title: Milk Intolerance, Beta-Casein and Lactose.
abstract: True lactose intolerance (symptoms stemming from lactose malabsorption) is less common than is widely perceived, and should be viewed as just one potential cause of cows' milk intolerance. There is increasing evidence that A1 beta-casein, a protein produced by a major proportion of European-origin cattle but not purebred Asian or African cattle, is also associated with cows' milk intolerance. In humans, digestion of bovine A1 beta-casein, but not the alternative A2 beta-casein, releases beta-casomorphin-7, which activates μ-opioid receptors expressed throughout the gastrointestinal tract and body. Studies in rodents show that milk containing A1 beta-casein significantly increases gastrointestinal transit time, production of dipeptidyl peptidase-4 and the inflammatory marker myeloperoxidase compared with milk containing A2 beta-casein. Co-administration of the opioid receptor antagonist naloxone blocks the myeloperoxidase and gastrointestinal motility effects, indicating opioid signaling pathway involvement. In humans, a double-blind, randomized cross-over study showed that participants consuming A1 beta-casein type cows' milk experienced statistically significantly higher Bristol stool values compared with those receiving A2 beta-casein milk. Additionally, a statistically significant positive association between abdominal pain and stool consistency was observed when participants consumed the A1 but not the A2 diet. Further studies of the role of A1 beta-casein in milk intolerance are needed.
authors.affiliation: School of Public Health, Curtin Health Innovation Research Institute, Curtin University, GPO Box U1987, Perth WA 6845, Australia. s.pal@curtin.edu.au.
authors.forename: Sebely
authors.initials: S
authors.lastname: Pal
authors.affiliation: Agricultural Management Group, Lincoln University, PO Box 85084, Lincoln 7647, Christchurch, New Zealand. keith.woodford@lincoln.ac.nz.
authors.forename: Keith
authors.initials: K
authors.lastname: Woodford
authors.affiliation: The a2 Milk Company (Australia) Pty Ltd, PO Box 180, Kew East, Victoria 3102, Australia. sonja.kukuljan@a2Milk.com.
authors.forename: Sonja
authors.initials: S
authors.lastname: Kukuljan
authors.affiliation: School of Public Health, Curtin Health Innovation Research Institute, Curtin University, GPO Box U1987, Perth WA 6845, Australia. Suleen.Ho@curtin.edu.au.
authors.forename: Suleen
authors.initials: S
authors.lastname: Ho
mesh_terms: D015746:Abdominal Pain / Q000201:enzymology / Q000209:etiology* / Q000503:physiopathology / Q000628:therapy; D000818:Animals; D002364:Caseins / Q000009:adverse effects* / Q000378:metabolism; D003672:Defecation; D041981:Gastrointestinal Tract / Q000187:drug effects* / Q000201:enzymology / Q000503:physiopathology; D005772:Gastrointestinal Transit; D006801:Humans; D018836:Inflammation Mediators / Q000378:metabolism; D007787:Lactose Intolerance / Q000201:enzymology / Q000209:etiology* / Q000503:physiopathology / Q000628:therapy; D017450:Receptors, Opioid, mu / Q000819:agonists / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D016896:Treatment Outcome
chemical_list: D002364:Caseins; D018836:Inflammation Mediators; D017450:Receptors, Opioid, mu
keywords: beta-casein; lactose; lactose intolerance; milk consumption