The mechanism: Why might A2 milk be better for gut health? Approximately 30% of the protein in milk is β-casein. In most commercially available cow milk, 25% to 75% of this β-casein is A1 β-casein, and the rest A2 β-casein, whereas in A2 milk 100% of the β-casein is A2 β-casein.^[2]^[3]

β-casomorphin-7 (BCM-7) is a peptide released during the digestion of A1 β-casein. Animal studies have found associations between BCM-7 and slower digestion time.^[4] BCM-7 has also been hypothesized to reduce lactase activity,^[5] (the enzyme responsible for digesting lactose), though the evidence for this claim is lacking.

A2 milk and the potential impact of BCM-7 on gut health

The research: Does A2 milk cause fewer GI issues than other milk? In the original 2024 study, A2 milk did not improve total gastrointestinal symptoms compared to regular milk. A2 milk generally had inconsistent effects on individual symptoms across the 2 conditions and actually increased bloating compared to regular milk.^[1] Furthermore, the fact that A2 milk did not alter the gut microbiota suggests that it had little effect on digestive factors like lactose metabolism.

Similarly, in several small studies, A2 milk had inconsistent effects on gastrointestinal symptoms compared to regular milk:

In a 2023 randomized crossover study in 10 adults with lactose intolerance (confirmed via breath test), drinking 8 ounces (250 ml) of A2 milk per day was associated with nominally less abdominal pain compared to drinking regular milk, but the difference was not statistical significant) (p=0.19). Interestingly, A2 milk resulted in slower digestion in the stomach.^[6]
In a 2024 randomized crossover study in 16 adults with lactose intolerance, drinking 8 ounces of A2 milk daily resulted in lower levels of 1 out of 5 gastrointestinal symptoms (fecal urgency) compared to drinking regular milk. A2 milk did not appear to improve lactose digestion.^[2]
In a 2020 randomized crossover trial in 25 adults with lactose intolerance, 8 ounces of A2 milk resulted in lower levels of 1 of 5 gastrointestinal symptoms (abdominal pain) compared to regular milk.^[3]
In a 2020 crossover trial, 40 women drank a large amount of A2 milk or regular milk daily. Although A2 milk resulted in lower levels of fecal urgency and nausea in participants with lactose intolerance, A2 milk increased flatulence in participants who were dairy intolerant (but not lactose intolerant) and increased diarrhea in those who were dairy tolerant.^[7]
In a 2016 randomized crossover study in 45 Chinese participants with self-reported lactose intolerance, 8 ounces of A2 milk twice per day did not consistently reduce gastrointestinal symptoms compared to regular milk.^[8]

However, in 2 larger studies, A2 milk generally improved gastrointestinal symptoms compared to regular milk:

In a 2017 randomized crossover study in 600 Chinese participants with self-reported lactose intolerance, drinking 9 ounces of A2 milk daily resulted in lower levels of 4 of 6 gastrointestinal symptoms compared to drinking regular milk (e.g., flatulence, bloating, and abdominal pain).^[9]
In a 2025 randomized controlled trial in 180 toddlers who regularly consumed dairy, formula made from A2 milk improved 3 of 4 gastrointestinal symptoms (e.g., bloating and gassiness) compared to regular milk.^[10]

Is A2 milk better for gut health? Original paper