The Answer to a Colon Cancer Mystery

Colorectal cancer is the third most common cause of cancer death in the world. Thankfully, the good bacteria in our gut take the fiber we eat and make short-chain fatty acids, like butyrate, that protect us from cancer. We take care of them, and they take care of us. If we do nothing to colon cancer cells, they grow. That’s what cancer does. But if we expose the colon cancer cells to the concentration of butyrate our good bacteria make in our gut when we eat fiber, the growth is stopped in its tracks. If, however, the butyrate stops, if we eat healthy for only one day and then turn off the fiber the next, the cancer can resume its growth. So, ideally, we have to eat a lot of fiber-rich foods—meaning whole plant foods—every day.

What about the populations, like those in modern sub-Saharan Africa, where they don’t eat a lot of fiber yet still rarely get colon cancer? Traditionallly. they used to eat a lot of fiber, but now their diet is centered around highly refined corn meal, which is low in fiber—yet they still have low colon cancer rates. Why? This was explained by the fact that while they may be lacking protective factors like fiber, they are also lacking cancer-promoting factors like animal protein and fat. But are they really lacking protective factors?

If you measure the pH of their stools, the black populations in South Africa have lower pH, which means more acidic stools, despite comparable fiber intakes. That’s a good thing and may account for the lower cancer rates. But, wait a second. Low colon pH is caused by short-chain fatty acids, which are produced by our good bacteria when they eat fiber, but they weren’t eating any more fiber, suggesting there was something else in addition to fiber in their diets that was feeding their flora. And, indeed, despite low fiber intake, the bacteria in their colon were still churning out short-chain fatty acids like crazy. But if their bacteria weren’t eating fiber, what were they eating? Resistant starch. “[T]he method of cooking and eating the maize [corn] meal as a porridge results in an increase in resistant starch, which acts in the same way as fiber in the colon,” as a prebiotic, a food for our good bacteria to produce the same cancer-preventing, short-chain fatty acids.

As I discuss in my video Resistant Starch and Colon Cancer, “[r]esistant starch is any starch…that is not digested and absorbed in the upper digestive tract [our small intestine] and, so, passes into the large bowel,” our colon, to feed our good bacteria. When you boil starches and then let them cool, some of the starch can recrystallize into a form resistant to our digestive enzymes. So, we can get resistant starch eating cooled starches, such as pasta salad, potato salad, or cold cornmeal porridge. “This may explain the striking differences in colon cancer rates.” Thus, they were feeding their good bacteria after all, but just with lots of starch rather than fiber. “Consequently, a high carbohydrate diet may act in the same way as a high fiber diet.” Because a small fraction of the carbs make it down to our colon, the more carbs we eat, the more butyrate our gut bacteria can produce.

Indeed, countries where people eat the most starch have some of the lowest colon cancer rates, so fiber may not be the only protective factor. Only about 5 percent of starch may reach the colon, compared to 100 percent of the fiber, but we eat up to ten times more starch than fiber, so it can potentially play a significant role feeding our flora.

So, the protection Africans enjoy from cancer may be two-fold: a diet high in resistant starch and low in animal products. Just eating more resistant starch isn’t enough. Meat contains or contributes to the production of presumed carcinogens, such as N-nitroso compounds. A study divided people into three groups: one was on a low-meat diet, the second was on a high-meat diet including beef, pork, and poultry, and the third group was on the same high-meat diet but with the addition of lots of resistant starch. The high-meat groups had three times more of these presumptive carcinogens and twice the ammonia in their stool than the low-meat group, and the addition of the resistant starch didn’t seem to help. This confirms that “exposure to these compounds is increased with meat intake,” and 90 percent are created in our bowel. So, it doesn’t matter if we get nitrite-free, uncured fresh meat; these nitrosamines are created from the meat as it sits in our colon. This “may help explain the higher incidence of large bowel cancer in meat-eating populations,” along with the increase in ammonia—neither of which could be helped by just adding resistant starch on top of the meat.

“[T]he deleterious effects of animal products on colonic metabolism override the potentially beneficial effects of other protective nutrients.” So, we should do a combination of less meat and more whole plant foods, along with exercise, not only for our colon, but also for general health.


This is a follow-up to my video Is the Fiber Theory Wrong?.

What exactly is butyrate? See:

For videos on optimizing your gut flora, see:

Interested in more on preventing colon cancer? See:

If you’re eating healthfully, do you need a colonoscopy? Find out in Should We All Get Colonoscopies Starting at Age 50?.

When regular starches are cooked and then cooled, some of the starch recrystallizes into resistant starch. For this reason, pasta salad can be healthier than hot pasta, and potato salad can be healthier than a baked potato. Find out more in my video Getting Starch to Take the Path of Most Resistance.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

How the Meat Industry Reacted to the New Cancer Warnings

What was the meat industry’s response to leading cancer charities’ recommendation to stop eating processed meat, like bacon, ham, hot dogs, sausage, and lunch meat? As I discuss in my video Meat Industry Reaction to New Cancer Guidelines, the industry acknowledges that the most recent international cancer prevention guidelines now urge people to avoid processed meat.

“It is evident that…such a statement represents ‘a clear and present danger’ for the meat industry,” reads one response in the journal Meat Science. However, processed meat, it continues, is “a social necessity.” (How could anyone live without bologna?) The challenge for the meat industry, the response outlines, is to find a way to maintain the consumption of these convenience products while somehow not damaging public health.

We’re still not sure what in processed meat is so carcinogenic, but the most probable educated guess for explaining the damaging effect of processed meats involves heme iron, along with nitrosamine and free radical formation, ultimately resulting in carcinogenic DNA damage. To reduce the nitrosamines, they could remove the nitrites, something the industry has been considering for decades because of the long-known toxic effects they cause. The industry adds them to keep the meat pink. There are, evidently, other coloring additives available. Nevertheless, it’s going to be hard to get industry to change “in view of the positive effects” of these substances as preservatives and in achieving a “desirable flavour and red colour developing ingredients.” No one wants green eggs and ham.

It’s like salt reduction in meat products. The meat industry would like to reduce it, but “[o]ne of the biggest barriers to salt replacement is cost as salt is one of the cheapest food ingredients available.” A number of taste enhancers can be injected into the meat to help compensate for the salt reduction, but some leave a bitter after-taste. To address that, industry can also inject a patented bitter-blocking chemical that can prevent taste nerve stimulation at the same time. This “bitter blocker is only the first of what will become a stream of products that are produced due to the convergence of food technology and biotechnology.”

The meat industry could always try adding non-meat materials to the meat, such as fiber or resistant starch from beans that have protective effects against cancer. After all, in the United States, dietary fiber is under-consumed by most adults, “indicating that fiber fortification in meat products could have health benefits.” But, of course, the meat industry’s own products are one of the reasons the American diet is so deficient in fiber in the first place.

The industry is all in favor of reformulating their products to cause less cancer, but “[o]bviously any optimization has to achieve a healthier product without affecting quality, particularly hedonic aspects.”

“It is important to realise that nutritional and technological quality [in the meat industry] are inversely correlated. Currently, improvement in one will lead to deterioration of the other.” Indeed, the meat industry knows that consumption of lard is not the best thing in the world—what with heart disease being our number-one killer—but those downsides “are in sharp contrast to their technological qualities that make them indispensable in the manufacture of meat products.” Otherwise, you just don’t get the same “lard consistency.” The pig’s fat doesn’t get hard enough, and, as a result, “a fatty smear upon cutting or slicing can be observed on the cutting surface of the knife.” Less heart disease versus absence of that fatty smear? I suppose you have to weigh the pros and cons…


According to the World Health Organization’s IARC, processed meat is now a Group 1 carcinogen—the highest designation. How is it that schools still feed it to our children?

How Much Cancer Does Lunch Meat Cause? Watch the video to find out.

For more on carcinogens, cancer, and meat, see:

Some of the meat industry’s finagling reminds me of tobacco industry tactics. See, for example, Big Food Using the Tobacco Industry Playbook and The Healthy Food Movement: Strength in Unity. You can also check out American Medical Association Complicity with Big Tobacco.

Skeptical about the danger of excessive sodium intake? Check out The Evidence That Salt Raises Blood Pressure. If you’re still not convinced, see Sprinkling Doubt: Taking Sodium Skeptics with a Pinch of Salt and Sodium Skeptics Try to Shake Up the Salt Debate. Why do the meat industries add salt when millions of lives are at stake? Find out in Big Salt: Getting to the Meat of the Matter.

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:

Foods to Avoid to Help Prevent Diabetes

We’ve known that being overweight and obese are important risk factors for type 2 diabetes, but, until recently, not much attention has been paid to the role of specific foods. I discuss this issue in my video, Why Is Meat a Risk Factor for Diabetes?

A 2013 meta-analysis of all the cohorts looking at the connection between meat and diabetes found a significantly higher risk associated with total meat consumption––especially consumption of processed meat, particularly poultry. But why? There’s a whole list of potential culprits in meat: saturated fat, animal fat, trans fats naturally found in meat, cholesterol, or animal protein. It could be the heme iron found in meat, which can lead to free radicals and iron-induced oxidative stress that may lead to chronic inflammation and type 2 diabetes, or advanced glycation end (AGE) products, which promote oxidative stress and inflammation. Food analyses show that the highest levels of these so-called glycotoxins are found in meat—particularly roasted, fried, or broiled meat, though any foods from animal sources (and even high fat and protein plant foods such as nuts) exposed to high dry temperatures can be potent sources of these pro-oxidant chemicals.

In another study, researchers fed diabetics glycotoxin-packed foods, like chicken, fish, and eggs, and their inflammatory markers––tumor necrosis factor, C-reactive protein, and vascular adhesion molecules––shot up. “Thus, in diabetes, environmental (dietary) AGEs promote inflammatory mediators, leading to tissue injury.” The good news is that restriction of these kinds of foods may suppress these inflammatory effects. Appropriate measures to limit AGE intake, such as eliminating meat or using only steaming and boiling as methods for cooking it, “may greatly reduce the already heavy burden of these toxins in the diabetic patient.” These glycotoxins may be the missing link between the increased consumption of animal fat and meats and the development of type 2 diabetes.

Since the 2013 meta-analysis was published, another study came out in which approximately 17,000 people were followed for about a dozen years. Researchers found an 8% increased risk for every 50 grams of daily meat consumption. Just one quarter of a chicken breast’s worth of meat for the entire day may significantly increase the risk of diabetes. Yes, we know there are many possible culprits: the glycotoxins or trans fat in meat, saturated fat, or the heme iron (which could actually promote the formation of carcinogens called nitrosamines, though they could also just be produced in the cooking process itself). However, we did learn something new: There also appears to be a greater incidence of diabetes among those who handle meat for a living. Maybe there are some diabetes-causing zoonotic infectious agents––such as viruses––present in fresh cuts of meat, including poultry.

A “crucial factor underlying the diabetes epidemic” may be the overstimulation of the aging enzyme TOR pathway by excess food consumption––but not by the consumption of just any food: Animal proteins not only stimulate the cancer-promoting hormone insulin growth factor-1 but also provide high amounts of leucine, which stimulates TOR activation and appears to contribute to the burning out of the insulin-producing beta cells in the pancreas, contributing to type 2 diabetes. So, it’s not just the high fat and added sugars that are implicated; critical attention must be paid to the daily intake of animal proteins as well.

According to a study, “[i]n general, lower leucine levels are only reached by restriction of animal proteins.” To reach the leucine intake provided by dairy or meat, we’d have to eat 9 pounds of cabbage or 100 apples to take an extreme example. That just exemplifies the extreme differences in leucine amounts provided by a more standard diet in comparison with a more plant-based diet.

I reviewed the role endocrine-disrupting industrial pollutants in the food supply may play in a three-part video series: Fish and Diabetes, Diabetes and Dioxins, and Pollutants in Salmon and Our Own Fat. Clearly, the standard America diet and lifestyle contribute to the epidemic of diabetes and obesity, but the contribution of these industrial pollutants can no longer be ignored. We now have experimental evidence that exposure to industrial toxins alone induces weight gain and insulin resistance, and, therefore, may be an underappreciated cause of obesity and diabetes. Consider what’s happening to our infants: Obesity in a six-month-old is obviously not related to diet or lack of exercise. They’re now exposed to hundreds of chemicals from their moms, straight through the umbilical cord, some of which may be obesogenic (that is, obesity-generating).

The millions of pounds of chemicals and heavy metals released every year into our environment should make us all stop and think about how we live and the choices we make every day in the foods we eat. A 2014 review of the evidence on pollutants and diabetes noted that we can be exposed through toxic spills, but “most of the human exposure nowadays is from the ingestion of contaminated food as a result of bioaccumulation up the food chain. The main source (around 95%) of [persistent pollutant] intake is through dietary intake of animal fats.”


For more on the information mentioned here, see the following videos that take a closer look at these major topics:  

AGEs: Glycotoxins, Avoiding a Sugary Grave, and Reducing Glycotoxin Intake to Prevent Alzheimer’s.

TOR: Why Do We Age?, Caloric Restriction vs. Animal Protein Restriction, Prevent Cancer From Going on TOR, and Saving Lives By Treating Acne With Diet

Viruses: Infectobesity: Adenovirus 36 and Childhood Obesity

Poultry workers: Poultry Exposure and Neurological Disease, Poultry Exposure Tied to Liver and Pancreatic Cancer, and Eating Outside Our Kingdom

Industrial pollutants: Obesity-Causing Pollutants in Food, Fish and Diabetes, Diabetes and Dioxins, and Pollutants in Salmon and Our Own Fat

The link between meat and diabetes may also be due to a lack of sufficient protective components of plants in the diet, which is discussed in my videos How May Plants Protect Against Diabetes?, Plant-Based Diets for DiabetesPlant-Based Diets and Diabetes, and How Not to Die from Diabetes.

In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations: