People eat to fuel their body. This gives patients strength and stamina to power through the day.

At no time is this more important than when a person is undergoing treatment for cancer. Chemotherapy and radiation treatments, whether lifesaving or life-preserving, can take a toll on a person's body and significantly affect the diet.

"Chemotherapy not only kills rapidly dividing cancer cells, but also it can destroy fast-growing healthy cells," says Rose Prissel, a Mayo Clinic dietitian. "This may cause nausea or appetite changes, leading patients to consume fewer calories than needed. Other treatments can cause uncomfortable dry mouth, diarrhea or constipation. Fortunately, these side effects can be lessened or even overcome and thereby improve nutrition during treatment."

One of the things patients and caregivers ask about is weight changes during treatment. Generally, if a patient loses more than 3 pounds in one week, it's important to discover if the loss was intentional or unintentional. If it's intentional, the patient's care team will discuss why this is occurring and make sure treatment plans are going well.

"If the weight loss is unintentional, it's important to seek out the cause and provide support. It's important to avoid a rapid decline in weight because muscle tissue is being broken down during treatment. This can lead to further loss of the patient's stamina," says Prissel.

Weight loss also can cause a poor appetite. This is a common side effect during cancer treatment.

"To improve nutrition during this time, it helps to plan for small, frequent meals," adds Prissel. "That can be daunting because patients and caregivers may not have the energy to make multiple meals each day. One way to get around this is to reserve a portion of what would have been normally eaten during breakfast, lunch and dinner for a fourth small meal. This makes it easier to plan and schedule additional meals with less work."

Damage to the stomach and intestinal lining during cancer treatment can cause nausea and vomiting. "A few things that can help would be choosing easily digestible foods, such as refined carbohydrates like white bread and potatoes. Also, avoid high-fiber, high protein foods, as these foods take longer to digest.

Eat small, frequent meals to avoid overloading the stomach.

Some cancer treatments and medications can cause dehydration and decreased saliva production, which can lead to uncomfortable dry mouth. Prissel says increasing fluid intake and chewing gum or sucking on candy or ice chips can help offset that from happening.

"Other side effects of some chemotherapy and radiation treatments can include a sore throat or mouth. This can make eating and drinking uncomfortable and painful. Eating hot or cold foods could irritate this so eat foods that are moderate temperature or eat foods that are bland or soft.," says Prissel. "Diarrhea can also be an uncomfortable problem, or a sign of something more serious. Limiting dairy, avoiding caffeine, and eating soft low fiber foods can assist from avoiding diarrhea from leading into other problems, such as severe dehydration."

It's important for patients to do what they can to maintain calorie, protein and fluid intake during cancer treatment. Prissel says following dietary guidelines offered by your health care team can help patients maintain their strength and stamina during treatment.

"In some cases, such as advanced cancer, eating may not affect the outcome of their illness or treatment. In these situations, trying to follow specific dietary guidelines, such as adhering to a low-sodium or low-fat diet, may not be practical. Patients should talk with their care team about what they can expect during treatment and how long symptoms could last — and discuss all their symptoms with their health care team, especially those that affect their diet," Prissel says.