Cellulose Stomach DigestionAre you sitting there asking yourself what cellulose even is or why you are reading this article about something you have never really heard about? Well just in case, let us go over a brief introduction on cellulose and why it is important in the debate of whether humans should be eating a plant based diet. Okay, so cellulose is “the chief constituent of the cell walls of plants and of wood, cotton, hemp, paper, etc.” as defined by Dictionary.com; obviously the important part for our discussion being the plants. Now to be clear, the crux of this argument is due to the fact that humans are unable to digest cellulose because we lack the necessary enzyme, called cellulase. Cellulase is responsible for converting cellulose into glucose or a disaccharide so that the body can digest it and utilize it.

Now I am going to be very open with you about this topic, as I love diving into this kind of research with an open mind and no preconceived outcome. When someone brought this topic up to me, I gave them my explanation for why it makes sense that humans would eat plants and not be able to digest cellulose, but I wanted to find out more and whenever I am doing research on these types of complex topics where I don’t necessarily have the full answer worked out, I really try to look at it from the anti-vegan standpoint; and with this one, I could easily see the other side of the argument making a lot of logical sense in arguing against veganism. Let’s jump into my analysis though, so you can see what I am talking about.

1) The first thing we need to discuss is the biology of animals, including humans. There are four types of digestive systems, including ruminant, pseudo-ruminant, avian, and monogastric. Because avian relates only to birds, we can eliminate that one from our discussion.

  • Animals with a ruminant digestion system (cattle, goats, sheep, etc.) ruminate their food. In other words, they swallow it and then spit it back up or regurgitate it to chew at a later time before swallowing it again. Ruminant animals have four stomach chambers to complete the digestion process and they are able to break down plant matter, including cellulose, and absorb the nutrient content from it by using foregut fermentation.
  • Pseudo-ruminants (hippopotami) have a similar digestive system to ruminants (obviously), except they only have three stomach chambers. These types of animals also use foregut fermentation to help them break down cellulose and digest it properly.
  • Okay, so the only one left that we need to discuss is the monogastric digestion system, which is found in canivores, omnivores, and herbivores. Humans are classified as monogastric and so are cats, dogs, rodents, etc. Monogastric animals are not as capable of digesting cellulose as ruminant and pseudo-ruminant animals. Part of the issue we are even dealing with is that some people classify pseudo-ruminant animals as monogastric and because of this it is hard to determine if any TRULY monogastric animals are capable of digesting cellulose at all, as humans are unable to do so. As you will see below, I am not sure this matters in the context of the point I will argue anyways.

Alright, so now that we covered a bit about the different types of digestive systems and where some uncertainty lies, we can dig into some other interesting areas of discussion.

For starters, non-vegans will argue that humans are not herbivores because they lack cellulase (the enzyme mentioned above) to break down cellulose. The interesting thing though is that there are many known herbivores, like cows, who lack the enzyme as well. In fact, like many herbivores, cows are able to break down cellulose because of bacteria in their gut. This anaerobic bacteria in their digestive tracts allows them to digest cellulose without the cellulase enzyme.

“The interesting thing though is that there are many known herbivores, like cows, who lack the enzyme as well.”

Now here is the most interesting point to me out of this whole debate. Humans are unable to digest cellulose, but is it possible that this was by design? You see, humans not being able to digest cellulose actually benefits us in a major way by creating fiber in our diet. The fiber created by eating plant based foods with cellulose that we are unable to digest actually helps us flush out our digestive tracts. While we gain the fiber benefit from not digesting cellulose, we still obtain the nutrient benefits from eating these plants. This is where to me, it still aligns with the idea of a plant based diet and should not be considered as evidence by non-vegans that we were not designed as herbivores. The human body is already unique in other ways from any other living being, so it should not be assumed that just because we slightly vary in this way that we are not herbivorous. That being said, I do like the mystery surrounding cellulose and enjoy the argument from the other side that if we are herbivorous by nature, then we should be able to digest cellulose. Obviously you will have to go with how you feel on the topic as well. Hopefully this at least shed some light on the issue for you.