Just to add to the complications there's soluble and unsoluble fibre.
Soluble fibre may be preferable to insoluble fibre if he has upset tummy. Soluble fibre stays in the gut longer, adding bulk to the colon, which helps the colon work normally.
You find soluble fibre in:
Dried or tinned beans
Lentils and chick peas
Peas
Oats
Rice
The flesh of fruits
Dried fruits
Vegetables such as potatoes and carrots.
For comparison, insoluble fibre is found in the skins of fruits and root vegetables, in whole-wheat products, wheat and corn bran, and in vegetables such as cauliflower, broccoli, onions, cabbage and green beans.
I eat oatflakes and oatabix with sultanas for breakfast and although I eat plenty of mixed fruit and veg, I avoid those that irritate me. (Can be soluble or insouble and for me its strawberries!)