For many Americans, the convenience of
pre-cooked and instant meals may make it easy to overlook the less-than-ideal
nutritional information, but a team led by researchers at Tufts University and
Harvard University hope that will change after recently discovering a link
between the 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
were at 29% higher risk for developing colorectal cancer — the third most
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 could be the cancer most impacted by diet compared to other cancer
types,” said Lu Wang, the study’s lead author and a postdoctoral fellow at the
Friedman School of Nutrition Science and Policy at Tufts. “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.”
The study analyzed responses from over
200,000 participants — 159,907 women and 46,341 men — across three large
prospective studies which assessed dietary intake and were conducted over more
than 25 years. Each participant was provided with a food frequency
questionnaire every four years and asked about the frequency of consumption of
roughly 130 foods.
For the study in BMJ, participants’ intake
of ultra-processed foods was then classified into quintiles, ranging in value
from the lowest consumption to the highest. Those in the highest quintile were
identified as being the most at risk for developing colorectal cancer. Although
there was a clear link identified for men, particularly in 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 analyses revealed differences in the
ways that men and women consume ultra-processed foods and the prospective
associated cancer risk. Out 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 the strongest association
between colorectal cancer and ultra-processed foods among men come from the
meat, poultry, or fish-based, ready-to-eat products. “These products include
some processed meats like sausages, bacon, ham, and fish cakes. This is
consistent with our hypothesis,” Wang said.
The team also found higher consumption
of sugar-sweetened beverages, like soda, fruit-based beverages, and sugary
milk-based beverages, is associated with an increased risk of colorectal cancer
in men.
However, not all ultra-processed foods
are equally harmful with regard to colorectal cancer risk. “We found an inverse
association between ultra-processed dairy foods like yogurt and colorectal
cancer risk among women,” said co-senior author Fang Fang Zhang, a cancer
epidemiologist and interim chair of the Division of Nutrition Epidemiology and
Data Science at the Friedman School.
Overall, there was not a link between
ultra-processed food consumption and colorectal cancer risk among women. It’s
possible that the composition of the ultra-processed foods consumed by women
could be different than that from men.
“Foods like yogurt can potentially
counteract the harmful impacts of other types of ultra-processed foods in
women,” Zhang said.
Mingyang Song, co-senior author on the
study and assistant professor of clinical epidemiology and nutrition at the
Harvard T.H. Chan School of Public Health, added that, “Further research will
need to determine whether there is a true sex difference in the associations,
or if null findings in women in this study were merely due to chance or some
other uncontrolled confounding factors in women that mitigated the
association.”
Although ultra-processed foods are often
associated with poor diet quality, there could be factors beyond the poor diet
quality of ultra-processed foods that impact 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 all promote cancer
development, Zhang noted.
Analyzing the Data
With more than a 90% follow-up rate from
each of the three studies, the research team had ample 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 for certain exposure on cancer
risk,” said Song. “Because of this lengthy process, it’s important to have
long-term exposure to data to better evaluate cancer risk.”
The studies included:
·
The
Nurses’ Health Study (1986-2014): 121,700 registered female nurses between the
ages of 30 and 55
·
The
Nurses’ Health Study II (1991-2015): 116,429 female nurses between the ages of
25 and 42
·
The
Health Professional Follow-up Study (1986-2014): 51,529 male health
professionals between the ages of 40 and 75.
After an exclusionary process for past
diagnoses or incomplete surveys, the researchers were left with prospective
data from 159,907 women from both NHS studies and 46,341 men.
The team adjusted for potential
confounding factors such as race, family history of cancer, history of
endoscopy, physical activity hours per week, smoking status, total alcohol
intake and total caloric intake, regular aspirin use, and menopausal status.
Zhang is aware that since the
participants in these studies all worked in the healthcare field, the findings
for this population may not be the same as they would be for the general
population, since the participants may be more inclined to eat healthier and
lean away from ultra-processed foods. The data may also be skewed because
processing has changed over the past two decades.
“But we are comparing within that
population those who consume higher amounts versus lower amounts,” Zhang
reassured. “So those comparisons are valid.”
Changing Dietary Patterns
Wang and Zhang previously published a
study that identified a trend in increased ultra-processed food consumption in
U.S. children and adolescents. Both studies underscore the idea that many
different groups of people may be dependent on ultra-processed foods in their
daily diets.
“Much of the dependence on these foods
can come down to factors like food access and convenience,” said Zhang, who is
also a member of the Tufts Institute for Global Obesity Research. “Chemically
processing foods can aid in extending shelf life, 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 the
healthier options easier to choose instead.”
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 recipe and formula changes, coupled with other healthy lifestyle habits, can improve overall health and reduce cancer burden. It will be important for us to continue to study the link between cancer and diet, as well as the potential interventions to improve outcomes.
Source: https://now.tufts.edu/2022/08/31/new-study-links-ultra-processed-foods-and-colorectal-cancer-men
Journal article: https://www.bmj.com/content/378/bmj-2021-068921
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