protein requirements

I don't know if I agree with what has been said regarding protein amounts needed, as far as I am aware from a leading Heart specialist vegetarians and animals get their protein from plants. Cattle Sheep etc don't have protein themselves they get it from the grass and plants they eat. The strongest animals in the planet the elephants and the gorilla's and in roman times the gladiators were and are vegetarians. Protein requirements I understand from the many doctors who support a WFPB diet state there has never been anyone who has suffered from a deficiency in protein and that you don't need a lot of vegetable to sustain your daily requirements. Everyone choice I know and I originally thought big chunks of steak were the only source of protein available.


  • @Podge

    When I discuss protein, I always emphasize that there is a big difference between deficiency and optimization. Provided someone is consuming enough calories, protein deficiency won't really occur. That said, it's possible that a low protein intake may not provide all needed amino acids or make it challenging to get enough of the nutrients found in protein foods, such as iron and zinc.

    In addition, athletes are a population that would be considered exempt from the RDAs for protein. Depending on their sport (and where they are in their training schedule), protein needs can become quite high.

    Hope this adds some clarification!

    Kind regards,

    Susan Macfarlane, MScA, RD
    Registered Dietitian Nutritionist
    As always, any and all postings here are covered by our T&Cs:

  • Many Thanks for your well detailed reply and help.


  • I have been reading that due to sarcopenia it is actually important for older people, such as myself, to eat more protein, equivalent to 1g/lb of body weight. And that lean meat is the most effective way to get the necessary amino acids and certain minerals in a more calorie efficient way. Would love thoughts.

  • Ruminants (cows and sheep) aren't really vegetarians. They eat grass to feed their microbiome, and they actually ingest the byproducts of the microbiome, and the bodies of the bacteria etc. Similarly in the hind gut of a gorilla, starches, sugars and fibres are fermented to produce the fats and proteins that are not in the foods they forage. We have much smaller digestive systems. We can't do this with our foods.

    And there is little evidence that gladiators were vegetarian. They ate a lot of grains, but nothing to suggest there was not meat, fish, dairy etc in their diets. Interestingly, apparently one reason they were given a lot of barley is to get a layer of fat to protect them from swords. Grains had the same effect on me, without the swords. But mostly they got it because they are slaves with short lives and grain is cheap. As long as they were well matched, you got a good show.

    It more informative to look at what the Romans army ate, while they concurred the world. Hint: they were not vegetarian.

  • We definitely shouldn't be basing nutrition recommendations on what gladiators did or did not eat - thankfully, nutritional science has come a long way :).

    Susan Macfarlane, MScA, RD
    Registered Dietitian Nutritionist
    As always, any and all postings here are covered by our T&Cs:

  • At the end of the day, the only important issue with respect to protein is that averaged over a 3-5 day period we consume the amount of total amount of protein that our bodies require, AND that we get at least the RDI for all of the essential amino acids. The average period is because our bodies aren't stupid and maintain a pool of free amino acids representative of the average of each amino acid consumed in the previous 3-5 days.

    It doesn't matter at all the source of that protein. It could be animal muscle, breast milk or birds ova, or it could be entirely from plants, or any mixture of the two. As for plant protein, all plant sources of protein contain some amount of ALL of the essential amino acids (EAAs). Saying plant proteins are "incomplete" as in plant proteins are devoid of one or more EAA is factually wrong. In fact the only source of protein that has zero amount of an EAA is gelatin, which comes from the cartilage in the joints of animals and which is boiled out of the bones after all the flesh is cut off, and is what is used to make "Jello". Gelatin is completely lacking in the EAA tryptophan. All other food, plant or animal, contain some amount of every EAA.

    An unappreciated fact where it is often said that plant proteins are lacking in one or more EAAs is that ALL EAAs ultimately from plants. This is because ONLY plants can make any of the EAAs from scratch. No animal is capable of making any of the EAAs from the basic chemical constituents, and so must get all of the EAAs they require from their diet the same as we do. So the EAAs in muscle tissue, organs, ova or breast milk are ultimately all made in plants and then are filtered through the body of an animal.

    However proteins from animal derived foods are judged to be sources of "High Quality" proteins often because they are misidentified as being the only source of "complete protein". This is for two reasons. One is that it is no surprise that our closest evolutionary cousins will have bodies made of proteins very similar to our own. Thus proteins from animals are judged to be "Higher Quality" since our body will have exactly the right ratio of each of the EAAs to make nearly identical proteins in our own bodies. Also animal foods are judged to be a "Higher Quality" source of protein because animal cells are less robust and so are more quickly broken down and their protein absorbed.

    Plants on the other hand are judged to be "Low Quality" sources of proteins, often mistakenly said to be "missing" one or more EAAs and thus are "incomplete" proteins. What is true is that the ratio of the EAAs in plant proteins are not as close a match to the proteins in our bodies. Also plant cells are tougher than animal cells and so take longer to break down and absorb. Fortunately, human, unlike carnivores, have very long and winding small intestines which gives a longer time for our digestive system to finish breaking down the food and absorbing the protein. The difference in absorption of the total protein present in animal and plant foods with a similar percentage of calories from protein is only a few percent. (

    In practice none of this matters. The only thing that matters with respect to protein is that our total diet provide sufficient amounts of absorbed protein and the amounts of each of the EAAs that are absorbed, again averaged over several days, meets or exceed the number of milligrams per day for each EAA research shows is sufficient and which is the basis of the Recommended Daily Intake (RDI) for each EAA issued by the USDA and the World Health Organization.

    This is because once a protein is broken down to individual amino acids and absorbed into the bloodstream, there is no way to tell whether a given amino acid came from a "High Quality" protein or a "Low Quality" protein. But it is human nature to prefer something that is "High Quality" over something that is "Low Quality". And thus many people, including nutritional professionals, falsely believe that we need to consume animal products with their "High Quality" "complete" proteins in order to meet our protein needs. And that a diet of only plant foods, with their "Low Quality" proteins is somehow deficient either in protein or at least in one or more EAAs.

    This is simply not true. Many researchers have tried and failed to create a protein or EAA deficient diet contain only whole plant foods which contain enough calories to maintain weight or provide gradual weight loss. In fact whole plant based body builders do not have any difficulty consuming the small amount of extra protein necessary to add more muscle tissue since their strenuous workouts require more calories, and by consuming the additional whole plant foods necessary to provide the extra calories by default they get the extra protein they need to add muscle.

    It is certainly possible to cobble together a plant based diet high in refined sugars and carbohydrates and pure plant oils, which have a lot of calories and little or no protein, that is deficient. But the same can be done with flesh based diets if these protein free foods are allowed to displace sufficient amounts of protein containing food.

    Interestingly, the "Low Quality" nature of plant protein might be why they have been shown to be healthier overall. This is because, again, our bodies are not stupid. It is definitely easier to build muscle and other tissue if the protein consumed as exactly the right ratio of EAAs. So when we do consume a piece of an animal our body recognizes that we have eaten something that is in fact perfect for building tissue. So our bodies increase the amount of a hormone Insulin-like Growth Factor one (IGF-1), which is the primary growth hormone in adults. IGF-1 is like our body saying "build something". So any muscle or tissue repair or hormone manufacturing that needs to be done, now is a good time to do it. But it also tells things we don't want to grow, like cancer, to start growing as well. In the early history of humans a large meat meal only came along somewhat infrequently and most of the times we lived on plants (that don't run away or fight back). Then increasing the amount of IGF-1 was a good thing. But now with most people eating large amounts of these high quality proteins multiple times every day, our tissues are being continuously bathed in high levels of IGF-1. This has been shown to be a large part of why people now have much higher rates of cancer, and at younger ages than ever before. We know it is the IGF-1 because there is a specific mutation that runs in families and results in no production of IGF-1. Those with this mutation also have a particular type of dwarfism. Those with this mutation also never develop cancer. In a lab study, the blood of women consuming a standard diet was dripped on breast cancer cells. The women were put on a plant-based diet for two weeks at which point their blood was dripped on a new culture of breast cancer cells. Cancer grow rate plummeted compared to that of just two weeks prior. But when the amount of IGF-1 equal to the reduction IGF-1 in each woman after two weeks eating plant based was added back, the cancer growth rate was the same as it was before they started eating plant-based.

    So please don't be mislead about the superiority or necessity of protein from animal sources. Eat whole plant foods, enjoy all of the many health benefits from eating plants and don't worry about protein.

  • Oh, and I highly recommend this paper by Dr. David Katz at the Yale School of Public Health

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