The risks of eating dairy - the facts

If you pay attention to nutrition and health bloggers, you don’t have to look very hard to find someone making the claim that diary should be removed from your diet. There are a number of different reasons that these claims come up, that can be generally grouped into two categories, namely:

  • You shouldn’t drink milk because it’s an animal product, and animal products are cruel
  • You shouldn’t drink milk because it’s bad for you

These two groupings overlap somewhat, with animal rights activists using a lot of the same arguments that those concerned about health do, and with those same health-conscious folks often including other animal foods in their hit-list.

This blog is not really going to touch on the animal welfare thing, because to do so in a written piece is impossible. The argument is nuanced and the only way to really go over it is to have a face to face conversation. For now suffice it to say that I think animals should not be caused undue suffering, but also that this can be achieved alongside drinking milk. Moving on.

The question, therefore, is: Is dairy good or bad for you? And to answer it I will do two things – first I’ll look at a number of the most commonly cited arguments against dairy consumption to see if they hold water, then I will talk about the benefits associated with the white stuff. Let’s start with the big one:

Milk causes gut health problems

This is probably the most commonly cited anti-milk argument, with two separate trains of thought – one being that milk leads to bloating and gas because humans aren’t adapted to drink bovine milk, and the other being that milk causes intestinal inflammation. Let’s look in turn.

First of all, lactose intolerance is definitely a thing. Lactose is the sugar present in dairy, itself being a disaccharide comprised of glucose and galactose. This large molecule can’t absorb through your intestine in tact, so it needs to be broken in half by an enzyme called lactase. Mammals naturally produce lactase in infancy (in almost all circumstances, of course some exceptions exist whereby a child will be lactose intolerant, but this is rare and unusual) but then as they age – because they stop drinking milk – they no longer produce the necessary enzyme. Thousands of years ago humans living in close proximity to cattle started to consume dairy from these beasts until later life, and as such they adapted – this happened unequally across cultures and so prevalence is different, depending on where your ancestors lived. As it stands, around 65% of the world population are lactose intolerant to some degree (1), although lactose intolerance is like a dimmer rather than an on/off switch, so many with lactose intolerant folks being able to tolerate around 200ml of milk at a time, for example. With that said, in some Scandenavian countries over 80% of adults can tolerate dairy (1) and in those of Northern European descent the U.S National Library of medicine places lactose intolerance prevalence at around 5% of the population (3). If you are of Asian, West African, Greek or Jewish descent you are at greater risk but everyone else is unlikely to have symptoms. Fortunately for those with lactose intolerance, lactose free milk is readily available and many dairy products (whey protein, especially) are either extremely low or just low (as is the case for cheese) in lactose, so just because regular milk is off the menu, doesn’t mean you can’t make a shake or enjoy some cheese on toast.

Also worthy of note on this fact, is that lactose falls under the category of FODMAPS, or Fermentable Oligo-, Di-, and Monosaccharides and Polyols, meaning that it is a fermentable kind of sugar to which some people can be sensitive. Again, if you are someone who gets gassy drinking milk (as well as eating beans, some vegetables, alliums and oats) then you may have an issue with FODMAPS, and could opt for lactose free alternatives.

Ultimately, though – if you get gas when you drink milk, probably don’t drink milk. The key thing there is ‘if’, though, because many, many folks will be just fine.

As for inflammation, this is somewhat harder to define, with very little being known about the impact specific active compounds within milk have on the digestive system. With that said a recent meta analysis of 52 peer reviewed journals found that “Stratifying the data by product categories associated both low-fat and high-fat products, as well as fermented products, with an anti-inflammatory activity.” (4) meaning that outside of the above instances where a person is simply unable to digest a specific sugar within dairy due to having a specific sensitivity to it, research suggests that dairy is actually anti inflammatory.

As a final little point on this, it’s often claimed that diary leads to ‘leaky gut’ or as it’s properly known, intestinal permeability. A Google Scholar search discovered no research as evidence for this, but there was one low-powered study with a small sample size that saw no difference (10), and some indications that a healthy gut bacterial population would be extremely useful for the prevention of this issue (11). As a final note, one rat study found that the sugars in bovine milk reduced intestinal permeability (12) – so it’s not likely that a glass of milk is really going to lead to what sounds like an incredibly complex issue, unless you’re specifically sensitive to it.

Milk causes skin problems

This is a tough one. A recent study looked at adolescents with or without acne, and while they found that total skim-milk intake was higher in the acne group than the acne-free group (5), there was no difference between groups for total dairy intake. Another paper reviews potential mechanisms for dairy leading to acne (6), and it settles on the idea that milk’s ability to stimulate IGF-1 and insulin is what leads to acne presenting, owing to the mechanism by which acne breaks out. This means that it is not simply dairy that is associated, but a diet that provides a high glycaemic load in general will likely lead to acne outbreak. This one is not all that damning on milk, but it’s worth noting that if you DO suffer with acne, reducing milk consumption may help – if you’re not a hormonal teenager, however, it’s exceedingly unlikely that you’re going to have a breakout because you drank milk – there is no evidence for a link between milk and spots in healthy adults.

Milk leads to cancer

This one is my personal pet peeve, because as soon as something is linked to cancer we are looking at scaremongering (often the fear-inducing yet abjectly meaningless word ‘toxin’ is thrown into this argument, too). This is a complex argument because there are a number of ways to look at it, firstly there is the mechanistic idea, whereby the abovementioned insulin and IGF-1 released upon consuming dairy can increase tumour growth rates (6). The problem here is that ANY food high in protein is likely to increase these two, as is a high calorie intake in general. At present the main way you can reduce production of IGF-1 (and activate a bunch of anti-cancer cellular processes) is potentially through long-term caloric restriction, though evidence for this is only in animal models (7). This would also generally mean eating an extremely low calorie, low protein diet for the long term – that’s not going to be congruent with having a lot of energy, doing exercise, or otherwise enjoying life in my opinion – though I’ll concede that some calorie restrictors disagree (they don’t look all that athletic, though). If you are eating a normal (perhaps higher protein) diet, then adding dairy won’t make a jot of difference.

In fact evidence to link dairy intake to various cancers is either lacking, inconsistent, or indicative of a preventative effect (8), and one long-term study showing a clear protective effect for colon cancer (9) meaning more dairy seems to result in less cancer, unless you’re eating less of everything overall.

Milk leads to weight gain

Really, the only thing that leads to weight gain is overconsuming calories. Sure, dairy causes insulin to increase but insulin can only cause fat gain if there are excess calories to store over a prolonged period of time. Insulin doesn’t ‘cause’ fat gain and neither does dairy per se, no food does – but what do the data say?

In a systematic review and meta analysis of 40 randomised controlled trials, the addition of dairy made no difference to bodyweight if calories were kept even, and the addition of dairy to a weight-loss intervention increased fat loss (13). Another meta analysis found that dairy had no effect on bodyweight over the long term but a positive effect in the short term (14). These combined mean that dairy at worst doesn’t do anything, but at best it may increase success on a fat loss diet. This could be due to the calcium which itself has a role in fat loss, or due to the protein, or due to the appetite satiating and craving reducing properties of dairy (15).

Milk leeches calcium from your bones

This is a weird one, because conventional wisdom tells us that dairy is rich in calcium, but there is a growing number of people who claim the opposite – that actually milk leeches calcium out of your bones and causes osteoporosis. This is partly down to the fact that countries with the highest amount of dairy consumption (16) also have the highest incidence of hip fractures (17), but this doesn’t tell the whole story. These countries are Western countries, where being overweight and inactive are also extremely common, as is the use of a number of medications that can cause bone problems. Not only that, country wide-dairy consumption is being looked at, not consumption in the populations likely to have osteoporosis. Many of the people in these countries don’t have osteoporosis and we can only assume that they are having about the same amount of milk as those that do.

In fact, it seems that a large calcium intake from milk in young age leads to greater bone mineral density, that can later result in reduced fracture risk (18), and it’s certainly the case that those who drink milk appear less likely to experience fractures in old age (19). Milk really does make your bones stronger, and that’s likely thanks to it’s highly bioavailable calcium. Calcium from dairy is absorbed at a rate of about 32% (20), meaning that for every 100mg you drink, 32 of those get into your system. For reference a 250ml serving provides 300mg of calcium, so 96mg absorbed.

Plant source bioavailability ranges from around 5% in spinach to around 60% in broccoli, which sounds great until you realise that to get the same 96mg of absorbed calcium you would need to eat 500g of broccoli because it just doesn’t have all that much calcium in to begin with (20). Then consider that the RNI for calcium in 700mg (21) and you’ll see that (though not absolutely vital, because milk subs, tofu and supplements can be used), dairy is definitely a useful addition to your diet.

Milk contains hormones

Yes – but not to a level that is physiologically relevant (22). Plant foods contain hormones, too, but it’s the dosage that matters.

But what does dairy do?

That’s a lot of “milk doesn’t’ do that”, but what in fact DOES it do? Well, along with the abovementioned benefits to cancer risk in some cases, potential links to gut health (these benefits are far more convincing for fermented dairy like cheese (23, 27)) dairy is associated with a ton of positive health states (23, 27).

It’s difficult to associate a food to a positive thing, of course, because looking at populations nobody is eating only dairy, there are other foods in a high dairy diet that can be useful, and beyond that we need to consider lifestyle. If someone is supremely healthy and eating a bunch of dairy that isn’t all they are doing – they are likely to be eating well generally, exercising, staying a healthy weight, sleeping well, staying hydrated, and in possession of some good genes. At the end of the day the main impact dairy will have is as a source of protein, fat, carbohydrate and calcium – as well as being an excellent recovery drink after exercise (24).

Looking specifically at dairy protein, we see that both whey and casein in isolation are excellent at curbing hunger (25), while milk protein has a biological value of 91 and whey has a rank of 104 (26) (BV is a rating scale out of 100, which indicates how useful a protein is for muscle building). This is reflected in the fact that whey protein supplementation can be beneficial for building muscle (28), losing weight (and improving cardiovascular disease risk) (27) and recovering from exercise (29). As mentioned, though, these benefits aren’t likely to be because of whey per se, but because it helps to achieve a high protein intake – itself useful in these ways (28).

Finally, dairy is rich in iodine, many b vitamins and even a little vitamin D, which never goes amiss.

As you can see – though it is much maligned in various circles, and though there is a significant amount of fear-mongering out there, dairy is an extremely useful foodgroup to include in your diet. Can you survive without it? Of course, you can thrive. You can thrive without wine, too…but I’m certainly not giving that up either!


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