The most common health problem concerning milk is lactose intolerance. This problem is due to the poor absorption of the sugar in milk (lactose) and is not an allergy or food sensitivity. Symptoms such as colic, flatulence and bloating arise due to fermentation of the unabsorbed sugars.

The reason that lactose remains unabsorbed is because the enzyme lactase, which is necessary for its breakdown, is either deficient or absent. This enzyme normally resides on the surface of the intestinal wall amidst finger-like projections called villi. As a consequence, lactose remains in the gut and feeds the intestinal bacteria which ferment it into gas. Lactose also draws fluids into the gut from the gut wall, causing a watery stool not long after consuming the milk.

Lactase deficiency is in fact the normal state for most mammals following weaning, and our own adult Palaeolithic ancestors were completely intolerant of lactose. In humans today it affects about three quarters of people, while some races experience this intolerance to a greater extent than others, particularly Asian, Australian Aboriginal and African people.¹

A prolonged tolerance in the lucky ones is due to the fact that a recent mutation in the gene responsible for lactase synthesis (LCT) has allowed the gene to stay turned on. This is notable amongst those people with ancestry in Britain, Germany and Scandinavia; nevertheless, lactase production is still at a level of about 10% of what it is at birth. It also declines further with age and late-onset lactase deficiency occurs at a minimal rate of 2% in Scandinavia, while it can be as high as 70% in some regions of Italy.²

Because of this intolerance, dairy consumption was probably restricted in early civilisations as our ancestors gradually evolved from hunter-gatherers to herders and farmers. The genetic mutation supporting the extended consumption of milk was a fortuitous development sometime in the last 13,000 years, a modern example of a gene-culture co-evolution. There has also been a more recent degree of gut flora adaptation which has allowed the widespread inclusion of dairy products in the diet of people since the Roman Era.

The development of lactose-reduced products, industrial fermentation and lactase supplements are more recent innovations designed to make dairy products more tolerable. Unfortunately, pasteurisation and ultra-processing has the opposite effect, by inactivating the valuable enzymes present in the raw milk. A modern urban diet containing a large proportion of such ‘devitalised’ foods necessarily draws heavily on the consumer’s own pancreatic enzyme secretions to compensate ad pancreatic insufficiency often results.

Secondary lactase deficiency can result from infection, parasites or disease in the gut which damage the surface of the villi, and therefore dysbiosis is another common factor in lactase deficiency. A much rarer inherited condition called congenital lactase deficiency would have given an infant a poor chance of survival before soy-based infant formulas were available. Premature infants are also usually deficient in lactase due to their immature gut, and the Holder pasteurisation used to treat donor milk, where the milk is heated to 62.5°C for 30 minutes, is unfortunately an obstacle to the development of lactose tolerance. By comparison, normal pasteurisation is brief at around 15 seconds.³

You can test for lactase deficiency with a simple test which involves drinking two glasses of plain whole-milk when you get up in the morning, eating nothing else for a several hours, and see what happens in your digestive system. You should also consider that milk is commonly consumed together with many other processed foods such as breakfast cereal, toast or chocolate so the source of any gut symptoms can be easily confused and needs to be sorted out with a rigorous elimination diet or IgG test.

Full-fat yoghurt, butter and other sour cheeses will, however, generally be better tolerated due to the lower lactose content if they are natural, unadulterated products. Fermented milk such as kefir is also a traditional strategy to reduce lactose content through fermentation, as well as help preserve the milk—the sourness of the product indicates how much sugar is lost. Drinking kefir also confers many health benefits via its probiotic bacteria: it improves gut health, modulates immunity, has a positive effect on serum cholesterol, is anti-microbial, anti-allergenic, stimulates wound healing and is anti-carcinogenic.⁴

Just to confuse you, lactose can be found in a broad range of processed factory foods in forms such as whey isolate or milk solids, so get into the habit of reading the labels or best of all avoid factory-foods altogether. In this way you efficiently eliminate lactose as well as a whole swathe of exotic problem chemicals, many of which have never been properly tested unless you call the globalisation and widespread consumption of such substances a clinical trial!

Other confounding influences during tests can arise from non-food sources such as the oral contraceptive pill, dust mites, mould, cat fur, electric blankets and common additives such as salicylates, colours and preservatives as Dr Benjamin Feingold discovered in the 1970s. Then there are the prevalent agri-chemicals which cause havoc with homeostasis and can only be avoided by buying organic milk, butter, yoghurt and cheese which, luckily for the tolerant or intolerant consumer, are all conveniently available in the supermarket.

Any residual gut symptoms may, however, be due to reactivity to proteins and fats in the milk which is the subject of a more detailed eBook called Milk, Allergy And Food Sensitivity In Alternative Medicine.

Disclaimer: this article is intended for the purpose of general education only, and is not a substitute for diagnosis, treatment advice, or a prescription that is given in a consultation with a qualified physician.

References:

1. Silanikove N, Leitner G, Merin U. The Interrelationships between Lactose Intolerance and the Modern Dairy Industry: Global Perspectives in Evolutional and Historical Backgrounds. Nutrients 2015;7:7312–31.
2. Vandenplas Y. Lactose intolerance. Asia Pac J Clin Nutr 2015;24 Suppl 1:S9-13.
3. Hanson C, Lyden E, Furtado J, Van Ormer M, Anderson-Berry A. A Comparison of Nutritional Antioxidant Content in Breast Milk, Donor Milk, and Infant Formulas. Nutrients 2016;8.
4. Bourrie BCT, Willing BP, Cotter PD. The Microbiota and Health Promoting Characteristics of the Fermented Beverage Kefir. Front Microbiol 2016;7:647.