Irritable bowel syndrome (IBS) is a prevalent functional bowel disorder in which recurrent abdominal pain is associated with defecation and altered bowel habits. Although the pathophysiology is incompletely understood, it is generally regarded as a multifactorial disorder involving host factors such as low-grade immune activation, altered intestinal barrier function and defense. Environmental factors, including diet, are also suggested to play a role. Dairy products such as cow's milk are widely produced and an important component of the human diet. Cow's milk is composed of various macronutrients, micronutrients and water. Beta-casein is a major protein component of cow's milk; most cows produce a mixture of A1 and A2 beta-casein (conventional milk), whereas some cows produce only A2 beta-casein (A2 milk). It has been suggested that specific components in cow's milk, such as A1 beta-casein, may trigger gastrointestinal symptoms after intake.~The purpose of this randomized, double-blind, cross-over study performed in Maastricht University Medical Center (MUMC+) is to explore the acute and mid-terms effects of A2 milk versus conventional milk on gastrointestinal symptoms and immune and defense markers in separate groups of patient with constipation-predominant IBS and in patients with diarrhea-predominant IBS.
This aim of this study is to evaluate the acute and mid-term effects of A2 milk versus conventional milk on gastrointestinal symptoms in patients with constipation-predominant IBS and in patients with diarrhea-predominant IBS. Moreover, the effect of immune and defense markers will be studied.