11

Dr. John McDougall writes:

People commonly believe: the more protein consumed the better. This faulty thinking dates back to the late 1800s, and was established without any real scientific research. [...] After observing the diets of laborers, soldiers, and workers in Western Europe and the USA, recommendations of 100 and 189 grams of protein a day were established.

and

The World Health Organization (WHO) recommends that men and women obtain 5% of their calories as protein. This would mean 38 grams of protein for a man burning 3000 calories a day and 29 grams for a woman using 2300 calories a day. This quantity of protein is impossible to avoid when daily calorie needs are met by unrefined starches and vegetables.

The idea that a basic vegetarian diet contains enough protein for health goes completely against the conventional thinking one hears everywhere, even from the experts (in the US, at least).

Who is right? Do humans need high-protein foods, or does a diet consisting of unrefined starches and vegetables contain enough protein?

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    What is the "conventional thinking" that these excerpts go against? As it goes, your two quotes don't quite line up - there's quite a difference between 100-189g and 29-38g - so what is the notable claim you're skeptical about, and what evidence do you have to support that? – HorusKol Jul 14 at 4:26
  • @HorusKol That's the point. 100-189 >> 29-38 – MaxB Jul 14 at 8:15
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    I think the claim is clear: It is widely believed that you need a large amount of protein and should try to meet that through diet (the corollary being vegetarian diets are difficult to maintain. The WHO (and various proponents of vegetarian diets) have more recently claimed that you don't need a large amount of protein, and you can basically ignore your protein needs if you are on a vegetarian diet. Who is right? – Oddthinking Jul 14 at 11:44
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    @LangLangC: The question was slightly clarified before your comment. I have to agree that when I read "lettuce with honey and plant oils" I wondered why you chose that as your baseline, rather than a typical vegetarian diet without special supplements - e.g. what a naive vegetarian might adopt and what carnists commonly dismiss as dangerously low in protein. – Oddthinking Jul 16 at 15:14
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    "Need" for what, exactly? Dietary requirements aren't independent from your lifestyle and what you intend to do with your body. – Ruther Rendommeleigh Jul 18 at 15:00
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Summary

In short: minimal protein intake requirements are unknown to this level of precision. But if high-protein is equated with animal-protein, then no, animal-protein is not really needed.

Animal protein is of excellent quality and high bio-availibity, and is not undesirable in the right amounts. To maintain adequate protein in a diet, diets which incorporate animal-derived protein are easier to maintain, and easier to compose, than those without.

While mal- and undernourishment can occur in all dietary patterns, vegetarianism as such increases the risk for inadequate protein supply slightly, and veganism slightly more. However, in affluent socio-economic conditions, protein-intake in observed patterns was found to be mostly adequate on average.

In case you don't believe this or don't care to read the detailed breakdowns below, just head over to Eat-This-Much / Put your diet on autopilot (excuse this ad, alternatively, play with nut):

  • Choose 'vegan' as dietary preference
  • 3000 calories as your target intake
  • Press calculate.

You can see that the algorithm produces quite simple, exclusively plant-based meal-plans that probably very well exceed the recommended minimum for dietary protein input.

Limited evidence for minimum protein requirements

As long as energy requirements are met with natural – that is largely minimally refined variety of food – protein-deficiency will most probably not occur as the main problem of a diet.

–– Jessica Brown: "We Don't need Nearly as much Protein as we Consume", BBC Future, 23 May 2018.

Summarised for lay-people:

One ounce (30 grams) of most protein-rich foods contains 7 grams of protein. An ounce (30 grams) equals:

1 oz (30 g) of meat fish or poultry
1 large egg
¼ cup (60 milliliters) tofu
½ cup (65 grams) cooked beans or lentils
1 tbsp (14 grams) peanut butter
Low fat dairy is also a good source of protein.

Whole grains contain more protein than refined or "white" products

As a function of ratio of protein to calorie consumption the guideline is most probably a much less than optimal marker.

New concepts about protein for the Dietary Guidelines

  • Protein is a critical part of the adult diet
  • Protein needs are proportional to body weight; NOT energy intake
  • Adult protein utilization is a function of intake at individual meals
  • Most adults benefit from protein intakes above the minimum RDA

–– Donald K Layman: "Dietary Guidelines should reflect new understandings about adult protein needs", Nutr Metab (Lond). 2009; 6: 12. 2009 Mar 13. doi: 10.1186/1743-7075-6-12

The above is an opinion piece that criticises older guidelines and has to be read with a lot of caveats regarding the 'benefit' and 'RDA' part

The absolute minimum is probably quite low, especially compared to the magical thinking of Liebig's time, where meat and thus protein was 'a piece of life-force'.

True safe minimal protein requirements are not known.

Not in the least because experimental studies about this are made with healthy adult humans, not with children, pregnant or lactating women, starving, sick or elderly people. For those groups only observational studies are available.

But also because almost every 'natural' food contains protein. Refined sugar does not, but refined wheat flour or polished rice does.

The method for establishing a policy goal is therefore based on calculations and estimates of a poorly understood protein metabolism, with safety margins added at all points in all directions.

The main points of orientation are "what do people do", "when do they starve". As it seems evident that large amount of protein eaters are not healthier than low-amount eaters on a population level.

As long as energy requirements are met with regular food the minimal amount of needed protein seems to be acquired on average.

The staple foods of cereals shows that wheat has excellent protein amount but of low quality, rice even in polished form lower amount but higher quality, and sorghum and maize both with lower amount and quality compared to the others. But all can sustain a population, as history has shown.

With 'quality' we understand the digestibility, bioavailibility and amino-acid composition. Of 20 proteinogenic amino-acids only those called essential are truely needed and only those can pose a really limiting factor for human diets, but they are seldom named in macronutrient analyses and recommendations on the population level.

Based on short-term nitrogen balance studies, the Recommended Dietary Allowance of protein for a healthy adult with minimal physical activity is currently 0.8 g protein per kg body weight (BW) per day. To meet the functional needs such as promoting skeletal-muscle protein accretion and physical strength, dietary intake of 1.0, 1.3, and 1.6 g protein per kg BW per day is recommended for individuals with minimal, moderate, and intense physical activity, respectively. Long-term consumption of protein at 2 g per kg BW per day is safe for healthy adults, and the tolerable upper limit is 3.5 g per kg BW per day for well-adapted subjects. Chronic high protein intake (>2 g per kg BW per day for adults) may result in digestive, renal, and vascular abnormalities and should be avoided.
–– Wu G: "Dietary protein intake and human health", Food Funct. 2016 Mar;7(3):1251-65. doi: 10.1039/c5fo01530h.

Protein 'completeness' of individual foods is now seen as less important than previously, as the body maintains a pool of amino acids to combine into proteins so that typically lysine-deficient cereals in one meal could be compensated for with the next lysine-richer meal.

Special needs like climate, illness, activity level and genetic disposition make this so complicated that a number digestible for general consumption of all 'humans' 'across the world' is unattainable, only rough guidelines.

Human adaptability also means the depending on input and need the protein metabolismcan change. As long as primarily energy requirements are met, plus aother nutrients, the need for dietary protein in homeostasis is quite low. In non-growing, non-pregnant, non-lactating people. Symptoms though losses take a long time to manifest in non-starvation/non-weight-loss scenarios. Amino-acids are relatively effectively recycled internally and shedded hair, skin or gastrointernally are low. This adaptability makes nitrogen-balance studies therefore limited in value for estimating the minimal requirements.

enter image description here
Schematic representation of the metabolic demands for amino acids.

enter image description here
Distribution of reported values for the protein requirements showing values for safe individual and population intakes. The bars are the distribution of individual values of intakes for nitrogen equilibrium expressed as protein equivalents (n 1⁄4 224 individual subjects from n 1⁄4 32 studies, after a 5% trim of outliers) from a meta analysis of N balance data reported by Rand et al. (2003). The minimum requirement after full adaptation is not known but likely to be less than the median value within the range shown.

These diverse biological demands for amino acids for maintenance represent an essential but probably quite small intrinsic metabolic demand for an equivalent amount of protein. The magnitude of this maintenance component is assumed empirically to be equal to the obliga- tory nitrogen loss (ONL) – that is, the sum of all nitrogen losses from the body observed in subjects fed a protein-free but otherwise nutritionally adequate diet after 7–14 days, by which time nitrogen losses have declined to a stable and re- producible low level with the subjects losing body protein at a constant daily rate. In normal adults, the daily obligatory urinary, fecal, and subcutaneous and other losses are ap- proximately 32, 10.5, and 4.8 mgN kg 1, respectively (i.e., 47.1 mg kg 1 d 1), in total equivalent to about 0.3 g protein per kg per day tissue protein mobilized to meet such demands. The ONL is a function of body weight and, as far as is known, varies little with age. After adaptation to a protein-free diet, net tissue proteolysis is assumed to provide for the nonprotein components of the obligatory demand at a rate determined by the metabolic consumption of the rate-limiting amino acid (the amino acid with the highest ratio of molar proportion in the metabolic demand to molar proportion in protein). Be- cause the obligatory metabolic demand is for a mixture of amino acids with a profile that is unlikely to match that of tissue protein, the actual nitrogen content of the metabolic demand is likely to be less than that indicated by the ONL (i.e., less than an equivalent of 0.325 g protein per kg per day).
–– Lindsay H Allen & Andrew Prentice & Benjamin Caballero (Eds): "Encyclopedia of Human Nutrition", Academic Press, 2013.

A WHO report on the matter, discussing the resulting policy recommendations based on the scientific estimates:
–– WHO Technical Report Series, 935: "Protein and Amino Acid Requirements in Human Nutrition", 2002.

There is little evidence that muscular activity increases the need for protein, except for the small amount required for development of muscles during conditioning. However, vigorous activity that leads to profuse sweating, such as in heavy work and sports, increases nitrogen loss from the skin. There is evidence, however, that with acclimatization to a warm environment, the excessive skin loss is reduced and may be partially compensated by decreased renal excretion. In view of the margin of safety in the protein allowance ance, no increment is added for work or training.

The recommended allowances for protein do not differ greatly from the 9th edition RDAs when considered on a g/kg body wt basis, although the basis for deriving them, especially for the adult, has changed significantly. The reduction of the allowance for very young children from 2.2 to 2.0 gkg-1 d’ is still well above the mean intake of 1.68 gkg-1’d found to maintain satisfactory growth in the United States. A more practical recommendation however is that the protein needs for this young age group will be met if the energy needs are met, provided that the food contains protein of quality and quantity equivalent to that of human milk. Allowances for children and adolescents now decrease from 1.64 g/kg at age 1 y to 0.83 g/kg at age 18 y compared with the previous values, which decreased from 1.80 to 0.80 g/kg over the same age range. The slight reductions are a result ofa reevaluation of both nitrogen balance data and the the FAO/WHO/UNU protein-requirement panel.
–– Peter L Pellett: "Protein requirements in humans", American Journal of Clinical Nutrition, 1990; 5 1:723-37.

Limited benefits and upper limits of high-protein diets regardless of source

Even in the other direction a protein intake that is through necessity of circumstances too high (Rabbit starvation or better protein poisoning) or because of unreasonable affluency resulting in 'self-optimisation' and the following of protein-myths is not precisely definable.

–– Stuart M. Phillips & Luc J.C. Van Loon: "Dietary protein for athletes: From requirements to optimum adaptation", Journal of Sports Sciences, Volume 29, 2011, p S29-S38.

Research on how much protein is the optimal amount to eat for good health is ongoing, and is far from settled. The value of high-protein diets for weight loss or cardiovascular health, for example, remains controversial.

One more thing: If you increase protein, dietary arithmetic demands that you eat less of other things to keep your daily calorie intake steady. The switches you make can affect your nutrition, for better or for worse. For example, eating more protein instead of low-quality refined carbohydrates, like white bread and sweets, is a healthy choice — though how healthy the choice is also depends on the total protein package.

If weight loss is your main concern, trying a higher-protein diet is reasonable, but don’t expect it to be a panacea. “Patients come to me all the time asking if more protein will help them in weight loss,” McManus says. “I tell them the verdict is still out. Some studies support it, some studies don’t.”

–– Daniel Pendick: "How much protein do you need every day?", Harvard Health, June 18, 2015, 4:22 PM , Updated June 25, 2019, 1:06 PM

Observed diets in highly active populations

The above assumes that a minimum requirement is the focus of "need". Strictly speaking Do humans need high-protein foods? has to be answered with "yes, of course". No one can reasonably expect to survive on an exclusively low protein diet of lettuce with honey and plant oils. "Do they need animal-derived high-protein foods?" No, but animal-protein foods make it easy to meet demands.

But how much nutritional science may have advanced since ancient times, it still isn't much ahead of the general advice of "everything in moderation".

And regarding meat vs animal protein: it is abundantly clear that in former times a restricted diet may have led to undernourishment due to protein. A hunter-gatherer living off of berries had a hard time meeting protein requirements that was then easily met with one meaty meal. But once food sources become diverse, the omnivoric nature of man pays off in having a large range of choices.

If we just look at professional athletes with everything food and everything science and everything experience at their disposal – and what they ate, we see:

Scientific texts saw in such overeating not gluttony, but a poor physical condition, making athletic training the sign of a bad body. A hippocratic text from the end of the fifth century criticizes a meat diet as causing diarrhea in some athletes and in the fourth century aristotle criticizes the vast diets of athletes for destroying the good proportion of the body ([hippocrates] Nature of Man 22, Regimen in Health 7; aristotle On the Generation of Animals 768b29–35; Visa 1992: 278–80; Golden 1998: 157–8).

–– Nigel Nicholson: "Representations of sport in Greek Literature" (in: Christesen & Kyle, 2014).

Gladiators’ bones can reveal much more information than just how these men died; they can also tell us vital facts about how they lived. For example, isotopic analysis of their bones has revealed that they ate a mostly vegetarian diet that was rich in carbohy- drates. One slang term for gladiators was hordearii, or “barley boys,” and this scientific analysis confirms that gladiators indeed probably ingested large quantities of grains. On such a diet, gladiators may have carried substantial layers of fat that actually would have helped them survive superficial cuts and slashes by blanketing vital organs and vessels under a thick fatty stratum.

–– Gregory S. Aldrete: "Material Evidence for Roman Spectacle and Sport", in: Paul Christesen & Donald G. Kyle: "A Companion to Sport And Spectacle in Greek and Roman Antiquity", Wiley-Blackwell: Chichester, 2014.

That these peaceful vegetarians called gladiators achieved their dietary goals may sound surprising, but the methods employed seem to indeed include 'supplements', but not for protein, for calcium.

–– Andrew Curry: "The Gladiator Diet", Archaeology, Volume 61 Number 6, November/December 2008. by

Animal-protein compared to plant-protein in dietary needs

A very simple calculation to establish a frame. Using the two established staple foods of wheat and potatos, equal weight until 3000 kcal are reached, with 1g protein providing 4.1 kcal:

   100g wheat + 100g potato 
=  200g food with 732.15 kcal and 14.6g protein
=> 732.15 * 4,098 = 3000 kcal and 14.6 * 59.82 g protein
=> 59.82g protein * 4.1 kcal = 245,28 => 8.18 % total energy from protein

Compared to the 5%/38g from the claim this a condition met. With this level of protein quality protein–energy malnutrition is unlikely to occur. Although hunger and starvation still are a problem in many parts of the world. But the profiles for essential amino-acids and nourishments from both staple foods are even higher than the measurement 'protein' suggests.

Wheat is considered non-ideal protein, as it had a too low lysine content. Combined with potatoes however:

Potato is a very good source of high quality protein. Average protein content of potato is 2% on fresh weight basis. The crude protein content in potato is higher than other major root and tuber crops lke seet potato, yam and cassava. Potato protein has a very high biological value because all essential amino acids are present in good proportion in it. It is much higher than major cereals and higher than even proteins of animal origin like milk and beef. With its high lysine content, potato can supplement diets which are limiting in lysine. Potato has a clear advantage over cereals in India because of its ability to provide high quality protein. –– Dhiraj K. Singh: "Potatoes: A complete Food", Agropedia, 2014.

Non-animal protein is also high in quite a number of other sources.

Hemp seeds, hulled, have 586 kcal per 100g of which 31.56 g are protein. Even if adjusted for Protein Digestibility Corrected Amino Acid Score, a score important for the quality of isolated protein of a single food – but less meaningful if foods are combined in a meal or through the day – we see

In summary, the protein from hemp seed is highly digestible in either its native form or as a hemp seed meal. Removal of the hull fraction from the hull improves the digestibility of the protein and the corresponding PDCAAS, likely due to the removal of significant NDF components that may limit protein digestion. While the lysine content of hemp proteins limits the PDCAAS valuation, using current accepted methods for the estimation of protein quality, the overall pattern of amino acid supply, including the relative abundance of arginine, position this protein source as a viable, vegetable-based protein for the human diet.
–– James D. House: "Evaluating the Quality of Protein from Hemp Seed (Cannabis sativa L.) Products Through the use of the Protein Digestibility-Corrected Amino Acid Score Method", J. Agric. Food Chem.2010582211801-11807

In other words, from an observational study of actual diets in affluent societies, a vegan diet indeed has typically lower protein score, often problems with calcium and B12, but for protein it is usually still 'fine':

The most restricted diet, i.e., the vegan diet, had the lowest total energy intake, better fat intake profile, lowest protein and highest dietary fiber intake in contrast to the omnivorous diet. Calcium intake was lowest for the vegans and below national dietary recommendations. The vegan diet received the highest index values and the omnivorous the lowest for HEI-2010 and MDS. Typical aspects of a vegan diet (high fruit and vegetable intake, low sodium intake, and low intake of saturated fat) contributed substantially to the total score, independent of the indexing system used. The score for the more prudent diets (vegetarians, semi-vegetarians and pesco-vegetarians) differed as a function of the used indexing system but they were mostly better in terms of nutrient quality than the omnivores.

              Vegans Omnivores
Total energy  2383   2985
Protein (g)     82    112 

–– Peter Clarys: "Comparison of Nutritional Quality of the Vegan, Vegetarian, Semi-Vegetarian, Pesco-Vegetarian and Omnivorous Diet", Nutrients 2014, 6, 1318-1332; doi:10.3390/nu6031318

Malnourishment can occur under any type of diet, and is clear that omnivorous diets are easier to maintain and under them it is easier to meet protein needs, not in the least because of established societal diet-patterns, also known as traditions. An extremely naive of otherwise additionally input restricted vegetarian or even vegan diet is therefore a bigger potential risk-factor, but still not risky. For the edge-case of pregnant women:

Althought plant-based diets are at risk of nutritional deficiencies such as proteins, iron, vitamin D, calcium, iodine, omega-3, and vitamin B12, the available evidence shows that well planned vegetarian and vegan diets may be considered safe during pregnancy and lactation, but they require a strong awareness for a balanced intake of key nutrients.

Diet is one of the most significant lifestyle-related factors in determining health state and predisposing the offspring to develop several diseases. Vegetarian and vegan diets are emerging worldwide due to the evidence that plant-based dietary patterns reduce the risk of coronary heart disease, high blood pressure, type 2 diabetes, and cancer. Pregnancy is a critical window of opportunity to provide dietetic habits that are beneficial for fetal healthy. It is also an exclusive condition in which the requirements of energy and micronutrients intake increase to maintain the supply of essential nutrients for fetal development. Each stage of fetal growth is dependent on appropriate maternal nutrient transfer, so a balanced diet is essential to avoid fetal complications. The choice of vegetarian or vegan diet is always in the preconception period due to ethical reasons or poor social condition, so a well-adjusted preconception nutrition is essential for healthy pregnancy. Available data demonstrated that micronutrients insufficiency and caloric restriction are more common in developing countries, where vegetarian diets are chosen because of socioeconomic reasons. On the contrary in developed countries, the consciousness and the concern of a balanced diet is taken more into account. Generally it is difficult to verify the effects of such diets on pregnancy outcomes and to separate them from other confounding factors such as ethnicity, lifestyles or smoking.

Finally, the current manuscript supports the evidence that maternal nutritional status is the key condition for health benefits of plant-based diets. Vegetarians and vegans are at risk of nutritional deficiencies, but if the adequate intake of nutrients is upheld, pregnancy outcomes are similar to those reported in the omnivorous population. So updated evidence highlights that well-balanced vegetarian and vegan diets should be considered safe for the mother’s health and for offspring during pregnancy and lactation.
–– Giorgia Sebastiani: "The Effects of Vegetarian and Vegan Diet during Pregnancy on the Health of Mothers and Offspring", Nutrients, 2019 Mar; 11(3): 557. DOI

Limitations for recommendations

Animal-derived protein is an excellent source of nutrients. But a few things it is not. Among them: Neither to meet minimal requirements is it really needed, nor is it strictly necessary to achieve a really high-protein dietary intake, should that be perceived as somehow desirable.

While this answer does argue against 'meat is needed' it should not be read as a pro-vegan statement. A restricted, or vegan, diet is possible, but protein from animals is much easier to obtain, digest and metabolise. It is neither advisable to require meat, not advisable to require animal-protein abstention.

There are a few competing approaches to evaluate protein content in the macronutrient balance of any diet. The latest usually thought of as best. Taking one of the latest approaches it confirms the protein quality of any given single food to be highest among the animal proteins. The Digestible Indispensable Amino Acid Score as well as numerous studies with a different outcome measuring methology confirm that a diet that includes animal protein has not only a higher total protein content but also protein of higher quality.

–– FAO Expert Consultation: "Dietary protein quality evaluation in human nutrition", FAO Food and Nutrition Paper 92, Food and Agriculture Organization of the United Nations Rome, 2013. (PDF)

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    The last paragraph sounds like a strawman. By "high protein" I meant foods other than ones that Dr. M advocates, i.e. animal protein: fish, meat. milk. – MaxB Jul 15 at 7:04
  • Layman's paper has some disturbing conflicts of interest. – MaxB Jul 28 at 7:33
3

There is a discussion of this on Reddit:

I'm not sure that 5% should be recommended as a minimum, since studies show that people experience muscle mass loss at this level of intake. 10% is more reliable, 15% is even better. This report recommends 10-15%: http://www.who.int/mediacentre/releases/2003/pr20/en/

Protein recommended daily intake is usually in grams, not calories, and it is 0.8g per kg of body weight, or 56 grams for an average adult of 70 kg body weight. This recommendation should be here: http://www.who.int/nutrition/publications/nutrientrequirements/WHO_TRS_935/en/

If we then go to the two cited sources, we find that the first is a press release about an "Expert Report" (PDF). That says 10-15% of calories should be protein and refers to

The suggested range should be seen in the light of the Joint WHO/FAO/UNU Expert Consultation on Protein and Amino Acid Requirements in Human Nutrition, held in Geneva from 9 to 16 April 2002 (2).

which in turn leads to

  1. Protein and amino acid requirements in human nutrition. Report of a Joint WHO/FAO/UNU Expert Consultation. Geneva, World Health Organization, 2003 (in press).

That report is at PDF, the second link. It looks like chapter 5 is the relevant portion. It says things like (p. 84)

Energy requirements change not only with age, sex and size, but also with the physical activity associated with lifestyle. In contrast, in this report – as in the past – we define protein requirements as independent of size, sex (in adult life) and adult age. Thus “situation-specific” values of the protein:energy ratio of the requirement need to be calculated based on weight, age, sex and lifestyle (physical activity).

In other words, it regards a simplistic percentage of calories as incorrect. Tables 3 and 4 on pages 87 and 88 strive to give more specific advice.

Also pp 83-84:

A further complication in calculating the protein:energy ratio of the diet relates to the actual available energy content of foods, i.e. taking into account true digestibility and metabolizability of the dietary energy. The 1985 report suggested that the influence of dietary fibre on energy digestibility reduced available energy by 2–3% at moderate levels and by an additional 2–3% at the levels found in vegetarian diets. Thus a correction for a 5% energy loss was suggested for diets with “moderately large” amounts of fibre from fruit, vegetables and wholemeal bread.

  • The ratio to calories is mainly for total energy intake, aka obesity-prevention. But apart from that 'energy' is not the thing proteins can make for a limiting factor. We need protein – for making protein. In muscles, bones other tissues and 'stuff'. I think you need go for minimal requirements in that respect and also shed a spotlight on 'rabbit starvation', then diet compositions? Deficiency, homeostasis and build-up are all different, but I guess the claim aims between the first two? – LangLangC Jul 14 at 11:01
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    If I am reading this right, it appears to answer the question "Is the WHO right?" with an answer "The WHO agrees." I think we need an answer that goes down to the next level of references - why does the WHO believe that? – Oddthinking Jul 14 at 11:49
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    @Oddthinking I don't see the question as "Is the WHO right?" but as "Does the WHO says this?" And if you missed it, the answer seems to be "No, the WHO does not say that 5% calories from protein is enough. Further, that's the wrong way to measure it." – Brythan Jul 14 at 15:14
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    @Brythan: Ahh, then I was reading it wrong. Sorry. Jumping from an question in g, to an answer in percentages (and then rejecting percentages as inappropriate) is confusing. Perhaps a summary would help? – Oddthinking Jul 14 at 15:28
-1

According to the review article in Nutrition&Metabolism, 2009: Dietary Guidelines should reflect new understandings about adult protein needs, protein needs should be adjusted to body weight, not calorie intake.

World Health Organization (WHO) recommends 0.83 g protein/kg body weight/day (Protein and amino acid requirements in human nutrition, WHO.int, 2002). I have found no article from them that would recommend consumption of 5% of energy as protein.

Institute of Medicine in the U.S. has set Recommended Dietary Allowance (RDA) for protein at 0.8 g/kg body weight/day, which is 56 g/day for a 70 kg person (Institute of Medicine). Their recommendations are based on "high quality proteins*." A review article published in Advances in Nutrition, 2017: Optimizing Protein Intake in Adults agrees that 0.8 g/kg body weight is an appropriate estimation of minimal protein needs and that higher intakes may be beneficial for some, especially older, individuals.

According to the following review in Critical Reviews in Food Science and Nutrition, 2017: Vegetarian, vegan diets and multiple health outcomes: A systematic review with meta-analysis of observational studies vegetarian and vegan diets can be associated with lower mortality and risk of ischemic heart disease and cancer than omnivorous diets, which indirectly suggests that they can contain sufficient amount of proteins.

*PROTEIN QUALITY

High quality protein sources are those that contain high amount of essential amino acids that are well digestible and highly bioavailable. They appear mainly in animal foods (meat, eggs, milk). This doesn't automatically mean that you meet your needs for protein with lower amounts of animal than plant foods. Even if plant proteins are considered to be of lower quality, combining them from various plant foods can make them high quality. I'm not sure if, from a practical perspective, one needs to re-calculate the amount of protein he/she needs based on "protein quality." Also, there is some evidence that consumption of plant protein is associated with lower mortality and incidence of diabetes type 2 and ischemic heart disease than consumption of animal protein (JAMA Internal Medicine, 2016, USDA.gov).

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    All protein is not created equal. The type of protein (amino acids contained therein) is important. – Daniel R Hicks Jul 24 at 12:50
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    @DanielRHicks, I updated my answer. Combining various proteins that are by themselves considered low-quality can make them high quality. – Jan Jul 24 at 14:27

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