Advances in breast cancer treatment mean more people than ever are surviving. There are nearly 4 million people living with breast cancer in the United States, and that number will continue to grow, thanks to lifesaving therapies.
People diagnosed with breast cancer can help their recovery by being aware of a common side effect of breast cancer treatment: weight gain.
“Most people experience weight gain following breast cancer diagnosis,” says breast medical oncologist Sherry Shen, MD, of Memorial Sloan Kettering Cancer Center (MSK). “That can cause anxiety. However, patients should know there are many ways weight gain can be managed, both during and after treatment.”
Dr. Shen conducts research on the complex relationship between the body’s metabolism and cancer. In her clinical practice, she introduces patients to a variety of ways to help them control their weight during and after breast cancer treatment.
New MSK Research on Weight-Loss Drugs and Weight Gain During Breast Cancer
One of Dr. Shen’s areas of focus is investigating whether well-known weight-loss drugs such as Ozempic, Wegovy, and others could play a useful role in managing weight gain during and after breast cancer treatment.
Dr. Shen led a team that published research in the journal Oncology in August 2025. They analyzed the medical records of 75 breast cancer patients at MSK who received these drugs — also known as GLP-1 agonists — and found that, on average, patients lost around 5% of their body weight after a year.
“I am encouraged to see that breast cancer patients taking GLP-1 agonists can prevent weight gain and actually lose weight on these drugs,” says Dr. Shen. “The average weight loss of 5% that we saw in these patients after a year is meaningful.”
Dr. Shen cautions that the research looked at a small number of patients, most of whom were given GLP-1s to treat diabetes — the drugs’ original purpose — rather than to treat weight gain from breast cancer treatment.
However, the research included a wide range of patients in terms of age, breast cancer type, stage of breast cancer, the treatment methods that were used, and other important variables. It included pre- and post-menopausal women.
These results are a signal, writes Dr. Shen and her research colleagues, that “support the development of clinical trials to optimize the use and dosing of GLP-1 agonists for weight loss in patients with breast cancer.”
Why People Often Gain Weight During and After Breast Cancer Treatment
Dr. Shen stresses that it’s more important for people with breast cancer to follow their treatment regimens than it is to worry about weight gain. However, it’s also important to understand how treatment can affect the body’s metabolism and address it appropriately.
“As part of chemotherapy for breast cancer, we give steroids and lots of fluids, which can induce weight gain,” Dr. Shen says. “And, due to nausea, many patients alter their eating habits, which can also result in weight gain.”
Dr. Shen notes that hormone therapy, which is very common for breast cancer, can alter metabolism: “Especially for younger patients, this treatment can put them into menopause, which tends to mean more weight gain.”
“Chemotherapy can also induce a temporary menopause,” she adds, “which deprives the body of the hormone estrogen and can lead to changes including weight gain.”
Why MSK Is Investigating Weight-Loss Drugs for Breast Cancer Patients
Dr. Shen says her interest in researching whether GLP-1 medications could be helpful to breast cancer patients stems in part from the large and growing number of survivors.
“We want them to be as healthy as possible to enjoy the best quality of life,” she says.
Preventing weight gain during breast cancer treatment and afterward can help in many important ways.
Improved Cardiovascular Health
Dr. Shen points out that better detection and treatment mean that “the leading cause of death after an early-stage breast cancer diagnosis now is actually cardiovascular disease, not breast cancer.”
As a result, she says, “it’s important for our breast cancer survivors to have medical care directed at cardiovascular risk factors such as blood pressure, cholesterol, diabetes, and others, which are made worse with significant weight gain.”
Dr. Shen explains that “We know that chemotherapy worsens cholesterol and hemoglobin A1C,” says Dr. Shen, “which is a measure of insulin resistance and diabetes.” It’s important, she stresses, “that we treat these risks, too, and not just focus everything on breast cancer.”
Reducing the Risk of Cancer Recurrence
Dr. Shen says that preventing weight gain can also improve cancer outcomes and may help reduce the risk of cancer coming back. “Weight gain of 5% of total body weight — and even more so at 10% — is associated with worse breast cancer survival rates,” she says.
The bottom line, she says, is that controlling weight gain during and after treatment can improve both cardiovascular and cancer outcomes.
How To Control Weight Gain During Breast Cancer Treatment
Nutrition and Food
Dr. Shen says there is no “one size fits all” approach to controlling weight during cancer treatment. Everyone has different preferences and appetites.
With her patients, Dr. Shen stresses a few key concepts.
- A plant-forward diet “That’s not saying people need to convert to being vegetarians or vegans,” she says. “But they should prioritize plant-based whole foods, including fruits and vegetables, whole grains, and eat less red meat and processed meat.” For protein, people should focus on seafood and plant-based sources.
- Dietary fiber Getting enough dietary fiber has been shown to reduce the risk of breast cancer recurrence. She says it’s especially important for cancer patients to also stay hydrated with a healthy water intake, as high dietary fiber without adequate hydration can lead to constipation.
- Calories Patients should know how many calories they are consuming and try to focus on the quality of the calories. “Consuming fewer calories leads to weight loss,” she says, “but the quality of those calories is important too.”
- Sugar Limit added sugars and follow the recommendations of MSK nutritionists, who urge people to consider healthier sweetening options, such as honey or maple syrup, rather than refined sugar. “People also need to be aware of the hidden added sugars in sodas and similar sweetened beverages,” Dr. Shen says.
Learn more about fiber and cancer
Learn more about sugar and cancer
Physical Activity
“Research shows that physical exercise can really help both with weight loss as well as improving breast cancer outcomes,” Dr. Shen says. “It can also help people who may have body image issues as a result of breast cancer.”
Her advice to patients, based on extensive research at MSK and elsewhere is:
- At least 150 minutes per week of moderate exercise — about the pace of a brisk walk.
- Or at least 75 minutes a week of vigorous activity that gets the heart rate up, such as playing a sport, running, or swimming.
Other MSK Research To Control Weight Gain During Breast Cancer Treatment
MSK is also leading pioneering new research to provide evidence on how people can control their weight during breast cancer treatment.
Pilot Project With Noom Mobile App
The app was provided to 31 patients with early-stage cancer (Stage 1 to 3) who were in the overweight or obese range and who had completed breast cancer treatment at least six months earlier.
“Noom is meant to help change a person’s thought process and habits so that they adopt overall eating patterns that are healthier,” says Dr. Shen. “In the app, people can access articles about healthy eating and exercise, talk with support groups and coaches, log the food they eat each day, as well as their weight and physical activity, and they don’t need to travel to a clinic to do it or check in repeatedly with a counselor, which many people find inconvenient.”
After six months on the program, “people lost an average of 5.6% of their body weight,” says Dr. Shen. “Research shows this amount of weight loss can improve breast cancer outcomes and makes people healthier. We also saw a noticeable improvement in people’s body image.”
Who Is Most at Risk of Gaining Weight After a Breast Cancer Diagnosis
Weight gain is particularly common among people with hormone receptor positive breast cancer, who account for nearly 70% of people diagnosed with breast cancer.
Dr. Shen says patients who are most likely to gain weight during breast cancer include: