Dairy intolerance is real, Kiwis scientists say, with a new study proving for the first time people don't have to be lactose intolerant to struggle with milk and yoghurt.
"Lots of people suspect that they have some intolerance to dairy foods, but testing shows they aren't lactose intolerant," Dr Amber Milan, a research fellow at the University of Auckland's Liggins Institute says.
"Before this study, there had not been any detailed analysis of dairy intolerance to see if something else could be causing it.
"Our findings show dairy intolerance is a 'real thing' with a particular symptom profile - not something that's just in people's heads."
The study gave 30 women who claimed to be dairy intolerant 50g of lactose - about how much you'd find in a litre of milk. In a separate visit, they drank 750ml of standard milk.
The lactose-intolerant women "experienced flatulence, stomach rumbling and cramping" about two hours afterwards, as well as raised breath hydrogen levels.
Those who weren't lactose-intolerant experienced stomach pain and bloating, but it came on much quicker - only taking 30 to 60 minutes - and there were no signs of raised hydrogen levels in their breath, a sign they were absorbing the lactose, which lactose-intolerant people can't do.
"With these women, it was as if their stomachs weren't digesting the milk as quickly," says Dr Milan.
"We need more research to identify exactly what's going on, but we know that some nutrients affect the speed of digestion, like fibre or the type of protein, as can the release of hormones, such as insulin and appetite hormones."
Dr Milan says the next step is to figure out exactly what's going on with dairy intolerance, if it's not lactose.
"You can have a healthy diet without dairy, but many people enjoy dairy products. Some of the dairy- and lactose-intolerant women in our study still ate foods like yoghurt and cheese, despite the discomfort it caused them.
"Dairy is ubiquitous in the Western diet. It's also a great source of calcium, protein and other nutrients. If we can better understand why some people have trouble with dairy, we can help make recommendations for them that are suited for their particular problem."
The research was funded by the High Value Nutrition National Science Challenge and the a2 Milk Company.