Longland et al. 2016]. During short term weight loss, a doubling of the recommendation to 1.6 g/kg/d both protects against muscle loss and promotes the loss of body fat, likely by acting upon anabolic sensitivity [Pasiakos et al. 2013]. Even if one relies entirely on high-quality protein foods during caloric restriction weight loss, at least 1.2 g protein/kg/d is necessary to maintain muscle mass, so that the accompanying caloric value of non-protein components is minimized [Wolfe et al. 2024].

Protein recommendations for older adults

It is perfectly possible for lean and healthy older men (70 ± 3 years) to maintain anabolic sensitivity that is similar to younger men, provided that there is enough physical activity and that the intake of essential amino acids is sufficiently high for muscle health [Horwath et al. 2024]. Maintaining a robust response to protein intake requires a compensatory increase in basal levels of proteins involved in anabolic signalling, but is not necessarily defined by age per se.

Older adults and elderly therefore benefit from higher intakes of essential amino acids [Wolfe et al. 2024]. Such individuals are about 40% less efficient than young adults at building muscle mass from protein, and require intake levels of 1.0-1.5 g/kg/d for healthy aging [Wolfe et al. 2008; Deutz et al. 2014; Traylor et al. 2018; Groenendijk et al. 2019; Nishimura et al. 2021; Campbell et al. 2023; Weiler et al. 2023]. An randomized controlled trial, using a two-meal eating pattern, has shown that an intake of 1.5 g/kg/d led to a more positive whole-body net protein balance than 0.8 and 1.1 g/kg/d in middle age and older adults [Church et al. 2025]. When older adults consume a 25-g whey or pea protein bonus twice per day in addition to the conventional protein recommendation of 0.8 g/kg/d, enhanced muscle protein synthesis and anabolic signalling was seen over a period of a week [McKendry et al. 2024].

Yet, in Dutch nursing homes, 85% of the residents were having a protein intake below the recommended 1 g/kg/d for elderly, corresponding with an average intake of only 0.8 (+/- 0.2) g/kg/d [Borkent et al. 2023].

Protein recommendations in the case of disease

Increased consumption of essential amino acids has beneficial in the case of critical illness, rehabilitation, wound healing, inflammation, cardiometabolic conditions, liver fat, renal failure, lung diseases, and brain injury [Wolfe et al. 2024]. Interventions wit low-calorie high-protein diets (35% of kcal), whether based on animal or plant protein, are able to improve incretin responses and a wide range of cardiometabolic markers, including those related to insulin resistance and inflammation [Rodrigo-Carbó et al. 2024].

In the case of acute or chronic disease, suggested intake levels are up to 2.0 g/kg/d or more [Wolfe et al. 2008; Bauer et al. 2013; Deutz et al. 2014], while an intervention trial has shown that increasing early protein intake from 0.8 to 1.5 g/kg/d helps to improve the nutritional status and prognosis of critically ill patients [Wang et al. 2024; Flores-Hernández et al. 2024]. A meta-analysis of 35 RCTs looking into patients undergoing cancer therapies has shown that high-protein supplementation mitigates weight loss, improves muscle strength, and lowers hospitalization rates [Orsso et al. 2024].

Protein intake above 1.0 g/kg/d also decreases hyperglycemia in patients with type-2 diabetes, in part due to their content of branched-chain amino acids (mainly leucine); this is especially the case for Paleo diets, due to their higher-quality protein and exclusion of grains, dairy products, salt, refined fats, and added sugars [Flores-Hernández et al. 2024].

Adequate protein as a percentage of energy intake

Suitable protein intake depends on the overall diet. Instead of using a minimum RDA, protein needs can be expressed as a percentage of caloric intake. The recommended protein range is set at 10-35% of daily energy intake.

The higher end of this range, corresponding with ancestral-type hunter-gatherer diets, has shown health benefits, including an improvement in cardiometabolic risk factors.

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Suitable intake also depends on the overall diet. For older adults eating three meals a day, a 1.2 g/kg/d target corresponds roughly to a 0.4 g protein/kg body weight/meal [Peters et al. 2023]. As a more pertinent recommendation than minimum RDA, an acceptable macronutrient distribution range (AMDR) for protein has been set at 10-35% on daily energy intake [Lupton 2020], of which the upper range is in the order of ancestral-type hunter-gatherer diets (19-35%) [Eaton et al. 1997; Cordain et al. 2000]. In Belgium, for instance, the protein intake constitutes 16% of the caloric intake for both males and females [Dénos et al. 2024]. Generally, the intake of proteins relative to energy tends to be higher for meat eaters (17-18%) than for vegetarians (14-15%) and vegans (11-14%) [Mariotti & Gardner 2019]. In a sedentary 19-year old male reference, the protein RDA would only constitute 8.5% of his energy intake, while 10 and 35% would correspond with 1.0 and 3.3 g/kg/d, respectively [Wolfe et al. 2008]. For healthy adults with ideal body weights, the recommended protein intake based on macronutrient considerations has thus been set at 1.4-2.0 g/kg/d.

Attempts have been made to link such % of intake to health outcomes. In the US (NHANES data), the worst outcome for all-cause mortality was found at 15% protein, and interestingly being slightly worse than 10%, while the lowest risk was found at 30-40%, which also matched better diet quality [Wabo et al. 2022]. When looking at global populations, diets leading to the least healthy cardiovascular outcomes were typified by lower protein intake (14% kcal) than the healthier ones (17% kcal) [Mente et al. 2023]. The upper range of intake % has been shown to lead to various health benefits, including the attenuation of gestational weight gain in pregnant women with obesity [Geiker et al. 2021].

A low-calorie, high-protein intervention (35% of kcal) has been shown to improve glucose metabolism and cardiometabolic profiles in subjects with prediabetes or type 2 diabetes and overweight or obesity [Rodrigo-Carbó et al. 2024]. When contrasting the upper range of protein intake (30%) with lower levels (15%) in prediabetic, obese subjects, improvement of blood glucose, insulin sensitivity, inflammation, and lean body mass outcomes is seen [Stentz et al. 2020]. Similarly, obese and insulin-resistant subjects improve their insulin sensitivity by 60–90% regardless of weight loss after a month on a high-protein diet (25-30%), compared to a normal protein diet (<20%) [González-Salazar et al. 2021]. Small yet favourable effects of such higher intake levels on cardiometabolic risk factors are also found for subjects with no chronic medical conditions [Vogtschmidt et al. 2021].

Protein sources differ in nutritional value

Protein sources vary in nutritional value, and a simple mass-based comparison is inadequate. Animal-derived proteins offer better quality than plant proteins, with higher anabolic responses for skeletal muscle. For older adults, meat-based meals are usually more effective than vegetarian options, unless the latter are properly designed. On average, vegetarian diets are associated with lower muscle mass and strength.

Plant-based strategies for muscle protein synthesis may need fortification or higher intake. A recommended animal-to-plant protein ratio is 50:50, with a 40:60 ratio potentially suitable but more risky with respect to the adequacy of micronutrients.

The True Ileal Digestibility (DIAAS) method is more accurate than PDCAAS for assessing protein value. Animal proteins have higher DIAAS values than most plant proteins. The Essential Amino Acid 9 (EAA-9) score, considering personalized requirements, provides an alternative for precision nutrition based on age or metabolic conditions.

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Anabolic responses of plant vs. animal proteins

Dietary guidelines fail to consider protein quality [Wolfe et al. 2024]. Protein sources differ substantially in nutritional value and should not be compared on a simple per mass basis [Gwin et al. 2021; Adhikari et al. 2022; Connolly et al. 2023]. When protein quality is taken into account, protein is found to be deficient for the average adult in most countries of the world (gross protein, in contrast, would suggest sufficiency for most countries) [Moughan 2021]. Typically, animal source foods improve protein quality when compared to plant proteins [Wolfe et al. 2018; Soh et al. 2024a, a]. Conversely, achieving high protein quality is a challenge in vegan diets [Soh et al. 2024].

Animal proteins are known to yield a higher anabolic muscle mass response, bringing in amino acids that may otherwise be in short supply (i.e., leucine, lysine, and methionine) [Berrazaga et al. 2019; van Vliet et al. 2019]. Randomized controlled trials have shown that this results in enhanced athletic performance in healthy individuals [Zhao et al. 2024]. The intake of leucine has been shown to be particularly critical in that respect [Traylor et al. 2018]. In addition to amino acid limitations, the food matrix needs to be accounted for, as this defines protein digestibility. The reason why animal proteins tend to outperform plant proteins is thus the combined effect of differences in amino acid profiles and protein digestibility. This combined effect has been quantified in protein quality metrics (PDCAAS and DIAAS), as discussed below.

Even if low-quality protein foods can be combined in a complementary manner to increase protein value, increasing the amount of low-quality protein will still be less effective than complementing a dietary pattern with a high-quality protein, while leading to increased caloric consumption due to non-protein components [Wolfe et al. 2024].

Protein quality metrics: PDCAAS and DIAAS

True ileal digestibility scores for the dietary indispensable amino acids (DIAAS) are superior when quantifying protein value compared to single faecal crude protein digestibility ones (PDCAAS) [FAO 2011]. Moreover, PDCAAS does not assign additional nutritional value to proteins with high biological value, overestimates the nutritional value/protein digestibility of foods that contain antinutrients, and overestimates the protein digestibility of foods with low digestibility when supplemented with the corresponding limiting AA [Tome et al. 2024]. For most ASFs, DIAAS values are ≥1, exceeding those of plant proteins (legumes: 0.6; cereals: 0.3-0.5), only approximated by soy (0.8-0.9) [Wolfe et al. 2018; Burd et al. 2019; Adhikari et al. 2022]. In plants, digestibility is reduced due to structural resistance, fibre, and anti-nutritional factors, which can be (partially) attenuated through processing [Wolfe et al. 2018; Almeida Sá et al. 2020]. For peas, for instance, the DIAAS increases from 0.6 in cooked peas to 0.8 in pea protein isolate [Rutherfurd et al. 2015]. For soy, DIAAS after processing and post-processing can either increase (e.g., for soy milk and soy concentrate) or decrease (e.g., for tofu and soy flour) [van den Berg et al. 2022].

With DIAAS rather than PDCAAS, nuts, seeds, tofu, and pulses (except chickpeas) cannot claim to be a 'good source' (DIAAS > 0.75) of protein [Marinangeli & House 2017]. To meet the requirements for all essential amino acids, the recommended protein intake should account for the DIAAS of the diet if the value is <100% (1.0). Since a plant-based diet yields a DIAAS of about 0.65 on average [Wolfe et al. 2018], a minimum amount of 0.8 g/kg/d would translate into a required intake of 1.2 g/kg/d to meet all essential amino acid needs, while a level of 1.5 g/kg/d for healthy aging would correspond with 2.3 g/kg/d. Indeed, when protein intake is 0.6-0.8 g/kg/d, vegan and lacto-ovo vegetarian diets are more likely to be deficient in essential amino acids, especially lysine [Tallman et al. 2023]. For strict vegan diets, consuming the RDA (0.8 g/kg/d) is inadequate to produce nitrogen balance in men [Bartholomae & Johnston 2023]. Also, meeting the same protein target with plant options comes with caloric intakes that are more elevated (often double or triple, even with beans and nuts) [Wolfe et al. 2018].

Similarly, the use of plant-based imitation foods fails to achieve the same response per unit of food as the animal-sourced variants they are trying to replace. About twice the amount of soy-based meat alternatives needs to be consumed by healthy 18-40 year-old participants to obtain the same anabolic effect as beef patty [Church et al. 2024]. In a Swiss sample, about 60% of the vegans did not reach the daily protein recommendation of 1 g/kg/d, which was partially ascribed to high quantities of low-protein soy drinks [Bez et al. 2024].

Older adults

Older adults in particular benefit from sufficiently high intakes of animal protein. For older adults in the UK, higher shares of animal protein have been associated with a slower atrophy rate in the hippocampus in the UK [Cui et al. 2024]. In Japan, a higher intake of animal protein has been inversely associated with all-cause mortality, independent of muscle mass [Kurata et al. 2023]. Muscles mass effects are, however, also critically important. When providing whole-food meal options (quinoa, chickpeas, edamame), those containing beef resulted in a 47-% enhanced muscle protein synthesis rate compared to vegan meals that were matched for calories and protein (isonitrogenous) [Pinckaers et al. 2024]. On average, consuming vegetarian diets parallels lower muscle mass and hand grip strength, when compared to omnivorous diets [Bartholomae et al. 2022].

Whereas meeting the protein target for older adults is feasible with meat-based meals, this is more difficult with vegetarian options, even when improving the flavour with spices [Peters et al. 2023]. Plant-based strategies to stimulate muscle protein synthesis are possible, but may require amino acid fortification, ingestion of multiple protein sources, or higher intake [Gorissen et al. 2016]. Other authors contend that meeting sufficient protein levels with plant-based options should not be problematic, albeit with more uncertainty in the case of older adults and provided that the diets are well-formulated [Mariotti & Gardner 2019]. Successful adoption of a well-balanced vegan diet has indeed been demonstrated with an intervention trial [Domić et al. 2024]. Yet, although flexitarian, pescetarian, and vegetarian scenarios can indeed be adequate if the diets are sufficiently nutritious, the risk of protein deficiency for adults is imminent when vegan diets are followed [Borkent et al. 2024].

To specifically take into account personalized requirements based on age or metabolic conditions, such as increased leucine needs for older adults, the Essential Amino Acid 9 (EAA-9) score has been developed as an alternative to DIAAS and PDCAAS [Forester et al. 2023]. As such, EAA-9 scores can be used to ensure that dietary recommendations are met for each essential amino acid, in the context of precision nutrition.

Animal protein and non-protein nutrient adequacy

Besides being of nutritional relevance as such, 'animal protein' is also a proxy for the supply of highly bioavailable priority micronutrients [see elsewhere]. In a 12-w randomized controlled trial, diets with only 30% of the protein coming from animals led to lower vitamin B12 intake and status compared to a 50% share, which in turn was lower than for a 70% share; iodine intake and status were also lower in diets set at 30-50% of animal protein compared to 70% [Pellinen et al. 2022]. Modelling suggests that animal protein should be about 50% of total protein to avoid dietary inadequacy. A 40% contribution could be suitable for some populations, but 30% would probably be too low [Vieux et al. 2022; Tome et al. 2024]. As a reference, the contribution of animal protein to total protein in global diets is currently 10-30%, 20-40% 30-60%, and 50-70% for most low-, lower-middle-, upper-middle-, and high-income countries, respectively [Drewnowski 2024; see elsewhere]. Finally, reaching protein adequacy on a vegan diet may also lead to a higher intake of ultra-processed foods [Leitão et al. 2024], which are often poor in nutritional content other than protein [see elsewhere].

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