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Nutr J. 2017 Oct 25;16(1):72. doi: 10.1186/s12937-017-0275-0.

Effects of cow's milk beta-casein variants on symptoms of milk intolerance in Chinese adults: a multicentre, randomised controlled study.

Author information

Beijing Research Institute for Nutritional Resources, Beijing, China.
Clinical Nutrition Center, Huadong Hospital Affiliated to Fudan University, Shanghai, China.
Department of Nutrition, School of Public Health, Sun Yat-Sen University, Guangzhou, China.
Department of Food Nutrition, National Institute for Nutrition and Health, Chinese Center for Disease Control and Prevention, Beijing, China.
Chinese Nutrition Society, 6# Guang An Men Nei. Street, Fenghua Square, Building A, Unit 5, Room 1601/1602, Xuanwu District, Beijing, 100053, People's Republic of China.



A 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.


In 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.


A 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).


Milk 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.


NCT02878876 , registered August 16, 2016. Retrospectively registered.


Beta-casein; Intolerance; Lactase; Lactose

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