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- 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)
Although more evidence is needed, being overweight or obese may also increase the risk for the following cancers:
- Non-Hodgkin lymphoma
- Multiple myeloma
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.
Weight gain after a cancer diagnosis
In cancer survivors, weight gain may cause the development of other diseases and lower cancer-related survival and overall survival. What's more, cancer survivors are at greater risk for developing second cancers and other diseases, such as heart disease and diabetes, conditions that are clearly linked to weight gain.
Another problem related to weight gain and cancer is a change in body composition from some treatments. Studies show that people with breast cancer, prostate cancer, non-small cell lung cancer, and acute lymphoblastic leukemia (ALL) who receive chemotherapy, hormone therapy, or radiation therapy to the head lose lean body mass (muscle) as they gain weight. Although actual changes in total body weight are small, patients often report that they are outgrowing their clothes.
Although eating too much can cause weight gain, recent reports suggest that a decrease in physical activity and a lower metabolic rate (the rate at which the body converts food into energy) may be more important factors for weight gain in people with cancer. To avoid weight gain, patients should reduce their normal calorie intake and/or increase exercise, such as resistance training, that helps build muscle. Talk with your doctor or other health care team member about an appropriate plan before you begin. Learn more about physical activity and cancer.
Recommendations for weight management
Reaching and maintaining a healthy weight is important for everyone, including patients undergoing cancer treatment and cancer survivors. Avoiding excess weight is associated with cancer prevention, more effective cancer treatment, the prevention of diseases in addition to cancer, and improved overall health and survival.
To avoid weight gain, it is important to be aware of your diet and make healthy choices about food and beverages. This can be challenging because eating a high-calorie diet is typical in the United States today. The reasons for this include a plentiful, relatively low-cost food supply, large portions, and an abundance of foods that are high in sugar and fat. Here are some tips to help:
- Choose foods with lower calorie content, such as vegetables, fruits, whole grains, and soups. Some of these foods also help a person feel "full" faster.
- Limit foods and beverages that are high in sugar and fat.
- Balance the calories from foods and beverages with the amount of calories burned through physical activity.
- Increase levels of physical activity. Most people should aim for 30 to 60 minutes per day of moderate-to-intense exercise on most days. However, even a small increase in physical activity has benefits.
- People currently overweight or obese should take steps to lose weight through nutrition and exercise. Aim to lose 5% to 10% of your body weight as your first goal.
Some people with cancer have the opposite problemâthey need to gain weight. A typical cause is loss of appetite, which may be worsened by nausea, vomiting, mouth sores, difficulty swallowing, and loss of taste. Your doctor and a dietitian can make recommendations for adding calories and improving nutrition. Learn more about how to manage weight loss.
Weight management tips for cancer survivors
People being treated for cancer or those with a history of cancer should follow the same guidelines set for weight management for the general population. Individualized counseling provided by a dietitian can help patients and survivors who have completed treatment lose weight. Weight loss plans that include exercise have also helped people with cancer avoid weight gain during chemotherapy. Weight loss in people with cancer or cancer survivors should be closely followed by a doctor. People should aim to lose no more than 2 pounds each week.
Weight loss approaches
The National Institutes of Health approach to obesity treatment includes:
A change in lifestyle behaviors. Behaviors that both reduce the amount of food eaten and increase the level of physical activity should be changed before other weight loss treatments are considered. A registered dietitian, exercise physiologist, clinical psychologist, or doctor who specializes in weight loss can help.
Pharmacotherapy. The use of drugs can help a person lose weight when changing diet and increasing exercise fail.
Surgery. This may be an option for patients with severe obesity who haven't lost weight with other approaches.
Questions to ask a medical professional about weight loss:
- Am I at an unhealthy weight?
- How is my excess weight harming my health?
- How will losing weight improve my health?
- How much weight do I need to lose?
- How much weight should I lose each week?
- What programs and treatments are available to help me lose weight?
- Can you recommend professionals that can help me develop a weight loss program?
- Where can I find information on healthy eating?
- Where can I find information on exercise?
Most hospitals and health-care organizations have professionals on staff that can provide weight management treatment.
Centers for Disease Control and Prevention: Overweight and Obesity
National Heart, Lung, and Blood Institute: Obesity and Physical Activity
Last Updated: June 09, 2011