Lactose Intolerance

Lactose (or milk sugar) is normally digested in the small intestine by the enzyme lactase to glucose and galactose, which are rapidly absorbed into the body.

People of Southern European, Arabic, African and Asian ethnicity tend to lose their lactase enzyme shortly after weaning and may therefore be susceptible to bloating and diarrhoea if they have IBS and drink more than half a pint of milk a day or eat significant quantities of cream or ice cream. 

NB: lactose behaves like a FODMAP for those who cannot digest it.