The consumption of dairy is a controversial subject. There is a real skepticism about its health benefits.
Think about how popular plant-based drinks have now become, especially soy and almond milk. But like so many facts when it comes to nutrition the truth, occasionally, well most of the time, is somewhat blurred. Dairy is no different.
We all know certain people, extreme vegans, eco-warriors, quacks, David Wolfe, people who are dead set against dairy consumption. To be honest they are pretty much against anything that is consumed from animals in any form.
You may of heard, or read things like….
It’s un-natural to consume dairy. Fact!
Cows milk is for rapidly growing calves not humans!
Drinking milk is like drinking pus!
Dairy causes cancer, strokes, diabetes, heart disease and worse still it makes you fat!
The list goes on.
Let me make it clear from the start, I have no issue at all with vegetarians, or vegans. None. I do have issues with David Wolfe and other well-known quacks. My main issue is propaganda. Think about what propaganda is. It’s basically information of a biased or misleading nature, used to promote a political cause or point of view. That being said the worst kind of propaganda is vegan propaganda.
Have you ever tried to reason with someone who is emotionally attached to their beliefs, it’s impossible. They are simply not open to thinking in a different way. Regardless of what information you put in front of them.
“You can sway a thousand men by appealing to their prejudices quicker
than you can convince one man by logic.” Robert A. Heinlein
All you can really do is present your case clearly using actual scientific evidence, cross your fingers, and hope for the best. You give them the facts, it’s up to them to decide whether to digest them or not.
I’ve recently seen a few stories reporting that dairy increases the risk of various chronic diseases such as obesity, cardiovascular disease, cancer, osteoporosis and type 2 diabetes. Hopefully in the rest of this post I can use science to distil some misconceptions about dairy, and maybe make you think a little more about information you are drip fed by the media, and supposed ‘experts’.
Where to start?
Let’s just dive straight in. In 2015, a large cohort study of 9835 Brazilian adults [1] found that full fat dairy, butter and yoghurt was inversely associated with (i.e. protective against), metabolic syndrome. Metabolic syndrome is a term used to cluster various conditions such as, increased blood pressure, obesity, and high cholesterol levels, which can unfortunately occur together to increase your risk of heart disease, stroke and diabetes. Interestingly, what this study also found was that these same associations were not found with low-fat dairy products.
With most studies that I found with regards to dairy intake the participants are generally adults. But what about studies conducted on the younger generation. How does dairy intake affect us as children, and how does it influence our later life?
In another large prospective cohort study on 37,038 US women [2], the researchers observed that greater dairy consumption during high school was significantly associated with a lower risk of type 2 diabetes from age 18 and above. Whilst they also showed that less weight gain also occurred in later life. Which nicely leads onto dairy intake making you fat.
Obesity can be an indicator of insulin resistance and is well known to increase the risk of type 2 diabetes among many other metabolic syndromes. So you could say if you can prevent obesity you could reduce the risk of suffering from other chronic diseases. We are all fully aware of the ever-increasing rise in obesity levels in the UK and the steps the government is taking to try and address it. But back to dairy.
In 1989, researchers in Sweden designed a cohort study with a 12-year follow up [3]. In total 1405 men participated in both surveys. The follow up survey included questionnaires, interviews, examinations and a laboratory test. Anthropometrics were taken at both baseline and the follow-up. They found that a high intake of dairy fat was associated with a lower risk of central (abdominal) obesity, and a low fat dairy intake was associated with a higher risk of central obesity. So that’s a win for dairy fat over the lower fat options.
Are all studies created equal?
No, they’re really not.
Before I carry on I just want to take a small diversion and explain a little more about study design and some of the inherent flaws that you can find. Most of the studies that I have found on dairy are of an observational/cohort design so they do have some potential drawbacks. The main one being that the participants generally report their dairy intake through food frequency questionnaires.
This way of gathering results is a typical choice for large epidemiologic studies such as ones on dairy consumption; but they can be fraught with errors, such as under/over reporting. Even so this should be taken into account by the researchers when quantifying their results.
This is a pyramid. I like pyramids. This one is called The Pyramid of Decreasing Bias. You can see that expert opinion is right at the very bottom. As in a lot of ‘expert’ opinion is rife with bias. Many are paid to offer certain opinions. Should you listen to them? Possibly, some of the time, depending very much on who they are, and what their background is. But, if they are self confessed experts (i.e David Wolfe) you can pretty much ignore everything they say. Mid-way up the table we have cohort studies. The studies I have already mentioned in this post sit within this category. As I said they do have flaws, but they are higher up in the pyramid meaning they should contain less bias. This is a good thing. Then right at the very top of the pyramid we have Systematic Reviews and Meta-Analyses. These should be pretty much bias free. You could view these as the gold standard, even better than Randomized Controlled Trials.
As much as randomized controlled trials are preferable, they are very difficult to accomplish in such long-term studies in real life environments. However, systematic reviews and meta-analyses of cohort studies are not, so I will talk about some of those now.
Back to the science
In 2013 a systematic review and meta-analysis of 17 cohort studies [4] looked at dairy intake and the risk of type 2 diabetes. The researchers concluded that intakes of dairy products, low-fat dairy products, and cheese were inversely associated with the risk of type 2 diabetes. Cheese has also been found to be associated with stroke prevention. In a recent systematic review and dose response meta-analysis published in 2016 [5] researchers also found that total dairy, low-fat dairy, full-fat dairy and butter, as well as cheese, were not associated with an increase in stroke risk.
It’s well known that milk and dairy products contain a vast array of nutrients that are required for building strong bones. Nutrients such as protein, calcium, phosphorus, magnesium, and zinc. So you would expect dairy to play a role in bone health and offer protective measures against osteoporosis. But what do the studies show?
In a 2008 meta-analysis [6] researchers found that an increase in dietary calcium increased total body, and lumber spine bone mineral content in children who initially had a low intake of dairy products. For those children that already had a high intake of dairy the researchers found no benefit to bone mineral content or density. In 2003, another observational study, this time on US women, [7] found that milk intake in childhood was associated with increased bone mass and density in adulthood, with the added bonus of a reduced risk of fractures.
However, I did find a meta-analysis of prospective cohort studies from 2011 [8] that happened to find no association between milk intake, and hip fracture risk in women. Even with a high intake of milk. Also with regards to men the researchers actually found an inverse association (protective against), but it was borderline significant.
So with regards to bone health and osteoporosis, there certainly seems to be a positive effect during childhood, but the evidence is somewhat limited as we age.
The last thing that I will touch on is the association of the consumption of dairy products to various cancers, such as colorectal, bladder, breast, pancreatic, colon, and prostate cancer.
Colorectal cancer is one of the most common causes of death amongst all of the cancers. From looking at reports from the World Cancer Research Fund and some of the latest meta-analyses that I could find, dairy intake, notably a high intake of milk, is consistently associated with a decreased risk of colorectal cancer [9,10]. A further meta-analysis of 60 observational studies on over 26,000 people [11] found an inverse relationship between calcium intake and a reduced risk of colorectal cancer. They also found a reduction in risk of colon and rectal cancer by 45%.
Breast cancer, I believe, is the most commonly diagnosed cancer and leading cause of cancer death in women worldwide. Like a lot of the observational studies on cancer, it is difficult to find anything conclusive. However, a recent meta-analysis from 2015 [12], which analyzed cohort and case controlled studies on around 1.6 million participants, concluded that high and modest dairy intake, greater than 400g/day, significantly reduced the risk of breast cancer when compared with low dairy consumption. To put into context, I work out that 400g is roughly around 320ml, which is approximately 1.5 average sized glasses. So it’s not a huge amount.
A very recent review article from 2016 [13] that looked at numerous randomized control trials, meta-analysis data and reports from the World Cancer Research Fund concluded that the consumption of milk and dairy products probably protects against colorectal, bladder, gastric and breast cancer. Whilst also showing that dairy intake isn’t associated with an increased risk of pancreatic, ovarian, or lung cancer.
Whilst dairy consumption appears to be beneficial and protective against most cancers, the evidence for prostate cancer is very inconsistent. Prostate cancer is one of the most common cancers in men worldwide. I believe the inconsistences with regards to prostate cancer are partly due to the fact that a high intake of dairy and milk, as already discussed, are generally associated with a significant reduced risk of developing colorectal cancer. So does that out-weigh the risk?
A meta-analysis I found that was published in 2015 [14] concluded that an increase in prostate cancer risk was associated with intakes of total dairy, milk, cheese, low fat and skimmed milk, total calcium, dietary calcium, and dairy calcium but no association with supplemental calcium. Interestingly the researchers also concluded that there was an inverse association through the intake of whole milk alone.
What I do like about this review is that the researchers concluded that the mixed bag of results for the differing types of dairy products, and sources of calcium, would suggest that other components of dairy other than fat and calcium could be what increase the risk of prostate cancer. Again, nothing 100% conclusive.
What should be made clear is that of all the diseases to attempt to conduct research on, any form of cancer is a very tricky topic to approach. I do not envy scientists and researchers one little bit in this regard.
My conclusion
When it comes to making associations between products and diseases what you have to take into account is human behavior. Do certain people show health seeking behavior’s like higher levels of activity and less smoking, or are they couch potatoes? Where does this sit within dairy intake?
I personally believe that when it comes to dairy, the benefits and health effects may well vary from person to person. However, dairy products are an important source of dietary calcium, vitamin D, protein, and magnesium. If you can tolerate dairy and you enjoy it, then certainly don’t cut it out of your diet.
It is my opinion that there is no compelling evidence to avoid it, and the recommendations to avoid full fat dairy are not generally that well supported by evidence.
“Facts are stubborn things; and whatever may be our wishes, our inclinations, or the dictates of our passion, they cannot alter the state of facts and evidence.”
REFERENCES
1. M. Drehmer, M.A. Pereira, M. I. Schmidt, S. Alvim, P. A. Lotufo, V. C. Luft, and B. D. Duncan. Total and Full-Fat, but Not Low-Fat, Dairy Product Intakes are Inversely Associated with Metabolic Syndrome in Adults. J Nutr 2015 doi: 10.3945/jn.115.220699.
2. V. S. Malik, Q. Sun, R. M Van Dam, E. B. Rimm, W. C. Willett, B. Rosner, and F. B. Hu. Adolescent dairy product consumption and risk of type 2 diabetes in middle-aged women. Am J Clin Nutr. 2011 Sep; 94(3): 854–861.
3. S. Holmberg, A. Thelin. High dairy fat intake related to less central obesity: A male cohort study with 12 years’ follow-up. Scandinavian Journal of Primary Health Care, 2013; 31: 89–94.
4. Dagfinn Aune, Teresa Norat, Pa ̊l Romundstad, and Lars J Vatten. Dairy products and the risk of type 2 diabetes: a systematic review and dose-response meta-analysis of cohort studies. Am J Clin Nutr 2013;98:1066–83.
5. Janette de Goede, PhD; Sabita S. Soedamah-Muthu, PhD; An Pan, PhD; Lieke Gijsbers, MSc; Johanna M. Geleijnse, PhD. Dairy Consumption and Risk of Stroke: A Systematic Review and Updated Dose–Response Meta-Analysis of Prospective Cohort Studies. Journal of the American Heart Association (2016).
6. Michael Huncharek, Joshua Muscat, Bruce Kupelnick. Impact of dairy products and dietary calcium on bone-mineral content in children: Results of a meta-analysis. Bone. 2008 Aug;43(2):312-21
7. Heidi J Kalkwarf, Jane C Khoury, and Bruce P Lanphear. Milk intake during childhood and adolescence, adult bone density, and osteoporotic fractures in US women. Am J Clin Nutr 2003;77:257–65.
8. Heike A Bischoff-Ferrari et. al. Milk Intake and Risk of Hip Fracture in Men and Women:
A Meta-Analysis of Prospective Cohort Studies. Journal of Bone and Mineral Research, Vol. 26, No. 4, April 2011
9. Lampe J. W. Dairy Products and Cancer. Journal of the American College of Nutrition, Vol. 30, No. 5, 464S–470S (2011)
10. Aune et. al. Dairy products and colorectal cancer risk: A systematic review and meta-analysis of cohort studies. Annals of Oncology 23: 37–45, 2012.
11. Huncharek et. al. (2009) – Colorectal Cancer Risk and Dietary Intake of Calcium, Vitamin D, and Dairy Products/ A Meta-Analysis of 26,335 Cases From 60 Observational Studies. Nutrition and Cancer, 61(1), 47–69.
12. Zang et. al. The Association between Dairy Intake and Breast Cancer in Western and
Asian Populations: A Systematic Review and Meta-Analysis. J Breast Cancer 2015 December; 18(4): 313-322.
13. Thorning et. al. Milk and dairy products: good or bad for human health? An assessment of the totality of scientific evidence. Food & Nutrition Research 2016. Volume 60.
14. Aune et. al. Dairy products, calcium, and prostate cancer risk: a systematic review and meta-analysis of cohort studies. Am J Clin Nutr 2015;101:87–117.