Milk is naturally produced by all female mammals as food for their young, and as such, contains everything needed for early growth. It is thus particularly rich in nutrients (1).
The main nutrients in milk are: calcium, magnesium and vitamins. 100ml of cow’s milk provides on average 120mg of calcium (ie 10%-15% of the RDA for children and adults), 11mg of magnesium (3% of the RDA for a woman) as well as 1 IU of vitamin D and 0.5mcg of vitamin B12 (2).
Milk also contains on average 3.4 g of protein per 100ml, including casein (which accounts for 80% of the protein in milk), lactoglobulin, lactalbumin and lactoferrin (3). The latter (which is available as a supplement, for example, Lactoferrin) is rich in immunoglobulin and is one of the most active components in the first form of breast milk, colostrum, (also available in supplement form, such as the product Colostrum).
During the production of cheese, it’s casein that makes the milk curdle and it remains concentrated in the final product, while the other, soluble, proteins are eliminated in whey. That’s why cheese is so rich in protein (with around 20g-30g per 100g) (4).
Milk also contains varying amounts of fat, with between 1g and 50g per 100 ml depending on the type of milk and farming method used. The lipids in milk have the particular feature of being 60% saturated fatty acids.
Finally, milk contains lactose, a carbohydrate specific to milk. Human breast milk is richer in lactose than cow’s milk, with an average of 60g and 45g per litre respectively (5).
Animal milks have only been consumed by humans since the birth of agriculture and domestication of cattle, around 10,000 years ago (out of 3 million years of human evolution).
However, since milk is a highly-perishable commodity, for thousands of years it was largely consumed by humans in the form of dairy products: cheese, butter, yogurts, fermented milks (6).
It was only in the 20th century, with wider availability of white goods, and a push by the dairy industry, that fresh, unprocessed, milk, became a major feature of the Western diet.
While breast milk is important for infant growth during the first months of life, mammals are ‘programmed’ to quickly wean themselves off milk, and adopt their permanent diet.
So in many cases, the human body gradually stops producing a specific enzyme called lactase, necessary for proper digestion of lactose. Lactase breaks down lactose into two simpler sugars, glucose and galactose, which are easily absorbed by the gut (7).
When the body produces little or no lactase, all or part of the lactose remains intact in the gut, where its inadequate digestion leaves it subject to fermentation by bacteria, resulting in digestive problems.
In Europe, around 40% of adults have trouble digesting lactose, while in Asia, some studies suggest this figure is close to 100%!
Poor lactose digestion causes a number of troublesome symptoms:
All these digestive problems are a sign of lactose intolerance, rather than, as is commonly believed, an allergy to lactose which does not actually exist!
What does exist, however, is an allergy to the proteins in cow’s milk. It is usually only new-borns (around 1 in 40 babies) who are affected by this allergy which disappears around the age of 1 to 2 years. It’s worth noting that this type of allergy causes digestive symptoms similar to those of lactose intolerance, as well as skin reactions such as eczema (8).
For an adult, drinking a litre of milk a day is unlikely to pose any risk. Having said that, it’s neither particularly manageable nor useful.
Generally speaking, it’s better to simply listen to your body and drink what you need: if you have no problem consuming a large serving of milk at breakfast, then why not, but is a whole litre a day really necessary?
If you obtain enough calcium from your diet, or you take calcium supplements, then you can simply drink the amount of milk that suits you and that you can easily digest.
No, drinking milk does not lead to weight gain, unless you only ever drink full-fat milk. Semi-skimmed milk is actually quite low in both calories (around 420kcal per litre) and fat (around 1.5g of fat per 100ml). However, milk contains sugar as well as fat, so it’s best to stick to reasonable quantities.
Cheese, on the other hand, contains 420kcal … per 100g! And with around 33% fat, it’s therefore more important to monitor your cheese intake rather than how much milk you drink!
Milk is neither good nor bad for adults. It’s only bad for those who can’t - or find it difficult to - digest it.
While it may be inappropriate to label milk as the perfect ‘miracle’ food, it’s also wrong to demonise it, at least for health reasons or its alleged harmful effects. Having said that, it’s important to avoid excess consumption, as we’ll now explore …
While many studies have looked at the effects of excessive milk consumption, the results have been inconsistent and somewhat contradictory. It’s therefore difficult to list with any certainty the disadvantages of drinking too much milk.
However, it does seem that:
Regarding the risk of bone health and fractures, the research is generally contradictory: quite logically, many come out in favour of milk for providing calcium and vitamin D while others argue that drinking too much milk increases the risk of hip fractures in menopausal women.
As is often the case, the truth lies somewhere between the two: drinking milk does not pose a risk to health as long as it’s consumed in moderation!
The best milk for adults is the one they digest easily and like. If cow’s milk is your first choice and you have no problem digesting it, then enjoy it in moderation. If you prefer soya or oat milk (or any other plant milk) for its taste, ease of digestion or environmental reasons, then enjoy that! You could also try the benefits of coconut milk.
Again, as is often the case, the most important thing is to listen to your body: if you experience abdominal pain and diarrhoea within 30 minutes to two hours of consuming animal-source milk, then you may be suffering from lactose intolerance.
If so, you can start by eliminating dairy products completely for a few weeks before gradually reintroducing them until you find the quantity or particular dairy product that disagrees with you. In this way, you’ll be able to adapt your diet accordingly.
You can also take enzymes in the form of dietary supplements to help you digest milk (such as Digestive Enzymes, which contains lactase, the enzyme that digests lactose and helps prevent digestive problems).
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