Study Shows Benefit of Vegetarian Diet in Helping Protect against Colorectal Cancer

by | Dec 30, 2015 | 2015, Cancer, Colorectal (Colon), Vegetarianism

Written by Greg Arnold, DC, CSCS. Analyzed data on 77,659 participants in The Adventist Health Study 2 revealed that when compared to non-vegetarians, all those in the vegetarian groups had a 19% borderline statistically significant reduced risk of colon cancer and a 22 % non-statistically significant reduced risk of colorectal cancers.

In a 2015 study (1), researchers analyzed data on 77,659 participants in The Adventist Health Study 2 (2) where participants completed a validated quantitative food frequency questionnaire (3) and were categorized into 4 vegetarian dietary patterns:

  • Vegans consumed eggs/dairy, fish, and all other meats less than 1 time/month
  • Lacto-ovo vegetarians consumed eggs/dairy 1 or more time/month but fish and all other meats less than 1 time/month
  • Pescovegetarians consumed fish 1 or more times/month but all other meats less than 1 time/month
  • Semivegetarians consumed non-fish meats 1 or more times/month and all meats combined (fish included) 1 or more times/month but 1 or less time/week
  • Nonvegetarians consumed nonfish meats 1 or more times/month and all meats combined (fish included) more than 1 time/week.

During an average follow-up of 7.3 years, the researchers found that compared to non-vegetarians, all vegetarians combined had a 22% reduced risk of colorectal cancers (p < 0.01), a borderline statistically significant 19% reduced risk of colon cancer (p = 0.053). For rectal cancer, the 29% reduction risk was not statistically significant (p = 0.09).

When specific vegetarian diets were analyzed for colorectal cancer risk, the most significant reductions were seen for pescovegetarians (42% reduced risk, p = 0.004) and a borderline statistically significant 18% reduction for lacto-ovo vegetarians (p = 0.08). A vegan diet was not statistically significant in reducing colorectal cancer risk (p = 0.32), neither was a semivegetarian diet (p = 0.69).

When attempting to explain the significant benefits of the pesco-vegetarian diet, the researchers suggested the benefits may lie in the omega-3 fatty acid intake from fish though current evidence is admittedly “limited and inconsistent” in the literature (4). They concluded that “vegetarian diets are associated with an overall lower incidence of colorectal cancers” and “If such associations are causal, they may be important for primary prevention of colorectal cancers.”

Source: Orlich, Michael J., et al. “Vegetarian dietary patterns and the risk of colorectal cancers.” JAMA internal medicine 175.5 (2015): 767-776.

© 2015 American Medical Association. All rights reserved.

Posted March 23, 2015.

References:

  1. Orlich MJ. Vegetarian Dietary Patterns and the Risk of Colorectal Cancers. JAMA Intern Med 2015 Mar 9. doi: 10.1001/jamainternmed.2015.59. [Epub ahead of print]
  2. Butler TL, Fraser GE, BeesonWL, et al. Cohort profile: the Adventist Health Study-2 (AHS-2). Int J Epidemiol. 2008;37(2):260-265.
  3. Jaceldo-Siegl K, Knutsen SF, Sabate J, et al. Validation of nutrient intake using an FFQ and repeated 24 h recalls in black and white subjects of the Adventist Health Study-2 (AHS-2). Public Health Nutr. 2010;13(6):812-819
  4. Gerber M. Omega-3 fatty acids and cancers: a systematic update review of epidemiological studies. Br J Nutr. 2012;107(S2)(suppl 2):S228-S239.