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Being overweight or obese is clearly linked to an overall increased risk of cancer. According to research from the American Cancer Society, excess body weight is thought to be responsible for about 11% of cancers in women and about 5% of cancers in men in the United States, as well as about 7% of all cancer deaths.
Being overweight or obese is clearly linked with an increased risk of many types of cancer, including:
Being overweight or obese might also raise the risk of other cancers, such as:
The link to body weight is stronger for some cancers than for others. For example, excess body weight is thought to be a factor in more than half of all endometrial cancers, whereas it is linked to a smaller portion of other cancers.
Excess body weight may affect cancer risk in a number of ways, some of which might be specific to certain cancer types. Excess body fat might increase cancer risk by affecting:
The links between body weight and cancer are complex and are not yet fully understood. For example, while studies have found that excess weight is linked with an increased risk of breast cancer in women after menopause, it does not seem to increase the risk of breast cancer before menopause. The reasons for this are not clear.
The timing of weight gain might also affect cancer risk. Being overweight during childhood and young adulthood might be more of a risk factor than gaining weight later in life for some cancers. For example, some research suggests that women who are overweight as teenagers (but not those who gain weight as adults) may be at higher risk for developing ovarian cancer before menopause.
Clearly, more research is needed to better define the links between body weight and cancer.
Research on how losing weight might lower the risk of developing cancer is limited. Still, there’s growing evidence that weight loss might reduce the risk of some types of cancer, such as breast cancer (after menopause) and endometrial cancer.
Some body changes that occur as a result of weight loss suggest it may, indeed, reduce cancer risk. For example, overweight or obese people who intentionally lose weight have reduced levels of certain hormones that are related to cancer risk, such as insulin, estrogens, and androgens.
While we still have much to learn about the link between weight loss and cancer risk, people who are overweight or obese should be encouraged and supported if they try to lose weight. Aside from possibly reducing cancer risk, losing weight can have many other health benefits, such as lowering the risk of heart disease and diabetes. Losing even a small amount of weight has health benefits and is a good place to start.
Modern life in America has led many people to eat more unhealthy foods, eat bigger food portions, and be less active. As a result, the number of Americans who are overweight or obese (very overweight) has been rising. More than 1 in 3 American adults is now obese, and another 1 in 3 is overweight.
Being overweight or obese can have far-reaching health consequences. According to the US Centers for Disease Control and Prevention (CDC), excess body weight increases a person’s risk for:
Overweight and obese people, on average, do not live as long as people who stay at a healthy body weight throughout their lives.
Not only are more adults overweight or obese, but more children are, too. Among children and teens, about 20% are now obese. This number is much higher than it was a few decades ago, although it has leveled off in recent years.
Some of the same health problems affecting obese adults can also affect obese children. These include heart disease risk factors such as high cholesterol levels and high blood pressure, as well as asthma, sleep apnea, type 2 diabetes, muscle and joint problems, and liver disease. Obese children and teens are also at higher risk for anxiety, depression, and social and psychological problems, such as being bullied and having poor self-esteem.
Overweight and obese children and teens are also more likely to have weight problems as adults, as well as the risk of health problems that can come with this.
Finding your body mass index, or BMI, is a way to help you figure out if you are at a healthy weight for your height. BMI is a number based on your weight and height. In general, the higher the number, the more body fat a person has. BMI is often used as a screening tool to decide if your weight might be putting you at risk for health problems such as heart disease, diabetes, and cancer.
BMI is used to broadly define different weight groups in adults 20 years old or older.
In adults, BMI is calculated the same way for both men and women. There are several ways to find your BMI. (See below for information about how to calculate BMI in children and teens.)
BMI can be easily calculated using our online calculator.
Charts are another easy way to find your BMI. To use the table below, find your height on the left side of the chart, then go across to the weight that is closest to yours. At the top of the chart you can see your BMI, and at the bottom of the chart you can see which category you fit into – healthy weight, overweight, or obese:
Some examples:
This table shows us that a woman who is 5 ft. 4 in. tall is considered overweight (BMI is 25 to 29) if she weighs between about 145 and 169 pounds. She is considered obese (BMI is 30 or more) if she is closer to 174 pounds or more.
A man who is 5 ft. 10 in. tall is considered overweight (BMI is 25 to 29) if he weighs between about 174 and 202 pounds, and is obese (BMI is 30 or more) if he is closer to 209 pounds or more.
You can also calculate your own BMI. The actual formula to determine BMI uses metric system measurements: weight in kilograms (kg) divided by height in meters, squared (m2).
When using pounds and inches, the formula needs to be altered slightly. Multiply your weight in pounds by 703. Divide that by your height in inches, squared:
BMI = (your weight in pounds x 703) ÷ (your height in inches x your height in inches)
For example, if you weigh 120 pounds and are 5 ft. 3 in. (63 in.) tall:
BMI = (120 x 703) ÷ (63 x 63) or 84,360 ÷ 3969 = 21.3
This is well within the healthy weight range.
BMI can be calculated the same way for children and teens as it is for adults, but the numbers don’t have the same meaning. This is because the normal amount of body fat changes with age in children and teens, and is different between boys and girls. So for kids, BMI levels that define being normal weight or overweight are based on the child’s age and sex.
To account for this, the US Centers for Disease Control and Prevention (CDC) has developed age- and sex-specific growth charts. These charts are used to translate a BMI number into a percentile based on a child’s sex and age. The percentiles are then used to determine the different weight groups:
An easy way to determine your child’s BMI percentile is to use the CDC’s online BMI percentile calculator at https://www.cdc.gov/healthyweight/bmi/calculator.html.
Doctors and nurses often use BMI to help find out if a person might have a weight problem. BMI gives a good estimate of total body fat for most people, but it doesn’t work well for everybody. For example:
For most adults, the BMI is a good way to get an idea of healthy weight ranges. But it’s not always the final word in deciding if a person is overweight or obese. There are other things to think about when judging how much someone should weigh.
A person with a high BMI should be evaluated by a health care provider, who might use other factors such as skinfold thickness (a measure of body fat), waist size, evaluations of diet and family health problems, and other factors to find out if a person’s weight might pose a health risk.
As part of its Guideline for Diet and Physical Activity for Cancer Prevention, the American Cancer Society recommends that people try to get to and stay at a healthy weight throughout life. The best way to stay at a healthy body weight is to balance how much (and what) you eat with how active you are. If you are overweight, the best way to get to a healthy body weight is to limit the calories you take in, and burn more calories through physical activity.
Follow a healthy eating pattern: You can lower the number of calories you take in by eating healthier foods; eating smaller amounts of food (smaller portion sizes); limiting between-meal snacks; and limiting foods and drinks that are high in calories, fat, and/or added sugars, and that provide few nutrients. Fried foods, cookies, cakes, candy, ice cream, and regular soft drinks should be replaced with vegetables and fruits, whole grains, beans, and lower calorie beverages.
Be physically active: The American Cancer Society recommends that adults get 150 to 300 minutes of moderate intensity or 75 to 150 minutes of vigorous intensity activity each week (or a combination of these). Getting more is even better. Children and teens should get at least 1 hour of moderate or vigorous intensity activity each day.
It’s also important to limit the time you spend sitting, lying down, watching TV, and looking at your phone or computer. Doing some physical activity on top of your usual activities, no matter what your level of activity, can have many health benefits.
Along with helping you get to or stay at a healthy weight, eating a healthy diet and increasing your physical activity can have their own health benefits, including lowering your risk of cancer.
More and more evidence suggests that being overweight or obese raises the risk of cancer coming back after treatment and may lower the chances of survival for many cancers. Both during and after cancer treatment, people should try to get to and stay at a healthy weight whenever possible.
Some cancer survivors can be malnourished and underweight when they are diagnosed or as a result of cancer treatment. These people may need help gaining or maintaining their weight.
Other people may be overweight or obese when they are diagnosed with cancer. While each person’s situation can be different, many people may choose to wait until after treatment is finished before making lifestyle changes that could result in weight loss. Others may choose to talk with their doctor about whether to try to lose modest amounts of weight during treatment, assuming it is monitored closely and does not affect treatment. If a person chooses to try to lose weight, it should be done safely, through a well-balanced diet and increased physical activity tailored to their specific needs.
After cancer treatment, weight should be managed with both dietary and physical activity strategies. One way to help get to a healthy weight is by reducing calorie intake. This can be done by eating lower-calorie foods (such as vegetables, fruits, and soups, and cooked whole grains), limiting your intake of fat and sugars, and limiting portion sizes – especially of high-calorie foods. Increased physical activity is also important in promoting weight loss, and in keeping weight off. Even if an ideal weight is not reached, it’s likely that any weight loss will still have health benefits.
For more information, see Nutrition and Physical Activity During and After Cancer Treatment: Answers to Common Questions.
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
American Cancer Society. Cancer Prevention & Early Detection Facts & Figures 2019-2020. Atlanta: American Cancer Society; 2019.
Centers for Disease Control and Prevention. About Child and Teen BMI. 2018. Accessed at www.cdc.gov/healthyweight/assessing/bmi/childrens_BMI/about_childrens_BMI.html on June 3, 2020.
Centers for Disease Control and Prevention. Adult Obesity Causes and Consequences. 2018. Accessed at www.cdc.gov/obesity/adult/causes.html on June 3, 2020.
Centers for Disease Control and Prevention. Childhood Overweight and Obesity. 2018. Accessed at www.cdc.gov/obesity/childhood/ on June 3, 2020.
Islami F, Goding Sauer A, Miller KD, et al. Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States. CA Cancer J Clin. 2018;68:31-54.
Renehan AG, Tyson M, Egger M, Heller RF, Zwahlen M. Body-mass index and incidence of cancer: A systemic review and meta-analysis of prospective observational studies. Lancet. 2008;371:569-578.
Rock CL, Doyle C, Demark-Wahnefried W, et al. Nutrition and physical activity guidelines for cancer survivors. CA Cancer J Clin. 2012;62(4):242-274.
Rock CL, Thomson C, Gansler T, et al. American Cancer Society guideline for diet and physical activity for cancer prevention. CA Cancer J Clin. 2020;70(4). doi:10.3322/caac.21591. Accessed at https://onlinelibrary.wiley.com/doi/full/10.3322/caac.21591 on June 9, 2020.
World Cancer Research Fund/American Institute for Cancer Research. Diet, Nutrition, Physical Activity, and Cancer: A Global Perspective. Continuous Update Project Expert Report 2018. Accessed at https://www.wcrf.org/dietandcancer on June 3, 2020.
Last Revised: December 15, 2023
American Cancer Society medical information is copyrighted material. For reprint requests, please see our Content Usage Policy.
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