The argument is, cows ferment grass for days in order to digest it. How can humans absorb nutrients from wheatgrass without fermenting in our stomach? Let’s use SCIENCE here, folks. I have to prove the benefits of wheatgrass to my skeptical boyfriend! I’m willing to accept that wheatgrass is unhealthy, but prove that too.
This blog Skeptico asserts that humans can’t digest wheatgrass. His sources include the following:
Here’s the explanation of why, from New Scientist Without their cargoes of microbes they would be unable to make use of it at all. In addition, unless microbes break down the plant cell walls, the herbivore’s own digestive enzymes would have difficulty gaining access to the cell’s contents. The reason that herbivores generally have complex digestive tracts is to slow the passage of food, and so prolong contact with the microbes that help to digest it. The digestion of cellulose is an anaerobic process, of the kind commonly known as fermentation. All parts of the gut absorb the volatile fatty acids produced in the process and these provide the herbivore with energy. ...
Secondly, animals with large bodies can also have large guts, and so can contain large amounts of material that is fermenting slowly. Large herbivores generally retain their food in their guts for longer than smaller animals, and this maximises the opportunity for the breakdown of cellulose. Small herbivores generally depend for their energy more upon the contents of a cell than its walls, and so they must select plant material of higher quality.
From Anatomy and Physiology of Animals/The Gut and Digestion: Ruminants swallow the grass they graze almost without chewing and it passes down the oesophagus to the rumen and reticulum. Here liquid is added and the muscular walls churn the food. These chambers provide the main fermentation vat of the ruminant stomach. Here bacteria and single-celled animals start to act on the cellulose plant cell walls. These organisms break down the cellulose to smaller molecules that are absorbed to provide the cow or sheep with energy. In the process, the gases methane and carbon dioxide are produced. These cause the “burps” you may hear cows and sheep making. Not only do the micro-organisms break down the cellulose but they also produce the vitamins E, B and K for use by the animal. Their digested bodies provide the ruminant with the majority of its protein requirements.