Vegan Diet's Impact: Lowering Colorectal Cancer Risk

Colorectal cancer is a type of cancer that affects the colon and rectum. Research has shown that a vegetarian diet may reduce the risk of colorectal cancer. This is because a vegetarian diet is rich in dietary fibre, which is a type of carbohydrate that cannot be digested by the body but still provides numerous health benefits. For example, a study of 77,659 people found that those who followed a vegetarian diet had a 22% lower risk of colorectal cancer compared to non-vegetarians.

However, one study found that vegetarians had a 39% higher incidence rate of colorectal cancer compared to meat eaters.

Nitrate and nitrite are found in high concentrations in certain foods, especially green, leafy and root vegetables, and processed meats, respectively. Ingested nitrate is reduced to nitrite by the bacteria in the mouth and digestive tract. Nitrite then reacts with other compounds in the body to form N-nitroso compounds (NOCs), which are known animal carcinogens.

One study found that high dietary nitrate intake among subgroups expected to have higher exposure to endogenously-formed NOCs increases the risk of colorectal cancer.

Vegetarians have a higher risk of colorectal cancer

Colorectal cancer (CRC) is a type of cancer that affects the colon and rectum, which make up the large intestine. CRC is often influenced by lifestyle and dietary choices. Research has shown that a vegetarian diet may reduce the risk of CRC in some people, with a pescatarian diet, which includes fish, offering the most benefits.

Vegetarian Diets and CRC Risk

Vegetarian diets are plant-based and typically include fruits, vegetables, legumes, and whole grains. They may also include animal-derived products like eggs and dairy. Several studies have linked vegetarian diets to a reduced risk of CRC compared to omnivore diets, which include both animal- and plant-based foods.

Research Findings

A seven-year study of 77,659 people found that those following a vegetarian diet had a 22% lower risk of CRC compared to non-vegetarians. Another 20-year study of 10,210 people also found a significant reduction in CRC risk for vegetarians compared to meat-eaters.

Mechanisms for Reduced CRC Risk

Rich in Dietary Fiber

Vegetarian diets are rich in dietary fiber due to the high intake of fruits, vegetables, legumes, and whole grains. Dietary fiber is associated with a reduced risk of CRC, and research suggests that a diet high in fiber may reduce CRC risk by 12%.

Dairy Products

Some vegetarians include dairy products like milk, cheese, and yogurt in their diets. Studies have shown that higher intakes of dairy products are associated with a reduced risk of CRC due to their high levels of calcium and vitamin D, which have cancer-fighting properties.

Avoidance of Red and Processed Meat

Vegetarian diets typically avoid red and processed meat, which have been linked to an increased risk of CRC. Processed meats like sausages and ham are smoked, cured, salted, or fermented to improve flavor and extend shelf life. Studies have found that higher intakes of these meats are associated with a greater risk of CRC.

Lower Intake of Refined Carbohydrates

Vegetarians tend to center their diets around low-calorie, nutrient-dense foods, leading to lower intakes of highly processed foods and refined carbohydrates, which are high in sugar. This can aid in weight control and reduce the chances of developing obesity and type 2 diabetes, which are risk factors for CRC.

Types of Vegetarian Diets

There are several types of vegetarian diets, ranging from flexible to rigid. These include:

• Lacto-vegetarian: Includes dairy but excludes eggs and meat.
• Ovo-vegetarian: Includes eggs but excludes meat and dairy.
• Lacto-ovo-vegetarian: Includes eggs and dairy but restricts meat.
• Pesco-vegetarian (or pescatarian): Includes fish but limits other meats.
• Flexitarian (or semi-vegetarian): Includes fish and other meats but limits consumption to no more than once a week.
• Vegan: Excludes all animal products, including honey.

Other Ways to Prevent Colorectal Cancer

While diet plays a critical role in CRC development, there are other risk factors to consider. According to the Centers for Disease Control and Prevention (CDC), non-modifiable risk factors include inflammatory bowel disease, genetic conditions, and family history of CRC. Modifiable risk factors include a low-fiber diet, high-fat diet, overweight and obesity, alcohol consumption, and tobacco use.

In addition to dietary modifications, the CDC recommends at least 150 minutes of moderate-intensity physical activity per week and limiting alcoholic drinks to reduce CRC risk. Regular CRC screenings are also important for early detection and prevention.

Vegetarians have a lower overall cancer rate

Colorectal Cancer

A 2009 study of 63,550 men and women in the UK found that, compared with meat eaters, vegetarians showed an 11% lower incidence rate of all cancers. However, for colorectal cancer, vegetarians showed a 39% higher incidence rate compared with meat eaters.

The EPIC-Oxford study, which includes many of the same people as the Oxford Vegetarian study, found that after 14.9 years of follow-up, vegetarians had a lower cancer rate than non-vegetarians.

The Adventist Health Study-2 (AHS-2) found that pescovegetarians in particular have a much lower risk of colorectal cancer compared with non-vegetarians.

Prostate Cancer

The AHS-2 study found that vegans had a lower risk of prostate cancer than regular meat-eaters, even after adjusting for BMI. In the EPIC-Oxford study, fish-eaters had a statistically significant, lower rate of prostate cancer than regular meat eaters.

Breast Cancer

The AHS-2 study found that female vegans had a lower risk of "all female cancers" before adjusting for BMI. The Health Food Shoppers study found that vegetarians had a higher rate of breast cancer. However, this study did not adjust for having children, which is protective against breast cancer, and vegetarian women tend to have fewer children.

Lung Cancer

The EPIC-Oxford study found that vegetarians had a lower rate of lung cancer than meat eaters.

Ovarian Cancer

The EPIC-Oxford study found that vegetarians had a lower rate of ovarian cancer than meat eaters.

Pescovegetarians have a much lower risk of colorectal cancer

Pescovegetarians, or pescatarians, are people who eat fish but limit their consumption of other meats, such as poultry or beef. They have a much lower risk of colorectal cancer compared to non-vegetarians. In fact, they have the lowest risk of all the vegetarian diets.

A 7-year study of 77,659 people found that those who followed a vegetarian diet had a 22% lower risk of colorectal cancer compared to non-vegetarians. Pescatarians had a 43% lower risk, while lacto-ovo-vegetarians, vegans, and flexitarians had an 18%, 16%, and 8% lower risk, respectively.

The reasons for the reduced risk are likely due to the high fiber and low red and processed meat intake of vegetarian diets. Pescatarian diets, in particular, may offer the most protection because of the inclusion of fish, which has been linked to a reduced risk of rectal cancer.

High nitrate intake increases the risk of colorectal cancer

Nitrate and nitrite are nitrogen-oxygen chemical units that are found in certain foods, especially green, leafy, and root vegetables, and processed meats. They are also used in food processing to reduce microbial spoilage and preserve meat products. When ingested, they react with amines and amides to form N-nitroso compounds (NOCs), which are known to cause cancer in animals and may cause cancer in humans.

A study on the association between dietary nitrate and nitrite intake and the risk of colorectal cancer in the Shanghai Women's Health Study found that high dietary nitrate intake among subgroups expected to have high exposure to endogenously-formed NOCs increases the risk of colorectal cancer. The study involved 73,118 women aged 40 to 70 residing in Shanghai, China. The study found that the median daily intake of dietary nitrate and nitrite was 300.7 mg/day and 1.4 mg/day, respectively.

The study's findings suggest that high nitrate intake among subgroups expected to have high endogenous NOC exposure, e.g. women with low vitamin C intake, are associated with an increased risk of colorectal cancer. Vitamin C is an antioxidant known to inhibit endogenous formation of NOCs, which are compounds that have demonstrated carcinogenicity in animal studies.

Another study, the Adventist Health Study 2 (AHS-2), which included 77,659 Seventh-Day Adventist men and women, found that vegetarian dietary patterns were associated with an overall lower incidence of colorectal cancers. Pescovegetarians in particular had a much lower risk compared with nonvegetarians.

A meta-analysis of 41 articles with 13 different cancer sites found that high nitrate intake was associated with an increased risk of thyroid cancer. When pooling all intake categories and comparing against the lowest category, higher nitrite intake was associated with an increased risk of glioma.

High dietary nitrate intake, especially among subgroups with high exposure to endogenously-formed NOCs, increases the risk of colorectal cancer.

Vegetarians have a lower risk of all cancers combined

Vegetarians and vegans have a lower risk of all cancers combined. This is because they do not eat meat and have a higher intake of plant foods, which are associated with a lower cancer risk.

Research

Research by the World Cancer Research Fund International found that diets rich in plant foods such as fruit, vegetables, and whole grains are associated with a lower cancer risk. On the other hand, eating red and processed meat increases the risk of colorectal cancer and may increase the risk of other cancers.

The EPIC-Oxford study found that vegetarians had a lower cancer rate than non-vegetarians. The Adventist Health Study-2 (AHS-2) also found that vegetarians may have a lower risk of developing cancer (all types combined) in comparison to meat-eaters.

Vegetarians and Cancer Risk Factors

Vegetarians and vegans have a lower body mass index (BMI) compared to meat-eaters. This is important because obesity is a known risk factor for several cancer sites.

Vegetarians and vegans also tend to have lower alcohol consumption and are less likely to smoke, which are also risk factors for cancer.

Limitations

It is important to note that vegetarian diets may be generally low in some important nutrients, and it is not yet known if this may increase the risk of some cancers.

Additionally, most studies on the link between vegetarian diets and cancer risk have been based on populations with Western-style diets, so further research is needed to determine if the results apply to other populations.

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