From The Wall Street Journal, Posted March 10, 2015
TO prevent certain types of cancer, a vegetarian diet with some fish might be the best protection, according to a new study.
The study, published online in the Journal of the American Medical Association, found that fish-eating vegetarians, or pescovegetarians, had a 43 per cent lower risk of colorectal cancers than nonvegetarians.
This beat out the results for vegans, who had a 16 per cent lower risk, and lacto-ovo vegetarians, who eat milk and eggs and who had an 18 per cent lower chance. Combined, all types of vegetarians had a 22 per cent reduced risk for colorectal cancers than nonvegetarians.
According to the researchers, the additional benefit from fish probably comes from omega-3 fatty acids. However, they note that even the nonvegetarian group in the study consumed less meat than the average American.
Colorectal cancer is the second most deadly cancer in the US, after lung cancer, and previous studies have suggested that meat-heavy diets, especially processed meat, can elevate risk for the condition.
This latest research is led by Michael Orlich, an assistant professor of preventive medicine at Loma Linda University, a Seventh-day Adventist institution in California.
Dr Orlich’s team tracked the food questionnaires and medical records of 77,659 Seventh-day Adventists over a mean period of 7.3 years. Seventh-day Adventists were chosen in part because the religion encourages a healthy lifestyle. Previous studies on the population found that their diet is associated with lower rates of obesity, diabetes and high blood pressure.
“There’s a history going back to the 1950s of studies on Seventh-day Adventists, and most have found that they’re healthy, long-lived populations, so it’s interesting to probe and see why,” says Dr Orlich.
The researchers sent detailed food questionnaires and follow-up surveys every other year. They sorted the participants into categories based on their reported food intake, rather than simply asking them if they were vegetarian. Among the participants, 52 per cent were vegetarians of various types, including 29 per cent lacto-ovo vegetarians, 10 per cent pescovegetarians and 8 per cent vegans.
Overall, the team found 380 cases of colon cancer and 110 cases of rectal cancer. The study participants had 34 per cent fewer cases of colorectal cancers than would a representative group from the US population at large, Dr Orlich says.
The various groups did have some lifestyle differences beyond diet. Vegetarians, for example, were usually older than nonvegetarians and were more likely to exercise, while vegans consumed less calcium. However, the benefits of the vegetarian diet still persisted after the researchers controlled for several of these factors, including exercise, alcohol consumption, smoking history and family history of colorectal cancer.
Dr Orlich says he hopes future research can look at more details of different types of vegetarians and follow up for a longer period.
According to the researchers, vegetarians might be protected from colorectal cancer not only because they eat less meat, but because they eat more plants. “Diets high in fiber are linked with decreased risk, and fiber comes from whole plant foods, so this could be a major reason why the risk is much lower,” said Dr Orlich.
The vegetarian groups also ate fewer fatty foods and snacks in general than the nonvegetarians. This helps reduce excess levels of insulin in the blood, which has been linked to elevated risk for colorectal cancers.
The benefits of eating fish are more difficult to interpret, since the pescovegetarians ate about as much fish as did the nonvegetarians, Dr Orlich says. Pescovegetarians’ extra protection against cancer may not be only from the fish itself, but perhaps from a combination of fish and increased consumption of plants, he says.