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July 21, 2021 | 6 minute read

How Diet and Exercise Affect Breast Cancer Survivors, Study Finds

The study adds an important understanding of how specific lifestyle actions affect survivors’ weight and body composition.

There are plenty of reasons why breast cancer survivors having overweight and obesity after treatment may be advised to shed weight. Research indicates that overweight and obesity increase the risk of cancer recurrence and even earlier death in women diagnosed with breast cancer. Too much body fat also increases the risk of type 2 diabetes and other chronic conditions that can have serious effects.

But weight loss comes with some risk of muscle loss, and how survivors can lose weight most healthfully remains an area of ongoing research. Now comes a study that isolates the two mainstays for weight loss, eating habits and exercise, finding that both dieting alone and dieting combined with exercise leads to breast cancer survivors’ losing weight. The majority of the weight lost was fat tissue—the culprit for higher disease risk—but some amount of loss also occurred in muscles and other lean tissue.

The paper, whose authors include AICR grantees, was published in Breast Cancer Research and Treatment. It adds an important understanding of how various lifestyle steps affect weight and body composition among breast cancer survivors.

Fewer calories, exercise and weight loss

In the study, 351 breast cancer survivors who had completed treatment at least six months before the study began were assigned to one of four groups. One concentrated on exercise, a second on diet and a third on diet combined with exercise. The fourth group had no lifestyle guidance, only advising the women to ask their health-care providers about diet and exercise.

The participants were all categorized as having overweight or obesity and, on average, about 60 years old.

The women assigned to the exercise group were prescribed both resistance and aerobic activities. The activities were in-person and home-based. The diet group participants attended regular dietitian-led sessions. They were given a particular diet for the first five months and then shifted to behavior modifications on food shopping and preparation. The goal was to lose 10 percent of their body weight, while eating plenty of fruits and vegetables. The diet plus exercise participants started with six weeks of exercise alone, then added the diet component.

After 52 weeks, when compared to the control group, the women in the diet group lost an average of 6 percent of their body weight and the women in the diet and exercise group lost slightly more than 7 percent. Exercise alone did not change body weight.

“This study shows that for weight loss, the key is caloric restriction, consuming fewer calories each day,” said Justin Brown, PhD, Director of the Cancer Metabolism Program at Pennington Biomedical Research Center and the paper’s first author. The reality is that exercise is good for weight maintenance—preventing weight gain—but it is not as successful for losing weight, says Brown, who is also an AICR grantee.

“You cannot outrun a bad diet, no matter how much exercise you do.”

Mostly fat loss but some lean

This paper also fills an important gap in understanding how diet, exercise and weight loss affect body composition. Your body weight—or mass—is made up of two main types: fat mass and everything else. That “everything else” is called lean body mass and it includes your muscles, bones and organs. With weight loss comes some reduction of lean mass, such as from muscle.

Although excess body fat poses clear risks for breast cancer survivors’ health, having low muscle mass also carries harmful health effects. Low muscle increases the risk of dying prematurely and frailty, which can hinder people’s ability to move, lift items and perform other daily functions.

In the current study, about two-thirds of the body weight lost was fat mass in both the diet alone and diet plus exercise groups.

“We found that when cancer survivors lose weight, about 65 percent of that loss is fat mass and the rest is muscle mass. That means the majority of weight they lose is in the form of fat, which is good,” said Brown. This ratio is similar to other populations.

Diet alone and diet plus exercise also reduced visceral fat, the fat deep in the belly that is independently linked to increased risk of type 2 diabetes and other diseases.

None of the groups experienced changes in bone mineral density, an indicator of bone health and risk of fractures.

“As an oncology dietitian the biggest concern I have about people losing weight during cancer treatment is that they will lose some lean body mass,” says Angela Hummel, MS, RDN, CSO, a certified specialist in oncology nutrition. “For breast cancer patients who are older, she said, it is especially hard to get that lean body mass back.” That risk of losing too much lean muscle remains after treatment, and this study’s findings on exercise were interesting, adds Hummel.

Experts advise cancer survivors having overweight and obesity to speak with their health-care providers about weight loss and risks. It is an individual, patient-centered decision.

“I think at the end of the day, exercise and diet provide unique health benefits and the best thing is to do both.”

Cancer survivors deserve to have all the information to make the best decision.

Healthy lifestyle and weight maintenance

This trial was relatively long and with a strong design, but it does have limitations. The women could not be assigned to their specific treatment group without their knowledge. That, in turn, may have biased their responses.

All the women had cancer-related lymphedema, a swelling of the arm or leg, and the exercise prescribed was more rehabilitative in nature. “That leaves open the question, if we had prescribed more vigorous exercise would that have helped prevent loss of muscle? We don’t know, based on this study,” said Brown.

The average American, including cancer survivors, gains approximately half a pound to one pound each year. At the minimum, notes Brown, it is beneficial for cancer survivors to be aware of their current body weight and prevent further weight gain as they age.

“If that scale is the same weight over the years that is in itself a success.”

Exercise and a healthy diet have long been studied for the potential beneficial effects on cancer survivors. AICR recommends that cancer survivors, if and when they are able, follow the same healthy eating and physical activity recommendations as the general population. Previous research suggests physical activity offers numerous health benefits to cancer survivors. In 2019 the American College of Sports Medicine updated their review of the evidence on exercise and cancer survivorship, recommending that survivors avoid inactivity finding that exercise could improve common cancer-related issues.

The authors of this paper used the same group of breast cancer survivors to investigate how exercise and diet affected breast cancer survivors’ quality of life, finding that diet linked to benefits.


This study was supported by the National Cancer Institute of the National Institutes of Health.

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