When Brad McDearman, 60, an urban economics researcher for the Brookings Institution who lives in Baltimore, was treated for metastatic colorectal cancer in 2018, he was eager to adopt the best diet to reduce the risk of his cancer progressing.

And he knew what that meant: a plant-based diet with lots of high-fiber whole grains, vegetables, fruits (including avocados), beans and lentils, nuts and seeds, modest amounts of fish, lean chicken and dairy foods, little or no red meat (especially cured meats), few processed foods and no more than two alcoholic drinks a day. Research by the American Institute of Cancer Research (AICR) shows that people with colorectal cancer who adhere to this dietary pattern after diagnosis are more likely to survive.

But he just couldn’t do it. And his nutritionist advised him not to try just yet.

“I had just had surgery—they removed a foot of my colon, and I had a temporary ostomy bag,” McDearman explains. (An ostomy procedure reroutes waste from the colon into a pouch, or bag, outside the body, often only until the colon is completely healed from surgery.) He couldn’t digest high-fiber foods, including those healthy fruits, vegetables and whole grains. “Once you have a foot of your colon taken out, your literally must relearn how to eat.” His oncology-trained nutritionist, Mary-Eve Brown, RDN, CSO, at the Johns Hopkins Hospital in Baltimore, suggested he start with easy-to-digest low-fiber foods, such as bananas, applesauce and toast. (RDN is a registered dietician nutritionist, also known as a RD, or registered dietician; CSO stands for a certified specialist in oncology nutrition.) “Mary-Eve likened it to a toddler—you wouldn’t feed a toddler high-fiber complex foods, but rather light, easy to digest mashed-up foods. She helped me stick to that diet, gave me new ideas, like protein shakes. Eventually, I started introducing [other] foods in small doses—nuts, berries, raw vegetables. She would suggest foods and let me know where in my ZIP code I could buy them.”  That transition took about a year.

Chemotherapy created additional obstacles. “Some foods just don’t taste good—when I tried to eat spinach, it made me sick—and it’s hard to eat when you’re nauseous,” he recalls. You lose your appetite.  When you’re on chemo, it’s hard to make yourself eat.” Brown suggested that he try—just a little. “‘The more you eat, the more you will want to eat,’ she told me,” he says. “That was really good advice.” He’s still on chemo as maintenance therapy, he adds, which creates “ongoing issues that I still deal with.” When he was having trouble eating because of side effects, Brown suggested healthier foods to manage his issues. For calories, he ate avocados, full of “good fats,” rather than processed foods. Instead of common protein replacement drinks, she recommended ones that were easy to digest.

Brown strongly supported McDearman’s goal of eating a healthy, plant-based diet. “The data are pretty strong that the better nourished you are, the better you do during and after treatment,” she says. “Your quality of life is better. You’re better able to handle your treatments. There’s less recurrence, which is huge.” Obesity, she notes, is linked to 13 cancers, “and if you’re eating more plants, more fiber, that will help maintain a healthy body weight. And there’s good evidence that a plant-based diet improves survival for cancer patients, not just for cancer but also for heart disease.” She cautions that some people may not be able to tolerate these types of foods during treatment. For people with side effects such as diarrhea, nausea or low appetite, for example, eating more high fiber foods will be difficult. Learning how to manage these issues during treatment, she adds, can mean not only improved nutrition but also a better quality of life.