Weight Changes During Cancer Treatment

Cancer and cancer treatment can change your weight in either direction. Side effects can make it hard to eat enough, which can cause weight loss. Some treatments cause weight gain instead. Either way, your care team watches your weight closely. Good nutrition helps you stay strong through treatment.

Cancer and its treatments can cause side effects that affect your taste, smell, and appetite. They can also make it harder to eat enough food or absorb its nutrients. Common examples include:

• loss of appetite.
• nausea and vomiting.
• mouth sores, dry mouth, or trouble swallowing.
• changes in the way food tastes.
• constipation or diarrhea.
• feeling full after eating only a small amount of food. Doctors call this early satiety.

Some cancers directly affect the digestive system, such as cancers of the head and neck, esophagus, stomach, pancreas, liver, or colon. People with these cancers are more likely to have trouble eating. But people with any type of cancer can find it hard to eat well during treatment.

When eating problems are not managed, they can lead to malnutrition, which means your body is not getting the nutrients it needs. Unmanaged malnutrition can lead to cancer cachexia, a wasting syndrome that causes weakness and the loss of weight, fat, and muscle. Cachexia can happen even when you are eating well.

Some treatments have the opposite effect. Hormone therapy is used to slow or stop cancers that rely on hormones to grow, such as breast, ovarian, and prostate cancer. It can cause weight gain. It can also cause fluid retention, called edema, and high blood sugar.

Good nutrition for people with cancer can differ from what we usually think of as healthy eating, according to the National Cancer Institute. During treatment, you may need extra protein and calories. Extra protein and calories keep your strength up, help prevent malnutrition, and support your quality of life. This can mean eating more meat, fish, eggs, dairy, fats, and plant-based proteins than someone without cancer would eat.

If you have trouble eating or keeping your weight steady, your nurse, doctor, or registered dietitian may ask you questions. They may ask about weight changes, changes in how much and what you eat, and eating problems like nausea. They may also ask about your ability to do daily activities.

If you are at risk of poor nutrition, your doctor can refer you to a registered dietitian, a specialist in food and nutrition. This dietitian reviews your food history, medications, weight, lab tests, and treatment side effects. They then build a nutrition care plan with ways you and your family can improve your eating.

If you have appetite loss, weight loss, or feel full quickly, the National Cancer Institute suggests ideas to talk through with your team or dietitian:

• Eat foods high in protein and calories, and eat the high-protein foods first in a meal.
• Eat five to six smaller meals and snacks a day instead of three large ones.
• Eat your largest meal when your appetite is strongest, whether that is breakfast, lunch, or dinner.
• Try milkshakes, smoothies, juices, or soups when solid food doesn't appeal to you.
• Drink most fluids between meals rather than during them.
• Find a physical activity you enjoy. Light activity can help increase appetite.

If eating stays very difficult, your team can discuss other options with you. These include medicines that increase appetite or nutrition support, such as tube feeding or IV nutrition. You and your doctor and dietitian make these decisions together.

Some treatments can also weaken your immune system. If this applies to you, your team may talk with you about food safety — handling and preparing food carefully to lower your risk of foodborne illness.

• Call your care team the same day if you cannot keep fluids down at all, or if you feel dizzy, weak, or confused. The National Cancer Institute names those three as signs of dehydration, and they are easier to correct early than late.
• Call your care team within a day or two if you have eaten almost nothing for several days, if your clothes are getting loose without you trying, or if swallowing has become painful. Nutrition support works better when it starts before a lot of muscle has gone.
• Call your care team within a day or two if you gain weight quickly and your ankles, legs, or abdomen look swollen. Rapid gain is usually fluid rather than fat, and hormone therapy can cause it.

Weight changes during cancer treatment are common. They are treatable medical concerns, not personal failures. Tell your care team early about eating problems or a changing number on the scale. This gives them the best chance to help you stay nourished and strong.