Vegetarian Dietary Patterns and the Risk of Colorectal Cancers

Introduction

Colorectal cancer (CRC) ranks among the top ailments affecting human health and the leading causes of death resulting from cancer conditions worldwide. It is a type of cancer condition affecting either the colon or the rectum and is highly influenced by lifestyle, particularly diet. In this respect, there is growing research that has put a great deal of emphasis on the importance of the role different dietary patterns play in either increasing or reducing the risk of CRC. Of the various related diets, vegetarian diets have been gaining prominence as such diets would be greatly helpful in controlling the risk of colorectal cancers. This article explains the relations that exist between vegetarian dietary patterns and the risk for colorectal cancer through current research.

How Do Vegetarian Diets Differ?

Vegetarian diets exclude meat, poultry, and fish but may include dairy products and eggs, depending on the type.

• The major types of vegetarian diets are as follows:

  • Lacto-Vegetarian: Includes all dairy products, excluding eggs, fish, and meat.

  • Ovo-Vegetarian: Excludes dairy products, meat, and fish but includes eggs.

  • Lacto-Ovo-Vegetarian: It comprises eggs and dairy products in its diet, excluding meat and fish.

  • Vegan: Nothing is given in the diet, which is animal food.

Various studies on plant-based diets comprising fruits, vegetables, legumes, nuts, seeds, and whole grains have shown that they may provide a high amount of fiber, minerals, and antioxidants, which currently are believed to have played a key role in lowering the risk for colorectal cancer.

What Is the Mechanism of Fiber in Reducing CRC Risk?

All vegetarian diets have a high intake of fiber. Research indicates that dietary fiber contributes to a reduction in the risk of colorectal cancer, probably due to increasing stool bulk and transit time, diluting harmful substances in the colon, and reducing exposure to carcinogens by the lining of the colon. Also, large amounts of short-chain fatty acids, including butyrate, are produced from undigested carbohydrates by gut fermentation of fibers. These often exhibit anti-inflammatory and anti-cancer activities.

Indeed, studies have estimated that a moderate increase in daily fiber intake can lower the risk of colorectal cancer by as high as possible. Given that vegetarian diets generally provide more fiber than non-vegetarian diets, one would anticipate that such diets afford quite substantial protection against CRC.

What Role Do Antioxidants and Phytochemicals Play in Cancer Prevention?

Vegetarian diets are highly rich in antioxidants and phytochemicals, two key substances well known to fight cancer. Compounds including vitamins C and E, carotenoids, and flavonoids have been identified as antioxidants that neutralize free radicals at work in the making of an illness, thereby lessening the stress of oxidation and, in effect, preventing deoxyribonucleic acid (DNA) damage, which is a precursor of cancer.

Non-nutritive biochemicals found in plants, called phytochemicals, also play a role in cancer prevention. Flavonoids and polyphenols contain properties that reduce inflammation, halt cell multiplication, and trigger programmed cell destruction, hence preventing the induction and promotion of cancer. Probably, high levels of these compounds in all vegetarian diets account for a decrease in the likelihood of colorectal cancer development in affected individuals.

How Does Excluding Red and Processed Meats Affect the CRC Risk?

Another very important distinguishing mark of vegetarian diets is their lack of red and processed meats, which have been linked in the literature to an increased incidence of colorectal cancer. For its part, red meat alone is notorious for its high content of heme iron, which is capable of providing substrates for the production of carcinogenic compounds within the colon. The preservatives- usually nitrites and nitrates-used in the processing of these meats can easily reduce to carcinogenic forms in the intestines. Vegetarians lower their intake of such toxins by abstaining from these meats. They could account for the lower CRC incidence seen in individuals on a vegetarian diet.

What Does the Literature Say About Vegetarian Diet and Risk of CRC?

There are many epidemiological studies that have undertaken the intake of vegetarian diets in relation to the development risk of CRC. In major studies conducted across the globe, it has been observed that vegetarians have low rates of CRC compared with those consuming meat. The subgroups representing vegetarian diets, including vegan or lacto-ovo vegetarian diets, have generally been observed to have low CRC risks.

Other large studies have also reported similar evidence for low rates of colorectal cancer in vegetarians as compared to that among meat-eaters. Overall, the evidence indicates an association between vegetarian diets and a lowered risk of developing colorectal cancer. However, the extent of protection will depend upon the type of vegetarian diet as well as on the population being studied.

What Are the Other Factors to Be Considered?

Although the evidence to suggest a protective effect of vegetarian diets on colorectal cancer is very strong, other factors that may influence these findings should be considered. For instance, vegetarians generally have healthier lifestyles characterized by regular physical activity, non-smoking, and moderate alcohol consumption, which can further result in risk reduction for CRC.

It is important to recognize that not all vegetarian diets offer the same level of benefits. High intakes of processed vegetarian foods, added refined sugars and unhealthy fats are unlikely to confer the same protection as diets abundant in whole, plant-based foods. The quality of the vegetarian diet is, therefore, an important determinant of its relationship with CRC risk.

What Are the Limitations of Current Research?

Although most recent studies on vegetarian diets and colorectal cancer risk are generally encouraging, there still exist limitations to these studies. A lot of data is from questionnaire responses, and undeniably, dietary information self-reported by the subjects contains inaccuracies and recall bias. Most of these studies are observational; hence, inferences regarding cause and effect can hardly be reached definitely.

Other challenges include the different definitions of vegetarianism that vary between studies. To be specific, the definitions vary between defining vegetarians to be those who eat fish or poultry occasionally, to defining them as people who, by and large, do without any product coming from animals. These variations make the results and interpretations of this bound to be different.

Conclusion

Based on the available evidence, a high intake of fiber, antioxidants, and phytochemicals is inferred to be the main cause of the correlation between vegetarian dietary patterns and decreased colorectal cancer risk. It appears that avoidance of red and processed meats, together with a high diet of various plant-based foods, is the protective factor regarding the cause. While this is one of the biggest potentials for risk reduction in colorectal cancer due to vegetarian diets, let it be reiterated that diet quality would most likely be the major concern in that scenario. A balanced vegetarian diet, preferably using more whole foods than processed ones, might offer the greatest protection against CRC. Further studies are warranted, as they were, randomized controlled trials, to confirm the findings and enable a more robust conclusion. A vegetarian diet can be postulated as a healthy lifestyle precondition for the prevention of colorectal cancer and improvement in health.