Milk is a white liquid produced from the breasts of female mammals to feed their young before they are old enough to eat for themselves. As such, it is highly nutritious and tailor made for the young mammal by its mother. Other animals take advantage of the nutrition available in milk, such as hedgehogs, cats, seagulls and the red-billed ox pecker. However, whether human or animal, there is a possibility that milk may disagree with your digestive system. This is because milk contains a sugar called lactose, that is broken down by the enzyme lactase. All babies have the enzyme lactase in their guts, but in most this enzyme disappears after weaning. People, mainly living in North West Europe and North America, are however able to drink milk without digestive problems. This is because they retain the enzyme, lactase into adulthood.
Safety of milk.
Untreated milk can cause a number of diseases including: diarrhoea (caused by E.Coli), food poisoning (caused by Staphylococcal enterotoxins), diptheria, typhoid fever and tuberculosis. These bugs can appear after contamination with water and human faecal material (E. coli) or after collecting milk from a cow with an udder infection (diptheria, streptococcal or staphylococcal infection). For this reason, at the turn of the last century a way of treating milk to kill off bacteria was introduced, called pasteurisation. This was primarily to reduce the scourge of the most important disease of the time, tuberculosis, which was passed into the milk by dairy workers already suffering from the disease1. Treated milk can also cause disease, although the incidence of illness caused by treated milk in the UK is pretty low, with 1 in 40 outbreaks of foodborne illness being caused by dairy foods (so less than this for milk alone).
Pastuerisation is named after the great French microbiologist, Louis Pasteur, who in the mid 19th century devised a way of treating beer and wine in order to preserve their flavour for longer. At the start of the 20th century, pasteurisation of milk was introduced in order to reduce the amount of illness caused by bugs present in untreated milk. Most milk is nowadays pasteurised to reduce the amount of bacteria, yeasts and molds present in it. Milk is heated to 71.7C for up to 20 seconds in the standard HTST (high temperature short time) pasturisation process. UHT (ultra-heat-treated) milk is heated to a higher temperature for a shorter time, 135C for at least 1 second2. This extra heat ensures that UHT milk lasts for longer than pastuerised milk. Most people would say however, that it does not taste as good. During the pasteurisation process after heating, the milk is cooled rapidly to below 6ºC using cold water.
Pastuerisation is effective at eliminating above 90% of harmful bacteria in milk1.
If you go back 30-40 years most milk was not homogenized, and bottles of whole milk were delivered by the milkman to the doorstep, with a band of cream on top. Nowadays milk is mostly homogenized and sold in supermarkets. Homogenisation basically involves passing the milk through small holes at high pressure in order to even out the distribution of creamy particles and particles giving flavour to the milk. This means that cream no longer rises to the top of the milk, but stays evenly mixed in the milk. This process does not effect the bacterial safety of the milk.
Pasteurised or raw?
Raw milk is neither homogenized or pasteurised. Although all milk was raw prior to the 20th century, it is nowadays not easy to get hold of raw milk in many countries. In the US up to 3% of people regularly drink raw milk in those states that allow it, with its popularity growing in the last 10 years. In the UK the percentage is lower with a reduction in the amount drunk over the last 15 years according to the FSA (Food Standards Agency). Perhaps as little as 0.01% of milk being raw in the UK. The reason there is so little raw milk owes to the fact that Government organisations have actively encouraged pasteurisation of milk as a public health measure. In the UK raw milk is legal, although not in Scotland4. Although it is legal in England, Wales and Northern Ireland it is restricted to direct sale. That basically means it can't be sold from shops or supermarkets on the high street, and must be sold direct from the farmer. This means that for most people access to raw milk will be via local farmer's markets. When sold in this way in the UK the milk is supposed to have a green top. In the US raw milk is legal in 29 of the 50 states, where in some it can be sold in supermarkets alongside pastuerised milk.
Benefits of raw milk.
Proponents say that raw milk is far more tasty than conventional pasteurised milk. It also contains more nutrients, including more beneficial probiotic bacteria. It is thought that the whey protein in pastuerised milk is denatured (destroyed) and that in raw milk the undenatured whey protein can boost levels of our most important anti-oxidant enzyme, glutathione5. Consumption of raw milk in childhood may also protect against later development of allergies such as asthma and allergies.
Risks of raw milk consumption.
Raw milk contains much more bacteria than pasteurised milk. Most of the bacteria is harmless. To assess the risks we need to look at the incidence of illness related to raw milk consumption. The Health Protection Agency have a list of incidences of foodborne disease in the UK from 1992-20103. This shows that roughly 58 out of 2,321 outbreaks of illness were related to milk and dairy consumption. So about 1 in 40 outbreaks were down to dairy produce. So dairy in itself is relatively safe, but of course in the UK most dairy is pastuerised or fermented and this may be making it more safe. Data from the US where much more raw milk is consumed suggests that the chance of developing illness from raw milk is 10 times greater than that of developing illness from pasteurised milk5a. If this is the case it would be true to say that raw milk consumption is actually relatively safe, probably as safe as eating chicken, which caused the most outbreaks of foodborne illness between 1992 and 2010. Please remember unpasteurised milk should be kept cold, below 4C.
With regard to the former scourge of bovine tuberculosis, in the UK it is illegal to supply any unpastuerised milk from a herd in which any cow has TB. Pasteurised milk can be supplied from such herds as the pasteurisation process kills of the bacterium that causes the disease.
Milk can be found in a large range of processed foodstuffs, as well as in pure milk drunk from a glass, or with breakfast cereal. However, milk consumption as an adult is only a recent innovation for humans. It came in with the advent of the domestication of grazing animals around 5,000 years ago. As such, most human guts are not well adapted to it.
Lactose intolerance is a well known condition for most of the human population, except those in North West Europe and North America. If you are not lactose tolerant you will suffer from digestive disturbance after drinking milk or consuming milk containing products. Lactose is a disaccharide that is made from glucose and galactose. For the lactose intolerant it is not broken down and absorbed in the small intestine. Instead it passes through to the colon from where it can cause stomach rumbles, diarrhoea, flatulence and vomiting. The prevalence of lactose intolerance in the population has not been reliably determined. It is likely to be somewhere between 2% (Sweden 1972) and 98% (Thailand 1972) depending on the country in which you live6.
Casein in general
Casein is the main protein in milk making up about 80% of the protein. Whey protein is the other 20%. Casein can cause allergic like reactions in many people. There are different types of casein in milk, the most common in dairy cattle is the alpha S1 and S2 types. The casein molecule is similar to gluten and both these proteins are associated with allergic style reactions in a number of people.
Beta casein along with alpha casein, is also common, and has two types, A1 and A2. More A2 milk is found in herds from Africa, Asia, France and the Channel islands than in the rest of Europe, Australasia and N. America. Does this matter? Well, A1 milk releases an opiod called beta casomorpin that some people think is linked to heart disease risk, autism and type I diabetes. Although beta casomorphin can be harmlessly broken down in the intestines, it is thought that this doesn't take place in everyone.
Some people find that unpasteurised "raw" milk provokes fewer allergies than pasteurised milk.
Full fat or skimmed?
There has been a move away from full fat milk to skimmed over the last 30-40 years due to various Governments round the world encouraging their population to adopt a diet lower in fat. The truth is that the amount of fat in your milk is probably unimportant unless you drink more than a pint of it. This is due to the fact that saturated fat is not bad for your health. Let's look at what is in the different types of milk.
|MILK (200ml - glass)||full fat||semi-skimmed||skimmed||rda - sedentary female|
|fat: saturated (kcal)||46.8||19.8||1.8||300*||#|
|fat: monounsaturated (kcal)||18||7.2||1.8||300*|
|fat: polyunsaturated (kcal)||1.8||tr||tr||90*|
|fat: trans (kcal)||1.8||1.8||tr||10*||#|
|vitamin a (ug)||62||40||2||900|
|vitamin b3 (mg)||0.4||0.2||0.2||14|
|vitamin b6 (mg)||0.12||0.12||0.12||1.3|
|vitamin b12 (ug)||1.8||1.8||1.6||2.4||#|
|vitamin d (ug)||tr||tr||tr||20|
|vitamin e (mg)||0.16||0.08||tr||15|
|*there is no rda for protein, sugar and fat. These figures are my suggestions.|
Nutrients with a "#" are significant in that a glass of milk contains at least 10% of the rda (recommended daily amount). The sugar, saturated fat, trans fat, vitamin b12, calcium, iodine and zinc fall into this category. Other nutrients can be considered insignificant, as a glass of any type of milk only provides small amounts of them.
- Sugar: While the fat in milk gets al lot of attention it is often forgotten that milk contains quite a lot of sugar in the form of lactose, which consists of glucose and galactose in equal proportion. While it is not as destabilizing for blood sugar levels as bread or sugar, lactose does have quite a high glycaemic index. It is about the same in all types of milk. In my opinion one litre of milk would provide your total allowable amount of sugar for one day.
- Saturated Fat: Whole milk can provide a reasonable amount of saturated fat. One glass of whole milk would contain about 1/6th of your total allowance for one day. As with the lactose, one litre will more or less blow your daily limit for saturated fat. On the other hand semi-skimmed milk contains less than half the saturated fat of whole milk, while skimmed milk contains virtually none.
- Trans fat: Despite what you may have previously read on this website, trans fat from dairy is probably in its natural form of trans vaccenic and conjugated linoleic acid. This is thought to pose no risk to health.
- Vitamin B12: You can't overdose on vitamin B12 so the amount in milk is not significant. If you are short on vitamin B12 you will probably need significantly more that you can get from a glass of milk.
- Calcium: Milk is famous for its calcium content and its supposed role in strengthening the bones. A glass will provide about 1/4 of your daily requirement. However, evidence that milk consumption can reduce risk of bone fracture is not strong7. Also, too much calcium could potentially decrease amounts of magnesium and zinc available to the body.
- Iodine: This trace element, vital for thyroid health, is found in high amounts in milk as a result of the addition of supplements to animal feed and potentially due to the industrial process used to clean the milk processing equipment. Organic milk has been found to be 42% lower in iodine that standard milk8. Milk is an important source of iodine, especially for those who do not eat fish and seafood. For vegetarians seaweed is an alternative non-dairy source of iodine. You would need to drink more than a gallon of milk each day to overdose on iodine.
- Zinc: This trace element is also found in meat, beans and nuts as well as milk.
So what do we make of all that data? It seems to me that for those that are tolerant to lactose and to all the milk proteins, a little milk could be a useful source of nutrition in the diet. For some people it could be their best source of iodine. Too much is unlikely to be good for many people though, as too much calcium and lactose are likely to cause problems. How much is too much? Probably about a pint (568ml) for people who don't have any noticeable issues with milk.
Other types of milk.
Condensed milk is 55% sugar and is used in toffee, caramel and fudge. Evaporated milk is concentrated milk that has roughly twice the concentration of whole milk, making it twice as sweet. Channel islands milk (Jersey/Guernsey) contains over 30% more fat that whole milk, and about the same amount of lactose.
The first dose of milk delivered to the baby by its mother has colostrum, which contains antibodies to help the infant fight off infection. Colostrum contains more protein and less fat than milk that is subsequently produced by the mother. It is likely that infants who receive colostrum get tangible health benefits later in life. There is some evidence that bovine colostrum can improve athletic performance9. I'll be looking at this in a future article.
The benefits of breast feeding are highly significant for the subsequent health of the infant. I'm not going to detail them here, but my personal opinion is that mother and baby should make a good attempt at breast feeding and only give up if there are major problems with it. If this is the case, then it is true that formula feed has improved over the last few decades, and that it is not the end of the world.
I've never been a great fan of milk, having been one of the few kids at my primary school to refuse to drink it on my first day at school. At that time Margaret Thatcher - "milk snatcher", would probably have got my vote! However, even at primary school I was drinking milky tea at home, it was just the pure milk drink that used to offend my taste buds. Other people of course love milk. Currently I have about 180ml of skimmed, pasteurised milk per day on my cereal.
For some people milk is not a great idea as they react badly to the lactose or milk proteins. Such people should not bother drinking milk. Your health will be better without it. If on the other hand you seem to get on with milk then consuming it in moderation should be OK for health. I do think raw milk, if you know the local farm that supplies it and trust their hygiene is not as dangerous as the Government authorities would have you believe. Raw milk is also likely to be better for the environment and for the animals. I suspect it would be too creamy a taste for me though.
1) http://msc-ks4technology.wikispaces.com/GCSE+FT+Unit+2+Lesson+7+Heat+treatment Great GCSE video re. pasteurisation of beer and milk.
2) http://en.wikipedia.org/wiki/Pasteurization General information on pasteurisation.
3) http://www.hpa.org.uk/Topics/InfectiousDiseases/InfectionsAZ/FoodborneOutbreakSurveillanceAndRiskAssessment/FoodborneOutbreaks/eFOSSFoodborneoutbreakspathogenbyfood19922010gi/ Foods causing disease.
4) http://www.food.gov.uk/business-industry/guidancenotes/hygguid/rawmilkcream#.ULyaKYPtQdU Food Standards Agency history of raw milk regulation in the UK.
5) http://chriskresser.com/raw-milk-reality-benefits-of-raw-milk Raw milk benefits discussion from the US.
5a) http://chriskresser.com/raw-milk-reality-is-raw-milk-dangerous Raw milk dangers discussion from the US.
6) http://www.foodreactions.org/intolerance/lactose/prevalence.html Lactose intolerance prevalence.
7) http://ajcn.nutrition.org/content/86/6/1579.full Extra calcium does not reduce hip fracture risk
8) http://epubs.surrey.ac.uk/184898/3/Bathmilk_short_communication22Feb2011MPR.pdf Iodine levels lower in organic milk
9) http://www.ncbi.nlm.nih.gov/pubmed/12188088 Colostrum from cows may benefit athletic performance.