How Your Diet Influences Your Colorectal Cancer Risk

New York Times

3 days ago

Katie Kennedy had always thought that colorectal cancer primarily affected older men. So she was shocked when, at 48, she was diagnosed with Stage 3 colon cancer.
'It just didn't compute,' especially since she had always been healthy and active, said Ms. Kennedy, now 55, a communications consultant in Westwood, Mass.
There has been an alarming increase in colorectal cancer diagnoses in younger people, and it's now one of the top causes of cancer-related deaths in those under 50. Experts don't know what's causing the uptick, said Dr. Kimmie Ng, an oncologist and the director of the Young-Onset Colorectal Cancer Center at the Dana-Farber Cancer Institute. But at any age, factors like obesity, smoking, alcohol use, a lack of physical activity and a poor diet can increase the risk.
While other types of cancer have been associated with what people eat, colorectal cancer has a particularly strong link, Dr. Ng said. In a 2019 study, researchers estimated that nearly 40 percent of colorectal cancer cases in the United States could be traced back to poor diet.
That may be because food directly contacts 'the insides of our intestines,' Dr. Ng said, and it influences the balance of 'good' and 'bad' microbes in our guts.
Focus on fiber-rich whole foods.
Following a diet that prioritizes fruits, vegetables, whole grains, nuts and legumes can reduce your risk of colorectal cancer, said Dr. Edward Giovannucci, a professor of nutrition and epidemiology at the Harvard T.H. Chan School of Public Health.
Fiber is especially protective, said Dr. Heather Greenlee, a professor of cancer prevention at Fred Hutch Cancer Center in Seattle. You should aim for about 30 grams of fiber per day, she added. (You can get about that much in a day if you eat an apple and a cup each of broccoli, cooked quinoa and cooked lentils.) On average, adults in the United States consume about half as much.
Eating a variety of fiber-rich foods feeds your gut microbes and promotes the growth of more 'good' bacteria, which may outcompete certain 'bad' gut microbes that can produce toxins that damage DNA in the cells lining the colon and rectum.
Ms. Kennedy, who has been cancer free since 2019, was happy to learn that coffee — one of her 'favorite things in life' — was associated with a reduced risk of colorectal cancer. Coffee, tea, fruits and vegetables can be anti-inflammatory and may protect against the development of cancer or its recurrence, Dr. Ng said.
Get enough calcium.
Research suggests that calcium-rich foods like milk, yogurt, tofu and dark leafy greens can reduce your risk. Calcium may attach to certain harmful compounds in the gut, preventing them from damaging cells lining your colon and rectum, Dr. Giovannucci said.
In a study published this year of nearly 500,000 people aged 50 to 71 in the United States, those who consumed the most calcium from food and supplements had a 29 percent lower risk of developing colorectal cancer over more than 20 years than those who consumed the least amount of calcium.
The evidence linking calcium with a decreased risk of colorectal cancer is strongest when it comes from food, especially dairy products, but research suggests that calcium supplements may be similarly protective, Erikka Loftfield Cronin, an epidemiologist at the National Cancer Institute who led the calcium study, wrote in an email.
Experts recommend that most adults get around 1,000 to 1,200 milligrams of calcium per day. (You can get about 400 milligrams from a cup of yogurt or a half cup of tofu.)
Yogurt has the added benefit of containing probiotics, which may prevent certain 'bad' bacteria linked to colorectal cancer from taking up residence in your gut, Dr. Giovannucci said.
Limit alcohol, red and processed meats, and sugary drinks.
Alcohol can increase the risk of colorectal cancer and at least six other types of cancer. According to the American Cancer Society, it's best to not drink alcohol at all; if you do, they suggest limiting your consumption to no more than two drinks a day for men and one drink a day for women.
There's also evidence that regularly consuming processed meats like deli meats, bacon, jerky, sausages and hot dogs, as well as unprocessed red meats like beef, pork and lamb, increases the risk of cancer, especially when charred, smoked or cooked at high temperatures, said Carrie Daniel-MacDougall, a nutritional epidemiologist at MD Anderson Cancer Center in Texas.
According to one recent analysis, diets high in red meats were associated with a 30 percent increase in the risk of colorectal cancer, and those high in processed meats were associated with a 40 percent increase. Avoid processed meats as much as possible, Dr. Daniel-MacDougall said, and limit red meat to one serving per week. Choose fish, poultry, tofu or legumes instead, she said.
Dr. Daniel-MacDougall also suggested cutting back on ultraprocessed foods and drinks such as sugary sodas and most packaged desserts and snacks, which recent studies have linked to poor gut health and a greater risk of developing colorectal cancer. These foods often contain additives that may negatively affect the gut microbiome or the protective lining of the intestines, she said.
Ms. Kennedy now avoids most ultraprocessed foods. Cooking at home — with plenty of fresh vegetables, tofu, fish and yogurt — has become a passion. And she's given up red and processed meats entirely. 'A hamburger smells good on the grill,' she said, but 'the smell does it for me now.'
Diet is important, but it's not everything.
Experts recommend that most people get a colonoscopy or an at-home stool test, which can catch early signs of colorectal cancer and prevent it from developing further, starting at age 45.
For general health, federal officials recommend that adults get at least 150 minutes of moderate-intensity exercise per week, such as walking, jogging, biking or swimming, as well as strength training twice per week. Following that advice can reduce your risk of colorectal cancer, Dr. Greenlee said. A recent study found that physical activity also prevented new or recurring colon cancers in survivors.
Your risk of cancer develops over many years and is influenced by your genetics, too, experts said. There's no guarantee that eating well and exercising will prevent it, but they will likely cut your chances — and reduce your risk of heart disease, Type 2 diabetes and other health conditions, too.
'Everything that's good for colon cancer is actually good for overall health,' Dr. Giovannucci said.