## 3 Results
### How Do \(\beta\)CM-7 and the Microbiota Interact in Gut Health and Disease Regulation?
It is important to note that research on the specific effects of A1 and A2 \(\beta\)-casein proteins on the human microbiota is ongoing, and results may vary between studies due to factors such as the population studied, the duration of the intervention, and the methodology used [35]. How Does Individual Susceptibility to \(\beta\)CM-7 Exposure Influence the Observed Effects of A1 \(\beta\)-Casein Consumption? \(\beta\)CM-7 may influence intestinal health, inflammation, and neurological function. An individual's response to its consumption depends on factors such as enzyme activity, gut microbiota, intestinal permeability, opioid-receptor expression, and genetic predisposition. Also, the amount of \(\beta\)CM-7 released during A1 \(\beta\)-casein digestion varies depending on each individual's digestive enzymes and intestinal conditions. In order for proteins to be absorbed in the intestinal tract, they first need to be broken down into amino acids or short-chain peptides, such as dipeptides and tripeptides. The digestion of casein starts in the stomach, where enzymes act to hydrolyze peptides of different lengths. This process continues in the duodenum and concludes in the jejunum, where further breakdown and absorption of smaller peptides takes place [59]. Dairy protein digestion showed no significant differences between people with or without lactose intolerances, based on blood amino-acid levels after consuming different types of milk. Only a slight variation in lysine was observed in the tolerant group, suggesting that intolerances do not significantly affect protein digestion [30]. \(\beta\)CM-7 degradation is largely dependent on dipeptidyl peptidase IV (DPP-4), an enzyme present in various cells, including enterocytes and neurons. DPP-4 is highly expressed in the membrane of small intestinal enterocytes and is secreted into the intestinal lumen via exosomes. The availability and activity of DPP-4 determine the rate of \(\beta\)CM-7 degradation in the small intestine [60; 61]. However, elevated DPP-4 activity in the small intestinal membrane can exacerbate the inflammatory process and can compromise the integrity of the intestinal barrier. Furthermore, single nucleotide polymorphisms (SNPs) in the DPP-4 gene have been associated with an increased risk of diseases such as heart failure, type 2 diabetes, and dyslipidemia, suggesting that these genetic variations may influence \(\beta\)CM-7 metabolism [60; 61]. DPP-4 activity is highly variable, and individuals with lower activity may have higher circulating levels of \(\beta\)CM-7 after consuming A1 \(\beta\)-casein. Studies such as [PERSON] et al. found that urine from autistic children consuming histidine \(\beta\)-casein milk showed higher BCM peptide levels compared to proline \(\beta\)-casein milk. Age-matched controls had no detectable BCM peptides [27]. [PERSON] et al. found elevated serum levels of \(\beta\)CM-7 in children with autism spectrum disorder (ASD) compared to healthy children, suggesting a possible role for \(\beta\)CM-7 metabolism in this group [22]. Intestinal permeability also varies between individuals, meaning that some may absorb more \(\beta\)CM-7 than others, intensifying its effects. As we saw in the previous section, animal studies have shown that the consumption of A1 milk triggers an inflammatory response, enhancing the immune response and possibly altering the intestinal barrier function. This inflammatory response can lead to increased intestinal permeability, compromising the barrier [17]. The inflammatory response to \(\beta\)CM-7 exposure can vary considerably between individuals due to genetic differences, gut microbiota, and overall health status. The study by [PERSON] et al. included participants with self-reported milk intolerance and found that the consumption of milk containing both A1 and A2 \(\beta\)-casein was associated with higher concentrations of inflammation-related biomarkers compared to milk containing only A2 \(\beta\)-casein [33]. [PERSON] et al.