Why Can’t We Live On Grass?

The other day I watched some cows contentedly chewing grass.  They looked well nourished and healthy.  Since humans can thrive on a totally vegetarian diet, I thought wouldn’t it be useful if we could also get some of our energy from digesting grass.

Grass, leaves, and other plant materials provide plenty of metabolic energy for cows, goats, sheep and other ruminants.  However, this kind of plant material is indigestible for humans.  It turns out we just don’t have the required digestive enzyme needed to break the grasses down.

The chemistry of life depends completely on enzymes which speed up and promote the chemical processes of life.  Our enzymes make us omnivorous, capable of eating and digesting grains, meat, and vegetables.  All the food we eat goes into the processing mill to translate it into the energy we require for movement and growth.

Our enzyme system converts virtually all the starches, sugars, fats and proteins we eat into useful energy, no matter what the original composition.  But in order to digest the cellulose that forms a large part of the fibre in our diets, we need a specific enzyme called cellobiase which we don’t have.  It’s produced, however, in the digestive system of animals like cows, which harbour the micro-organisms that are able to make it.  Although we can’t digest cellulose, we still need to include foods rich in fibre because it seems to reduce the risk of some cancers.

So next time you enjoy a picnic, go easy on the wood chips and grass!