A special type of milk containing the same amount of lactose as conventional cow's milk prevents some symptoms of dairy intolerance and eases others, New Zealand research has suggested.
Sold mostly in Australia, New Zealand, China, US and the UK, A2 Milk comes from cows that naturally produce only the A2 type of beta-casein protein, which itself makes up around 25 to 30 per cent of total milk protein.
Conventional milk contains both the A1 and A2 types of beta-casein.
While it was originally thought that all cows produced only the A2 protein type, the A1 mutation appeared in European herds 5000 to 10,000 years ago.
The latest findings, being presented at a major conference in Chicago this weekend, found a "strikingly different pattern" of digestive symptoms in people identified as lactose intolerant after drinking A2 Milk compared to conventional milk, study leader Dr Amber Milan said.
"A2 Milk was at least as effective as lactose-free milk at preventing or easing some of the symptoms of lactose intolerance, including nausea, stomach pain and bloating, but didn't improve ratings of 'overall digestive comfort', suggesting other symptoms over the course of 12 hours were unpleasant enough to not shift overall digestive comfort."
Milan, a research fellow at the University of Auckland's Liggins Institute, said the lactose intolerant women in the study reported the same levels of flatulence and gastric reflux on average after drinking A2 Milk as after conventional milk.
"There is some evidence that the symptoms of lactose intolerance may be influenced by the proteins in milk," said study co-author Matthew Barnett, a scientist a Crown research institute AgResearch, which has been carrying out the research alongside Liggins.
"We wanted to investigate this more closely."
Globally, about 70 per cent of adults consider themselves lactose intolerant, and experience bloating, nausea or other unpleasant symptoms after consuming it.
The study compared the digestive response to conventional milk, a2 Milk and lactose-free conventional milk between people who are able to digest lactose, people with lactose intolerance and people with dairy intolerance.
The study, which the researchers aim to publish in a journal in coming months, was funded through the New Zealand Government High-Value Nutrition National Science Challenge, with co-funding from The A2 Milk Company Limited.
Participants were 30 healthy young women who said they had trouble digesting milk, and a control group of 10 dairy-consuming women.
First they drank 50g of lactose - equivalent to about a litre of milk - to determine if they had lactose intolerance or not.
Then, on three separate visits, the same women drank 750ml of the three types of milk.
Immediately after the women consumed the milk, and at 30 minute intervals for three hours, the researchers took blood, urine and breath samples, measured their waist, and performed MRI scans.
The women also recorded how they felt for the 12 hours following consumption.
Milan said animal studies showed a breakdown product of the A1 protein causes inflammation in the small intestine, which seemed to somehow exacerbate lactose intolerance.
"What our findings suggest is while we can't fix the inability to digest lactose, we might be able to minimise the exacerbating action of the A1 protein."
Analysis also confirmed that dairy intolerance was distinct from lactose intolerance.
The dairy intolerant women reported all three milk types as equal in terms of digestive discomfort over the three hours.
A planned second study by the same team would track the effects of A2 Milk on gut comfort over two weeks, focusing on small intestinal inflammation.
The study is expected to add to the business success story of the a2 Milk Company Limited, which has become the country's fifth-biggest company on the back of growing exports to Australia and China. Its share price has quadrupled to almost $8 in the last year.