A glass of cow’s milk: is it the perfect recovery drink that it’s made out to be? Part 2

Posted by Simone do Carmo

In part 1, I looked at milk through a performance nutrition lens. The research seems to support the use of milk as part of a post-workout nutrition plan. But when I add my integrative nutrition lens, it becomes clear that most of the research fails to consider two important factors: individuality and quality.

 There is a negative side to milk. Many athletes cannot tolerate milk – either due to lactose intolerance or casein sensitivity, which is more common than first thought.

Sure, one could argue that athletes can supplement with lactase if they really want to drink milk, but a better alternative would be kefir, a fermented milk that is rich in natural probiotics. The fermentation process results in relatively low lactose levels and may be an option for some lactose intolerance sufferers (1). Sadly, there’s a lack of research into kefir for athletes, but I suspect it may be even better than skimmed milk or chocolate-flavoured milk due to its gut-health benefits. However, there is one interesting study worthwhile mentioning. Eighteen healthy young men, who were not used to regular exercise, participated in each of three trials in a double-blind manner: (i) rest with placebo intake, (ii) exercise with placebo intake, and (iii) exercise with fermented milk intake. Fermented milk supplementation improved glucose metabolism and attenuated the effects of muscle soreness after high-intensity exercise, which the researchers suspected may be due to the regulation of antioxidant capacity (2). It would be interesting to see this study replicated in athletes.

The casein found in milk exists in various forms. Beta-casein is the second most common form, which has two common variants: A1 beta-casein and A2 beta-casein (3). The proportion of each variant in a glass of milk depends on the breed of cow it came from (3):

  • - A1 beta-casein: mainly from breeds of cows that originated in Northern Europe (e.g. Holstein-Friesian, Ayrshire and British Shorthorn).
  • - A2 beta-casein: mainly from breeds of cows that originated in the Channel Islands and Southern France (e.g. Guernsey, Jersey and Charolais).

Regular milk contains both variants, but A2 milk contains only A2 beta-casein, which is often considered the healthier choice. The A1 beta-casein in regular milk is partly broken down in the stomach to a bioactive peptide called beta-casomorphin-7 (BCM-7). Casomorphins have opioid-like effects that may target the brain, but also increase the release of histamine, a potential mediator of inflammation (4). BCM-7 has also been linked to several adverse health effects, such as increased mucus production, asthma, an increased risk of type 1 diabetes, heart disease and autism, but more research is required as the evidence is very limited (3, 5, 6). Growing evidence shows that A1 beta-casein may affect digestive function, causing more bloating and softer stools (7), but further clinical trials are needed.

One of the most important questions we should ask: how is the cow raised? Grass-fed cows produce milk with up to five times more conjugated linoleic acid (CLA) than cows fed processed grains. Research has shown that high levels of CLA offer heart-healthy benefits (8) and may extend to the prevention of diabetes and cancer. Ironically, CLA is also an extremely popular weight management supplement. Several studies have also shown that grass-based diets increase precursors for vitamins A and E, omega-3s, as well as glutathione and superoxide dismutase activity (9). Additionally, while growth hormones are not permitted in the UK and antibiotic use is restricted (significantly lower than in the US), there is some concern regarding the use of reproductive hormones and overuse of antibiotics within the veterinary medicine sector, mainly to ensure cows produce more milk than normal. This is concerning due to the global issue of antimicrobial resistance and from an animal welfare perspective – a whole other discussion for another day.

From a purely performance nutrition standpoint, milk seems to be the ‘perfect’ recovery drink. But if we bring some integrative thinking into the mix, where individuality is key and health comes before performance, a glass of cow’s milk may not be suitable for everyone. If it is a suitable option, I believe we should encourage athletes to seek good-quality milk, such as A2 and grass-fed milk, or kefir despite its research limitations. Since everything points towards these being healthier and more nutrient-dense options, why not encourage athletes to drink them?

References 
  1. Hertzler & Clancy (2003). Kefir improves lactose digestion and tolerance in adults with lactose maldigestion. J Am Diet Assoc. 103(5):582-587.
  2. Iwasa M et al (2013). Fermented milk improves glucose metabolism in exercise-induced muscle damage in young health men. Nutrition Journal. 12:83
  3. Kiminski S et al (2007). Polymorphism of bovine beta-casein and its potential effect on human health. J Appl Genet. 48(3):189-198.
  4. Kurek M et al (1992). A naturally occurring opioid peptide from cow’s milk, beta-casomorphine-7, is a direct histamine releaser in man. Int Arch Allergy Immunol. 97(2):115-120.
  5. Truswell AS (2005). The A2 milk case: a critical review. Eur J Clin Nutr. 59(5):623-631.
  6. Sodhi M et al (2012). Milk and protein and human health: A1/A2 milk hypothesis. Indian J Endocrinol Metab. 16(5):856.
  7. Ho S et al (2014). Comparative effects of A1 Versus A2 beta-casein on gastrointestinal measures: a blinded randomised cross-over pilot study. Eur J Clin Nutr. 68(9):994-1000.
  8. Smith LA et al (2010). Conjugated linoleic acid in adipose tissue and risk of myocardial infarction. Am J Clin Nutr. 92(1):34-40.
  9. Daley CA et al (2010). A review of fatty acid profiles and antioxidants content in grass-fed and grain-fed beef. Nurt J. 9:10.