Effects of milk containing only A2 beta casein versus milk containing both A1 and A2 beta casein proteins on gastrointestinal physiology, symptoms of discomfort, and cognitive behavior of people with self-reported intolerance to traditional cows’ milk

Abstract

BackgroundCows’ milk generally contains two types of β-casein, A1 and A2 types. Digestion of A1 type can yield the peptide β-casomorphin-7, which is implicated in adverse gastrointestinal effects of milk consumption, some of which resemble those in lactose intolerance. This study aimed to compare the effects of milk containing A1 β-casein with those of milk containing only A2 β-casein on inflammation, symptoms of post-dairy digestive discomfort (PD3), and cognitive processing in subjects with self-reported lactose intolerance.MethodsForty-five Han Chinese subjects participated in this double-blind, randomized, 2 × 2 crossover trial and consumed milk containing both β-casein types or milk containing only A2 β-casein. Each treatment period was 14 days with a 14-day washout period at baseline and between treatment periods. Outcomes included PD3, gastrointestinal function (measured by smart pill), Subtle Cognitive Impairment Test (SCIT), serum/fecal laboratory biomarkers, and adverse events.ResultsCompared with milk containing only A2 β-casein, the consumption of milk containing both β-casein types was associated with significantly greater PD3 symptoms; higher concentrations of inflammation-related biomarkers and β-casomorphin-7; longer gastrointestinal transit times and lower levels of short-chain fatty acids; and increased response time and error rate on the SCIT. Consumption of milk containing both β-casein types was associated with worsening of PD3 symptoms relative to baseline in lactose tolerant and lactose intolerant subjects. Consumption of milk containing only A2 β-casein did not aggravate PD3 symptoms relative to baseline (i.e., after washout of dairy products) in lactose tolerant and intolerant subjects.ConclusionsConsumption of milk containing A1 β-casein was associated with increased gastrointestinal inflammation, worsening of PD3 symptoms, delayed transit, and decreased cognitive processing speed and accuracy. Because elimination of A1 β-casein attenuated these effects, some symptoms of lactose intolerance may stem from inflammation it triggers, and can be avoided by consuming milk containing only the A2 type of beta casein.Trial registration ClinicalTrials.gov/NCT02406469 Electronic supplementary materialThe online version of this article (doi:10.1186/s12937-016-0147-z) contains supplementary material, which is available to authorized users.

British Dietetic Association systematic review and evidence‐based practice guidelines for the dietary management of irritable bowel syndrome in adults (2016 update)

“…Cows’ milk supply typically contains A1‐ and A2‐β‐casein in a 1 : 1 ratio; however, during digestion of A1‐β‐casein, β‐casomorphin 7 is released, which may lead to gastrointestinal symptoms, although this has not been observed with A2‐β‐casein. Some preliminary research in subjects with self‐reported milk intolerance has shown that these symptoms may be avoided with milk containing only A2‐β‐casein ; further research is warranted to determine whether these findings can be repeated in patients with IBS.…”

“…Gluten-containing diet increased abdominal pain (P = 0.02), dissatisfaction with stool consistency (P = 0.03) and tiredness (P = 0.001 gastrointestinal symptoms, although this has not been observed with A2-b-casein. Some preliminary research in subjects with self-reported milk intolerance has shown that these symptoms may be avoided with milk containing only A2-b-casein (169,170) ; further research is warranted to determine whether these findings can be repeated in patients with IBS. Food is a complex matrix of variable components and, depending on its solubility and fermentability, the different types of dietary fibre have a variety of actions on the gut and its environment (62) .…”

Redox properties of transitional milk from mothers of preterm infants

“…31 A2β-casein proteins, which can influence gastrointestinal physiology, cognitive behaviour and induce symptoms of discomfortin people, are present in protein fraction but not in whey proteins. 32 The antioxidant activity of caseins was mediated by its constituent amino acids, whereas the activity in whey was largely dependent on the free thiol group of β-lacto globulin. Taking also into the consideration the possible problems with micro-RNA 33 and casein, it appears that whey may be safest preterm transitional milk fraction with largely preserved antioxidative potential.…”

Leites A1 e A2: revisão sobre seus potenciais efeitos no trato digestório

“…Este estudo aponta para impacto negativo do consumo da variante A1 da β-caseína, sugerindo agravo da resposta inflamatória. Em outro estudo envolvendo 45 adultos chineses, os quais se auto-identificaram como sendo intolerantes ao leitecomercial ou do tipo A1, mas sem prévio diagnóstico de causa, foram consumidas duas porções diáriasde 250 mL de A1/A2 (relação de 40:60) ou leite A2 [36] , durante 14 dias. Observou-se que houve um aumento na auto-identificação de marcadores de desconforto digestivo, frequência e consistência das fezes mais macias, sendo empregada a escala de Bristol.…”