Beta-casein comprises 30% of the protein content in cows’ milk and regular milk contains both A1 and A2 beta-casein. These have different outcomes upon digestion when compared to one another due to a slight difference in the amino acid sequence on the peptide chain. A1 beta-casein preferentially releases the opioid peptide beta-casomorphin 7 (BCM-7) on digestion. In contrast, the structure of A2 limits the release of BCM-7 on digestion.
An infographic providing an overview of the A1 and A2 beta-casein protein variants. The graphic displays how upon regular milk consumption, BCM-7 is released resulting in gastrointestinal differences.
Beta-casein protein makes up around 30% of the protein contained in cows’ milk, which is around 2.5 grams per glass. Owing to natural genetic variation, beta-casein may be present as one of two major types, the progenitor A2 type or the mutated A1 type. Cows’ milk which is free of A1 beta-casein is produced by cows specially selected for their genes to produce only the A2 type of beta-casein protein (e.g. a2 Milk™ in Australia). In contrast, A1 beta casein is present in milk produced by most cows of European breed.
Lactose intolerance has been described as one of the most common intolerance responses to cows’ milk, with an estimated prevalence of around 10% in Caucasian Australians. However, for a proportion of adults who report intolerance symptoms following milk intake, lactose intolerance is not the cause, as cases of perceived lactose intolerance are more common than its prevalence in adults.
Emerging evidence suggests that the ingestion of dairy foods, particularly whole or fat-free milk, may represent an ideal food source to enhance muscle protein synthesis and thereby skeletal muscle hypertrophy. Research findings in men and women have shown that consumption of whole milk following resistance training can promote muscle protein synthesis and/or inhibit protein breakdown leading to improved net muscle protein balance.
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