Diet and Chemotherapy: Foods to Avoid

Chemotherapy, which works by killing bad-acting cancer cells, can be effective for treating many cancer types. But because chemo can also damage healthy cells in the process, it can cause side effects, including stomach trouble and mouth sores. Choosing the right foods during treatment can help.

Everyone reacts differently to chemotherapy, so it's important to bear in mind that the diet that works for you during treatment may not be the same diet that works for your friend or family member during chemo.

"There are no specific foods that need to be avoided during chemotherapy, although some therapies may have different regulations than others," says Joseph Dowdell, RDN, LD, a clinical dietitian at Cleveland Clinic's Taussig Cancer Center in Ohio. "The major concern regarding nutrition during treatment is choosing the right foods at the right times, based on any specific side effects a patient may be experiencing."

To help you identify this individual best diet, Dowdell says it is always best to meet with a registered dietitian nutritionist. While no two experiences are the same, there are some foods that can be smart to approach with caution if you're experiencing specific side effects.

If you find yourself having loose stools or diarrhea during chemotherapy, Dowdell says it can help to limit your consumption of high-fat, greasy or spicy foods. He also recommends foods with soluble fiber, which can have a thickening effect on loose stools.

If you're experiencing nausea during chemo, it can also help to choose lower-fat, bland foods such as toast or saltine crackers over high-fat, greasy options, according to Stanford Health. Avoiding foods with very strong scents can also be a good idea, as can choosing cold foods over hot foods and eating small portions throughout the day, according to UCSF Health.

​Read more:​ Foods to Eat With Nausea

Another chemotherapy side effect that can complicate your food choices is an irritated mouth. According to Dowdell, chemo drugs can limit the body's immune response and ability to fight off bacteria. This, in turn, may cause people to develop irritations in their mouth or esophagus.

"The important thing is to communicate with your providers if this does occur, so that they can help to guide you on treatments to help reduce these symptoms," Dowdell says. He adds that if painful mouth sores are bothering you, eliminate foods that can cause irritation and burning, such as citrus-based foods, heavily acidic foods, and spicy foods. (Maybe reach for the pretzels instead of the Flamin' Hot Cheetos or Takis.)

Because chemotherapy can make it harder for your body to fight off bacteria and infection during the course of treatment, it can also be smart to avoid unwashed or undercooked foods, which could result in food-borne illnesses, according to the American Cancer Society (ACS).

The ACS also recommends avoiding food from self-serve salad bars or delis, since these are more likely to contain germs and bacteria than properly sealed packaged foods or foods that you cook in your own kitchen (assuming you follow the proper sanitary procedures).

Finally, while it may seem counterintuitive to advice you may have received in the past, Memorial Sloan Kettering Cancer Center recommends that people undergoing chemotherapy skip foods labeled "diet," "low-fat" or "fat free." A lot of people experience a loss in appetite during treatment, and your body needs the calories to stay strong and tolerate the treatment.

This doesn't mean you should go all out with fried foods and greasy foods. These kinds of fats are the ones Dowdell says can exacerbate diarrhea and nausea. Healthy fats can be found in avocados and nuts, and certain nutritional shakes can help you increase your calorie intake, too.

​Read more:​ 15 Healthy Fat-Rich Foods to Add to Your Diet