The researchers, from Liverpool Hope University and Northumbria University in the UK, wanted to investigate whether A2 cow’s milk offers the same benefits as milk containing both A1 and A2 proteins to athletes after exercise.
A1 protein to blame for tummy trouble?
A2 milk – a naturally occurring variant of cow’s milk which contains only the A2-beta casein protein – has been growing in popularity in recent years, as studies have shown the A1-beta casein protein may be responsible for non-lactose-related gastrointestinal issues in some people.
“Bovine beta-cosmorphin-7 (BCM-7), derived from A1-beta casein in regular milk, but not A2-beta casein, expresses opioid receptors in the human GI tract upon digestion which may cause motility disorders, inflammation, abdominal pain and loose stools,” wrote the researchers in their paper, published in Nutrients.
“Consequently, an alternative option for athletes who suffer from these GI discomforts with regular milk is warranted. A2 milk is a natural, biologically-occurring form of cow’s milk, identical in nutrient composition to regular milk, but lacks A1-beta casein and therefore BCM-7 expression, and as such may offer a substitute,” they added.
To investigate the effect of A2 milk on post-exercise recovery, the researchers recruited 21 healthy males in their 20s who regularly played Gaelic football, soccer or rugby, and subjecting them to vigorous exercise consisting of jumps and sprints, over four days.
After each exercise the subjects were split into three groups receiving 500ml of regular milk, A2 milk, or a placebo consisting of 50g maltodextrin mixed with water, according to a double-blind protocol.
Both milks boosted recovery
“We found 500 ml of A2 or regular cow’s milk consumed immediately after the repeated sprint bout reduced decrements in 20-m sprint time (5.1 and 5.2%, respectively) and [counter-movement jump] height (7.2 and 6.3%, respectively) 48 h after [exercise-induced muscle damage],” wrote the authors.
“The pertinent new finding from our data show there were no differences in measures of muscle function or soreness between milk treatments,” they added. “From a practical perspective, these findings suggest that A2 milk might offer an alternative to athletes who experience GI issues with regular milk.”
The authors noted their study did not show any reduction in soreness 48 hours after exercise, as had been demonstrated in previous studies.
“We postulate the milk dosages administered in the present study (~18 g [protein] in 500 ml), which is slightly less than that reported in [other studies] might have been inadequate to maximise the post-exercise [protein] metabolism response associated with perceptions of soreness,” they suggested.
Published online ahead of print, doi: 10.3390/nu9020094
“A2 Milk Enhances Dynamic Muscle Function Following Repeated Sprint Exercise, a Possible Ergogenic Aid for A1-Protein Intolerant Athletes”
Authors: Kirk, B.; Mitchell, J.; Jackson, M.; Amirabdollahian, F.; Alizadehkhaiyat, O.; Clifford, T.