Effectiveness of Growing-Up Milk Containing Only A2 beta-Casein on Digestive Comfort in Toddlers: A Randomized Controlled Trial in China

Background: Emerging clinical evidence indicates the potential gastrointestinal (GI) benefits of milk containing only A2 b-casein, but data from randomized controlled trials is sparse among pediatric populations. We aimed to evaluate the effectiveness of growing-up milk (GUM) containing only A2 b-casein on GI tolerance in toddlers. Methods: A total of 387 toddlers aged 12-36 months were recruited in Beijing, China, and randomized in a 1:1:1 ratio to consume one of two commercially available A2 GUMs (combined in the analysis as A2 GUM) or continue their current feeding regimen of conventional milk for 14 days. The primary outcome was the total Gut Comfort Score (GCS) (range: 10-60; higher values indicate greater GI distress) derived from a 10-item (score range: 1-6 per item) parent-reported questionnaire, reflecting GI tolerance. Results: The GCS (mean +/- SD) was comparable between the A2 GUM and conventional milk groups on day 7 (14.7 +/- 5.0 vs. 15.0 +/- 6.1, p = 0.54) and day 14 (14.0 +/- 4.5 vs. 14.3 +/- 5.5, p = 0.51). Parents reported less constipation in those consuming A2 GUM vs. conventional milk on day 14 (1.3 +/- 0.6 vs. 1.4 +/- 0.9, p = 0.020). Among 124 participants with minor GI distress at baseline (GCS >= 17, top tertile range 17-35), GCS was significantly lower in those consuming A2 GUM on day 7 (18.2 +/- 5.1 vs. 21.2 +/- 6.8, p = 0.004) and day 14 (17.1 +/- 5.3 vs. 19.6 +/- 6.3, p = 0.026), as were individual GI symptoms (all p < 0.05). In the toddlers without GI issues at baseline (GCS < 17), a low GCS was maintained throughout the study period after switching to A2 GUM (mean values range 10-13). Conclusions: Growing-up milk containing only A2 beta-casein were well-tolerated and associated with lower parent-reported constipation scores after two weeks when compared to conventional milks. In healthy toddlers with minor GI distress, A2 GUM improved overall digestive comfort and GI-related symptoms within one week.