14 Ways the Vegan Diet Can Help Prevent Colon Cancer

It probably doesn’t come as a huge shock to hear that the vegan diet offers some pretty amazing benefits when it comes to avoiding colon cancer. I know in my own research in the plant-based eating and cancer risk, cancers of the stomach come up the most often when searching the literature databases.

But, why is that? While many cancers such as breast and prostate may benefit greatly from healthy dietary habits, the GI tract has a clear advantage: food comes in direct contact with it. That’s right, many of the compounds in food thought to be beneficial in preventing chronic disease come into direct contact with the colon.

And as we’ll see in the following paragraphs, it seems that a whole food vegan diet offers some pretty amazing benefits in protecting these lucky epithelial cells.

We won’t be touching on too much pathophysiology here, as I’ll be publishing an article shortly that examines the relationship between the vegan diet and cancer in general, which will cover some basic pathophysiology. We’ll go ahead and dive right in, and cover some physiology here and there as need be.

Benefits Related to the Elimination of Animal Products

Vegans Don’t Consume Red Meat

Without even going into any specific components of red meat (which we’ll do in a bit), the consumption of red meat, in general, has long been associated with higher incidences of colorectal cancer.

Indeed, a rather recent body of evidence incriminates red meat intake in colon carcinogenesis.1

There have been several fairly large cohort studies, finding the consumption of red meat to be associated with a greater risk of developing colon cancer.2

Animal flesh, in general, is hardly great when it comes to colorectal cancer outcomes. In one cohort study, intakes of both white and red meat increased the risk of developing colon cancer.3

The Red Meat-Colon Cancer Connection

These are just observational studies—the types of studies that serve as the initial impetus to investigate diet-disease relationships. We’ll get into the mechanistic stuff below. When I first encountered this relationship, the first thing that came to mind was oxidative damage.

On the other hand, maybe the meat displaces healthier foods—foods that offer protection against cancers of the GI tract. After all, when you include more servings of meat your diet at a given calorie level, you end up with fewer servings of fruits and veggies over the course of the day.

After all, diets rich in whole plant foods tend to reduce free radical formation in the GI tract as well as lower levels of mutagenic activity.4 Probably due to the higher fiber and antioxidant content of minimally processed whole plant foods. Some micronutrients, like folate found ubiquitously in plant foods, are linked to a lower risk of cancer.5

If you’ve done prior research into the health benefits of plant-based eating, then I’m sure your intuition tells you it probably has something to do with both the meat-free and plant-based nature of a healthy whole food vegan diet.

I don’t emphasize epidemiological evidence, because there’s just not enough of it examining vegans thus far, and not a ton on vegetarian populations. For this reason, I usually come at things from the mechanistic angle. There is one group of vegetarians that have been studied with regards to colon cancer, and that’s the Seventh Day Adventists (SDAs).

One SDA study of 30,000 members, found meat consumption within the population to be positively associated with all-cause mortality.6 When the study was later analyzed, researchers found that among the many diet-related variables, colon cancer was most strongly related to the intake of meat.7

Another study (one referenced above) showed rates of colon cancer to be 88% higher in non-vegetarians compared with vegetarians.8

Vegans Have Low Saturated at Intakes

Recent laboratory data have indicated that a low PUFA to SFA ratio (characteristic of red meat) may lead reduce insulin sensitivity, perhaps by increasing cell membrane permeability to insulin receptors.9,10

The SFA-Colon Cancer Connection

For starters, high insulin levels translate into higher levels of IGF-1, and high levels of IGF-1 are associated with a number of cancers, including colon cancer.11

Vegans Avoid N-Nitroso Formation from Meat Proteins

There are carcinogenic molecules known as N-nitroso compounds. Meat contains nitrates, which your colonic bacteria convert to these carcinogenic compounds. How do researchers know this? For starters, the consumption of meat protein increases levels of fecal nitrates.

One study demonstrated that subjects, upon switching to a high-meat diet experienced a THREEFOLD increase in N-nitroso formation.12

Vegans Avoid Heterocyclic Amines

Sugimanura, et al demonstrated that cooking meat protein produces certain types of compounds known as heterocyclic amines, molecules long implicated as a dietary component potentially increasing the risk of colon cancer.13

Where do they come from?

These compounds form on the charred surface of meat, and frequent intake of cooked meats is associated with increased risk of colorectal cancer.24,25

But, where do they come from?

There are certain amino acids present in especially large quantities in meat. These specific amino acids combine with creatine (also found in meat) to form their respective heterocyclic amines—there are four carcinogenic heterocyclic amines total.

So far there’s a decent amount of evidence suggesting that these four compounds have carcinogenic and mutagenic effects, which can’t be a good thing when it comes to colon cancer.13,14

One of the four amines, MeIQ, was shown to produce as much as 109 times more DNA mutations than other known food toxins, including N-nitrosamines covered above.

Some studies have shown a strong genetic component when it comes to the effect of heterocyclic amines on cancer risk. In examining heterocyclic amine metabolism, a certain phenotype was shown to increase colon cancer risk.15,16 So, some people may be at higher risk than others when it comes to consuming these compounds. But, it’s best to stay clear of them altogether.

No Animal Protein Intake Equals Lower IGF-1 Levels

As mentioned above, high circulating levels of IGF-1 are positively associated with the risk of various cancers, including colon cancer. Vegans have lower IGF-1 levels compared to other populations.17

The Animal Protein-IGF-1 Connection

The consumption of animal protein in general (including whey and casein proteins from milk) is strongly linked to IGF-1 levels.

IGF-1 is a hormone that’s structurally similar to insulin. However, unlike insulin, IGF-1 also promotes each stage of cancer development—from the growth of cancer cells to the vascularization and metastasis of the of these cells.

Vegans Have Lower Intakes of Heme Iron

If you read my article on iron overload and hemochromatosis, you already know that iron from meat is a bit different than the iron found in plant foods (non-heme iron). Your body can regulate non-heme iron absorption so that you absorb the amount that you need. However, when it comes to heme iron the body tends to zap it up regardless of needs, current storage, etc. Non-heme iron has a bioavailability of about 2.5%. Compare that with the whopping 26% bioavailability of heme iron—a tenfold difference.18

Normally, higher bioavailability is a good thing, and it definitely has it’s upside—you’re much less likely to be iron deficient if you’re eating heme iron all else equal. However, excessive iron intake, in the long run, is implicated in the development of all sorts of diseases—cancer included.

The Heme Iron-Colon Cancer Connection

Red meat is just loaded with heme iron. And studies have shown that an increased intake of red meat is linked to a higher colon cancer risk.19-23

Liver intake may be worse than red meat, as it’s one of the highest sources of heme iron.19

Vegans Avoid Preservatives Used in Meat Processing

Obviously, convenience is one factor that determines which meat products will be popular among consumers. Unfortunately, convenient is a synonym for processed in the food industry.

The most commonly consumed meats  (read: processed) are often treated with additives as they allow for long-term preservation. While they can make meat safer to eat for long periods of time, many of the additives commonly used are considered potentially carcinogenic. Specifically, nitrates and nitrites.

Above we touched on nitrates derived from the protein itself. Well, cured and processed meats have quite a bit of nitrates added to them. These compounds accomplish a number of things:

  1. Stabilize the nice, shiny red/pink color in meat.
  2. Serve as antioxidants.
  3. Flavor development.

In order to accomplish these goals, the nitrates first must be converted to nitrites. Enter sodium nitrite: a flavor enhancing colorant, an antimicrobial agent used in cured and processed meats.

For some time these compounds have been thought to potentially play a role in gastric and colonic carcinogenesis by forming N-nitroso compounds.26

N-nitroso compounds aside, the salting and curing process itself is thought to play a role in the etiology of gastric cancer as salt irritates gastric epithelial cells.27

Benefits Related to What a Whole Food Vegan Diet Emphasizes

Higher Intakes of Fruits and Veggies (General)

So, at the beginning of the article, we talked about why it is that plant-based diets confer special benefits in helping prevent certain types of cancers. It just so happens that fruits and vegetables are at their best when it comes to protecting us from cancers involving the epithelial cells. Think, lung cancer, esophageal cancer, and cancers of the cervix stomach, and colon.

Results from one large study showed that relative risk (RR) of the more common epithelial cancers ranged from 0.2 to 0.5, between the lowest and highest vegetable intakes, respectively.29

Veggies seemed to edge out fruit in protecting against many cancers of the epithelial cells, but different fruits and veggies provided more or less protection depending on the location. As for colorectal cancer, the cruciferous veggies (broccoli, cabbage, cauliflower, etc.) performed the best.

Vegans who follow whole food diets are known for their varied intake of plant foods, so that’s a good thing.

One systematic review looked at 206 epidemiological studies and found vegetables and fruits to be effective in preventing many types of cancer, including colon cancer.30

Specifically, 174 out of the 206 found evidence that fruit and veggies play an important role in preventing colon cancer among other epithelial cancers.

Higher Intakes of Blue-Red Fruits and Vegetables

Any vegan primarily consuming whole plant foods will no doubt eat some in the blue-red spectrum. In most cases, anthocyanins are the pigments that account for this coloration. Other purplish pigments exist such as betaine (beats), but anthocyanins are the most common.

Anthocyanins are blue-red, water-soluble pigments found in fruits such as blueberries, strawberries, cherries, grapes. They’re thought to be antioxidants and potentially play a variety of helpful roles—preventing the oxidation of cholesterol, etc.31

One other phytochemical present in many blue-red fruits is resveratrol. It’s a chemical found in the skin of grapes that the wine industry loves to talk about. Some studies have shown it to be protective against colon cancer.

Higher Intakes of Whole Grains

There are several epidemiological studies indicating that whole grains likely play a protective role in preventing cancers, especially of the GI tract. 32,33

One systematic review of 40 case-control studies involving colon polyps, showed whole grains to be protective in 95% of the studies involved.

How is this possible? Well, of course, fiber plays a role which we’ll cover in here in a bit. But, there are also numerous other potential ways in which whole grains can exert anticarcinogenic effects—antioxidant activity, etc.

One function fiber is thought to carry out is one of detoxification. Fiber, especially insoluble fibers found in whole grain, bind many toxic substances for excretion. Soluble fibers do this too,  by a different mechanism (they’re known to bind cholesterol). But it’s the insoluble fibers that are thought to aid in detoxification.34

Higher Intakes of Soy (Isoflavones)

If you’ve read the breast cancer article, then you know that certain phytoestrogens like isoflavones (e.g. genistein, ipriflavone, and daidzein) can be protective against cancer—not just breast cancer, though that’s the context they’re usually brought up in.

It’s been known for a while that Chinese populations who regularly consume soybeans in many forms—fermented soy products or tofu—have a much lower rate of certain cancers compared to Chinese populations who rarely consume soy. One study by Messina et al showed some Chinese populations to have half the rate of various epithelial cancers, including colon and stomach cancer.35

Higher Intakes of Allium Vegetables

Onion and garlic among other sulfury-smelling veggies belong to the Allium genus. They’re not only pungent in smell but are probably the most potent anticancer superfoods out there. When you eat enough, they can be as good at keeping cancer away as they are at keeping your friends and neighbors away.

Anyway, there are so many studies showing benefits in the area of preventing stomach cancers, that I’m just going to go over a few rapid fire:

1. Onion extract has long been known to inhibit tumor growth.36

2. A Greek study demonstrated high intakes of garlic and onions to be protective against cancers of the stomach.37

3. The Netherlands Cohort Study on diet and cancer followed men and women from 55 to 69 years of age and found that those with the highest onion consumption had half the level of cancer in the lower stomach compared to those with the lowest onion intakes.38

4. One study found chives, another in the Allium genus, to have a significant protective effect against colon cancer.39

5. There are three studies showing garlic to be able to reduce the development of stomach and colon cancer.40-43

6. One China study showed persons with the highest intakes of Allium vegetables to have a risk of stomach cancer 40% lower than those with the lowest intakes.43

7. In one study known as the Iowa Women’s Health Study, garlic consumption was associated with a 32% lower risk of colon cancer for those with the highest vs. lowest intakes.44

8. Three studies have demonstrated that the regular use of garlic and onions can decrease the risk of colon and stomach cancers by 50 to 60%.37,38,45

The Allium-Colon Cancer Connection

You probably won’t be surprised to hear that no one knows for sure what’s going on here. There’s a certain bacterium known as Helicobacter pylori—the one that causes ulceration—that’s been implicated in the etiology of various stomach cancers. It so happens that this bacterium has shown a fairly high level of sensitivity to small amounts of garlic. And for this reason, it’s been speculated that garlic and similar vegetables may be related to the lower risk of stomach cancers seen in folks with higher intakes of Allium vegetables.46

Higher Intakes of Dietary Fiber

I know we touched on whole grain above. But this section is referring to dietary fiber more broadly—it’s found in fruits, vegetables, and tubers, etc.

The idea that dietary fiber might protect against colon cancer has been around for some time.47

In the time since the idea was first floated, numerous cohort studies and several case-control studies have examined this relationship.

The majority of such studies yielded results that supported the original notion that dietary fiber does indeed play a protective role in the etiology of colon cancer.

One systematic review found 11 out of 17 of the case-control studies involved to show an inverse relationship between colorectal cancer and dietary fiber intake.48

Another review looked at 5,255 colorectal cancer patients finding a significant inverse relationship between colon cancer risk and dietary fiber intake. And this was after controlling for other potentially beneficial nutrients such as beta-carotene.49

Lower Incidence of Obesity Among Vegans

It’s no secret that vegans have the lowest BMI of all populations.50 At least not to you guys, because I keep talking about it.

This is important when it comes to colon cancer because studies consistently demonstrate that excess body fat and obesity are risk factors for cancer, with obesity being especially suspect when it comes to the etiology of colon cancer.51

The Obesity-Colon Cancer Connection

So far insulin is the most well-established mediator between colon cancer and obesity.

Hyperinsulinemia is implicated here. Obesity often (but not always) leads to insulin resistance, and as a result, high circulating levels of insulin, which as we know means higher levels of IGF-1.

You might ask, “well what’s the obesity-insulin resistance relationship?”

Great question! This association especially applies to men. All adipose tissue is not created equal. There’s a certain type of fat that’s especially insidious: visceral abdominal fat. Unlike the fat directly under the skin, this type of fat is found deeper in the abdominal cavity and is associated with insulin resistance.

It turns out that most men love to store fat in this area (at least their bodies do). You may have heard of essential fat. Well, visceral abdominal fat is like essential fat…  essential for serving as a depot for pathogenetic theories! (as put by EE Freza et al).52

Don’t get me wrong, it’s good stuff. It protects and insulates our internal organs. But you don’t want too much of it.

Anyway, all that to say that researchers, upon evaluating the relationship between obesity and colon cancer risk, have found that obesity imposes a greater risk for men.52


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