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Breast Cancer Weight Gain: Does Obesity Lead to Breast Cancer or Does Breast Cancer Lead to Obesity?

Updated: Jul 26, 2023

Breast Cancer Background

In the United States, breast cancer is the second most common type of cancer. It is common enough that many people know of a friend or relative who has breast cancer. Treatment for breast cancer can include surgery, radiation therapy, or chemotherapy. Improved treatments have lead to higher breast cancer survival. There is a known link between breast cancer and weight gain. This article will discuss how obesity is a risk factor for breast cancer, and in turn, how breast cancer can lead to gaining weight.

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Risk Factors for Breast Cancer

There are numerous risk factors for breast cancer. These include being female (though males can also have breast cancer,) increasing age, family history of breast cancer, mutations in certain genes such as the BRCA1 and BRCA2 genes, having never been pregnant, and obesity.

I would like to discuss the final risk factor mentioned--obesity. Why is obesity a risk factor for breast cancer? Most people with a higher BMI have more adipose tissue. Adipose tissue cells create a hormone called estrogen, so people with more adipose tissue can have higher estrogen levels. Higher levels of estrogen are linked to breast cancer. Additionally, some people who have a higher weight also have higher insulin levels. Higher insulin levels are also associated with some cancers, including breast cancer.

Can Breast Cancer Cause Weight Gain?

There are a few reasons that people with breast cancer might gain weight. Some breast cancer treatments, such as radiation therapy or surgery can damage the lymphatic system causing a condition known as lymphedema. Lymphedema is the buildup of excess fluid that came from the lymphatic system. In some cases, enough fluid builds up that the weight gain from this excess fluid is significant. This weight gain is not initially an increase in adipose or fat tissue. Still, some studies show that lymphedema may cause further weight gain of adipose tissue.

Another way breast cancer can lead to weight gain is with some of the medications used to treat breast cancer. One of the most common breast cancer drugs, tamoxifen, is linked to weight gain. Another medication category used in cancer treatment, called steroids, can also lead to weight gain.

What Does Breast Cancer Weight Gain Mean for the Patient with Breast Cancer?

Unfortunately, society has conditioned many people to feel bad about weight gain. For some people, understanding that their personal choice did not cause their weight gain can be comforting. For others, there may be a sense of unfairness in it all they they are likely to gain weight through no choices of their own.

As a dietitian who works with people who have gained weight for all sorts of reasons, I frequently hear both views. Understanding the many causes of obesity can be helpful to some, while others will hear that and double down on diet because that is the only factor they can control. I also hear other concerns and worries people have about their weight, body image, and their "bad eating." Working with a dietitian can be helpful to a patient's understanding of how nutrition relates to their health.

Fortunately, good nutrition can lower risk of diseases including cancer, regardless of a person's weight. Nutrition counselling can help a person make improved lifestyle choices. Sometimes it will lead to weight loss, sometimes it won't. But even without weight loss, good nutrition will keep you healthier.

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