Question

It is observed that constipation is common among people in the western countries who eat more meat and processed food than us what can be that reason for this

Answer 1

Interesting question!. Actually according to classical Ayerveda, every illness is the cause of our eating habits. Western and especially American diets are composed on highly refined flour, sugar and meat. These are highly processed foods which are not anywhere close to their natural form.
This makes it difficult for body to digest and absorb these foods and their nutrients in our body. 
On the other hand a more natural diet such as unprocessed flour, is easy to digest and full of fibre, which prevents constipation.
Foods which are more in their natural states contain not only fibre but many other nutrients which make it easy for the body digest them leading to less bloating and constipation

Answer 2

Constipation is common among people in western countries who eat more meat and processed food because there is no enough roughage in their bodies which prevents constipation .Fruits and vegetables like  corn etc contains lot of roughage.