## 3 Results
### How Do \(\beta\)CM-7 and the Microbiota Interact in Gut Health and Disease Regulation?
The consumption of A1 \(\beta\)-casein versus A2 \(\beta\)-casein appears to influence digestive health differently in various populations, primarily due to the production of the \(\beta\)CM-7 peptide during A1 \(\beta\)-casein digestion, whereas A2 \(\beta\)-casein produces minimal amounts of \(\beta\)CM-7. Several studies conducted with children of different ages suggest that milk containing only A2 \(\beta\)-casein may be more beneficial in terms of gastrointestinal discomfort compared to A1/A2 (regular) milk. Thus, in a study with infants, an A2 \(\beta\)-casein-based formula without A1 was compared with a conventional infant formula (IF). Better gastrointestinal tolerance was observed in the A2 IF group, with stool frequency and consistency more like those of exclusively breastfed infants [36]. Two trials carried out with toddlers (1-3 years) evaluated conventional growth formulas with comparable nutritional compositions versus those free of A1 \(\beta\)-casein. Formulas made exclusively with A2 \(\beta\)-casein were better tolerated and linked to lower constipation scores as reported by parents, when compared to standard formulas [37]. In healthy toddlers experiencing mild digestive issues, the use of A2-based formula led to noticeable improvements in gastrointestinal comfort and related symptoms within just one week. In another study, while the incidence of acute respiratory infections and diarrhea remained similar between groups, children who consumed formulas free of A1 \(\beta\)-casein experienced shorter episodes of respiratory infections and better outcomes related to diarrhea. Additionally, they showed reductions in bloating, flatulence, and regurgitation [35]. In [PERSON]'s study were included children (1 to 12 years) diagnosed by a pediatrician with chronic functional constipation (CFCs). The authors concluded that there is an association between CFCs and cow's milk consumption, but no effect was found for casein type on the resolution of constipation. They suggest that some other component in cow's milk, common to both A1 and A2 milk, might be causing the problem in these susceptible children [25]. In 5- to 6-year-old children with milk intolerance, consumption of milk containing A2 \(\beta\)-casein was shown to be associated with a reduction in parent-reported gastrointestinal symptoms compared to conventional milk [34]. Some studies investigated the effects of A2 milk on the digestive health of adults. The reviewed trials found that in individuals who experienced gastrointestinal discomfort after milk consumption, switching to A2 milk caused less abdominal pain, fecal urgency, and rumbling compared to A1/A2 milk [32; 33; 40; 41; 42; 43]. Milk containing A2 \(\beta\)-casein could significantly reduce the proportion of abdominal bloating and bowel movement difficulty, increase bowel movement frequency, and change stool characteristics compared to regular milk (containing A1 and A2). Some studies have compared the effect of A2 milk, conventional milk, and lactose-free conventional milk on individuals with different types of lactose intolerance. According to the study by [PERSON] et al. using MRI for people with lactose maldigestion, gastric emptying was significantly faster after consuming conventional milk (containing both A1 and A2 \(\beta\)-casein) compared to milk containing only A2 \(\beta\)-casein. Abdominal pain symptoms tended to be fewer with A2 milk, although the difference did not reach statistical significance in this small sample, leading the authors to suggest that this difference in gastric transit time could mediate the symptoms of lactose intolerance [41]. A2 milk could offer some advantages such as decreasing the sensation of bloating and fullness and fecal urgency in both milk-tolerant and non-lactose-intolerant subjects [40; 43; 50; 51; 64]. Furthermore, these results appear to become more evident over time [50].