I think most veg*ns in countries where meat consumption is high, such as the UK where I live, are accustomed to being asked "Where do you get your protein?" but it's widely accepted that even vegan diets provide plenty of protein, though sources of lysine may need to be consciously included.

Nonetheless, whenever I enter a health food shop online or off, I find loads of vegan protein supplement products. In and out of such contexts, I often feel like advertisers are urging me to load up on protein, while cutting down on fat and carbs.

However, I frequently get emails from vegan organisations with statistics about North Americans and Europeans eating much more protein than they need (but nowhere near enough fibre, and falling well short of recommendations on eating fruit and vegetables). These statistics would be more useful to me if I could explain why eating too much protein should be discouraged.

I think eating more protein than the optimum quantity for good health is bad in terms of resources, carbon footprint, equity and so on, but I am being encouraged to think that there are health reasons to avoid eating excessive protein and I don't know whether that is true.

What are the disadvantages of consuming more protein than is necessary for good health?

  • Is this a question about outreach?
    – Nic
    Commented Dec 30, 2018 at 1:34
  • @Nic I didn't think of it that way
    – Zanna
    Commented Dec 30, 2018 at 6:44
  • I am well used to such questions. I have been vegetarian and near vegan for 40 years now. It used to be much worse. Many people would not believe that it was possible to be healthy, or even stay alive, without me. Even pointing out that I was still alive did not convince some. I argue that we get enough protein but I don't claim that they might be getting too much. Including claims with poor evidence may weaken your case.
    – badjohn
    Commented Jan 4, 2019 at 15:06

5 Answers 5


A recent and oft-cited scientific literature survey concludes (from the abstract):

The adverse effects associated with long-term high protein/high meat intake in humans were (a) disorders of bone and calcium homeostasis, (b) disorders of renal function, (c) increased cancer risk, (d) disorders of liver function, and (e) precipitated progression of coronary artery disease.

a) includes heightened risk of osteoporosis, b) means malfunctioning kidneys, development of kidneystones, and quicker dehydration, e) means heightened risk of a heart attack. Metabolizing proteins for lack of carbohydrates also causes bad breath.

  • That is NOT the conclusion of the study. You have misquoted based on the abstract, not even the abstract of the conclusion sais what you say the conclusion sais. Even then, it's a poor quality meta-study with no explication of methodology and zero statistical analysis apparent. Commented Dec 27, 2018 at 3:25
  • @Metatron I didn't say that I qouted the conclusion. I said this is what the literature review concludes. It's not a great study, I agree. Feel free to write a different answer, based on better studies. Commented Dec 27, 2018 at 9:33
  • Fair enough. As far as a better answer goes, the studies either don't exist or are unavailable to mere mortals like us - that's my greatest bugbear. Commented Dec 27, 2018 at 10:05

I did not find any reliable source that would claim that high protein intake is harmful for healthy people with normal kidney function.

Dietary protein intake and renal function (Nutrition and Metabolism, 2005)

While protein restriction may be appropriate for treatment of existing kidney disease, we find no significant evidence for a detrimental effect of high protein intakes on kidney function in healthy persons after centuries of a high protein Western diet.

According to the same source, high protein intake is also not a risk factor for kidney stones.

According to NAP.edu, high protein diet is not associated with coronary heart disease, obesity or cancer.

There seems to be no known side effects of long-term (>20 years) high-protein diet (Diabetes Care).

According to two articles in PubMed and Journal of Nutrition, consumption of protein from plant sources is associated with better health outcomes than protein from animal sources, but the direct cause-effect relationship is not certain.

I agree that high protein diet that would include very little dietary fiber could be bad for health.


Too much protein causes a high BUN (Blood Urea Nitrogen) in a standard blood test. I am on a vegetarian diet (not by choice) and the doctor recommended to lower the protein level of my food because of a consistently high BUN. I believe it stresses the kidneys.


From a simple point of view, too much protein will cause a back up in the digestive system, especially if the fibre intake is low or non-existent. Holding onto waste is detrimental to good health as it will cause a sense of feeling full which can lead to loss of appietite or lessen food intake. It can cause constipation or impaction that can lead to hemorrhoids, piles, and anal fissures, which can lead to serious infection, surgery and even death. There are many studies that prove fibre is essential, by not eating enough fibre it can lead to cancer. NurtionFacts.Org has a lot of helpful and useful information on health and food.

  • 1
    Hi. Would you mind extending your answer by adding some links/references for your claims? You mentiond a certain website, it would improve the answer if you could perhaps link to a specific article on said site which talks about the subject in more detail. Commented Jan 27, 2019 at 12:05

Yes it's true, too much protein is not healthy, even if it's plant protein, because our body is "made" to use carbohydrates for energy and protein for building (muscles, tissues, hormons and so on), when it must use protein for energy because of lack of carbs or because of too much protein, this causes a hyperacidity, that means our body becomes sour, and this is very dangerous and can cause many deseases, first of all cancer and rheuma, but also kidney problems and many other things. Calculate your protein need (more or less 1g/Kg bodyweight, if it's plant protein) and adjust your intake.

  • 1
    Hi Silvia, welcome to Vegetarianism SE. I personally agree with your overall answer but was wondering if you could maybe provide some sources for the claims about the effects on the organism, like hyperacidity and such? Would like to learn more. Commented Aug 10, 2020 at 13:30
  • Hi Alexander, thank you very much for you suggestion, sorry but this is not my way of working, I am a clinical working therapist, not a scientific writer, so I guess I'm here in the wrong place. Sorry, I thought you really need some help so I gave useful suggestions. I have surely not the time nor the will to look for studies about all things I write, that would take too long, and I cannot write the source I have learned the things I write because they are mostly not in Internet, either they are books (in german) or it's clinical experience, mine or my former teachers'. Thank you
    – user3928
    Commented Aug 10, 2020 at 14:21
  • 1
    Simple, don't post then. SE isn't a blog. Additionally, the fact that you're a therapist has nothing to do with nutrition (needless virtue signaling).
    – adamaero
    Commented Aug 10, 2020 at 16:38

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