A1 protein free milk benefits mood and subjective cognition in free-living Australian adults: a pragmatic, exploratory, open label randomised controlled trial

Abstract

Background: Adverse effects of milk containing A1-type β-casein on digestion, immune response, and cognition have been identified in milk-intolerant individuals, but health effects in healthy individuals without symptoms of milk intolerance are yet to be examined.

Objective: The objective was to explore the impact of reducing A1 type β-casein intake via switching milk type from conventional A1/A2-type β-casein milk (A1/A2 milk) to A1-type β-casein protein free milk (A1PF) on brain, immune response, gastrointestinal, and skin (BIGS) outcomes in a real-world setting.

Methods: An open-label, pragmatic, exploratory randomised controlled trial was conducted in 997 healthy, free-living Australian older adolescents and adults (16-65 years) who regularly consume A1/A2 protein-containing milk and milk products. Participants were randomised into two groups, to consume ≥250 mL/day of A1/A2 milk (control) or to switch to ≥250 mL/day of A1PF milk (intervention) for 28 days, while continuing to follow their usual diet (including up to 1 serve a day of A1/A2 dairy products). A sub-group of 265 participants conducted stool, saliva and cognitive testing on days 0 and 28. All participants completed subjective questionnaires on days 0, 14, and 28.

Results: No differences in gut microbiome composition, alpha-diversity, or function were found by switching milk type. After switching to A1PF milk, a small increase in stool consistency was reported (-0.16, p = 0.007), and females experienced a marginal reduction in gastrointestinal symptoms (p = 0.015) and improved subjective cognition (p = 0.03). Switching to A1PF milk reduced anxiety (-0.61; p = 0.002), depression (-0.56; p = 0.023), stress (-0.70, p = 0.012) and fatigue (p = 0.001; females only), compared to drinking A1/A2 milk, with stronger effects in females. No consistent effects on markers of immune response or skin health were identified.

Conclusion: Switching from conventional A1/A2 milk to A1PF milk may benefit mood and subjective cognition, particularly in females, without the need for complete elimination of A1 β-casein from the diet. Further investigations are warranted.

Clinical trial registration: https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=385966, identifier ACTRN12623000628640.

Keywords: A1 protein free milk; brain health; gastrointestinal microbiome; gut-brain axis; mental health; mood; pragmatic clinical trial; β-casein.

Figure 1

BIGS Trial study design. A 2-day run-in period was followed by a 28-day intervention period in which participants consumed at least 250 mL/day of either A1 protein-free (A1PF) milk or conventional (CON) milk, with up to one serve per day of conventional (A1/A2) dairy products (e.g., cheese, yoghurt). All participants completed a dietary intake assessment (Intake24) and online questionnaires, while the biological subgroup also completed faecal and saliva sampling, as well as the Subtle Cognitive Impairment Test (SCIT) (52). CON milk is milk containing both A1 and A2 β-casein proteins. A1PF milk contains A2 β-casein only.

Figure 2

CONSORT diagram detailing the flow of participants through the BIGS Trial. CON milk, conventional milk containing both A1 and A2 β-casein proteins; A1PF milk, milk containing A2 β-casein only.

Figure 3

Differential abundance of the Firmicutes A phylum at baseline and post-intervention for each of the conventional (CON) milk (A) and A1 protein free (A1PF) milk (B) study groups. Analysis was conducted for unadjusted (i) and adjusted (ii) datasets. Significance was taken as p < 0.05 after correction for false discovery rate (FDR). CON milk is milk containing both A1 and A2 β-casein proteins. A1PF milk contains A2 β-casein only.

Figure 4

Microbiome composition (A) and differential diversity (B) at the genus level for conventional (CON) milk compared to A1 protein free (A1PF) milk. Diversity was measured as richness (i) and Shannon diversity (ii). There was no effect of milk type on either outcome. CON milk is milk containing both A1 and A2 β-casein proteins. A1PF milk contains A2 β-casein only.

Figure 5

Change in (A) gastrointestinal symptoms (GSRS, Gastrointestinal Symptoms Rating Scale) and (B) stool consistency (BSC, Bristol Stool Chart) over the course of the trial for CON milk (open marker, hashed lines) compared to A1PF milk (solid marker, solid lines) for males (blue) and females (red). CON milk is milk containing both A1 and A2 β-casein proteins. A1PF milk contains A2 β-casein only.

Figure 6

Differential effects of sex on subjective brain-related health outcomes over the course of the trial for CON milk (open marker, hashed lines) compared to A1PF milk (solid marker, solid lines) for males (blue) and females (red), including (A) cognitive function; (B) anxiety; (C) stress; and (D) fatigue. CON milk is milk containing both A1 and A2 β-casein proteins. A1PF milk contains A2 β-casein only.