I am a meat eater. I would happily be carnivorous if I could get away with it (though I do enjoy my veges). But there has been some conjecture in the media about whether meat causes cancer or other conditions.
Though there are many benefits of consuming animal protein, including boosting serotonin and mood as I posted, the truth is that there has been much research that has demonstrate an association between elevated meat consumption and a significantly higher risk of cancer and cancer mortality. But, you must keep in mind, these are association studies, not cause and effects. You have to look a little deeper.
One of the biggest recent studies was published in JAMA Internal Medicine (one of the most respectable journals in the the world) in 2016. It examined meat consumption and all-cause mortality and cancer-related mortality. This study found something very interesting that is important to consider; confounding factors. It demonstrates that a high intake of animal protein was only associated with a higher mortality rate and cancer mortality rate in people that had at least one other factor associated with an unhealthy lifestyle such as obesity, a history of smoking, sedentary lifestyle or heavy alcohol drinker. Meat eaters that were non-smokers, physically active, and moderate drinkers did not did have a higher mortality rate or cancer mortality rate. 
Research suggests a critical factor in the meat consumption and cancer link is that protein triggers insulin-like growth factors (IGF-1) production. IGF-1 is beneficial for muscle hypertrophy, which is very important as we age to prevent frailty and sarcopenia, but in regards to cancer is worth keeping an eye on. Amino acids, especially essential amino acids like leucine, are abundant in meat and the most strong nutritional instigator of the IGF-1 pathway.
IGF-1 has many roles. Like many hormones and systems in the body, it has good and bad outcomes. It has a major role in early children’s development, hypertrophy of muscle mass, and nervous system function. Those are the benefits. The downside is IGF-1 preserve damaged cells. It does not damage the cell but it does allow damaged cells to reproduce, i.e. make more damaged cells. This also applies to cancer cells.
The cancer fire can be stoked by various mechanisms that damage DNA and leads to damaged cells and onto cancer, like reactive oxygen species made through metabolism and inflammatory cytokines made by the immune system. We have protective mechanisms that detect these injured cells and exterminate them but with excessive IGF-1 this is overridden and can save the life of the damaged cell. Thus IGF-1 does not cause but can fuel cancer growth.
As a pathway, IGF-1 is very interesting to both cancer and longevity researchers. Studies on mice have found those that are deficient in IGF-1 are cancer resistant. Similarly, some people have polymorphisms in the encoding gene for the IGF-1 receptor that causes a reduction in IGF-1 activity, and research shows a reduction in cancer incidence and longer lifespans in these persons.
Conversely, when people have genetic polymorphisms that lead to increased IGF-1, they have an increased cancer risk. Even without genetic polymorphisms, higher than average blood IGF-1 has also been associated with an increased risk of several populous cancers, like breast, colon and prostate.
So, elevated IGF-1 equals elevated cancer risk. Decreased IGF-1 equals reduced cancer risk and greater lifespan – it also inhibits the longevity gene FOXO3. With this information, you could be very tempted to adopt a vegetarian, no meat, diet and very easy to take an absolutist position and never touch meat again, especially considering the other pros to a high vegetable diet.
However, as above, there are benefits to IGF-1. Whilst helping build muscle, IGF-1 helps burn adipose (fat) tissue, facilitates the growth of new brain cells – is a neurotrophic factor – and prevents brain cells from dying.
Exercise is important to ensure you get the benefits from IGF-1 without the consequences. All exercise lowers blood IGF-1 by causing the muscles to soak up the hormone. Exercise also causes IGF-1 in animals to cross the blood-brain barrier, increasing brain cells (neurogenesis).
Therefore, exercise decreases IGF-1 circulating in the blood so it has less chance to help the growth of injured cells or inhibit FOXO3. This makes sense in regards to the JAMA paper I mentioned in which meat eating was only associated with a increased death if you had one other unhealthy lifestyle factor.
Since I do not smoke nor am I obese, lead an active lifestyle and drink alcohol in (somewhat) moderation, I allow myself meat in my diet. In fact, I deliberately choose to lead a healthy lifestyle so that I can engage in some enjoyable activities like meat eating and the occasional glass of alcohol.
Where you source your meat plays a big role in how healthy it is.
Choosing free ranged, organic sources is best to avoid pollutants and ensure the animal gets a varied diet of grass and seeds. A local grocer, butcher or farmers’ market is best. Buy wild ocean fish (e.g. Alaskan salmon), grass-fed beef, and pasture-raised chicken with no antibiotics or hormones.
There is my take on my choice to eat meat.
What is your opinion, animal rights aside?
Enjoy whatever you eat,
Scott
PS. Some may accuse this post and reasoning as a piece of confirmation basis, but feel free to say so in the comments below.
