Here we go - this is from Dr Briffa's blog:
"Some of my relative enthusiasm for yoghurt comes from the fact that, in practice, this food is generally less likely than milk and cheese to pose problems due to food intolerance. Dairy products such as milk and cheese are rich in proteins that can be quite difficult to digest, and may make their way into the body in partially digested form where they may trigger a variety of health issues including sinus congestion, asthma and eczema. Because yoghurt and milk are essentially the same food, one might expect that they have a similar capacity to induce food intolerant reactions. However, studies show that the bacteria deployed in the fermentation process that converts milk into yoghurt aid and abet the digestion of milk proteins. The pre-digestion of protein by bacteria help to explain why, compared to milk and cheese, yoghurt is less likely trigger unwanted reactions.
Apart from protein, another component of dairy products that some individuals may have difficult digesting is the sugar lactose. This problem ? known as lactose intolerance ? is relatively rare in individuals of Northern European decent, but is very common in those of Southern European, Asian, Afro-Caribbean and South American stock. Individuals affected by lactose intolerance are prone to symptoms such as bloating, diarrhoea and gas after consuming milk (which is rich in lactose). However, some strains of bacteria used in the making of yoghurt have lactose-digesting ability, and this is reflected in the fact that yoghurt contains less lactose than milk. As a result, those who struggle to digest lactose generally find they tolerate yoghurt better than the liquid from which it is derived.
In addition to helping the digestibility of dairy, studies suggest that the organisms found in ?live? and ?bio? yoghurts have the potential to help alleviate gut-related issues such as constipation and diarrhoea. These beneficial bugs are also seem to help keep the gut free from unwanted organisms including those responsible for food poisoning and the bacterium Helicobacter pylori (the bug now recognised as a common underlying factor in digestive conditions such as stomach and duodenal ulcers, stomach inflammation and stomach cancer)."