Lactose intolerant Aucklanders are being sought for a study that researchers hope will help them tolerate dairy.
The Liggins Institute and AgResearch study follows a trial completed last year that found one glass of a2 Milk prevented some symptoms of lactose intolerance while containing the same amount of lactose as conventional milk.
This year's study, dubbed Los aMiGoS, will look at the effects over two weeks rather than one sitting.
Last year the study only involved woman aged 20-30, but this year researchers are looking for 20 males and 20 females aged 20-40.
Liggins Institute Dr Amber Milan, who is leading the research, said this time they wanted to make sure the findings are applicable to both men and women.
"Last time we were trying to get a handle on what exactly we were looking for so we tried to limit variability between participants."
The Los aMiGos study will be broken up into three parts. Participants will first avoid all dairy for two weeks.
Then, without researchers or participants knowing the order, participants will consume conventional cheese and milk for a fortnight and a2 milk cheese and milk for two weeks, with a recovery break between.
Researchers will be looking to see if benefits of a2 milk identified in an earlier study by the same researchers persist over a longer period.
In last year's study researchers showed that a2 milk reduced symptoms including nausea, stomach pain and bloating, but didn't improve ratings of "overall digestive comfort". It also produced the same levels of flatulence and gastric reflux as regular milk.
Globally, about 70 per cent of adults consider themselves lactose intolerant, and experience bloating, nausea or other unpleasant symptoms after consuming it.
Milan said lactose intolerant people can sometimes build up their tolerance to lactose over time by including lactose or milk in their diet.
"If we can help that process along, hopefully we can improve digestion of lactose after just a few weeks.
"We're hopeful that consuming dairy with only the A2 protein will reduce symptoms by avoiding inflammation that might make intolerance worse," Milan said.
AgResearch scientist Matthew Barnett said there was evidence from animal studies that a breakdown product of the A1 protein causes inflammation in the small intestine.
"This could make lactose intolerance symptoms worse," Barnett said.
Los aMiGoS has been designed to minimise uncomfortable symptoms by limiting daily lactose to the equivalent of two glasses of milk - an amount that is usually tolerable for people with lactose intolerance.
To spare participants unnecessary discomfort, researchers will top up their protein consumption with daily servings of cheese, which is nearly lactose-free.
This study is funded through High Value Nutrition to AgResearch and in partnership with the a2 Milk Company.