Are We More Plant-Eater or Meat-Eater?

We’re probably not going to resolve definitively exactly where we are on the spectrum between carnivore and herbivore, but let’s look at some undeniable facts to start with, to help you make up your own mind whereabouts on this spectrum we reside.

We’ll look at the whole range of all possible mammal types to see where humans fit into the picture:

Types of mammal

  • Carnivore 1 
  • Omnivore 2 
  • Herbivore 3 
  • Frugivore 4 

And then there’s us.

Scope of discussion

Our scope will be limited to the following factors:

  1. Physiological food
  2. Limbs
  3. Walking method
  4. Mouth opening
  5. Canines
  6. Incisors
  7. Molars
  8. Jaw
  9. Chewing vs shearing
  10. Salivary glands
  11. pH of urine and stomach acid
  12. Dietary fibre
  13. Cholesterol and vitamin A
  14. Sweat glands
  15. Intestinal length
  16. Large intestine (colon)
  17. Cellulose metabolism
  18. Digestion time

1. Physiological food

That is, the type of food that is absolutely necessary for the particular mammal to maintain life.

  • Carnivore – meat
  • Omnivore – meat and vegetables
  • Herbivore – herbs
  • Frugivores – fruit, vegetables & nuts
  • Human – fruits, vegetables & nuts

Humans do not need any animal products, the only things they require that people mistakenly think need to be derived from animals are:

  • Vitamin B12
  • Omega 3
  • Vitamin K2

Vitamin B12 does not come from the animals we eat, rather they get it from bacteria in soil and water. Humans can cut out the middle mammal/bird/fish and get it directly from soil-based bacteria in supplement form. In the past, before our farming methods transformed the natural state of the soils in which we grow plants and feed for animals, there would have been plenty of B12 eaten by humans without the need for animal consumption. 5

Regarding omega-3, EPA 6 and DHA 7 come from algae and, in any case, we can make our own. ALA 8  comes from walnuts, chia and flaxseeds etc and can be converted into EPA/DHA in most humans, with some exceptions because of a genetic influence that reduces the body’s ability to enzymatically convert ALA into EPA and/or DHA . You’d think that plant-eating humans who could not make this conversion would have died out; but we don’t know how long this genetic feature has existed (before or since modern diets and farming methods) or whether historical plant  breads were sufficiently different from modern ones to mean that the inability to convert ALA to EPA/DHA was not an issue. Maybe ancient humans ate a lot more algae species than we do today 9 . Even if some humans had to consume animal foods to ensure they received sufficient EPA/DHA, they would have been more likely to have been eating worms, lizards, snails etc rather than neat slices of chicken or nicely carved chunks of steak. In any event, plant-based EPA/DHA supplementation is easy enough to get these days.

Vitamin K2: Since our bodies need both vitamin K1 (phylloquinone – which we get from plants) and vitamin K2 (menaquinone – which is mostly derived from animal foods, being synthesised by intestinal bacteria) it’s claimed by some to be proof that we are really designed to be omnivores. However, there is a flaw in this argument. The scientific consensus 10 , as pointed out on the nutritionfacts.org site 11  is that either one, vitamin K1 or K2, can maintain human vitamin K status perfectly well, with the recommended daily intake being around 100 mcg. Half a cup of kale is greater than 500 mcg.  Our bodies can convert K1 to K2, and it’s likely that the more K1 you eat, the more our gut bacteria can convert into K2. It’s worth pointing out that not everyone is in agreement with this, and there’s an in-depth article available 12 for those who want to delve deeper.

In this respect, humans are more like frugivores.

2. Limbs

  • Carnivore – 4 paws with claws
  • Omnivore – 4  paws with claws or hooves
  • Herbivore – 4 paws with hooves
  • Frugivore – Prehensile hands and feet
  • Human – Prehensile hands 

Human hands are pretty useless for catching and disabling large prey. They are, however, perfect for collecting and manipulating plants for food.

In this respect, humans are more like frugivores.

3. Walking method

  • Carnivore – Walks on 4 paws
  • Omnivore – Walks on 4 paws
  • Herbivore – Walks on 4 paws
  • Frugivore – Walks on 4 paws/upright
  • Human – Walks upright

Bipedalism has several advantages. Because the head is higher up, it gives a wider field of view to look for prey and keep an eye out for predators. It also makes it easier to reach up into trees for food (with the hands or the mouth) and it frees up the hands to hold and carry things. Self-defence using the front limbs is also possible with bipedalism. Overall, quadrupeds run faster on four limbs than animals that use bipedal locomotion, but in endurance running, humans can outrun most quadrupeds. 13

In this respect, humans are more like frugivores.

4. Mouth opening

  • Carnivore – Large
  • Omnivore – Large
  • Herbivore – Small
  • Frugivore – Small/Medium
  • Human – Small

Human mouths are not designed to bite onto prey. In this respect, humans are more like herbivores and frugivores.

5. Canines

  • Carnivore – Large sharp fangs
  • Omnivore – Large sharp fangs
  • Herbivore – Rudimentary blunt canines
  • Frugivore – Small sharp canines
  • Human – Rudimentary blunt canines

Human canines are not designed to pierce, rip flesh or to be large enough to plunge into the bodies of prey animals and either subdue or kill them.

In this respect, humans are more like herbivores.

6. Incisors

  • Carnivore – Short pointed incisors
  • Omnivore – Short pointed incisors
  • Herbivore – Large flattened incisors
  • Frugivore – Large flattened incisors
  • Human – Large flattened incisors

In this respect, humans are more like herbivores and frugivores.

7. Molars

  • Carnivore – Blade-shaped molars
  • Omnivore – Blade-shaped/crushing molars
  • Herbivore – Flattened strong molars
  • Frugivore – Flattened molars
  • Human – Flattened molars

Human molars are neither designed for tearing meat like a carnivore nor for grinding huge quantities of fibrous plant matter like herbivores and omnivores.

In this respect, humans are more like frugivores.

8. Jaw

  • Carnivore – Lower jaw embedded inside the top; no lateral or forward mobility
  • Omnivore – Lower jaw embedded inside the top; no/minimal lateral or forward mobility
  • Herbivore – Upper jaws sits on the bottom; great lateral and forward mobility
  • Frugivore – Upper jaws sits on the bottom; great lateral and forward mobility
  • Human – Upper jaws sits on the bottom; great lateral and forward mobility

In this respect, humans are more like herbivores and frugivores.

9. Chewing vs shearing

  • Carnivore – shear; swallow without chewing
  • Omnivore – shear/crush without chewing
  • Herbivore – no shear; chew a lot
  • Frugivore – no shear; chew before swallowing
  • Human – no shear; chew before swallowing

In this respect, humans are more like frugivores.

10. Salivary glands

  • Carnivore – small salivary glands; acid saliva without ptyalin 14
  • Omnivore – small salivary glands; acid saliva without ptyalin
  • Herbivore – large salivary glands; alkaline with ptyalin
  • Frugivore – large salivary glands; alkaline with ptyalin
  • Human – large salivary glands; alkaline with ptyalin

Omnivores are designed to handle both vegetable matter and animal tissue. It’s claimed by some that humans have adapted to eating starch from having developed agriculture. Furthermore, there are some (Dr John McDogall, for instance) who claim that we are in fact starchivores – best suited to eat, digest and utilise the complex sugars in starchy plants. 15

In this respect, humans are more like herbivores and frugivores.

11. pH of urine and stomach acid

  • Carnivore – acid urine; renal secretion of uricase 16
  • Omnivore – acid urine; renal secretion of uricase, strong gastric hydrochloric acid
  • Herbivore – alkaline urine; no renal secretion of uricase, weak gastric hydrochloric acid
  • Frugivore – alkaline urine; no renal secretion of uricase, weak gastric hydrochloric acid
  • Human – alkaline urine; no renal secretion of uricase, weak gastric hydrochloric acid

Whilst diet will determine the pH or urine, with animal foods causing more acidity and plant foods more alkalinity, the weak stomach acid is a significant difference from the acidic stomach acid found in omnivores.

In these respects, humans are more like herbivores and frugivores.

12. Dietary fibre

  • Carnivore – does not require fibre to stimulate peristalsis 17
  • Omnivore – does not require fibre to stimulate peristalsis
  • Herbivore – does require fibre to stimulate peristalsis
  • Frugivore – does require fibre to stimulate peristalsis
  • Human – does require fibre to stimulate peristalsis

In this respect, humans are more like herbivores and frugivores.

13. Cholesterol and vitamin A

  • Carnivore – metabolise large amounts of cholesterol and vitamin A
  • Omnivore – metabolise large amounts of cholesterol and vitamin A
  • Herbivore – metabolise small amounts of cholesterol and vitamin A
  • Frugivore – metabolise small amounts of cholesterol and vitamin A
  • Human – metabolise small amounts of cholesterol and vitamin A

Carnivores can eat unlimited amounts of cholesterol with no negative effects, herbivores, on the other hand, are extremely sensitive to dietary cholesterol intake which can lead to heart disease (particularly atherosclerosis). If, however, you feed carnivores a diet moderate in sugar and starch, which herbivores have no trouble in handling, they can then develop atherosclerosis.

Herbivores can easily convert beta-carotene to vitamin A (hence why their body fat is white), but they cannot detoxify dietary vitamin A from their bodies. Carnivores, on the other hand, are poor converters of beta-carotene to vitamin A, but can detoxify high amounts of dietary vitamin A from their bodies, (hence why their fat, in contrast, is yellowish).

As an aside, it is claimed 18  that herbivores are also very good converters of ALA (alpha linolenic acid – a type of omega-3 fatty acid) to the long-chain fatty omega-3 acids EPA and DHA. Carnivores, on the other hand, are poor converters of ALA. This is also the case with taurine 19 , with herbivores being able to synthesise it at very high rates, while carnivores are low-rate taurine synthesisers – in fact, cats, as obligate carnivores 20 , can’t make any taurine at all.

In these respects, human are more like herbivores and frugivores.

14. Sweat glands

  • Carnivore – sweat glands are in the paws; gasp to cool the blood
  • Omnivore – sweat glands in whole body
  • Herbivore – sweat glands in whole body
  • Frugivore – sweat glands in whole body
  • Human – sweat glands in whole body

In this respect, we are only unlike carnivores.

15. Intestinal length

  • Carnivore – intestine from 1.5 to 3 times body length
  • Omnivore – intestine 3 times body length
  • Herbivore –  intestine 20 times body length
  • Frugivore –  intestine around 9 times body length
  • Human –  intestine around 9 times body length

Carnivores eat a smaller amount of food that’s higher in energy and easier to digest than the cellulose-containing plants eaten by herbivores. Carnivores thus have much shorter intestines. The toxins that are ever-present in meat are much more easily removed from the body in shorter intestinal tracts. There is some divergence on opinions about the average length of intestines, but the above is a reasonably fair estimate.

In this respect, humans are more like frugivores.

16. Large intestine (colon)

  • Carnivore – colon is short, smooth and alkaline
  • Omnivore – colon is short, smooth and alkaline
  • Herbivore – colon is long, complex and acidic
  • Frugivore – colon is longsacculated 21 and acidic
  • Human – colon is longsacculated and acidic

In this respect, humans are more like frugivores.

17. Cellulose metabolism

  • Carnivore – cannot metabolise cellulose
  • Omnivore – cannot metabolise cellulose
  • Herbivore – can metabolise cellulose
  • Frugivore – cannot metabolise cellulose
  • Human – cannot metabolise cellulose

In this respect, they are only unlike herbivores.

18. Digestion time

  • Carnivore – complete digestion takes 2-4 hours 
  • Omnivore – complete digestion takes 6-10 hours 
  • Herbivore – complete digestion takes 24-48 hours 
  • Frugivore -complete digestion takes 12-18 hours 
  • Human – complete digestion takes 12-18 hours 

In this respect, humans are more like frugivores.

Summary

The above is summed up, to a large extent, in the following chart:

Final thoughts

The above is a very brief – almost fleeting – review of the similarities and differences between difference animal groups. It is not meant to prove or disprove that humans are omnivores. What can be said with certainty is that, based on the foregoing, we are more like frugivores than anything else.

For me, the fact that we can live, not only healthy, but optimally healthy lives if we only eat plants is sufficient evidence for me to favour any viewpoint that makes humans less, rather than more, of a meat-eater.

And this isn’t just a matter of myopically looking at physiological factors; when we throw into the mix the issues of animal cruelty, human health and environmental impact, a diet consisting of mostly or solely (whole-) plant foods is hard to argue against.

Just because we may have had ancestors who occasionally had to rely on animal food sources because of the lack of readily-available plant food alternatives does not mean that we have to do the same in the 21st century – especially when we know as much as we now know about the health benefits of a WFPBD. And this is without the horrendous impact on animals themselves and on the environment.

For so many reasons, it seems sensible to consider ourselves as more plant-eater than meat-eater, whatever our precise physiological definition might be.


References

  1. Wikipedia: Carnivore definition []
  2. Wikipedia: Omnivore definition []
  3. Wikipedia: Herbivore definition []
  4. Wikipedia: Frugivore definition []
  5. 12 Questions Answered Regarding Vitamin B12 by Dr Thomas Campbell []
  6. Wikipedia: EPA – Eicosapentaenoic acid definition []
  7. Wikipedia: DHA – Docosahexaenoic acid []
  8. Wikipedia: ALA – Alpha-linolenic acid definition []
  9. Where do Algae Grow? – Algae Growth Environments []
  10. Vitamin K in Health and Disease (Oxidative Stress and Disease) by John W. Suttie. []
  11. What are the best sources of vitamin K? Written By Michael Greger M.D. FACLM on November 8th, 2012. []
  12. Healthline: Vitamin K2: Everything You Need to Know. []
  13. Biology Dictionary: Advantages of Bipedalism []
  14. Ptyalin: An enzyme (amylase) found in the saliva of humans and some other animals []
  15. Dr John McDougall Newsletter April 2013: ”Vegan,” “Plant-Based,” “Starchivore”: What Do You Call Yourself? []
  16. Uricase definition: Uricase is an enzyme present in the liver and kidneys of most mammals, but not humans. This enzyme is capable of oxidising uric acid into allantoin and carbon dioxide. []
  17. Peristalsis definition: Peristalsis is a series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the oesophagus when a bolus of food is swallowed. []
  18. Quora: What are the differences and similarities between herbivores, omnivores, and carnivores? []
  19. Taurine definition: Taurine is a non-essential amino acid-containing sulphur and is important in the metabolism of fats. []
  20. Obligate carnivores definition: Obligate carnivores, or “true” carnivores, are those carnivores whose survival depends on nutrients which are found only in animal flesh. While obligate carnivores might be able to ingest small amounts of plant material, because of their evolution they lack the necessary physiology required to digest that plant matter. In fact, some obligate carnivorous mammals will only ever ingest vegetation for its specific use as an emetic to self-induce vomiting to rid itself of food that has upset its stomach. []
  21. Sacculated definition: Sacculated means having or formed of a series of saccular (sac-like) expansions []