pregnancy and puking sensation

Why do woman puke during pregnancy?
For my wife it is the 3rd month and she is been puking during the end of the day i.e towards the evening. I did some search on the internet to find the reason behind it, but in vain.

One reason, which repeated in the search results was about indigestion. This seems to be true to some extent as the number of puking tendency reduced drastically when she had been on strict porridge diet.

It is weird and annoying behavior for pregnant women. Wish there are good solutions.
BTW a strict diet does starts to bother me now, as she need nutritious food to compliment her diet.

Can some one suggest me some good proven or tried solutions, thanks a ton in advance.