Abstract
BackgroundA major protein component of cow’s milk is β-casein. The most frequent variants in dairy herds are A1 and A2. Recent studies showed that milk containing A1 β-casein promoted intestinal inflammation and exacerbated gastrointestinal symptoms. However, the acute gastrointestinal effects of A1 β-casein have not been investigated. This study compared the gastrointestinal effects of milk containing A1 and A2 β-casein versus A2 β-casein alone in Chinese adults with self-reported lactose intolerance.MethodsIn this randomised, crossover, double-blind trial, with a 3-day dairy washout period at baseline, subjects were randomised to consume 300 mL of milk containing A1 and A2 β-casein (ratio 58:42; conventional milk) or A2 β-casein alone; subjects consumed the alternative product after a 7-day washout period. Urine galactose was measured at baseline after a 15 g lactose load. Subjects completed 9-point visual analogue scales for gastrointestinal symptoms (borborygmus, flatulence, bloating, abdominal pain, stool frequency, and stool consistency) at baseline and at 1, 3, and 12 h after milk consumption.ResultsA total of 600 subjects were included. All six symptom scores at 1 and 3 h were significantly lower after consuming A2 β-casein versus conventional milk (all P<0.0001). At 12 h, significant differences remained for bloating, abdominal pain, stool frequency, and stool consistency (all P<0.0001). Symptom scores were consistently lower with A2 β-casein in both lactose absorbers (urinary galactose ≥0.27 mmol/L) and lactose malabsorbers (urinary galactose <0.27 mmol/L).ConclusionMilk containing A2 β-casein attenuated acute gastrointestinal symptoms of milk intolerance, while conventional milk containing A1 β-casein reduced lactase activity and increased gastrointestinal symptoms compared with milk containing A2 β-casein. Thus, milk-related gastrointestinal symptoms may result from the ingestion of A1 β-casein rather than lactose in some individuals.Trial registrationNCT02878876, registered August 16, 2016. Retrospectively registered.
Highlights
A major protein component of cow’s milk is β-casein
Secondary objectives included the following: (1) to compare the effects of both milk products on lactase activity, which was assessed in terms of urinary galactose after an oral lactose load; (2) to compare/contrast the shifts in lactase activity induced by the type of β-casein with self-reported symptoms of lactose intolerance; and (3) to determine whether age was correlated with the symptoms of milk intolerance or urinary galactose, the subjects were divided into two age groups (20–35 years and 36–50 years)
We propose the hypothesis that the gastrointestinal symptoms in some subjects with self-reported lactose intolerance might be related to A1 β-casein rather than lactose itself
Summary
The primary objective was to compare the effects of consuming milk containing solely the A2 type of β-casein with conventional milk containing both A1 and A2 types of β-casein on acute self-recorded lactose intolerance and gastrointestinal discomfort occurring within several hours of consuming milk. The primary endpoint was gastrointestinal symptom scores assessed by VAS. Secondary objectives included the following: (1) to compare the effects of both milk products on lactase activity, which was assessed in terms of urinary galactose after an oral lactose load; (2) to compare/contrast the shifts in lactase activity induced by the type of β-casein with self-reported symptoms of lactose intolerance; and (3) to determine whether age was correlated with the symptoms of milk intolerance or urinary galactose, the subjects were divided into two age groups (20–35 years and 36–50 years). Improvements in gastrointestinal symptoms after consumption of milk containing A2 β-casein relative to conventional milk were classified as follows: no symptoms; significant improvement in symptoms (reduction in score of ≥4 for that symptom); slight improvement in symptoms (reduction in score of 1 to ≤3 for that symptom); or no difference or worsening in symptoms (no change in score or an increase in the score)
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