Guidelines always say to eat a lot of fiber and vegetables, but these can be very hard on the digestive tract. How do I take this into account for my diet?

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Cara Anselmo, clinical dietitian-nutritionist at Memorial Sloan Kettering Cancer Center in New York City​. Photo courtesy of Cara Anselmo

CARA ANSELMO: ​​This is a complicated question because the answer depends on you, the type of cancer you have, and other factors, like your treatment and any side effects it may cause. The short answer is that there is no one set of guidelines to follow when it comes to fiber and cancer. Keep in mind that there are differences between eating fiber for cancer risk reduction versus eating fiber as someone living with cancer.

USDA guidelines say that women should get 25 grams of fiber a day and men 25 to 40 grams per day. That’s appropriate for most people, but if an individual is getting treatment that’s causing diarrhea or gas and bloating or if they are having any issues with bowel motility, then I might recommend adjusting their diet to include less fiber. If someone has a gastrointestinal or gynecologic cancer that has contributed to an obstruction, I might very well recommend a low-fiber diet to limit the amount of undigested food passing through their body. If you are on chemotherapy or radiation and that’s contributing to diarrhea, then you don’t necessarily want to cut fiber out of your diet, but I might not recommend a diet that’s high in fiber either. If someone wants or needs to increase their fiber intake, it is best to add in fiber slowly for best tolerance.

There also are different kinds of fiber. If you want to eat a fiber-rich diet but you’re having diarrhea, this might improve by eating more soluble fiber. Oats are more soluble, and therefore easier on the gut, than wheat bran or raw vegetables. The preparation of fiber-rich foods also influences how digestible they are. If you have diarrhea, I’d recommend cooked vegetables over raw vegetables, for instance.

The question is: What is your diagnosis and what are your symptoms, and how can those be managed best? If you’ve determined you should get more fiber, it’s typically best to get it from food, not supplements. That’s true of all nutrients generally. That said, there are situations in which a soluble fiber supplement such as Metamucil might be helpful. If you are already eating a diet that includes plenty of fiber and you’re struggling with constipation, then my first suggestion would be to make sure you’re drinking enough fluid. Before taking stimulant laxatives, you could try adding a fiber supplement along with plenty of water.

I encourage anyone with cancer to talk with their own registered dietitian or nurse about questions like these. There’s no way to make global recommendations without knowing what a person is experiencing and what their diet looks like already. Take advantage of nutrition services that are available to you where you’re getting care and talk one-on-one about what you can and should do. There’s no “one size fits all” approach.

FIBER FACTS // The American Institute for Cancer Research describes ways to add fiber to your diet. // University of Michigan Health explains the different ways that cancer treatment can change your fiber needs. ​​ 

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