Chemotherapy can change the way your body reacts to food. Your diagnosis and treatment may also affect your eating and exercise habits. As a result, some women gain weight during their treatment. Others may experience just the opposite.

How will chemotherapy affect my weight?

One study found that normal weight women are more likely to gain weight during treatment and overweight women are more likely to lose weight during treatment.

Studies show that women treated for breast cancer often continue to gain weight for years after their diagnosis, which increases their risk of breast cancer recurrence.

Factors that may contribute to weight gain after chemotherapy include:

  • Being premenopausal at the start of chemotherapy
  • Changes in hormonal status
  • Fluctuations in body composition
  • Lack of physical activity

Factors that may make eating more difficult and lead to weight loss with chemotherapy include:

  • Loss of appetite
  • Altered sense of taste or smell
  • Vomiting or diarrhea
  • Pain or physical discomfort

Nausea tops the list and is the number one reason women lose weight during chemotherapy.

How can I achieve a healthy weight during and after chemotherapy?

Many women with breast cancer may benefit from dietary and weight loss interventions. Before making changes to your diet, ask your doctor to measure your BMI, or body mass index, to determine if you should lose weight, gain weight, or maintain your current weight.

The American Cancer Society recommends the following steps to maintain your health and avoid weight gain:

  • Take steps to remain physically active. Exercise can be done safely after a diagnosis of cancer. Physical activity may come with benefits for your weight, muscle strength, fatigue and depression. Ask your doctor what kinds of physical activities would be best for you.
  • Eat plenty of fruits, vegetables, and whole grains. Limit your intake of high fat foods, processed and red meat, and refined grains.

Research shows that a Mediterranean-based diet rich in vegetables and grains may help to prevent weight gain with chemotherapy. The study included dietary changes throughout treatment, along with cooking classes, and group meals.

If you’re looking to lose weight, the Mayo Clinic recommends taking slow steps and losing no more than two pounds per week.

What should I do if I’m losing too much weight?

If you have nutritional deficiencies or experience excessive weight loss, ask for a referral to a registered dietician. Nutritional guidelines from the American Cancer Society offer the following advice:

  • Consume frequent, smaller meals.
  • Drink between meals to avoid filling your stomach with liquids at mealtime.
  • Consume fortified or nutrient-rich beverages or foods.
  • For those at risk of becoming malnourished, appetite stimulants or intravenous nutrition may be considered.

Why is it important to maintain a healthy weight during or after cancer treatment?

For those battling cancer or cancer survivors, weight gain can trigger health problems for all of the usual reasons. These factors are a growing concern as more cancers are caught earlier and treated. Many people with cancer today can expect to live for years beyond their diagnosis.

Weight gain may also come with special risks for women with breast cancer. Overweight women, and those who gain weight during treatment, are more likely to have their cancer come back. Hormone levels in women who are obese are elevated which can encourage some breast cancers to grow.

Excessive weight loss can lead to nutritional deficiencies and negatively affect your quality of life.

Your healthcare team may suggest basic strategies to help you maintain or reach a healthier weight. They can also refer you to a registered dietician. Studies show that dietary counseling can improve patient outcomes and reduce treatment side effects.

Be gentle with yourself. And remember to consider your overall treatment plan when thinking about your weight goals.