There is a lot of information out there about the best foods to help us lose weight, prevent cancer, fight inflammation – the list goes on. In fact, for everything about our health we try and improve, there’s someone out there with a new theory on how to do it. But what does the science say?
Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to give you the evidence-based approach to take the mystery out of the best way to live a healthier, longer life.
Today we take a close look at how dairy affects our health and well being. First up is research about the a sugar found in milk called galactose. As it turns out the galactose in milk may explain why milk consumption is associated with significantly higher risk of hip fractures, cancer, and premature death.
Milk is touted to build strong bones, but a compilation of all the best studies found no association between milk consumption and hip fracture risk, so drinking milk as an adult might not help bones. But what about in adolescence? Harvard researchers decided to put it to the test.
Studies have shown that greater milk consumption during childhood and adolescence contributes to peak bone mass, and is therefore expected to help avoid osteoporosis and bone fractures in later life. But that’s not what they found. Milk consumption during teenage years was not associated with a lower risk of hip fracture, and, if anything, milk consumption was associated with a borderline increase in fracture risk in men.
It appears that the extra boost in total body bone mineral density you get from getting extra calcium is lost within a few years, even if you keep the calcium supplementation up. This suggests a partial explanation for the long-standing enigma that hip fracture rates are highest in populations with the greatest milk consumption. Maybe an explanation why they’re not lower, but why would they be higher?
This enigma irked a Swedish research team, puzzled because studies again and again had shown a tendency of a higher risk of fracture with a higher intake of milk. Well, there is a rare birth defect called galactosemia, where babies are born without the enzymes needed to detoxify the galactose found in milk, so they end up with elevated levels of galactose in their blood, which can cause bone loss even as kids. So maybe, the Swedish researchers figured, even in normal people that can detoxify the stuff, it might not be good for the bones to be drinking it every day. And galactose doesn’t just hurt the bones. That’s what scientists use to cause premature aging in lab animals. They slip them a little galactose and you can shorten their lifespan, cause oxidative stress, inflammation, brain degeneration, just with like the equivalent of one to two glasses of milk’s worth of galactose a day. We’re not rats, though, but given the high amount of galactose in milk, recommendations to increase milk intake for prevention of fractures could be a conceivable contradiction. So they decided to put it to the test, looking at milk intake and mortality, as well as fracture risk, to test their theory.
A hundred thousand men and women followed for up to 20 years; what did they find? Milk-drinking women had higher rates of death, more heart disease, and significantly more cancer for each glass of milk. Three glasses a day was associated with nearly twice the risk of death. And they had significantly more bone and hip fractures too.
Men in a separate study also had a higher rate of death with higher milk consumption, but at least they didn’t have higher fracture rates. So a dose-dependent higher rate of both mortality and fracture in women, and a higher rate of mortality in men with milk intake, but the opposite for other dairy products like soured milk and yogurt, which would go along with the galactose theory, since bacteria can ferment away some of the lactose. To prove it though, we need a randomized controlled trial to examine the effect of milk intake on mortality and fractures. As the accompanying editorial pointed out, we better figure this out soon, as milk consumption is on the rise around the world.
So how do we explain the increased risk of prostate cancer but the decreased risk of colon cancer associated with dairy consumption? Let’s find out.
Studies comparing country-by-country cancer rates “have shown up to a 70-fold variation in the incidence of prostate cancer worldwide with low rates in parts of Asia and Africa and high rates in North America, Australia, New Zealand, and Northern Europe.” Could dairy consumption have something to do with it, given Northern Europeans, Americans, and Australians drink a lot of milk, whereas most non-Caucasians in the world are lactose intolerant? But just because a country drinks a lot of milk and has a lot of cancer doesn’t mean the individuals within the country that are drinking the milk are getting the cancer. That’s why we need “cohort studies,” where you find out how much milk people drink, and follow those individuals over time, and see if those who drink more milk get more cancer.
There have been dozens of such studies done. Put them all together, and “intakes of total dairy products including low-fat milk were indeed associated with increased prostate cancer risk.” The question is, why? Maybe it’s just all the calcium. They found that the more calcium people consumed, the higher their risk of prostate cancer. Yeah, but most people get their calcium from dairy. So, how do we know this isn’t just a dairy effect? Before we start worrying about kale and other non-dairy sources of calcium, it would be nice to see dairy calcium teased out from non-dairy calcium intakes. And that’s exactly what they did. Yes, the more calcium from dairy sources, the higher the risk of cancer, but non-dairy sources of calcium were found to be protective. So, it wasn’t a calcium effect; it was a dairy effect. This suggests that “other components of dairy” may be to blame.
They suggest it’s the animal protein, boosting the levels of a cancer-promoting growth hormone called IGF-1: insulin-like growth factor 1. If you look at 28 studies involving nearly 28,000 people, this is what’s called an albatross plot. This could also explain why plant-based diets can be so protective. Put watch-and-wait cancer patients on a whole-food, plant-based diet for a year, no chemo, no radiation; lifestyle changes only and get “a significant reduction in PSA levels,” indicative of tumor shrinkage: their bloodstream becoming nearly eight times better at suppressing the growth of cancer cells. Do biopsies, and you can show changes in gene expression, a down-regulation of critical cancer genes, effectively switching off cancer growth genes at a genetic level. Whereas, if you instead eat lots of dairy after a prostate cancer diagnosis, you may suffer “a 76% higher risk of” death overall, “and a 141% increased risk of” dying specifically from your cancer.
Even without IGF-1, the milk protein casein appears to be a cancer cell “proliferation promoting factor,” increasing the growth of prostate cancer cells, at least in a petri dish. And the same thing with whey, the other major animal protein in dairy. See, “nearly 100% of advanced” prostate cancers thrive by upregulating a growth enzyme called TOR. And, dairy protein boosts TOR signaling even higher, which only makes sense. Calves have to grow like 40 times faster than human babies, and so cow’s milk has to be packed with growth promoters, not to mention the hormones in milk. Especially from cows who are already pregnant again.
This “commercialized milk production by pregnant cows releases uncontrolled amounts of bovine steroid hormones into the human food chain.” And so, the combination “may well explain the observed association between high dairy consumption and increased risk of prostate cancer.”
“From an evolutionary perspective, the persistent ‘abuse’ of the growth-promoting signaling system of bovine milk by humans over their entire life span not just drinking milk during infancy maintains the most important hallmark of cancer biology:” this “sustained proliferative signaling” to grow, grow, grow. And so, there’s this interest in trying “to define the safe upper limits for long-term milk and dairy intake for the prevention of the most common dairy-promoted cancer in men.” But if you look at diet and cancer guideline recommendations, yeah, milk may increase risk of prostate cancer. “However, no recommendation was provided for cutting down on dairy because the evidence for prostate cancer conflicted with decreased risk of colorectal cancer.” High dairy intake is associated with increased prostate cancer risk, but decreased colon cancer risk.
So, it’s like alcohol may be an “intoxicating carcinogen,” but “policymakers hesitate to introduce effective alcohol policies, or even to support the addition of cancer-warning labels, for fear they might undermine any possible health benefits of alcohol use.” Now, I’ve talked about how the purported benefits of alcohol appear to be “evaporating.” Is dairy really protective against colon cancer?
If you put all the cohort studies together, where they measured dairy consumption and followed people for years to see who got cancer, milk and total dairy consumption was indeed “associated with a reduction in colorectal cancer risk,” one of our deadliest cancers. Now, people who drink more milk just happen to tend to exercise more, smoke less, drink less, eat less meat which could explain some of the association. “However, many of the studies adjusted for these kinds of confounding factors.” More likely, it was the protective effects of the calcium, “which may bind up pro-inflammatory bile acids in the gut,” though high-fat dairy products, like cheese, may actually increase bile acids, explaining why the cheese appeared to cancel out the calcium benefit. So, might we be able to get the best of both worlds by consuming non-dairy calcium sources?
If you randomize people to calcium supplements, you can get a significant reduction in recurring colon polyps, which can otherwise turn into cancer, though calcium pills have been associated with adverse cardiovascular effects. And so, the best of all worlds, if you want to take a precautionary approach in terms of nutrition and cancer, is to obtain calcium through low-oxalate dark green leafy vegetables, beans, split peas, chickpeas, and lentils or, if necessary, “calcium-fortified foods,” such as soy or almond milk.
Finally today we look at how the meat and dairy industries design misleading studies that show their products have neutral or even beneficial effects on cholesterol and inflammation.
Observational studies, suggesting dairy might not be so bad, can be confounded by extraneous factors, such as the fact that people who eat more cheese tend to be of higher socioeconomic class. Fine, but what about this interventional study? A randomized, crossover trial, which compared a high-fat cheese diet, to a high-fat meat diet, to a low-fat diet. A high-cheese diet: CHEESE, which is loaded with saturated fat; a high meat diet: MEAT, which is loaded with saturated fat; versus CARB, a low-fat diet. And, people ended up with the same cholesterol levels.
Let’s see how they did it. Half the study was paid for in part by the dairy industry, and the other half paid for by dairy, dairy, dairy, and dairy. If you’re the dairy industry, and you’re trying to design a study to show that a high-cheese diet doesn’t raise cholesterol, how would you go about doing that?
Anyone remember this video? It’s one of my favorites. The beef industry was in the same pickle as the cheese industry. Beef has saturated fat, which raises cholesterol, which raises the risk of dying from our #1 killer. What’s an industry to do? So, they designed a study where they added beef, and cholesterol went down.
How is that possible? Here’s the two diets. They added beef, and the cholesterol went down. They did this by cutting out so much dairy, poultry, pork, fish, and eggs that their overall saturated fat intake was cut in half. They cut saturated fat levels in half, and the cholesterol levels went down. Well, duh. They could have swapped in Twinkies and said snack cakes lower your cholesterol, or frosting or anything.
Okay, so now that you know the trick, let’s go back to this study. The way to get the same cholesterol levels is to make sure all three diets have the same amount of saturated fat. How are you going to do that; how are you going to get a high-fat cheese diet and a high-fat meat diet to have the same saturated fat level as a diet with neither? Unless, wait, don’t tell me. What? They added coconut oil or something to the other diet? They added so much coconut oil and cookies to the so-called low-fat diet that they all had the same amount of saturated fat, and voilà! That’s how you can make a cheese or meat-rich diet that doesn’t raise cholesterol.
That reminds me of the desperation evident in this study that compared the effects of dairy cheddar cheese to a non-dairy cheddar cheese called Daiya. Milk consumption has plummeted in recent years as people have discovered plant-based alternatives like soy milk and almond milk. And now there’s plant-based cheese alternatives? What’s the National Dairy Council to do? How are you going to design a study that shows it’s healthier to eat cheese; design a study where cheese causes less inflammation than the vegan alternative. They got their work cut out for them. Daiya is no health food by any stretch, but definitely three times less saturated fat than cow cheese. So, I give up. How could you possibly show more inflammation from Daiya?
Well, there is one fat that may cause more inflammation than milk fat: palm oil. In fact, it may raise cholesterol levels as much as trans fat-laden partially hydrogenated oil. Yeah, but what are you telling me? They like slipped the Daiya group some extra palm oil on the side. Yes, can you believe it? They compared cheese to Daiya “plus palm oil”; so much extra palm oil that the vegan alternative meal ended up having the same amount of saturated fat as the cheese meal. That’s like proving tofu is worse than beef by doing a study where they compared a beef burger to a tofu patty…stuffed with lard. Oh, wait, the meat industry already did that, but at least they had the decency to concede that “Replacement of meat by tofu in the habitual diet would not usually be accompanied by the addition of butter and lard.”
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