Does this study actually say that eating meat is as bad as smoking?
Let’s get that out of the way – no.
What was this study investigating?
The study was actually a 2-for-1 – an epidemiological human study, and a direct mouse study.
Okay, what was the human study?
The study took self-reported data and tried to look at any connections between protein-intake and things that can kill you.
They looked at only people 50+ years old, and split them into two groups: 50-65, and 65+.
They then further broke down each group into low protein (~10% or lower of dietary intake), middle, and high protein (~20% or higher of dietary intake).
They found that for people in the 50-65 group, the people in the moderate and high-protein diet were more likely to die than those in the low.
The opposite happened in the 65+ group – higher protein helped! The one exception to this was diabetes-related mortality.
It should be noted that for people who track their fitness closely, 20% likely sounds low, not high.
What was the mouse study?
They took mice, injected them with cancer cells, and then saw what effect high-protein vs low-protein had on tumours. They found that high-protein lead to bigger tumors.
They found that eating more protein meant more IGF-1 in your bloodstream, which predicted tumor growth. IGF-1 is an anabolic agent that helps cells grow. It doesn’t differentiate – it can help both good cells (e.g. muscle tissue) or bad cells (e.g. tumors) grow.
Any issues with the study?
Beyond standard issues with epidemiological research like this (cannot prove causation, and while reporting dietary intake is getting better it is still not perfect on large scales like this) this one study had a few notable issues. Many good controls were in place to refine the results except two very relevant ones: ‘attempted weight loss’ was a control whereas ‘exercise’ was not.
This means that the study assessed people who had their weight maintained (and thus, if you are losing weight, the study cannot be used as evidence for you) and it couldn’t assess if a protective effect of exercise existed or not. Since exercise is inherently something that spikes IGF-1 in the blood yet is associated with reduce cancer and mortality, it seems like something that should have been accounted for.
Finally, the food source was not accounted for beyond its macronutrients. If a pile of processed meats and a marinated steak with veggies shared the same macronutrients, they were considered equivalent in this study.
Give it to me straight – should I give up meat?
Not based on this study. If you eat a lot of processed and smoked meat, then maybe you should cut back on that. It’s quite easy to “find” that eating causes cancer.
What if I’m diabetic?
When you look at an actual meta-analysis on protein-intake and diabetes, they found that a high-protein diet actually helped with variou diabetes markers. Take that as you will.
I’d like to know more.
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Original image “Steak” by Flickr user soyculto and used here under Creative Commons Attribution license.