How diet impacts your colorectal cancer risk

If you're under a certain age, you might not give too much thought to things like heart disease and Alzheimer's — or colorectal cancer. After all, you might be too busy dealing with a toddler or your upcoming presentation at work to worry about diseases that seem like an issue for Future You. But the timeline for colorectal cancer, which affects the colon or rectum, has started to creep up over the past few decades, and it’s no longer a far-off concern. By 2030, it's projected to be the leading cause of cancer related death for people between 20 and 49 years old.

And while that's an alarming stat, the good news is that the rise in cases is closely linked to lifestyle habits —like the food you eat and how often you work out — which are factors under your control. Here, we take a closer look at how nutrition and exercise impact your early-onset colorectal cancer risk, and what you can do to reduce your risk now and later.

How diet affects your colorectal health

There’s a lot going on in your gastrointestinal tract — including millions of interactions between the food you eat, intestinal cells, bacteria, and enzymes. Because of that, "pinpointing a single cause for something as complex as cancer is nearly impossible, but we do have some knowledge that helps guide us," says Dr. Ragavan Siddharthan, M.D., a board-certified colorectal surgeon who researches early-onset colorectal cancer at the Fred Hutchinson Cancer Center at the University of Washington Medical Center. "Large population studies have shown a strong association between chronic inflammation, gut microbiome dysbiosis, and abnormal cell turnover — factors that can contribute to the development of cancer.”

One of the biggest culprits behind all three is the Western diet, which tends to be low in fiber, high in added sugar, and high in saturated fat. It also includes lots of ultra-processed foods, which are those that have undergone so much processing that they don’t resemble whole foods whatsoever (think candy, breakfast cereal, and hot dogs, to name a few).

But how exactly do these foods lead to cancer? For one, it seems that when they’re broken down, the components tend to activate the immune system — although experts aren't exactly sure how or why it happens. "However, we do know that people who consume a Western diet tend to have higher levels of inflammatory markers compared to those who follow other dietary patterns," says Siddharthan.

On top of that, Western diets also impact both the gut microbiome and contribute to obesity, both of which are risk factors for cancer. "Although our understanding of the microbiome is still in its early stages, evidence shows that an overgrowth of certain bacteria can lead to dysbiosis — a disrupted microbial balance associated with conditions like colitis and colorectal cancer,” says Siddharthan. He points to ultra-processed foods in particular as one link between your diet, poor gut health, and the higher risk of colorectal cancer (though more research is needed in this area).

Why colorectal cancer is showing up earlier and earlier

You can’t really isolate a single cause for colorectal cancer’s rise — and the same goes for its rise among young people. Many factors “have changed over time that could contribute to an earlier onset,” says Mary Playdon, Ph.D., a nutritional and cancer epidemiologist at the University of Utah. These include, but are not limited to, higher rates of sedentary lifestyle and obesity, higher red meat and alcohol intake, and lower fiber intake, she adds.

"Some studies that have looked at this question have shown major differences in fiber intake for early versus later onset colorectal cancer," she explains, pointing to one in particular that found that low fiber intake was more strongly linked to cancer in the rectum rather than the colon. Supporting that, new research has also found a strong link between childhood exposure to colibactin — a bacterial toxin — and colon cancer cases in people under 40. Colibactin is naturally produced by certain gut bacteria that many people have, but researchers think that a Western diet may fuel overgrowth of this bacteria — leading to more colibactin.

Still, the research for early-onset colorectal cancer is very much a work in progress. “Most epidemiological studies enrolled participants over age 50 years, so it has been difficult to study this question,” says Playdon. “However, some groups looked at lifestyle risk factors for colorectal adenomas, or benign tumors, and reinforced that unhealthy or Western-style dietary patterns are linked to higher risk of early-onset adenomas.”

What you can do to reduce your risk

Like any other disease, there are risk factors that are out of of control when it comes to colorectal cancer — including sex at birth and racial or ethnic background. But there are also many lifestyle-related risk factors that are addressable, according to Siddharthan, beginning with diet.

It also helps to take a holistic approach to your health by reducing your weight if you’re living with overweight or obesity. “Obesity rates are directly correlated with colon cancer rates,” says Siddharthan. “Obesity and the lack of physical activity puts your body in a pro-inflammatory state that affects cell turnover.” That can pave the way for cell mutations that ultimately result in early-onset colorectal cancer. With that, here are science-backed ways to reduce your risk.

Stick with a fiber-rich, anti-inflammatory diet

Fiber is one of the best macronutrients you can eat — full stop. “First, it can quicken transit time for stool, so the gut may have less time to be exposed to carcinogens in the diet,” says Playdon. “Second, fiber feeds healthy gut bacteria, which are linked to lower cancer risk by producing short-chain fatty acids that are anti-inflammatory.” It also seems to play a role in metabolizing bile acid, which can influence your cancer risk, she says.

Together, these can counteract some of the biggest contributors to colorectal cancer, like an unhealthy gut microbiome and obesity. And the benefits of fiber are more than the sum of its parts: A meta analysis found that eating lots of dietary fiber — the recommendation in the US is 25 grams per day for women and 38 grams for men — not only lowers your risk of colorectal cancer, but also that of breast cancer, pancreatic cancer, stomach cancer, and more. It's also something you can easily track (along with other nutrients) using the WeightWatchers app.

Loading up on fiber works best if you pair it with diets that lower inflammation and insulin. These eating styles usually consist of “green, leafy and red or orange vegetables, whole grains, and fatty fish — but also coffee and tea,” Playdon says; conversely, they’re also low in high-fat red or processed meat (like cold cuts) and sugar-sweetened drinks.

Reduce intake of high-fat red meat and ultra-processed food

Two commonly consumed foods in the Western diet are high-fat red meats and ultra-processed foods. One large study of more than 12,000 colorectal cancer patients found that red and processed meat were closely associated with colorectal cancer. While the International Agency for Research on Cancer has classified red meat as "probably carcinogenic" based on studies like this, it’s important to remember the “probably carcinogenic” label is given to foods that have limited research in humans.

Ultra-processed foods are similar, with one study finding that the more of these you eat, the higher your risk of colorectal cancer, especially in men. (In particular, ready-to-eat meat products, like chicken nuggets and fish sticks, and sugary drinks increased risk.) Although — again — more research is needed in this area, what we do know is that focusing on an anti-inflammatory diet rich in fruits, veggies, and fish can help, as can a weight-loss program like WeightWatchers. In fact, in a recent study conducted in partnership with Georgia Southern University, people on WeightWatchers ate 22% fewer calories from ultra-processed foods over the course of six months compared to those who followed standard nutritional guidance. They also reduced their calorie intake from ultra-processed foods by almost a third.*

Stick with your workout regimen

Turns out, exercise is one of the best things you can do to lower your colorectal cancer risk — and it doesn’t have to be an extended gym session five times a week. A new study just found that colon cancer survivors who exercised (with brisk walking for 45 minutes four days a week for three years) — lowered their risk of cancer recurrence or new cancer by 28%. It doesn't cost anything, has no side effects, and is easy for most people to do — making it one of the simplest lifestyle tweaks out there.

Just as compelling: Research has found that while a pro-inflammatory diet is a major factor in colorectal-cancer risk, physical activity actually seems to reduce it. That doesn't mean that running a 5K after a double cheeseburger will offset its effects, but it does indicate that exercise is incredibly powerful when it comes to your colorectal health.