An "inflammatory diet" may increase a person's risk of colorectal cancer, a new study suggests.
The researchers found that men and women who had a diet high in foods thought to increase levels of inflammation in the body were more likely to develop colorectal cancer during the study period, compared with men and women who had a different type of diet.
Specifically, men who followed an inflammatory diet were 44 percent more likely to develop colorectal cancer, and women who followed an inflammatory diet were 22 percent more likely to develop colorectal cancer, over about two decades, compared with those who had a different type of diet.
The findings suggest that "strategies to reduce the adverse role of a pro-inflammatory diet may reduce colorectal cancer risk," the researchers wrote in the study, published today (Jan. 18) in the journal JAMA Oncology.
Previous studies have suggested that inflammation in the body plays a role in colorectal cancer development. For example, several studies have shown that people who regularly take anti-inflammatory medications, such as aspirin, have a lower risk of developing colorectal cancer, compared with people who don't regularly take these medications.
In addition, the foods people eat can influence levels of inflammation in their bodies, as measured by markers of inflammation in the blood, the researchers said. So it's possible that eating foods linked with higher levels of inflammation in the body could raise colorectal cancer risk. [11 Ways Processed Food Is Different from Real Food]
To examine this link, the researchers analyzed information — gathered from the long-running Health Professionals Follow-Up Study and the Nurses' Health Study — on more than 121,000 men and women who were followed for about 25 years. At the start of the study, women were 30 to 55 years old, and men were 40 to 75 years old. During the study period, about 2,700 participants developed colorectal cancer.
Every four years, participants answered questions about their current diets. The researchers used this information to calculate an "inflammatory score" for participants' diet. Lower scores indicate anti-inflammatory diets, or diets that contain foods linked with low levels of inflammation in the body; and higher scores indicate pro-inflammatory diets, or diets that contain foods linked with high levels of inflammation in the body.
Examples of pro-inflammatory foods include processed meats, refined grains and high-calorie beverages such as soda, according to the study. Examples of anti-inflammatory foods are tea, coffee, dark-yellow vegetables (such as carrots, yellow squash and sweet potatoes) and green leafy vegetables, the researchers said. (Interestingly, pizza was also determined to be an anti-inflammatory food, possibly because tomato paste contains high levels of a compound called lycopene, which has been shown to have anti-inflammatory properties, according to a previous paper by the same group of researchers.)
Participants were then divided into five groups based on the inflammatory scores for their diets. Among men, the rate of colorectal cancer was 113 cases per 100,000 people per year in the group with the lowest score, compared with 151 cases per 100,000 people per year in the group with the highest score. Among women, the rate of colorectal cancer was 80 cases per 100,000 per year in the group with the lowest score, compared with 92 cases per 100,000 people per year in the group with the highest score.
Overall, among both men and women, those with the highest inflammatory scores were 32 percent more likely to develop colorectal cancer over the study period, compared with those who had the lowest inflammatory scores.
The findings held even after the researchers took into account factors that could affect the risk of colorectal cancer, including age, a family history of cancer, alcohol intake, physical activity, smoking and regular aspirin use.
Still, the researchers noted that there may be other factors that influence colorectal cancer risk that the study was not able to take into account, such as a person's levels of the hormone insulin. What's more, the study did not prove cause and effect; instead, it found an association between an inflammatory diet and colorectal cancer risk.
This isn't the first study to link an inflammatory diet to cancer. Last year, a separate group of researchers found that women who had an inflammatory diet as teenagers were at greater risk of breast cancer as adults, compared with women who had anti-inflammatory diets as teenagers.
Original article on Live Science.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.