For many Americans, the convenience of precooked and instant meals can make it easy to overlook less-than-ideal nutritional information, but a team led by researchers at Tufts University and Harvard University hopes that will change next of recently discovering a link between high consumption of ultra-processed foods and an increased risk of colorectal cancer.
In a study published Aug. 31 in The BMJ, researchers found that men who consumed high rates of ultra-processed foods had a 29 percent higher risk of developing colorectal cancer, the third most commonly diagnosed cancer in the United States, than men who consumed much smaller amounts. They did not find the same association in women.
We started out thinking that colorectal cancer might be the cancer most affected by diet compared to other types of cancer. Processed meats, most of which fall into the category of ultra-processed foods, are a strong risk factor for colorectal cancer. Ultra-processed foods are also high in added sugars and low in fiber, which contribute to weight gain and obesity, and obesity is an established risk factor for colorectal cancer.”
Lu Wang, lead author of the study and a postdoctoral fellow at the Friedman School of Nutrition Science and Policy at Tufts
The study analyzed the responses of more than 200,000 participants, 159,907 women and 46,341 men, in three large prospective studies that assessed dietary intake and were conducted over more than 25 years. Each participant received a food frequency questionnaire every four years and was asked about the frequency of consumption of about 130 foods.
For the study in BMJ, participants’ ultra-processed food intake was ranked into quintiles, with a value ranging from lowest to highest consumption. Those in the highest quintile were identified as having the highest risk of developing colorectal cancer. While a clear link was identified for men, particularly for cases of colorectal cancer in the distal colon, the study did not find an overall increased risk for women who consumed higher amounts of ultra-processed foods.
The impacts of ultra-processed foods
The analyzes revealed differences in the way men and women consume ultra-processed foods and the potential associated cancer risk. Of the 206,000 participants followed for more than 25 years, the research team documented 1,294 cases of colorectal cancer among men and 1,922 cases among women.
The team found that the strongest association between colorectal cancer and ultra-processed foods among men came from meat, poultry or fish-based and ready-to-eat products. “These products include some processed meats such as sausages, bacon, ham and fishcakes. This is consistent with our hypothesis,” Wang said.
The team also found that higher consumption of sugary drinks, such as soft drinks, fruit drinks and sweetened milk drinks, is associated with a higher risk of colorectal cancer in men.
However, not all ultra-processed foods are equally harmful when it comes to colorectal cancer risk. “We found an inverse association between ultra-processed dairy products such as yogurt and the risk of colorectal cancer among women,” said co-senior author Fang Fang Zhang, a cancer epidemiologist and interim chair of the Division of Nutrition Epidemiology and Friedman School Data Science. .
Overall, there was no link between consumption of ultra-processed foods and risk of colorectal cancer among women. It is possible that the composition of ultra-processed foods consumed by women is different from that of men.
“Foods like yogurt can counteract the harmful impacts of other types of ultra-processed foods in women,” Zhang said.
Mingyang Song, co-senior author of the study and assistant professor of clinical epidemiology and nutrition at the Harvard TH Chan School of Public Health, added that, “Further research is needed to determine whether there is a true sex difference in the associations , or whether the null findings in women in this study were due to chance alone or to other confounding factors not controlled for in women that moderated the association.”
Although ultra-processed foods are often associated with poor diet quality, there could be factors beyond the poor quality of ultra-processed food diet that affect the risk of developing colorectal cancer.
The potential role of food additives in altering gut microbiota, promoting inflammation, and contaminants formed during food processing or migrated from food packaging may promote cancer development, Zhang noted.
Analyzing the data
With a follow-up rate of more than 90% in each of the three studies, the research team had extensive data to process and review.
“Cancer takes years or even decades to develop, and from our epidemiological studies we have shown the potential latency effect; it takes years to see an effect of a certain exposure on cancer risk,” Song said. “Because of this lengthy process, it is important to have long-term exposure to the data to better assess cancer risk.”
The studies included:
- Nurses’ Health Study (1986-2014): 121,700 registered nurses between the ages of 30 and 55
- The Nurses’ Health Study II (1991-2015): 116,429 nurses aged 25 to 42
- The Health Professionals Follow-up Study (1986-2014): 51,529 male health professionals aged 40-75.
After an exclusion process for previous diagnoses or incomplete surveys, the researchers were left with prospective data from 159,907 women from the two NHS studies and 46,341 men.
The team adjusted for potential confounders such as race, family history of cancer, history of endoscopy, hours of physical activity per week, smoking status, total alcohol intake, and total calorie intake, regular aspirin use, and menopausal status.
Zhang is aware that because all of the participants in these studies worked in the healthcare field, the findings for this population may not be the same as the general population, as participants may be more inclined to eat healthier and stay away from ultra-processed foods. The data may also be biased because processing has changed over the past two decades.
“But we’re comparing within this population those who consume higher amounts versus lower amounts,” Zhang said. “So these comparisons are valid.”
Change in dietary patterns
Wang and Zhang previously published a study that identified a trend toward increased consumption of ultra-processed foods in children and adolescents in the United States. Both studies underscore the idea that many different groups of people can depend on ultra-processed foods in their daily diet.
“Much of the reliance on these foods can be put down to factors such as access and convenience of food,” said Zhang, who is also a fellow at the Tufts Institute for Global Obesity Research. “Chemically processed foods can help extend lifespan, but many processed foods are less healthy than unprocessed alternatives. We need to make consumers aware of the risks associated with consuming unhealthy foods in quantity and make healthier options are easier to choose.”
Wang knows that change won’t happen overnight and hopes that this study, among others, will contribute to changes in dietary regulations and recommendations.
“Long-term change will require a multi-step approach,” Wang added. “Researchers continue to examine how nutrition-related policies, dietary recommendations, and prescription and formula changes, along with other healthy lifestyle habits, can improve overall health and reduce the burden of cancer. It will be important for us to continue studying the link between cancer and diet, as well as possible interventions to improve outcomes.
Source:
Journal reference:
Wang, L. et al. (2022) Association of ultra-processed food consumption with risk of colorectal cancer among men and women: results from three prospective US cohort studies. BMJ. doi.org/10.1136/bmj-2021-068921.