The Science of Food

I like milk but, lets face it, the rear end of a cow is a pretty grotty place. You’ve got the business end of the alimentary system, a tail swishing around spreading manure all round the place and the udder, the source of our milk, is right there in the middle. Cows aren’t great at hygiene, especially when there is a lot of them in confined spaces, and if you want to get safe milk from a cow you need to be careful. Udders needed to be cleaned, milking equipment needs to be sanitised, the humans involved need to look after their own hygiene and the utmost care needs to be taken that milk is not contaminated straight from the source with harmful bacteria. And that’s not all. Both cows and the humans who are doing the milking are susceptible to infection and some of these infections can be transmitted via milk. Human diseases such as typhoid, diphtheria and streptococcal infections have all been transmitted via milk, and if that’s not enough, humans, particularly infants, are susceptible to bovine tuberculosis and brucellosis both caused by bovine microbes. Dairy can be dangerous and we need to be careful when producing milk and dairy products for mass consumption.

Now I’m not trying to throw shade at cows for their bad hygiene, until recently humans were not particularly good at hygiene either, especially when there was a lot of us in a confined space. As a matter of fact until recently, like 20th century recent, the number one cause of human mortality was infectious disease and a lot of our vulnerability can be attributed to our historic inability to provide adequate sanitation and food security. Many of us are here right now only because we managed to conquer infectious disease over the course of the 19th and 20th century. And although many think that antibiotics and vaccines were the cause of this victory, the truth is that the war was waged on multiple fronts and improvements in sanitation, personal hygiene and the provision of clean water and food free of contaminants were crucial to controlling infectious disease.

One of the victories over infectious disease was the introduction of pasteurisation in milk production. As I discussed in my post on milk, dairy products had been a traditional source of calories for thousands of years, particularly so in Europe. But one of the effects of the industrial revolution, that kicked off in the late 18th century, was the movement of a lot of people from the country to the city and this urbanisation had consequences for milk production and its patterns of consumption.

Firstly, there was a marked decline in the quality of urban milk supplies. Under the best of conditions it is hard to get clean milk but new urban dairies were crowded, often up to 2,000 head in a single dairy, and unsanitary. They were often associated with distilleries in which cows were fed ‘slop’, a by-product of the distilling process, that resulted in very unhealthy cows; ulcerated mouths, tails falling off, tuberculosis of the lung and intestines, that kind of thing. The milk coming from these cows was cloudy and sometimes, amazingly, pale blue in colour. This poor quality milk was then distributed to consumers without the benefit of adequate refrigeration. Distillers, acting as business so often does, didn’t try to improve the conditions of the dairy cows, instead responding by trying to ‘tart up’ the milk, trying to improve it’s appearance using sugar, eggs and even plaster of Paris.

Secondly, urbanisation led to a decrease in the frequency of breast-feeding as woman were forced out of the home and into work. To compensate for the decrease in breast-feeding formulas based on commercial cows milk were introduced and used as a substitute for breast milk. These demographic shifts, the appallingly poor quality milk, inadequate refrigeration and the increase in the consumption of commercial cows milk by infants inevitably led to a lot of dead infants, particularly in the summer months when the temperature was conducive to microbial growth in tainted milk. But bad milk was not the only consequence of urbanisation in the 19th century. Overcrowding, poor sanitation and housing led to widespread outbreaks of cholera, typhoid and tuberculosis, and in the face of these epidemics scientists began to question previously held theories of disease.

Prior to the 18th century the dominant theory of human disease was that it was the result of miasmas, or bad air, that emanated from the ground or decomposing matter (the word ‘malaria’ for example is literally ‘bad air’ in Italian). This theory of disease transmission had it’s roots in Greek and Roman thought, Hippocrates, for example, had advanced the theory in the 4th century BC. But, as we know now, the real culprits, and the cause of much of that smelly air, were bacteria and other micro-organisms and by the middle of the 19th century scientists were starting to realise this. Louis Pasteur, in France, showed that fermentation and putrefaction were both caused by micro-organisms and Robert Koch, in Germany, was able to link micro-organisms to specific diseases such as cholera and tuberculosis. The work of Pasteur and Koch turned germ theory, the name given to this new theory, into the dominant way that we thought about disease and it underpinned almost all the advances subsequently made in the prevention and treatment of infectious disease.

One of these advancements was the process that Louis Pasteur developed and lent his name to: pasteurisation. Informed by germ theory he developed a process where liquids like beer, wine and milk could be briefly heated to kill micro-organisms responsible for spoilage and disease. Given the harm caused by urban milk production the practical application of pasteurisation was obvious and ultimately the combination of mandated pasteurisation and improvements in milk production intended to decrease the contamination and proliferation of micro-organisms in milk got us to where we are today. In the 21st century milk is a relatively low risk food and we can grab a bottle from the supermarket with little fear of harm to ourselves or our families. Pasteurisation wasn’t a magic bullet in our fight against infectious disease but it was an important part of ensuring our food security, especially for children who are more vulnerable to milk borne disease.

But it wasn’t all plain sailing for pasteurisation. There was considerable opposition to the introduction of pasteurisation as a part of the milk production process. This in itself is an interesting story, one which I don’t have the space to go into (you can read more about it here if you are interested), but it is worth noting that the arguments made then against the adoption of pasteurisation are pretty much the same arguments we encounter now from proponents of raw milk. That is that pasteurisation removes the essential nutritional benefits of milk and that certification and development of standards for milk production would be sufficient to protect the public from milk borne disease. At the time the ongoing risks of milk borne disease and elusive evidence for the greater nutritional value of unpasteurised milk eventually swayed the debate in favour of pasteurisation and today I cant see see how any thing has changed to alter that calculation.

The decision to eat any food stuff involves an assessment of the risks and benefits of eating that food. If I could have a cow in my apartment and milk it daily I might be happy to consume raw milk. I’d know what precautions I’ve taken, how sanitary my methods are, whether I have a communicable disease and how healthy my cow is and if I screwed up I’d only have myself to blame. If I buy a bottle of raw milk in the supermarket I have no idea where the farm is, what the cows conditions are, what the sanitary practices are, if there was some problem with a truck whose air conditioning was bad, whether the store accidentally let it sit around on a loading dock too long and all sorts of other potential issues. This is where pasteurisation is protecting us, milk is really nutritious, that’s why we like it, but micro-organisms also love milk and given half a chance they will multiply rapidly and this is what makes milk one of the most dangerous foods that we consume.

Pasteurisation gives us a fighting chance if we want to consume milk that is more than a day or two old and has been transported far from where it was produced in anything less than perfect conditions. By reducing the bacterial load of milk it reduces the chances of a life threatening build up of bacteria occurring over the usable life of the milk. Even with pasteurisation milk and dairy products can still lead to disease outbreaks but, despite the vastly smaller amount consumed, raw milk causes more. For example, in Canada, between 2007 and 2020, there were 12 disease outbreaks caused by pasteurised milk compared to 20 for raw milk (the paper is here). In the United States, between 2009-2014, one study showed that 96% of milk borne illnesses were caused by raw milk, despite being consumed by only 3.2% of the population, so raw milk consumption caused 840 times more illnesses and 45 times more hospitalisations than pasteurised milk consumption (this paper is here).

Drinking raw milk is a high risk activity when compared to drinking pasteurised milk and when I am undertaking a high risk activity I normally expect the pay off for that activity to be high. Otherwise why risk it? And this is another problem with raw milk: I’m not too sure what you get in return for the high risk. Raw milk advocates make a lot of claims for its health benefits and if you go to websites advocating for raw milk consumption they will list a whole bunch of research papers about the purported benefits of raw milk. Almost all of these are concerned with the possibility that raw milk is protective against asthma and atopy if drunk in childhood (atopy is a tendency to inappropriately react to environmental antigens, so allergies).

These papers are good science and most of them deal with the tendency of children raised on farms to have low rates of allergy and asthma and raw milk consumption is often a variable that can be correlated with this effect. But the vast majority of these papers are cross-sectional (a type of observational study that is performed at a single point in time and involves questionnaires and often depends on the recall of historical details by study participants) and there has been no definitive mechanism identified for the alleged effects of raw milk consumption apart from a few papers showing some effects in mouse and rat models (rather than me doing a full literature review a good paper of the strengths and weaknesses of these studies can be found here).

Does this evidence suggest that there might be something to investigate further? Sure, it definitely does. Is it conclusive proof? Absolutely not. The majority of the studies are restricted to Alpine regions in Europe, data from Poland shows a much weaker or absent effect and there is ample opportunity for confounding factors. For example, it has been suggested that the effect could be explainable as a form of the hygiene hypothesis and not directly related to raw milk except as a vector for bacterial exposure. I couldn’t find any other compelling evidence for the benefits of raw milk over pasteurised milk and this one effect seems to be confined to childhood consumption of raw milk with no benefits for adults. I could also find no evidence that raw milk can cure asthma. I am no expert on this topic but I think it is fair to say that the evidence for raw milk is preliminary and certainly doesn’t suggest, given the documented risks of raw milk consumption, we should start selling raw milk. Even the scientists conducting these studies agree with that statement (see this New York Times article here).

The problem is that raw milk advocates have taken this preliminary data and run with it. For example, while researching this article I came across a submission to the Australian government in 2015 called ‘The Case for Certified Milk‘ and in it they cite evidence from the 1920’s where a:

diet of raw milk to treat allergies, skin problems, tuberculosis, oedema, heart failure, high blood pressure, prostate disease, urinary tract infections, diabetes, kidney disease, chronic fatigue and obesity, by giving his patients up to 8 litres of raw milk per day. Pasteurised milk was not effective.

The citation for this statement was a campaign brochure from 2006 published by a lobby group in Washington DC, not a primary or scientific source. In none of my readings did I encounter any scientific evidence for this extraordinary statement and the outlandish claims that are being used to support raw milk consumption. In fact the majority of the claims made in this document were not backed with citations to scientific research but referred to websites for other raw milk advocate groups. For example, they claim that there have been no health problems from raw milk vending machines in New Zealand, when in fact there was an outbreak of campylobacteriosis from a vending machine in 2014, plus other outbreaks in NZ in 2011 (paper here). The authors ask (on page 6) where is the evidence of illness caused by raw milk? Well the answer is here, here, here, here, here, here, here and here (and this is just a small sample). This document is not a serious attempt to summarise the risks and benefits of raw milk, it is marketing masquerading as science.

Another common claim is that milk is nature’s ‘perfect’ food and that we have always drunk milk. But here’s a thought: for most of human history, well up to the 18th century, only 1 in 2 children made it to the age of 15. So if the cows milk didn’t get you in childhood then measles, cholera, diphtheria, whooping cough, influenza, tuberculosis or smallpox would get you anyway, would anyone have even noticed if children were dying of diarrhoea caused by drinking cows milk? We certainly notice today but the global childhood mortality rate in 2022 was 4.3%, and in some countries like Japan, Norway and others it is around 0.03% (see here if you want to read about where these numbers are coming from). Increases in human life expectancy have to a great part been the result of our amazing success in reducing infant mortality rates, and pasteurisation was a part of that success not raw milk. Do we want to gamble with children’s health on the strength of a few observational studies? I’d rather have a kid alive with the possibility of asthma than a memory.

If you are an adult who really wants to drink raw milk then you will find a way and as far as I am concerned good luck to you. I could find absolutely no reported scientific evidence for the benefits of raw milk in adults but we all have our dangerous foods we like to eat. I like steak tartar, homemade egg mayonnaise, mussels and raw oysters and others like medium rare hamburgers but we are adults and we should have an idea of the risks we are taking. What I never did was feed steak tartar or my raw egg mayonnaise to my daughter as a child. I know the risks I’m taking and I accept them, a child does not, they can’t give informed consent to take on the same risks you are taking with your food and they are often more vulnerable so there is even more risk for them. It’s simply a risk/benefits decision – the risk is serious infection and possibly death, something that has been demonstrated over and over again, and the health benefits for raw milk are vague and unproven.

I’m not saying that raw milk doesn’t help protect against asthma and potentially helps the developing immune system, what I’m saying is there is more evidence that raw milk is a serious risk than there is evidence of its benefits. I’m happy to change my mind if new evidence comes along, or even better if new pasteurisation methods are developed that preserve the protective effect of raw milk (if it exists). Because of our ancestors success in improving infant mortality rates our children will have their whole lives to enjoy raw milk, medium rare burgers and beef tartar if that’s what they want to do when they are old enough to understand the risks and rewards of their behaviour (and have developed an immune system capable of fighting off some food poisoning). As parents all we have to do is refrain from taking stupid risks with their health and get them old enough to be able to make stupid risky decisions of their own.