The Relationship Between Cancer and Obesity

Globally, 1.9 billion adults are overweight or obese, according to the World Health Organization. Roughly four in 10 adults are overweight, and more than one in 10 are obese, a condition that increases the risk of heart disease, diabetes, kidney problems and joint disorders in addition to multiple types of cancers. 20% of all cancers diagnosed in the US are related to body fatness, physical inactivity, excess alcohol consumption, and/or poor nutrition, and thus could also be prevented.

These factors are all related and may all contribute to cancer risk, but body weight seems to have the strongest evidence linking it to cancer. Excess body weight contributes to as many as 1 out of 5 of all cancer-related deaths.

The evidence is mounting and proves that higher amounts of body fat are associated with increased risks of a number of cancers including:

• Endometrial cancer
• Esophageal adenocarcinoma
• Gastric cardia cancer
• Liver cancer
• Kidney cancer
• Multiple myeloma
• Meningioma
• Colorectal cancer
• Gallbladder cancer
• Breast cancer
• Ovarian cancer
• Thyroid cancer

Why is being overweight linked to many types of cancer?

Fat cells in the body are active and produce hormones and proteins that are released into the bloodstream and carried around the body. Because they are spread through the circulation, these ‘chemical messengers’ can affect many parts of the body, and increase the risk of several different types of cancer.

Fat cells can also attract immune cells to body tissues. These immune cells release chemicals that cause long-lasting inflammation which can raise the risk of cancer.

How might obesity increase the risk of cancer?

Several possible mechanisms have been suggested to explain the association of obesity with increased risk of certain cancers:

• Fat tissue produces excess amounts of estrogen, high levels of which have been associated with the risk of breast, endometrial, and some other cancers.
• People with obesity often have increased levels of insulin and insulin-like growth factor-1 in their blood (a condition known as hyperinsulinemia or insulin resistance), which may promote the development of certain tumors.
• Fat cells produce hormones, called adipokines, which may stimulate or inhibit cell growth. For example, leptin, which is more abundant in obese people, seems to promote cell proliferation, whereas adiponectin, which is less abundant in obese people, may have antiproliferative effects. Thus, the leptin-adiponectin ratio in the microenvironment may be important for tumor cell aggressiveness.
• Fat cells may also have direct and indirect effects on other tumor growth regulators, including mammalian target of rapamycin.
• People with obesity often have chronic low-level, or "subacute" unresolved inflammation, which has been associated with increased cancer risk.

Suggestions for people who are overweight or obese

If you are currently overweight or obese, it is best to start by taking steps to lose weight through nutrition and exercise. Aim to lose 5% to 10% of your body weight as your first goal. Although this amount may seem small, research shows that even losing 5% to 10% of your weight is beneficial. 

Sometimes nutritional changes and increasing physical activity aren’t enough. But there are other steps you can take. The National Institutes of Health approach to obesity treatment includes:

• A change in lifestyle behaviors
  First, change behaviors to reduce the amount of food eaten and increase physical activity before considering other weight loss treatments. A registered dietitian, exercise physiologist, clinical psychologist, or doctor who specializes in weight loss can help.
• Behavior change support
  For many, being overweight or obese is more complex than simply eating too much and exercising too little. It’s important to get support when you are trying to lose weight. Most weight loss programs include sessions with a dietitian or weight loss specialist to help you make healthy lifestyle changes and stick with them over time.
• Medications
  Weight loss drugs are usually only recommended when a combination of diet, exercise, and behavior change support have not worked. Or, if you have other serious health conditions from being obese.
• Surgery
  Weight loss surgery, or bariatric surgery, is a term for a variety of procedures that make a person’s stomach smaller. This may be an option for people with a BMI of 40 or higher. Or, for those with a BMI of 35 or higher who have another serious health condition related to obesity.

For more information on cancer prevention, check out the World Cancer Research Fund at www.wcrf.org/int/research-we-fund/our-cancer-prevention-recommendations.