Milk with only A2 β-Casein may lead to less gastrointestinal symptoms in lactose maldigesters

Milk with only A2 β-casein protein may help reduce gastrointestinal discomfort in people with lactose maldigestion.

A recent study published in Nutrients1 found that milk containing only the protein A2 β-Casein caused fewer symptoms of gastrointestinal intolerance in subjects with lactose maldigestion and intolerance, compared to conventional milk that contains A1 and A2 β-caseins. In the randomized, double-blind, cross-over trial, 25 subjects with lactose intolerance, and eight lactose maldigesters were given either milk containing A2 β-casein protein only (from the (The a2 Milk Company based in Boulder, CO), Jersey milk, conventional milk, and lactose-free milk following an overnight fast. Symptoms of GI intolerance and breath hydrogen concentrations were analyzed for six hour after ingestion of each type of milk.

Results showed that subjects with lactose intolerance that consumer the A2 milk has significantly lower total symptom scores for abdominal pain, compared to those who consumed conventional milk. However, there were no significant differences between groups of total symptom scores for bloating, flatulence, diarrhea, and fecal urgency, or combined total symptom scores for abdominal pain, bloating, flatulence, and diarrhea reported by subjects.

When including the eight lactose maldigesters who did not meet the criteria of lactose intolerance for a total of 33 subjects, total symptom scores for abdominal pain were lower for subjects consuming the A2 milk, compared to conventional milk. While total symptom scores for flatulence, diarrhea, and fecal urgency were similar in subjects consuming milk containing A2 β-casein only, Jersey milk, and conventional milk, the combined total symptom scores for abdominal pain, bloating, flatulence, and diarrhea showed there were fewer symptoms with milk containing A2 β-casein only compared to conventional milk.

The reason conventional milk can cause gastrointestinal discomfort is because digestive enzymes act on A1 β-casein and hydrolyze it, releasing beta-casomorphin-7 (BCM-7). “The histidine residue in A1 β-casein allows cleavage to form BCM-7, whereas the proline residue in A2 β-casein limits such cleavage and BCM-7 formation,” the authors explain. Animal studies have shown that BCM-7 is both pro-inflammatory and associated with slower gastrointestinal transit. The inflammation may be the result of BCM-7 downregulation of glutathione, an important antioxidant.

Because of the small sample size, the results cannot be generalized to a larger population but the results warrant further research and confirmation in a larger study population.


  1. Ramakrishnan M et al. “Milk containing A2 β-Casein ONLY, as a single meal, causes fewer symptoms of lactose intolerance than milk containing A1 and A2 β-Caseins in subjects with lactose maldigestion and intolerance: a randomized, double-blind, crossover trial.” Nutrients, vol. 12, no. 12 (2020): 3855