Introduction
Is lactose intolerance only about lactose?
• Globally, approximately 70% of adults consider themselves lactose intolerant.
• This is characterised by gastrointestinal (GI) symptoms such as nausea / bloating, and is managed by avoiding dairy, or consuming lactose-free dairy products.
• However, there is growing evidence that the symptoms of lactose intolerance may be influenced by the protein component of milk.
• β-casein is a major milk protein, comprising 25-30% of total protein. There are several β-casein variants, which fall into two major classes: A1 or A2.
a2 Milk™ - what’s the story?
• Originally, all cows produced only A2 β-casein.
• The A1 mutation developed in some European dairy herds 5-10,000 years ago.
• a2 Milk™ products contain only the A2 form of β-casein.
• Functional differences between A1 and A2 variants may result from differences in their digestion, for example the generation of different bioactive peptides, including the opioid β-casomorphin 7 (BCM-7), which is released from A1 but not A2 β-casein.
• There is growing evidence that some individuals have different GI responses to A1 and A2 β-casein, which may relate to differences in digestion and peptide release.
Where’s the evidence?
• Pre-clinical data show differences in intestinal transit [1] and inflammatory response [1,2] resulting from consumption of conventional milk (containing A1 β-casein) and a2 Milk™ (free of A1 β-casein).
• Recent human clinical data [3] shows that consumption of conventional milk may lead to differences in GI comfort and physiology relative to a2 Milk™.
• To consolidate this evidence, further human studies on the benefits of consuming a2 Milk™ for GI health are required.

Objectives & Hypothesis
The 「a2 Milk™ for Gut Comfort」 HVN project has three primary objectives:
1. To demonstrate the benefits of A2 dairy protein on reduction of small intestinal inflammation, using measures such as faecal markers of inflammation;
2. To complete a proof-of-concept study to show that dairy products containing A2 β-casein are tolerated by lactose-intolerant consumers, and a2 Milk™ can thus deliver benefits in terms of GI function to these consumers; and
3. To apply novel techniques for identifying biomarkers of dairy protein intolerance. Here, we describe the 「a2 Milk™ for Gut Comfort (aMiGo)」 clinical trial (Objective 2) which investigated the acute effects of milks either containing A1/A2 β-casein(conventional milk) or free of A1 β-casein (a2 Milk™) on digestive responses and GI comfort.
The primary hypothesis of the aMiGo trial was that a2 Milk™ does not result in GI discomfort and inflammation in lactose intolerant consumers relative to conventional milk or lactose-free conventional milk.

Methods
Lactose intolerant female subjects confirmed by lactose challenge (n = 10) ingested a single dose (750 mL) of conventional milk, a2 Milk™, or lactose-free conventional milk (in random order) on three separate occasions .

Breath hydrogen, plasma glucose and urinary galactose were measured as markers of lactose malabsorption for
three hours post-ingestion. Visual analogue scoring (VAS) was used to assess GI symptoms, while magnetic resonance imaging (MRI) was used to measure gastric volume and digestion in a subset (n = 3) of participants .

Results
Lactose-free conventional milk did not impact breath hydrogen. Compared to conventional milk, a2 Milk™ ingestion delayed and attenuated increases in breath hydrogen. Subjective GI comfort differed between conventional milk and a2 Milk™. Over 3 hours, a2 Milk™ resulted in reduced nausea and faecal urgency compared with drinking conventional milk, similar to the extent experienced with lactose-free conventional milk.

Conclusions
• Compared to conventional milk, a2 Milk™ reduced lactose malabsorption (breath hydrogen) and reduced acute symptoms of GI discomfort (particularly faecal urgency and nausea) in lactose intolerant subjects.
• The mechanisms for this improved symptomology require further investigation.

Future Work
• A second study investigating the effects of chronic (two weeks) ingestion of a2 Milk™ products on GI comfort, and focusing on small intestinal inflammation, is scheduled for completion by March 2018.
• Analysis of live GI symptom (LGS) data from the aMiGo trial to understand the potential effects of acute dairy ingestion beyond three hours is ongoing.
• Assessment of MRI images from the aMiGo trial for possible differences in digestion of a2 Milk™ compared to conventional milk (e.g., curd formation, gastric air content) is ongoing.