The way I grew up, meat was what was for dinner. Potatoes, asparagus, rice, broccoli, even (gasp) pasta – they were sides. Steak was the main course.
Nowadays I’m still a meat lover. My dinner, for instance, is typically high protein (40-50 grams), and that protein always comes from a creature with either hooves or gills. If that sounds barbaric, consider that every animal on the planet survives by eating other living things. Plants are alive too.
I like meat, not just for the taste, but because it’s more nutrient dense than plant protein. Creatine, carnitine, carnosine, B12, CLA, zinc, iron, choline, omega 3s, saturated fat; you can’t get that stuff from beans or peas. (Vegetarians: you may need to supplement, especially with B12.) Plus meat has a broader spectrum of essential amino acids, the building blocks of the human body.
Many people avoid meat for ethical reasons, which is admirable. Many others, however, avoid meat for “health reasons”.
What health reasons? Well, if you’ve been following the news, you’ve probably heard rumors that meat not only gives you cancer, but also decreases your lifespan.
Ouch. It doesn’t get much worse than that, outcome-wise. Should meat eaters like myself be worried?
I’ll answer that in a minute. But first, let’s review the anti-meat side of the argument.
Meat and Cancer Risk
Since a certain 2014 study hit the press, it’s been fashionable to claim that eating meat causes cancer. The study showed that people aged 50-65 had a significantly higher risk of death and cancer if they ate loads of animal protein. In those over 65, however, loads of animal protein were actually protective against bad outcomes.
The age discrepancy thing is weird. Why would meat give cancer to a 55 year old but protect a 68 year-old from the very same cancer? Leaving that to one side for the moment, meat-cancer associations have shown up elsewhere, so the issue bears further discussion.
When it comes to meat and cancer risk, association is the operative word. In other words, it’s not clear that meat causes cancer. There’s just a correlation between the two variables. Other causes may be lurking in the shadows.
For instance, the 2014 study didn’t control for cancer risk factors like obesity, smoking, or heavy drinking. These unhealthy factors promote both DNA damage and inflammation, which in turn increase cancer and mortality risk. They are well established killers.
Look at it this way: maybe meat eaters are also more likely to be smokers, and it’s the smoking that drives the cancer risk. Not the meat.
In 2016, a group of smart scientists took this line in another protein / longevity analysis of a massive population. Before they controlled for unhealthy lifestyle factors – smoking, drinking, obesity etc. – the association between meat and mortality was there as ever before. But after they controlled for them? Poof, it disappeared.
So according to that data, if you live a healthy lifestyle, eating meat does not increase your mortality risk. But if you smoke, drink, and sit on the couch all day while eating your burger, not only will you smell bad, your mortality stats will stink too.
Protein, IGF-1, and Longevity
Let’s move now from correlation to mechanism. Why might eating meat be dangerous? Perhaps it’s all that protein.
In the “The Longevity Diet” (worth reading), Dr. Valter Longo points to the fact that eating protein spikes insulin-like growth factor 1 (IGF-1), a growth hormone similar to insulin. High IGF-1 levels, in fact, have been linked to higher cancer risk. We’ll dig into that in a minute.
So is IGF-1 an absolute bad? Not at all. IGF-1 helps us maintain muscle, form strong bones, and even generate brain cells. And since IGF-1 declines with age, higher levels of this hormone in one’s twilight years are actually a marker of vitality.
Given the importance of IGF-1, low protein diets (and the resulting low IGF-1 levels) are arguably antithetical to healthy aging. Immunity suffers. Muscles waste away. Bones become brittle. Metabolism slows. And even though centenarians have lower levels of circulating IGF-1 than the general population, the centenarians with the lowest levels have increased risk of dementia. Getting the picture?
But you don’t want too much IGF-1. According to one meta-analysis, in fact, both very high and very low IGF-1 levels increase mortality risk.
So for healthy aging, we want some IGF-1 around. But not too much. Sunlight is good for you, but too much turns you into a prune.
Does IGF-1 Cause Cancer?
In this case, the prune represents increased cancer risk. This is where low protein diets gain some traction. It is true, after all, that rats fed a low protein diet are protected against tumor growth. Why? Probably because low protein diets result in lower IGF-1 levels, which in turn suppress growth (including cancer growth) in the body.
But in the absence of preexisting cancer, the picture becomes more complex. A recent meta-analysis, in fact, found no difference in colorectal cancer risk between people eating high and low protein diets. If protein causes cancer, why isn’t it showing up here?
Coming back to that 2014 study, higher animal protein intakes were actually protective against cancer in those 65 and up. Not to mention mortality. In light of these findings, to conclude that meat causes cancer would be a strange conclusion indeed.
The Importance of Exercise
Okay, so meat alone doesn’t cause cancer. But remember: in the presence of an unhealthy lifestyle factor (like being sedentary), the meat-cancer link rears its ugly head. And as much as I want to dismiss this link out of hand, I can’t. I want to be objective here.
To be safe then, if you like eating meat, you should probably pay extra attention to your lifestyle. Exercise, for instance, mitigates the downside of a high protein diet by shuttling IGF-1 out of your blood and into your muscles. This process not only reduces circulating IGF-1, it also makes you stronger.
And if you’re very active, even super high protein intakes won’t unduly spike your resting IGF-1 levels. Case in point: in strength athletes, moderate protein intakes actually raised IGF-1 levels more than high protein intakes. It’s a weird finding, but it suggests that athletes can tolerate a bigger hit of protein without jacking up IGF-1.
Have your steak
Despite rumors to the contrary, animal protein is actually good for you. In rare cases, certain cancers perhaps, low protein diets might be therapeutic. In most other cases, however, eating meat is healthy, provided the meat is grass-fed, pasture-raised, and (preferably) from a local farm.
Assuming you like meat, you should eat enough to maintain healthy muscles, bones, immunity, metabolism and IGF-1 levels. Around 1 g protein / kg body weight is a decent yardstick, but serious athletes need more.
Finally, don’t neglect the importance of lifestyle. Recall: the case against meat only holds up in the presence of an unhealthy life. When you live primally, however, this case vanishes, leaving behind only a stack of benefits.
The bottom line? You can, as they say, have your steak and eat it too.
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