Jilly Pearce knows this well. The 40-year-old from Bexleyheath, south-east London, suffered from irritable bowel syndrome for years before realising that it was at its worst just after breakfast. "Putting two and two together, I deduced that it was probably the milk in my cereal and morning tea that was causing the issues and, sure enough, when I cut down on milk, I noticed a difference very quickly. I no longer felt bloated or lethargic."

Pearce took the logical next step of cutting milk out of her diet completely, and when she continued to feel better, she put her IBS down to a lactose intolerance. "But I missed my porridge and hot drinks like mad and the likes of soya and almond milk just don't taste as nice. So one day, when I came across a2 on the supermarket shelf, I thought I'd give it a try. It tasted great, as cows' milk always does, but as it still contained lactose, I waited for the symptoms to come. But they didn't and I have to say that it's changed my life dramatically."

There are thousands of stories like this, including among children. Leia Greasby's daughter Jessica, 13, for example, was 11 when Leia realised that she had a problem with cows' milk. "She had all the typical symptoms of someone suffering an issue with cows' milk, such as bloating, cramping, diarrhoea and generally feeling low. But we hadn't spotted it before because she also had a gluten allergy, which was masking all her symptoms," explains Leia.

Jessica was apprehensive about trying an A2 milk. "For her, milk meant living on the toilet – dreadful for a teenager," says Leia. "But it's turned her life around and she's been able to eat home-made ice cream, enjoy milkshakes and even cereal, with no bloating or cramping. Six months on, she's got more energy and is growing again."

But although the Curtin study included a subset of people with self-reported intolerance to commercial milk – and it was they who reported the greatest benefits of A2 over A1 milk – the vast majority of participants did not consider themselves to be milk intolerant at all. And it is this group that has most surprised Professor Pal.

"Yes, the study is great news for the milk-intolerant because the calcium in cows' milk has key health benefits when it comes to bone health and the prevention of osteoporosis, for instance. But for me, by far the most interesting bit of the study is that the bulk of participants thought that they were milk tolerant and drink it regularly. Yet, when we looked at their gut reactions to A1 milk under the microscope, we found that they experience gut inflammation and have changes in their stool consistency that they don't get when they drink A2 milk. I think people must just get used to reacting to A1 milk, considering the symptoms normal. But our study shows that people don't have to put up with it."

Professor Pal has high hopes for future research around milk proteins. "I'd like to explore whether the different proteins in milk may be used to help prevent or treat conditions including autism, diabetes and heart disease. There's already some animal evidence around this. It's just a matter of doing a human trial. This could be huge news."

Dr Ditte Hobbs, a nutritionist and research fellow in the Hugh Sinclair Unit of Human Nutrition at the University of Reading, describes the Curtin study as "interesting, timely and much needed".

But it's only a preliminary step, she adds. "Participants consumed the milks for quite a short duration. Also, the study lacks any kind of microbiology, which is needed to find out exactly what is going in our colons. Thirdly, it's the only human study in the area and it's therefore important not to take this data as concrete evidence."

Meanwhile, the British Dietetic Association (BDA) warns that dairy intolerance is widely misunderstood. "More people than ever perceive that they are intolerant to milk, whereas in fact a very small percentage have a genuine intolerance," says Sioned Quirke, a dietician and BDA spokesperson. "I think the misperception is a lot to do with celebrities endorsing avoiding certain food groups and the growing market for self-test kits, despite them having no scientific basis. Other factors are the growing 'free from' ranges in supermarkets and the assumption that alternative, more expensive milks must be better for you. None of this is helped by the fact that there is no clear and simple test for milk intolerance."

A lot of people tell their dieticians that milk gives them constipation when further exploration reveals that they hardly eat fibre, she says. "Or they tell us that milk makes them bloated when actually we find that they have IBS. Our bowels are a complex organ and it's not always one single thing that affects them. Even the amount of physical activity one does or their fluid intake can affect how the bowels work. So whilst this study is fascinating, I wouldn't want to raise people's hopes by suggesting it is the answer to all their problems."