what cant the human body digest?

Answer 1

Obviously there are a whole list of things that humans cannot digest - metal, plastic, glass, chinaware and so on. But what I think you mean is what foods or food-like materials can a human not digest...

The most important of these is...
Cellulose - the stuff that the cell walls of plants is made of. This makes up the bulk of what is known as "dietary fibre" and is expelled in the faeces.

In fact, no mammal (or indeed any animal other than bacteria) is able to digest cellulose, and many of those that do eat large amounts of plant material (eg cows) rely on bacteria in their gut to break down the cellulose cells walls of their food and so release the nutients inside for the cow to digest. This is true of all "wood-eating" creatures, such as woodlice.

You can see this demonstrated if you examine the faeces of cows and horses - cow dung is obviously the product of a greater degree of digestion (because they use bacteria to break down the grass or hay) while horse dung still has a lot of "hay" in it which appears to be hardly digested at all. This is because horses don't have cellulose-bacteria so they get much less nutrition out of the grass and it pases through them in a much less digested state. Cell wall breakdown by animals such as horses is purely a physical process - mainly by grinding with the teeth, rather than chemical (digestive).

Also...
A large number of adults in the world are unable to digest the sugar found in milk. This sugar is called LACTOSE and such people are known as "Lactose Intolerant". As babies, up to the age of about 4 all humans produce a digestive enzyme called "Lactase" which enables them to digest Lactose. At the age of about 4, in some people this enzyme is "genetically switched off" and from then on they are unable to digest lactose. This occurs in some races more than others - it is particularly common in the Chinese, for example.

Some people are "starch intolerant" and are unable to digest foods made from wheat or other grains (eg bread).

Answer 2

Hair. If a person chews on their hair and actually swallows some of it, it goes to the stomach and actually keeps rolling into a ball (called a bezoar) and may have to be removed surgically. The acid in the stomach does not break hair down.

Answer 3

It is quite possible for Human beings to eat raw meat. Just look at the Inuit culture!

Answer 4

Cellulose

Answer 5

*******

Answer 6

Brick?

Answer 7

metal, wood, plastic, rubber, milk from other animals (sometimes), rocks, chewing gum

Why are people marking this as a bad answer?

Answer 8

Gum for one.

Answer 9

hair, plastic, metal, rocks

Answer 10

corn