What we eat may play a role in whether we develop cancer
Something quiet and cumulative is happening inside the bodies of younger Americans, and a new study suggests the everyday food supply may be partly to blame. Research tracking more than 29,000 female nurses over 13 years found that those eating around 10 daily servings of ultraprocessed foods faced a 45 percent greater risk of developing precancerous colorectal growths before age 50 — a finding that lands against a backdrop of steadily rising early-onset colorectal cancers worldwide. The study does not establish direct causation, but it adds weight to a growing body of evidence suggesting that the industrialized diet, now comprising 70 percent of the American food supply, is reshaping human health in ways medicine is only beginning to measure.
- Colorectal cancer is striking younger people at rising rates, and researchers are urgently searching for the dietary patterns driving this generational shift.
- Women eating roughly 10 daily servings of ultraprocessed foods — breads, condiments, sweetened drinks — showed a 45% higher risk of precancerous polyps compared to those eating far less.
- Ultraprocessed foods now make up 70% of the US food supply and 60% of adult calories, flooding daily life with additives, refined grains, and engineered ingredients that may disrupt gut bacteria and fuel chronic inflammation.
- Scientists caution the link is associative, not yet causal, and note that study limitations — including dietary recall and changing food formulations — leave key mechanisms still unresolved.
- Doctors are urging colorectal screening starting at age 45, earlier for those with family history, while prevention researchers point toward whole foods, ingredient-label awareness, and reduced ultraprocessed consumption as actionable steps now.
Colorectal cancer is getting younger, and researchers are asking why. A new study published in JAMA Oncology followed more than 29,100 female nurses for 13 years, tracking their diets and watching for the development of adenomas — precancerous polyps that can turn malignant over time. The result was striking: women who ate roughly 10 daily servings of ultraprocessed foods had a 45 percent higher risk of developing these growths by age 50 compared to those eating just over three servings. The main culprits were familiar: mass-produced breads and cereals, bottled sauces and condiments, and sweetened beverages.
Ultraprocessed foods now account for about 70 percent of the American food supply and nearly 60 percent of adult calories. Engineered with preservatives, emulsifiers, and flavor enhancers, they tend to be low in fiber and high in sugar, sodium, and unhealthy fats. This study is the first to specifically examine the link between ultraprocessed consumption and precancerous adenomas in younger people — and even after accounting for obesity, diabetes, and low fiber intake, the association held.
The study's senior author, Dr. Andrew Chan of Mass General Brigham, was careful to note the findings are not proof of direct causation. The likely mechanisms are multiple: disruption of protective gut bacteria, chronic inflammation, toxic byproducts of digestion, and obesity itself — all of which ultraprocessed foods may promote. The study also carries limitations, including reliance on dietary recall and the fact that food formulations have changed considerably since the research began in the 1990s.
Prevention researchers like Dr. David Katz recommend building meals from whole foods — vegetables, fruits, whole grains, beans, nuts, and water — and reading ingredient labels carefully. Whole foods tend to satisfy more naturally than ultraprocessed ones, which are designed to keep people eating. For those worried about risk, screening beginning at age 45 is now recommended, or earlier for those with a family history. Precancerous adenomas rarely cause symptoms until they grow large, making early detection essential. The broader message is becoming harder to ignore: the food choices made daily are quietly shaping long-term health outcomes.
Colorectal cancer is getting younger. Over the past few decades, doctors have watched cases climb steadily among people in their thirties, forties, and fifties—a shift that has alarmed the medical community and prompted researchers to ask why. A new study published Thursday in JAMA Oncology points to a culprit many suspected: the food most Americans eat every day.
The research followed more than 29,100 female nurses for a median of 13 years, tracking their diets and monitoring for the development of adenomas—noncancerous polyps in the colon and rectum that can become malignant over time. The finding was stark: women who consumed roughly 10 servings of ultraprocessed foods daily had a 45 percent higher risk of developing these precancerous growths by age 50 compared to those eating just over three servings daily. The ultraprocessed foods driving the risk were familiar staples: mass-produced breads and breakfast cereals, bottled sauces and condiments, and sugary or artificially sweetened drinks.
Ultraprocessed foods now account for roughly 70 percent of the American food supply and nearly 60 percent of the calories adults consume. These products are engineered in industrial facilities using techniques and ingredients rarely found in home kitchens—preservatives to extend shelf life, emulsifiers to prevent separation, flavor enhancers, and dozens of other additives designed to make food more appealing and profitable. They tend to be low in fiber and high in added sugars, refined grains, sodium, and unhealthy fats. The connection between this diet and rising colorectal cancer rates has been building for years, but this is the first study to specifically examine the link between ultraprocessed food consumption and precancerous adenomas in younger people.
Dr. Andrew Chan, a gastroenterologist at Mass General Brigham Cancer Institute in Boston and senior author of the study, was careful about the limits of his findings. "Our study isn't cause and effect," he said, "so we can't say that this is definitive." But the evidence points in a direction worth taking seriously. Even after accounting for other known risk factors—obesity, type 2 diabetes, low fiber intake, body mass index—the association between ultraprocessed foods and adenoma risk held firm. The mechanism likely involves multiple pathways: these foods may alter the protective bacteria in the gut, trigger chronic inflammation, or produce toxic molecules during digestion. Obesity itself, which ultraprocessed foods promote, is an independent risk factor for colorectal cancer.
The study has limitations. Participants recalled their diets every four years, relying on memory that may not be perfectly accurate. The tumors were mostly discovered before 2015, before screening guidelines shifted to age 45, meaning many of the women screened may have had additional risk factors. And the ultraprocessed foods of the 1990s, when the study began, were not identical to today's products—formulations have changed, new additives have been introduced, and the proportion of ultraprocessed foods in the diet has only grown. One consistent thread, though, has been the widespread use of omega-6-rich seed oils, which some researchers believe may be a key driver of early-onset colorectal cancer.
Dr. David Katz, founder of the True Health Initiative and a prevention researcher at Yale, offered straightforward advice: avoid ultraprocessed foods where possible and build meals from whole foods as close to nature as they come. The best diets, he noted, consist mostly of vegetables, fruits, whole grains, beans, nuts, seeds, and plain water. Reading ingredient labels and paying attention to sodium content can help. Whole foods tend to be more satisfying than ultraprocessed ones, which are engineered to keep people wanting more.
For those concerned about colorectal cancer risk, screening matters. Dr. Robin Mendelsohn, codirector of the Center for Young Onset Colorectal and Gastrointestinal Cancers at Memorial Sloan Kettering Cancer Center in New York, recommends screening beginning at age 45, or earlier for those with a family history of the disease. Precancerous adenomas usually cause no symptoms, but when they grow large enough, they can produce dark or bloody stools, pain, iron-deficiency anemia, unexplained weight loss, or constipation. The earlier these growths are found, the more effectively they can be treated. As colorectal cancer continues to rise in younger populations, the message is becoming clearer: what we eat shapes our risk, and the choices we make now may determine whether we develop disease later.
Notable Quotes
Our study isn't cause and effect, so we can't say that this is definitive. But it does serve as some clues that what we eat may play a role.— Dr. Andrew Chan, gastroenterologist at Mass General Brigham Cancer Institute
To the extent possible, you should try to avoid ultraprocessed foods and build your diet out of real, whole foods, as direct from nature and minimally processed as possible.— Dr. David Katz, founder of the True Health Initiative
The Hearth Conversation Another angle on the story
Why does this study matter now, when we've known for years that diet affects cancer risk?
Because colorectal cancer is getting younger, and we're finally asking why. This study is the first to connect ultraprocessed foods specifically to precancerous polyps in younger people. That's the piece that was missing.
The 45 percent increase sounds significant, but how do we know it's not just correlation?
We don't, and the researchers are honest about that. But they controlled for obesity, diabetes, fiber intake—all the other things we know matter. The association held up anyway. That suggests something real is happening, even if we don't yet know exactly what.
What's actually in these foods that causes the problem?
That's the harder question. It could be the additives, the seed oils, the lack of fiber, the way they alter gut bacteria, or some combination. The foods are engineered to be hyper-palatable and profitable, not to keep us healthy. The study hints at the mechanism but doesn't prove it.
If I eat one ultraprocessed meal a day instead of ten servings, am I safe?
The study doesn't tell us where the threshold is. It compared the highest intake to the lowest. The real answer is probably that less is better, but we don't know if there's a safe level or if the risk drops linearly as you eat fewer of these foods.
Why were all the study participants nurses?
That's actually a strength in some ways—nurses are more likely to accurately report what they eat than the general population. But it also means the findings may not apply equally to everyone. The study was designed to follow women, so we don't know if men face the same risk.
What should someone actually do with this information?
Start reading labels. Notice how much sodium and added sugar you're consuming. Shift toward whole foods when you can. Get screened at 45 if you haven't already. And understand that this isn't about perfection—it's about reducing your intake of foods engineered to be addictive and unhealthy.