Colorectal cancers are the second-deadliest kind in the United States.
Much progress has been made on screening – mostly via colonoscopies.
But much remains to be done to reduce Americans’ lifestyle-related risks for colorectal cancer.
Current evidence suggests that diets high in processed red meats (e.g., cold cuts and hot dogs) raise the risk ... as do physical inactivity, obesity, smoking, and heavy alcohol use.
In contrast, diets high in vegetables, fruits, and whole grains are linked to a lower risk for colorectal cancers.
Diets rich in omega-3 fatty acids from seafood have also been linked (albeit inconsistently) to lower risk for colorectal cancer and/or reduced tumor growth.
However, that link weakens when a study population’s diet is – like most American’s diets – overloaded with omega-6 fatty acids from cheap vegetable oils (i.e., corn, soy, safflower, sunflower, cottonseed) … and the many processed and prepared foods that abound in them.
There are three main reasons for this:
- When consumed in excess, omega-6 fatty acids blunt the positive effects of dietary omega-3s.
- Omega-6 fatty acids exert stronger influences on the immune system, versus the same amount of dietary omega-3s.
- When consumed in excess, omega-6 fatty acids from plant foods and oils slash the body's ability to convert plant-source omega-3s (ALA) into the seafood-source forms we actually need (DHA and EPA).
The encouraging evidence about omega-3s comes from epidemiological studies, which cannot prove a cause-effect relationship.
But the positive epidemiological evidence is supported by ample lab evidence showing that omega-3s exert anti-cancer effects in animals and in isolated human cells alike.
And the results of a new epidemiological study bolster the idea that fishy diets can help prevent colorectal cancers.
Pesco-vegetarian diets linked to lowest colon cancer rates
Most of the media headlines about the recent diet-health study buried the lead.
A majority characterized it this way: "Vegetarian diets linked to lower risk of colorectal cancers”.
That's accurate, and the finding aligns with most prior studies, which – compared with the standard American diet – link vegetarian diets to better health and longer lives.
But the key revelation was that people eating "pesco-vegetarian” diets – fish and plant foods only, with no meats or dairy – had the lowest colon cancer rates.
In fact, their risk was lower than among people who follow either pure vegan diets (only plant foods) or lacto-ovo versions (plant foods plus milk and eggs).
The new finding makes perfect sense, given the abundant evidence that seafood-source omega-3s beat plant-source omega-3s at promoting optimal heart, immune, and overall health.
Results place pesco-vegetarian diets above vegan diets
The new findings come from California’s Loma Linda University.
This school was founded and is run by Seventh-day Adventists, most of whom follow vegetarian or near-vegetarian diets. And Loma Linda University hosts the biggest medical school and hospital in North America.
Lead author Michael J. Orlich, M.D., Ph.D., and his Loma Linda team analyzed data from 77,659 participants (average age 59 years) in Adventist Health Study-2
… a large, ongoing epidemiological study that looks for links between lifestyle and health.
Compared with the risk among people eating a non-vegetarian diet, the scientists calculated the risks of colorectal cancer among people following any one of four kinds of vegetarian diet (Orlich MJ et al. 2015).
The results fit with much prior epidemiological evidence … and the preponderance of lab evidence concerning omega-3s and cancer:
- Vegans had a 16 percent lower risk.
- Pesco-vegetarians (eat fish) had a 43 percent lower risk.
- Semi-vegetarians (eat some meat) had an 8 percent lower risk.
- Lacto-ovo vegetarians (eat milk and eggs) had an 18 percent lower risk.
The truly striking revelation is that people eating "pesco-vegetarian” diets had the lowest colon cancer rates, by far … lower than the rates seen in vegans or any other kind of vegetarian.
When they combined the data from people who followed any of the four kinds of vegetarian diet, the average vegetarian's risk for colorectal cancers was 22 percent lower than the non-vegetarian’s average risk.
Specifically, the average vegetarian’s risk for colon cancer was 19 percent lower and their average risk for rectal cancer was 29 percent lower, compared with non-vegetarians.
Why would pesco-vegetarian diets reduce risk the most?
As noted above, diets rich in omega-3 fatty acids from seafood have been linked to lower risk for colorectal cancer and/or reduced tumor growth.
And that encouraging evidence is bolstered by lab evidence that omega-3s exert anti-cancer effects in animals and in isolated human cells alike.
The bodies of people who never or rarely eat seafood (such as vegetarians) appear to adapt to this lack by raising the rate at which they convert the sole plant-source omega-3 (ALA) into the seafood-source kinds our bodies actually require (DHA and EPA).
Despite that increased capacity, their immune defenses may be at a disadvantage compared with pesco-vegetarians … whose fishy diets provide ample amounts of the seafood-type omega-3s actually required by the immune system.
Vegetarians who follow their diet for health reasons may want to reconsider the wisdom of that decision.
And vegetarians who eat that way to avoid eating animals should consider taking supplemental omega-3 DHA derived from algae.
- Norat T et al. Meat, fish, and colorectal cancer risk: the European Prospective Investigation into cancer and nutrition. J Natl Cancer Inst. 2005 Jun 15;97(12):906-16.
- Orlich MJ, Singh PN, Sabaté J, Fan J, Sveen L, Bennett H, Knutsen SF, Beeson WL, Jaceldo-Siegl K, Butler TL, Herring RP, Fraser GE. 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]
- Orlich MJ, Singh PN, Sabaté J, Jaceldo-Siegl K, Fan J, Knutsen S, Beeson WL, Fraser GE. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA Intern Med. 2013 Jul 8;173(13):1230-8. doi: 10.1001/jamainternmed.2013.6473.
- Pham NM, Mizoue T, Tanaka K, Tsuji I, Tamakoshi A, Matsuo K, Wakai K, Nagata C, Inoue M, Tsugane S, Sasazuki S; Research Group for the Development and Evaluation of Cancer Prevention Strategies in Japan. Fish consumption and colorectal cancer risk: an evaluation based on a systematic review of epidemiologic evidence among the Japanese population. Jpn J Clin Oncol. 2013 Sep;43(9):935-41. doi: 10.1093/jjco/hyt094. Epub 2013 Jul 21. Review.
- Wu S, Feng B, Li K, Zhu X, Liang S, Liu X, Han S, Wang B, Wu K, Miao D, Liang J, Fan D. Fish consumption and colorectal cancer risk in humans: a systematic review and meta-analysis. Am J Med. 2012 Jun;125(6):551-9.e5. doi: 10.1016/j.amjmed.2012.01.022. Epub 2012 Apr 17. Review.