Obesity has links with several kinds of cancer, including breast cancer after menopause and colorectal cancer. Having obesity can also affect cancer treatment and outlook.

Obesity is a condition involving excess body fat. The Centers for Disease Control and Prevention (CDC) recent estimates indicate that roughly 42% of adults in the United States have obesity.

The effects of obesity can increase the chance of several health conditions, such as heart disease and type 2 diabetes. Obesity also has links with a higher chance of some types of cancer.

This article looks at how obesity affects your chance of cancer, how obesity may affect cancer treatment, and what effects obesity can have on cancer survivors. Keep reading to learn more.

Obesity has links to 13 types of cancer. According to the CDC, these cancers make up 40% of all cancer diagnoses each year in the United States.

Cancers with links to obesity include some of the most common cancers in the United States, such as colorectal cancer and breast cancer in postmenopausal women.

Other cancers that have links with obesity include:

The link between obesity and cancer is complex, and the exact ways obesity contributes to cancer are unknown. However, it’s likely that obesity increases the chance of cancer through one or several of the following ways:

After a cancer diagnosis, obesity can also affect cancer treatment. These effects can vary depending on the type of treatment.

Surgery

Surgery can treat many different types of cancer. A 2019 review notes that research has linked obesity with the following complications after surgery:

Chemotherapy

Obesity can also affect chemotherapy (chemo) dosing, which doctors base on body weight or body surface area. Due to concerns about side effects, some people with obesity may not receive a chemo dose based on their actual body weight.

In fact, older research estimates that up to 40% of people with obesity receive a limited dose of chemo that’s not based on their body weight. The lower dose could potentially affect treatment outcomes.

A 2015 study found that cancer patients with obesity have worse clinical outcomes compared with patients without obesity. Researchers thought this could be due to doctors giving a lower dose of chemotherapy to reduce toxicities. The study suggests that chemotherapy dose intensity is an important factor that affects cancer outcomes and should not be reduced regardless of obesity.

Some studies have also linked obesity and specific types of chemo to a higher chance of side effects in people with certain cancer types. These side effects include peripheral neuropathy and heart damage.

Radiation therapy

Obesity may also increase side effects from radiation therapy. For example, a 2021 study found a link between higher body mass index (BMI) and a higher chance of dermatitis after radiation therapy in women with breast cancer.

Immunotherapy

People with obesity may respond better to immunotherapy than those without obesity. The exact mechanism behind this remains unknown.

A 2022 study found that people with obesity receiving a type of immunotherapy called immune checkpoint inhibitors (ICIs) had improved:

  • response rates to ICIs
  • progression-free survival (the time a person lives without the disease worsening)
  • overall survival

Having obesity can also affect cancer outlook. A 2021 review that looked at obesity and cancer outlook found a link between obesity and the following:

  • increased cancer recurrence
  • lower cancer-specific survival
  • reduced overall survival

This association was strongest for breast, colon, and uterine cancer. On the other hand, the researchers found that obesity was associated with improved survival in those with lung cancer, kidney cancer, and melanoma.

Researchers also think obesity may be associated with a higher chance of developing a second cancer. For example, a 2021 study on breast cancer survivors found that the chance of a second cancer became higher as BMI increased.

Which cancer is most associated with obesity?

A 2019 study in the United States found that 36.5% to 54.9% of uterine cancers were associated with excess body weight. Other cancers with a strong link with excess body weight included:

  • esophageal cancer
  • gallbladder cancer
  • kidney cancer
  • liver cancer

Does losing weight reduce cancer recurrence?

Losing weight may help reduce the recurrence of some cancers. Evidence suggests that obesity increases the chance of breast cancer recurrence. As such, doctors recommend managing your weight to help prevent breast cancer from coming back.

Should you lose weight if you’ve been diagnosed with cancer and have obesity?

According to the American Cancer Society, choosing whether or not to lose weight after a cancer diagnosis can depend on your individual situation.

Some people may choose to take steps to lose weight during treatment, while others may choose to wait until after treatment has finished. Regardless, it’s important that weight loss is done safely and under the supervision of a doctor.

Obesity is associated with a higher chance of some types of cancer, including colorectal cancer, uterine cancer, and breast cancer after menopause. Having obesity can also affect cancer treatments and outlook.

The exact way in which obesity contributes to cancer risk isn’t known. However, it’s likely that a variety of factors, such as increases in inflammation or changes in hormone levels, play a role.

If you have obesity and are concerned about health risks, including the chance of cancer, have an open discussion with your doctor. They can help to recommend safe ways to manage your weight.