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Scurvy, Gout, and More: Why the “Carnivore Diet” Is Unhealthy – And What to Eat Instead!

The carnivore diet is on a steep rise - but many health advocates and nutritionists are worried about the long-term effects of this diet that makes no sense from a biological perspective!

Followers of the meat-only diet often report health benefits at first because they leave out unhealthy foods from their previous diet. In addition to avoiding processed foods, avoiding inflammatory plant foods like grains, nightshades, and high oxalate foods (and the like) undoubtedly can be beneficial for health. However, a high-meat diet can start to show its side effects after a while – like many followers report!

7 Reasons to Avoid the Carnivore Diet

Learn why the carnivore diet mismatches our biology in the first place and how to avoid inflammatory plant foods with another approach than the carnivore diet – by sticking to our proper dietary biology!

1. Humans are not carnivores

Let’s address the pink elephant in the room first: a carnivorous diet is the natural diet of biological carnivores. Humans are not biological carnivores, but frugivores. Most of us do not like raw meat like carnivores do – we feel repulsed even to see others eating it! Read about typical carnivore adaptations here.

Humans can eat meat, however, we are not adapted to a high-meat diet. To understand why, let’s have a look at our closest living relatives, the chimpanzees:

Chimpanzees are genetically, anatomically and physiologically very similar to humans – also in terms of diet. What do chimpanzees eat? Chimpanzees’ preferred food is fruit, which makes up around 70% of their diet. The rest is nuts, greens tubers, and other plant foods. Animal foods – mainly insects and eggs – make up a small portion of around 6%. And vertebrate meat (like smaller monkeys) is only eaten very rarely! Some populations and individuals have not been observed eating meat!

Chimpanzees are categorized as frugivorous omnivores, and in scientific literature they are referred to as frugivores – specialized fruit-eaters! In short, chimpanzees are biological frugivores – and so are humans!

Expand pics by clicking!

Why do humans eat so many different types of meat-heavy diets? Humans eat omnivorous diets due to our history and cultural background: We need to survive in colder climates when migrating out of the tropical habitats! Cooking enabled us to turn – otherwise inedible – non-foods into edible survival foods. Only tropical forests can sustain larger frugivores throughout the year. Read more here.

Not convinced yet? Maybe the following genetic fact does:

2. Carnivores synthesize their own vitamin C – humans do not!

We have a fascinating physiological signal that speaks clearly against carnivory in humans: we have lost our vitamin C genes, while carnivores did not!

Vitamin C is an essential nutrient for humans. This means we need to obtain it from food. Across animal species, only those with a high-fruit diet do not produce vitamin C themselves! Carnivores do synthesize vitamin C internally, because their diet does not contain enough vitamin C.

If this did not convince you, maybe the stress a high-meat diet puts on the kidneys does:

3. Human kidneys are not equipped for that much protein!

The human kidneys are not adapted to process the amount of protein in a high-meat diet. The trend of high-protein diets is highly damaging for kidney health, even for people with no previous kidney issues!

“…it is time to unleash the taboo and make it loud and clear that a high-protein diet is not as safe as claimed, as it may compromise kidney health…”

Kalantar-Zadeh et al., (2020)

Our ancestors avoided excess protein by choosing meat high in fats while avoiding lean meat (read more here). Humans kidneys are not adapted to excrete the amount of urea that carnivores do! Not surprisingly the kidneys of different dietary types (carnivores, omnivores, herbivores) are different in their urea permeability proportional to their natural meat intake (Liu et al., 2010).

On a meat-diet, not only is getting too much protein a problem for our kidneys, but also getting too little fibers is to our disadvantage, as a recent nature-published study concludes:

“Patients with CKD (chronic kidney disease) had insufficient vegetable and fruit intake and a lack of β carotene and dietary fiber from vegetables and fruits.”

Nakano et al., 2022

4. Raw meat is not appealing

Is raw and bloody organ meat or raw, fatty meat what humans would instinctually eat in nature?

Inuits – cold-indigenous people that survive on meat only – eat their meat raw. This practice helps to obtain important nutrients that are lost due to heating. Raw organ meat provides vitamin C! Inuits are also known to eat meats with a high fat content, which ensures enough energetic macronutrients and lowers the amount of protein (see below)!

The question arises: is raw meat instinctually what humans would prefer as their food source in nature? Or is this survival food? I tend towards the latter, due to our natural instincts and the low life expectancy of Inuits.

Humans do not naturally feel appealed by raw meat! We need to clean, process (heat), and season it to make it palatable! Humans have evolved to be appealed by sweet taste – an adaptation that hypercarnivores (obligate carnivores) do not have!

Carnivores naturally have the instincts (and anatomical adaptations) to hunt, kill, and eat their meat raw. Humans do not. Most of us are offended to see an animal being killed, and are disgusted to see someone eating raw meat, let alone feeling appealed to eat raw meat themselves!

This raw meat eater flavors the meat with sweet honey or salt… because he is not biologically “made” to actually like or eat meat

Besides instinctual approach, there is also a safety signal, showing us, that we are not optimized for eating meat:

Raw meat is not really safe for humans

All animals in the wild eat their foods raw. Everything that has to be cooked to be edible and appealing is not our natural food. (Read more about why we do not need cooked foods, and why our natural diet is still raw here!)

This has a good reason: raw meat is not safe for humans to eat. We do not have the immunity against meat-borne diseases that carnivores naturally have.

5. Gout and scurvy revival on the carnivore diet

Gout and scurvy are two well-known dietary diseases that certainly could become a problem on a carnivore diet:

Scurvy is back” is the title of this recent study, which raises awareness of the forgotten, ancient vitamin C deficiency disease. The comeback of scurvy results from a decrease in fresh food intake, especially in low-income parts of the populations in colder countries. However, the carnivore diet is certainly a potential candidate for a spike in scurvy. This is the reason for the newest movement within the community: the “meat and fruit” diet. 

Fruits bring missing nutrients into the diet without adding the unwanted anti-nutrients (see below). However, this improvement is merely an attempt to mitigate the damage of a meat-only diet! Simply adding fruit will not eliminate the health risks of this diet, because the sheer amount of meat alone is detrimental. This bring us to gout, another ancient dietary, meat-related disease:

Gout is a type of arthritis (accumulation of uric acid crystals) that has been well-known to be linked to a high meat intake. Gout is a combination of genetic predisposition for the condition, decreased kidney efficiency to excrete uric acid, and dietary intake of uric acid-forming foods (meat!). Meat is a double whammy in the development of gout, as the protein load negatively impacts kidney functions!

6. The ketogenic metabolism is not meant for long-term

The carnivore diet is a ketogenic diet – a very low-carb diet. The main issue with any ketogenic diet is that the energy production from fat is our back-up program under stressful condition – starvation!

Undoubtedly short-term periods of activated ketogenic metabolism, during fasting, are highly beneficial for regenerative processes. However humans have not evolved to run on the energy of fatty acids (ketogenic metabolism) long-term. Humans – as frugivores – are adapted to primarily run on simple sugars obtained from fruits!

Ketogenic diets, like the carnivore diet, force the body to produce glucose for the brain. Even on no-carb diets certain level of glucose are always maintained by the body! The process of synthesizing glucose – called gluconeogenesis – requires the stress hormone cortisol! In simple words: ketogenic diets cause a stress response in the body!

“On a truly traditional diet, says Draper, recalling his studies in the 1970s, Arctic people had plenty of protein but little carbohydrate, so they often relied on gluconeogenesis. Not only did they have bigger livers to handle the additional work but their urine volumes were also typically larger to get rid of the extra urea.”

www.discovermagazine.com

While ketogenic diets were praised as a panacea in the last decade or so, critical voices from the scientific field are finally getting louder: ketogenic diets are not safe!

“The ketogenic diet… may cause hyperlipidemia, vitamin and mineral deficiencies, fatigue, and kidney damage, among other complications. Increased acid production from a ketogenic diet may cause metabolic acidosis and related issues… people with chronic kidney disease and those without prior kidney problems are experiencing a decline in kidney function.”

Ayele et al., 2023

This is no surprise, given our evolutionary dietary background: frugivores are not meant to eat a carnivorous diet! Once more, simplicity is the ultimate sophistication.

When will nutrition science start to consider our evolutionary anatomy and physiology as tropical apes?

7. Not all plant parts contain harmful secondary metabolites

One (very valid) argument of the carnivore diet proponents is that plants contain toxins to protect themselves from predators. This is true, and is a problem in most of today’s diets.

But are the potent chemicals produced by plants all bad? No, some compounds are beneficial for health. Do all plant parts contain toxic secondary metabolites? No! Edible fruits are chemically friendly to humans!

Fruits do not contain the substances that the Carnivore Diet proponents warn us of. This is gaining importance in the light of humans being high-fruit creatures, which – unlike herbivores – have not evolved to live off green plant parts – and ingest high amounts of other plant parts than fruits! 

Plants communicate via chemical cues. Some cues are repelling to herbivores, which are self-protective chemicals. We recognize this as an unpleasant bitter taste. Some cues are highly toxic to consumers. However, some cues are appealing, like the smell of flowers – and of fruits! Why? Because the plant has the same goal as animals: survive and reproduce!

Plants warn and poison who damage them and attract mutualists that help them procreate, like pollinators and seed-dispersers. Fruit-eaters – including humans – are seed dispersers. It is an evolutionary dance between plant and fruit eater called “dispersal syndrome“, where the fruit is shaped in its taste and appearance to the preference of its seed-disperser.

Fruits – which have co-evolved with humans – do not have the protective secondary Phyto-metabolites towards us. So why are some types of fruits toxic? Because they have evolved with other seed-dispersing animals, like birds!

The point the carnivore diet is certainly right, is that plants do protect their vegetative parts (greens, roots) and their progeny, the seeds (grains, legumes) – in contrast to fruits, which is beneficial for the plant if eaten! Therefore it is in those parts, that we find all sorts of bioactive, potent phyto-chemicals!

Read more about the biological suitability of foods here.

Seeds contain the embryos of the plants, which contain the infamous “anti-nutrients” as protection from predators. Grain-eaters (granivores) contain special tolerance to those compounds – but humans do not! Grains and legumes are known to be inflammatory – not only by the carnivore diet community – for a good reason (read more here)!

However, to avoid those components, we do not need to consume a carnivorous diet, but instead, look to our biological adaptations – those of specialized fruit-eaters!

Conclusion: The carnivore diet is not suitable for humans.

Biology does not lie and shows us on many levels that the carnivore diet is not suitable for humans.

However, the idea of avoiding harmful phytochemicals found in many plant foods per se, is certainly plausible and health-promoting. To understand this conflict, we need to know about our dietary biology, which is that of highly frugivorous (fruit-eating) tropical apes!

Fruits do not contain the plant compounds that the carnivore diet followers strive to avoid! Therefore a high-fruit diet (frugivorous diet) is the evolutionary sound alternative to the carnivore diet!

Go to How to do the Frugivore Diet

If you are new to this, visit this overview about frugivores and frugivory here!

References

  1. B. S. Lennerz, J. T. Mey, O. H. Henn, D. S. Ludwig, Behavioral characteristics and self-reported health status among 2029 adults consuming a “carnivore diet.” Current Developments in Nutrition5, 5012005 (2021). (link)
  2. G. Drouin, J.-R. Godin, B. Page, The genetics of vitamin C loss in vertebrates. Current Genomics12, 371–378 (2011), doi:10.2174/138920211796429736. (link)
  3. K. Kalantar-Zadeh, H. M. Kramer, D. Fouque, High-protein diet is bad for Kidney Health: Unleashing the Taboo. Nephrology Dialysis Transplantation (2019), doi:10.1093/ndt/gfz216. (link)
  4. L. Liu et al., Erythrocyte permeability to urea and water: Comparative study in rodents, ruminants, carnivores, humans, and birds. Journal of Comparative Physiology B181, 65–72 (2010), doi:10.1007/s00360-010-0515-5. (link)
  5. Nakano, T. et al. (2022) ‘Low intake of β carotene and dietary fiber from vegetables and fruits in patients with chronic kidney disease’, Scientific Reports, 12(1). doi:10.1038/s41598-022-24471-4. 
  6. P. Gadsby, The Inuit paradox. Discover Magazine (2020) (available at https://www.discovermagazine.com/health/the-inuit-paradox). (link)
  7. Life expectancy in the Inuit-inhabited areas of Canada, 1989 to 2003 – Findings. Health Reports: Life expectancy in the Inuit-inhabited areas of Canada, 1989 to 2003 (available at https://www150.statcan.gc.ca/n1/pub/82-003-x/2008001/article/10463/4149059-eng.htm). (link)
  8. C. A. Callus, S. Vella, P. Ferry, Scurvy is back. Nutrition and Metabolic Insights11, 117863881880909 (2018). (available at https://pubmed.ncbi.nlm.nih.gov/30479485/). (link)
  9. G. Ragab, M. Elshahaly, T. Bardin, Gout: An old disease in new perspective – A Review. Journal of Advanced Research8, 495–511 (2017), doi:10.1016/j.jare.2017.04.008. (link)
  10. K. Milton, Nutritional characteristics of wild primate foods: Do the diets of our closest living relatives have lessons for us? Nutrition15, 488–498 (1999), doi:10.1016/s0899-9007(99)00078-7. (link)
  11. S. Watanabe, A. Hirakawa, S. Aoe, K. Fukuda, T. Muneta, Basic ketone engine and booster glucose engine for Energy Production. Diabetes Research – Open Journal2, 14–23 (2016), doi:10.17140/droj-2-125. (link)
  12. L. R. Engelking, Gluconeogenesis. Textbook of Veterinary Physiological Chemistry, 225–230 (2015), doi:10.1016/b978-0-12-391909-0.50037-2. (link)
  13. N. Helms, Is the keto diet safe? what are the risks? University Chicago Medicine (2023) (available at https://www.uchicagomedicine.org/forefront/health-and-wellness-articles/ketogenic-diet-what-are-the-risks). (link)
  14. Ayele, G.M. et al. (2023) ‘Is losing weight worth losing your kidney: Keto Diet resulting in renal failure’, Cureus [Preprint]. doi:10.7759/cureus.36546. 
  15. Plant toxins. The Carnivore Diet Coach (available at https://www.thecarnivoredietcoach.com/plant-toxins.html).
  16. K. Valenta, O. Nevo, The dispersal syndrome hypothesis: How animals shaped fruit traits, and how they did not. Functional Ecology34, 1158–1169 (2020), doi:10.1111/1365-2435.13564. (link)

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Martina Spaeni, MSc

"We are frugivores - specialized fruit-eaters!" It was passion at first sight when I came across the intriguing concept that humans are adapted to a high-fruit diet, similar to chimpanzees...

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