Lactase-Treated A2 Milk as a Feasible Conventional Milk Alternative: Results of a Randomized Controlled Crossover Trial to Assess Tolerance, Gastrointestinal Distress, and Preference for Milks Varying in Casein Types and Lactose Content

Abstract

Background: Previous research indicates that gastrointestinal discomfort from milk consumption may be attributable to A1 β-casein, rather than lactose intolerance alone. A2 milk (free of A1 β-casein) consumption may result in fewer symptoms compared to conventional milk containing both A1/A2 β-casein. Objective: In this five-week, double-blind, double-crossover study, we assessed the physiological responses to doses escalating in volume of lactose-free conventional milk (Lactaid), A2 milk, and lactose-free A2 milk in fluid milk-avoiding participants. Methods: Each milk type was consumed over three separate weeks with three increasing doses across five days per week, >one week washout. Gastrointestinal symptoms, blood glucose, and breath gases were monitored for twenty-four, two-, and three-hours post-consumption, respectively. Sensory evaluation was completed for each sample. Results: Fifty-three participants consented and were randomized, with forty-eight participants completing the study. Overall, symptoms were minimal. On Days 1 and 3, lower ratings of bloating and flatulence were observed in A2 compared to lactose-free A2. Breath hydrogen responses reflected lactose content, but were higher in lactose-free A2 than Lactaid on Day 5. Thirty-three participants were deemed lactose-intolerant and had higher fasting and average breath hydrogen for all samples. The only symptom corresponding to the increase in breath hydrogen among these participants was flatulence after A2 consumption. Surprisingly, flatulence was apparently higher for lactose-tolerant individuals when consuming Lactaid compared to A2. Conclusions: These findings suggest that adults who avoid conventional fluid milk consumption may experience minimal GI discomfort from lactose-free and/or A1-free milks.

Keywords: A2 milk; beta-casein; breath hydrogen; fluid milk; gastrointestinal tolerance; lactose.

Figure 1

Schematic of study design and flow. Participants (n = 48) consumed nine total samples over a five-week period. Conventional milk pre-treated with lactase (Lactaid), milk from a2/a2 cattle (A2), and lactase-treated A2 (A2 Lactase) were provided blinded in ascending doses each week. Gastrointestinal symptoms, blood glucose, and breath gases were assessed before and after consumption of each sample.

Figure 2

Consolidated Standards of Reporting Trials (CONSORT) diagram of study flow.

Figure 3

Consumer preferences measured by the 5-point Just-About-Right (JAR) sensory scale for (a) Day 1 of each sample, and (b) Days 1, 3, and 5 combined. For panel (a), all 48 participants rated all three samples on Day 1 (n = 141). For panel (b), all 48 participants rated all three serving sizes (Days 1, 3, 5) of all three samples (n = 423).

Figure 4

Aggregated gastrointestinal symptoms reported by study participants consuming fluid milk samples varying in casein type and lactose content across days, measured by Visual Analog Scale (VAS): (a) abdominal pain, (b) bloating, (c) flatulence, and (d) diarrhea. Each day includes symptoms reported prior to consuming the sample and post-consumption at +30, +60, +90, +120, and +180 min, and +12 and +24 h (n = 3667 for each panel).

Figure 5

Aggregated gastrointestinal symptoms across a 24 h time period, pre- and post-consumption of fluid milk samples varying in casein type and lactose content, measured by 1-10 Visual Analog Scale (VAS): (a) abdominal pain by time, (b) bloating by time, (c) flatulence by time, and (d) diarrhea by time (n = 3667 for each panel).

Figure 6

Comparison of H₂ and CH₄ production between A2, A2 Lactase, and Lactaid milk: (a) total H₂ levels measured on Days 1, 3, and 5, expressed in parts per million (PPM); (b) total CH₄ levels measured on Days 1, 3, and 5, expressed in parts per million (PPM); and (c) total H₂ difference on Day 5, between samples across time points (n = 2931).

Figure 7

Comparison of hydrogen production: (a) Post A2 Lactase consumption H₂ levels measured on across time, (b) Post A2 consumption H₂ levels measured on across time, (c) Post Lactaid consumption H₂ levels measured on across time, measured in PPM and flatulence severity, (d) Post A2 Lactase consumption over time (e) Post A2 consumption over time, (f) Post Lactaid consumption over time, measured on a scale of 1–10 VAS, between likely lactose-intolerant (n = 33) and lactose-tolerant (n = 15) participants.