I’ve written about the link between meat and colon cancer; I’ve addressed epidemiological studies and mechanisms. Here’s a recent post: Evidence That Meat Increases Risk For Colon Cancer Is “Convincing”. This is what the British Journal of Cancer said in 2011:
The associations between consumption of red and processed meat with an increased risk of colorectal cancer were considered to be ‘convincing’.
There are no dietary guidelines concerning recommended levels of consumption of red and processed meat; as for alcohol, it is assumed that ‘less is better’ and that there is no threshold below which consumption presents no risk. In this section, we assume that the optimum (or target) is zero consumption.
They said any consumption of red or processed meat increases the risk for colon cancer. I thought those were strong words coming from a respected, mainstream, professional medical journal. It pretty much disembowels the phrase “in moderation.”
Here’s a new clinical trial out of Australia, a country whose people love their meat:
Dietary Manipulation Of Oncogenic MicroRNA Expression In Human Rectal Mucosa: A Randomized Trial, Cancer Prevention Research, August 2014
These findings support increased resistant starch consumption as a means of reducing risk associated with a [high red meat] diet.
Editorial: Resistant Starch May Reduce Colon Cancer Risk From Red Meat, Journal of the National Cancer Institute, October 2014
There’s so much evidence that eating meat contributes to colon cancer that both of these papers start off with a statement of presumed fact: “A diet high in red meat increases risk of colon cancer.” They fed their subjects meat anyway, for just 4 weeks:
Their study involved 23 healthy volunteers, aged 50–75 years. Participants were randomly assigned to either a high-red-meat diet (300g raw per day of lean beef or lamb) or that same diet plus a resistant-starch supplement called StarPlus (40g per day of butyrylated high-amylose maize starch). After 4 weeks on one diet, participants switched to the other for another 4 weeks.
They ate about two-thirds of a pound of meat each day. It was a crossover design, so participants acted as their own controls. They found:
A high-red-meat diet statistically significantly increased cell proliferation in the mucosa. Adding resistant starch to the meat diet reversed [some of this increase].
How can eating starch reduce cancer risk? The mechanism, as I’ve written about before, involves short-chain fatty acids (SCFAs) produced by bacteria in the colon as they consume starch left over from our digestion.
Unlike most carbohydrates, resistant starch passes undigested to the colon. There, gut microbes ferment it, yielding short-chain fatty acids, such as butyrate, which promote colon health. Those short-chain fatty acids, the study suggests, also reduce expression of microRNAs that are associated with severe colon cancer and that increase cell proliferation.
Heme iron and heterocyclic amines from red meat cooked at high temperature alter gene expression and increase proliferation. Butyrate from microbes decreases proliferation.
Resistant starch is not fiber in the way many people think of fiber:
This paper shows it’s not the bulk fiber – like bran muffins or Metamucil – that’s important for reducing cancer risk, [it’s] types of fiber, like resistant starch, that are metabolized by colonic bacteria.
Resistant starch is in green bananas; peas, beans, lentils, and other legumes; root vegetables (including potatoes that have been cooked and cooled, as in potato salad); whole grains (especially oats); and virtually all other plant foods consumed at room temperature or below. Even pasta made from processed wheat flour contains resistant starch, as long as it is cooked al dente and served cold or at room temperature.
Cooling the starch after heating it rearranges the granules into a shape and structure that make it difficult for our digestive enzymes to access. We don’t derive as many calories from resistant starch as the Nutrition Facts label suggests because it passes unabsorbed into the colon. So, a bowl of hot pasta has more calories than a bowl of cold pasta, and the cold pasta (or potatoes, etc.) protects our colon to boot!