WEIGHT CONTROL, PART I

This section has been reviewed and approved by the Cancer.Net Editorial Board, 6/2011

Key Messages:

• Being overweight or obese increases a person's risk of several types of cancer.
• People with cancer may gain or lose weight during their treatment, causing health problems that may affect their chance of survival.
• Many resources are available to help a person with cancer maintain a healthy weight, including doctors and dietitians. Talk with your doctor about an appropriate plan for you.

Being overweight or obese (extremely overweight) raises the risk of many health conditions, including cancer. In the United States, it is estimated that overweight and obesity cause 14% to 20% of all cancer-related deaths each year.

Although more studies are needed to better understand how being overweight or obese affects cancer risk, evidence suggests that maintaining a healthy weight is important for cancer prevention and recovery from cancer.

Understanding weight gain

It is estimated that more than two-thirds of American adults are overweight or obese. People who are overweight or obese are at greater risk for type II diabetes, high blood pressure, and heart disease. Many factors cause people to become overweight or obese, including genetic, biochemical, environmental, psychosocial, and cultural factors.

When a person is overweight or obese, it means that they have too much body fat in relation to lean body tissue, such as muscle. Obesity is often measured with body mass index (BMI), the ratio of a person's weight and height, and waist measurements. A normal BMI is between 18.5 and 24.9, and a BMI of 30 or higher is considered obese. A normal waist measurement is under 40 inches for men and under 35 inches for women. People with larger waist measurements are at a higher risk for various diseases, such as heart disease.

Common terms used in discussions about weight include:

Energy balance. The relationship between how many calories people eat and their energy needs.

Energy imbalance. Taking in more calories than the body uses, which results in weight gain.

Weight maintenance. When the calories eaten equals the calories used for energy. As a result, no weight gain or loss occurs.

Types of cancer linked to overweight or obesity

Some types of cancer appear to be closely linked to weight, although this association has not been proven for all cancers. Strong evidence suggests that being overweight or obese increases the risk of the following cancers:

• Breast (in postmenopausal women)
• Colon
• Uterine
• Kidney
• Esophageal

Although more evidence is needed, being overweight or obese may also increase the risk for the following cancers:

• Gallbladder
• Thyroid
• Ovarian
• Pancreatic
• Cervical
• Liver
• Non-Hodgkin lymphoma
• Multiple myeloma
• Prostate

Why obesity increases cancer risk

Several studies have explored why being overweight or obese may increase cancer risk and growth. People who are obese have more fat tissue, which can produce hormones, such as insulin or estrogen, and may cause cancer cells to grow.

How much a person weighs throughout various points in his or her life may also affect the risk for cancer. Although more research is needed, studies have shown:

• High birth weight is modestly associated with cancer risk.
• Weight gain during adulthood is consistently linked with increased cancer risk.
• Weight cycling (losing and regaining weight repeatedly) may slightly influence cancer risk.