1. Based on date from a large cohort of Seventh-Day Adventist church-goers from the US and Canada, there was a greater number of colorectal cancer cases amongst non-vegetarians compared to vegetarians.
2. Additionally, pesco-vegetarians (those who ate fish but not other meats) had the lowest likelihood of developing colorectal cancer amongst the five different vegetarian groups.
Evidence Rating Level: 2 (Good)
Study Rundown: Colorectal cancer is the second leading cause of cancer deaths in the United States. While screening and treatment for this disease is well studied, primary prevention, namely through modifiable risk factors such as diet, has gained increasing popularity. This study, the data for which was gathered from a cohort consisting for Seventh-Day Adventists, was carried out to determine if a vegetarian diet was associated with colon cancer risk. The results showed that there were a greater number of cases of colorectal cancer amongst non-vegetarians compared to vegetarians. Additionally, pesco-vegetarians (those who ate fish but not other meats) had the lowest likelihood of developing colorectal cancer amongst the five different vegetarian groups.
The strength of the study came from the large number of participants included and a relatively long follow up period. However, given that colon cancer has a long latency period, it is possible that a number of cases were missed. Also, using food frequency questionnaire does add some uncertainty to the data. Lastly, since participants were chosen from one specific church group, there was likely very limited ethnic diversity.
In-Depth [prospective cohort]: This study’s data was based off of the Adventist Health Study 2 (AHS-2) cohort. Participants were recruited from Seventh-Day Adventist Churches from 2002 – 2007 across the US and Canada. While a number of different vegetarian categories were initially defined, investigators ended up combining them and comparing “vegetarians” and “non-vegetarians”, since there were not enough participants within each of the groups. A previously validated food frequency questionnaire was used to determine the dietary patterns. In addition, a large amount of demographic and past medical history data was also gathered.
The mean follow-up period was 7.3 years. The results showed a lower incidence of colorectal cancers amongst vegetarians compared to non-vegetarians (HR 0.78; 95%CI, 0.64-0.95). Vegetarians had a lower risk of colon cancer and rectal cancer when analyzed separately as well (HR 0.78 and 0.81 respectively). Amongst the five different vegetarian diet categories (vegan, lacto-ovo vegetarian, pesco-vegetarian, semi-vegetarian, non-vegetarian), pesco-vegetarians (those who consumed fish, but not other meats) had the lowest risk of developing colorectal cancer (HR 0.57; 95% CI, 0.40-0.82).
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