A study of colorectal cancer survivors shows those who consume higher amounts of red and processed meats before a colorectal cancer diagnosis are at higher risk of death from any cause compared to those who eat less of both types of meat.
Previous studies have linked red and processed meat with a higher risk for developing colorectal cancer. The current study, published in the Journal of Clinical Oncology, now shows that those who are diagnosed with colorectal cancer who ate less red and processed meat before their diagnoses, could live longer compared to those who consume higher quantities of these types of protein on a weekly basis.
“The association between red and processed meat and overall mortality was driven by prediagnostic intake. This underscores the importance of a lifelong healthy diet,” said Marjorie McCullough, nutritional epidemiologist at the American Cancer Society and lead author of the study.
Still, more studies are needed to understand how meat in the diet relates to outcomes after a colorectal cancer diagnosis including cancer recurrence and survival.
The study analyzed 2,315 colorectal cancer survivors (1,282 men and 1,033 women) from the American Cancer Society’s Cancer Prevention Study II (CPS-II) Nutrition Cohort. Patients included in this analysis had non-metastatic colorectal cancer, either localized or regional colon or rectal cancer. The average age at colorectal cancer diagnosis was 73 years of age. During the analysis, 966 patients with colorectal cancer died during an average 7.5-year follow-up period.
Those participants who were frequent meat eaters were more likely to be smokers, to drink more alcohol, to be overweight, have less education, and a less healthy overall diet compared to those who consumed less meat. Those with the highest red and processed meat consumption had an average of 10.4 servings per week while the lowest meat consumption quartile had an average of 1.5 servings per week.
Consuming the highest amounts of red and processed meat reported in the study compared with the least prior to a cancer diagnosis was associated with a 29% higher relative risk of death from any cause and a 63% higher relative risk of death from cardiovascular disease. The association with cardiovascular disease was not statistically significant, however. The analysis specifically accounted for age, disease stage, body mass index, and other factors when comparing participants.
The study found that those who continued to consume a high amount of red and processed meat after their cancer diagnosis had a 79% higher risk of death from their colorectal cancer compared to those who continued to consume below average amounts of red and processed meat. However, the study did not find a link between consumption of meat before cancer diagnosis and death from colorectal cancer.
The results were not surprising, according to McCullough. “Our findings are consistent with other studies showing that a diet low in red and processed meats is good for many reasons, including lowering the risk of colorectal cancer, heart disease, diabetes, and overall mortality.”
While the study had detailed diet, lifestyle, and medical information for all participants, there were limitations on the types of treatments the subjects received for their cancer.
The results did not show that exposure to red and processed meat after a colorectal cancer diagnosis affects the path of the disease, said Jeffrey A. Meyerhardt, MD, clinical director of the Gastrointestinal Cancer Center at the Dana-Farber Cancer Institute in Boston, in his editorial on the study. Meyerhardt postulates that recurrence of colorectal cancer is related to micrometastases, which may be less influenced by the carcinogenic effects of a red and processed meat diet than new primary tumors. Various epidemiological studies in the United States and in other countries have shown that eating more red and processed meats increases colorectal cancer risk. This link is convincing according to expert panels for the World Cancer Research Fund and the American Institute of Cancer Research, said McCullough.
Potential hypotheses for how red and processed meat can contribute to carcinogenesis have to do with consumption of carcinogens that are formed during digestion and also when the meat is cooked at high heat.
But, the link between diet and cancer outcomes and risk of cancer recurrence for cancer survivors is still not well understood. Red meat consumption may promote inflammation and micrometastasis.
“We know too little about the role of diet in cancer survivorship,” said McCullough. “For the most part, dietary recommendations for survivors are based on studies of cancer prevention, so this is an important area that deserves more attention.”
According to Meyerhardt, future studies need to better address whether those patients with colorectal cancer who consumed high amounts of red meat before their diagnosis could minimize their chance of recurrence by lowering their meat consumption. The author highlights that the available data on diet and colorectal cancer are from observational studies that have potential biases. Yet randomized trials are also challenging because it is difficult to demonstrate statistical significance.
Meyerhardt and McCullough agree on a link between diet and cancer prevention. “Although a message that prediagnosis diet influences outcomes may seem to have limited utility for a patient when they develop cancer, it furthers the strength of the recommendation for people to maintain a healthy diet and lifestyle throughout their life to maximize the health benefits.”
McCullough said that more studies are needed to understand the relationship between the timing of diet and survival after a cancer diagnosis. “However, our results suggest that long-term diet matters.”