Weight gain


About half of women being treated for breast cancer gain weight. This can range from just a few pounds to 20 pounds or more.

Body Mass Index (BMI) is often used to measure whether a person’s weight is healthy or not. Though it’s not a perfect measurement, in most people it gives an accurate sense of whether there is too much body fat. A healthy BMI is between 18.5 and 24.9. BMI of 25-29.9 is considered overweight. BMI of 30-39.9 is considered obese. BMI of more than 40 is considered morbidly obese. There are many tools on the internet that can help you find your BMI, or you can ask your doctor to calculate it for you.

A high BMI puts people at risk for a number of health problems, including breast cancer. And in people who have had breast cancer, obesity is linked to a higher risk of breast cancer recurrence and death.

Weight gain can also have an effect on your body image and self-esteem at a time when those things may already be affected by breast surgery, hair loss, or other treatment side effects.

What causes weight gain after a breast cancer diagnosis?

Many factors can lead to weight gain after a breast cancer diagnosis. Medicines like chemotherapy and hormonal therapy can speed up some of the natural effects of aging that cause weight gain. They can decrease your muscle mass and slow your metabolism, the process your body uses to convert the calories you eat into energy. When you eat more calories than are used for energy, you gain weight.

Lifestyle is also a factor. Breast cancer treatments, including surgery, radiation therapy, and medicine, can leave you exhausted, in need of recovery, and short on time. For these reasons, many people exercise less after a breast cancer diagnosis, leading to weight gain.

The food you eat can also have an impact. Medicines like chemotherapy can change the way some foods taste, and many women find that bland, fatty foods taste better than other, healthier foods while their sense of taste is different. And, for some people, food can be a huge comfort during a stressful situation like cancer. But if you start eating a lot of foods that are high in fat, sugar, and calories, you will probably gain weight.


The weight gain concern is mentioned often, and it’s frustrating. There's no magic fix. We advise a healthy, plant-based diet, along with consistent activity. Studies emphasize the importance of not just cardio but also incorporating weights at least twice a week. This builds muscle and aids fat breakdown. While there's no magic solution, maintaining a healthy lifestyle is important. Be kind to yourself; a few pounds are, unfortunately, part of the journey for many patients.

Evelyn Robles-Rodríguez, DNP, APN, AOCN, Managing treatment side effects of anti-estrogen therapies


How can I manage my weight?

The causes of weight gain in the previous section may seem like things you can’t control, but there are some ways to maintain your weigh while going through treatment. It’s important to remember, though, that your first goal is to treat the cancer – don’t be too hard on yourself if you do gain weight. If it’s easier after treatment ends, you can take steps then to lose any weight you might have gained.


Try to exercise regularly, even if you feel tired. It may sound strange, but regular exercise can actually make you feel less tired. The exercise doesn’t have to be difficult. Start by taking a short walk every day and try to work up to meeting national fitness guidelines, which suggest all adults get 150 minutes of moderately hard exercise, or 75 minutes of very hard exercise, per week.

Resistance training, like push-ups, sit-ups, and lifting weights can help you build muscle. More muscle can speed up your metabolism and help you burn calories more easily. Some people worry that resistance training will increase their risk of lymphedema, but research suggests it is safe when done carefully.

Talk to your doctors before starting any fitness program. They may refer you to a physical therapist or other fitness professional who has experience helping people with cancer and who can teach you how to exercise safely. If you were an athlete or very active before diagnosis, a personal trainer with experience working with people with cancer may be able to help you create a program to keep you on track with your fitness plan while keeping your treatment in mind.

Learn more on our exercise page.

Eating healthy

The good news about changes in taste caused by chemotherapy is that the effect usually goes away once chemotherapy ends, and foods will taste the way they did before. For now, focus on trying to choose healthier foods, even if you eat less of them than you normally would. Be aware of your portion sizes and the fat and sugar content of what you’re eating. A cancer nutritionist can help you plan meals that you are able to eat and are reasonably healthy.

If you’re overeating to deal with difficult emotions, consider seeing a dietician, a mental health expert, or both.

Don’t lose hope if you’re exercising more and eating healthier, but still seeing some weight gain. Research shows that regular exercise and a diet high in fruits and vegetables lowers your risk of breast cancer recurrence regardless of how it affects your weight.

Your body, including your weight, may change because of breast cancer, but remember: That doesn’t stop you from being you. If your changing body image is making you feel bad not just about your appearance but about other aspects of your life, you may find it helpful to talk to a professional counselor or to other people who are going through the same experiences.


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Reviewed and updated: July 11, 2019

Reviewed by: Christine Zoumas, MS, RD


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