On Monday, the World Health Organization announced that processed meats like bacon & sausage were classified as “causing cancer” and red meat as “probably causing cancer.”
Let’s just say, its caused quite a stir. So does this mean that a Paleo or low-carb diet is going to kill you???
No. But there are a few things you should know before eating loads of bacon with impunity.
The risk is small
The report stated that 50g of processed meat a day (less than 2 pieces of bacon) caused an increase in colorectal cancer of 18%. What does that 18% increased risk really look like though? Let’s say 6 out of 100 people get bowel cancer in their lifetimes. And all of those 100 people eat an extra 50g of processed meat a day. An 18% increased risk means 7 people will develop develop bowel cancer instead of 6. That’s one extra case of cancer per 100 people eating 50g of processed meat every day.
The risk is still smaller than that from smoking or alcohol consumption
Cancer Research UK put it this way- 21% of bowel cancers can be attributed to processed and red meat consumption whereas 86% of lung cancer can be attributed to tobacco. In the larger context, 19% of all cancers can be attributed to tobacco, whereas just 3% of all cancers can be attributed to red and processed meat. So it would make no sense to stop eating red meat if you’re going to continue to smoke or drink alcohol excessively.
Red meat can cause cancer
There are several mechanisms by which it appears that red & processed meats can cause cancer. (And it should be noted that these mechanisms have NOTHING to do with whether the meat is of the grain-fed, feedlot-raised variety. That is, eating only grass-fed red meat will not protect you from these potential cancer-causing pathways.) One of those pathways is the digestion of the heme protein. Cytotoxic compounds can be created that damage the gut lining and can lead to cell proliferation- and increased cancer risk. Another mechanism is the metabolism of L-carnitine, an amino acid particularly abundant in red meat. Gut bacteria metabolize L-carnitine into a compound called TMA (trimethylamine). TMA crosses into the blood stream, goes to the liver and is metabolized into TMAO (trimethylamine-N-oxide). TMAO is strongly linked to cancer and heart disease. Another potential mechanism are mutagens that can be created when cooking red meat, particularly grilling and frying (heterocyclic amines and polycyclic aromatic hydrocarbons).
All these mechanisms are modified by vegetable consumption
Chlorophyll (the compound that makes plants green) and heme have almost identical chemical structures. Because of this similarity, chlorophyll can block the metabolism of heme into toxic, gut-destroying compounds allowing it instead to be metabolized to inert (inactive) compounds.
Indoles found in cruciferous vegetables like broccoli, kale, cabbage, and cauliflower have been shown to suppress the growth of tumors caused by heterocyclic amines and polycyclic aromatic hydrocarbons.
As for the link between L-carnitine and TMAO, that is a little more complex. In turns out that a particular species of gut bacteria, Prevotella, is mostly responsible for increased blood levels of TMAO from L-carnitine consumption, according to a 2013 study published in Nature Medicine. Conversely, gut microbiomoes that have more Bacteroides sp. instead of Prevotella converted significantly less L-carnitine into to TMA and eventually, TMAO. Prevotella specialize in fermenting polysaccharides in grains (but not those in fruits & vegetables), so they appear to predominate in the microbiomes of those with high consumptions of grains. Though we can’t say this conclusively yet, it appears from what we currently know, that eating a grain-free diet and getting most of your fiber from vegetables helps moderate the danger of processed and red meat consumption from this particularly pathway.
So I don’t think anyone needs to give up red meat or enjoying bacon from time to time. It comes back to the same, basic, intuitive advice: eat a variety of foods (mix in white meats & fish in for protein sources) and make sure to get at least 5 servings of vegetables a day. That means that there should be veggies on your plate at every meal. I encourage folks to think of building their plates around 4 ounce of animal protein (about 1/3 of their plate) and to fill in the other two-thirds of plate with vegetables. Not only is it a simple way of creating a meal, but it helps ensure that you get the healthiest balance of animal to plant foods.
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