FACT SHEETS

Obesity and Risk

What is ? Despite the limitations of the study • : People who are over- Obesity is a condition in which a per- designs, there is consistent evidence that weight or obese are up to twice as likely son has an unhealthy amount and/or higher amounts of body fat are associ- as normal-weight people to develop distribution of body fat. ated with increased risks of a number liver cancer. The association between To measure obesity, researchers com- of (6), including: overweight/obesity and liver cancer is monly use a scale known as the body • : Obese and stronger in men than women (11, 12). mass index (BMI). BMI is calculated by overweight women are two to about • Kidney cancer: People who are dividing a person’s weight (in kilograms) four times as likely as normal-weight overweight or obese are nearly twice by their height (in meters) squared (com- women to develop endometrial cancer as likely as normal-weight people to monly expressed as kg/m2). BMI pro- (cancer of the lining of the uterus), develop renal cell cancer, the most vides a more accurate measure of obesity and extremely obese women are about common form of kidney cancer (13). than weight alone, and for most people seven times as likely to develop the The association of renal cell cancer with it is a fairly good (although indirect) more common of the two main types obesity is independent of its association indicator of body fatness. of this cancer (7). The risk of endome- with high blood pressure, a known risk trial cancer increases with increasing factor for kidney cancer (14). What is known about the relationship weight gain in adulthood, particularly • Multiple myeloma: Compared with between obesity and cancer? among women who have never used normal-weight individuals, overweight Nearly all of the evidence linking menopausal hormone therapy (8). and obese individuals have a slight (10% obesity to cancer risk comes from • Esophageal adenocarcinoma: People to 20%) increase in the risk of develop- large cohort studies, a type of obser- who are overweight or obese are about ing multiple myeloma (15). vational study. However, data from twice as likely as normal-weight people • Meningioma: The risk of this slow- observational studies can be difficult to develop a type of growing brain tumor that arises in the to interpret and cannot definitively called esophageal adenocarcinoma, membranes surrounding the brain and establish that obesity causes cancer. and people who are extremely obese the spinal cord is increased by about That is because obese or overweight are more than four times as likely (9). 50% in people who are obese and about people may differ from lean people in • Gastric cardia cancer: People who are 20% in people who are overweight (16). ways other than their body fat, and it is obese are nearly twice as likely as nor- • : People who are possible that these other differences— mal-weight people to develop cancer in overweight or obese are about 1.5 times rather than their body fat—are what the upper part of the stomach, that is, the as likely to develop pancreatic cancer explains their different cancer risk. part that is closest to the esophagus (10). as normal-weight people (17). ▶ FACT SHEETS

• : People who are women who have never used meno- performed on the stomach or intestines obese are slightly (about 30%) more pausal hormone therapy (24). to induce weight loss). Obese people likely to develop colorectal cancer than • Thyroid cancer: Higher BMI (spe- who have bariatric surgery appear to normal-weight people (18). cifically, a 5-unit increase in BMI) is have lower risks of obesity-related can- • : Compared with associated with a slight (10%) increase cers than obese people who do not have normal-weight people, people who are in the risk of thyroid cancer (25). bariatric surgery (35). overweight have a slight (about 20%) Stronger evidence for a relationship increase in risk of gallbladder cancer, Does avoiding weight gain or losing between weight loss and cancer risk and people who are obese have a 60% weight decrease the risk of cancer? comes from studies of people who have increase in risk of gallbladder cancer Most of the data about whether avoiding undergone bariatric surgery. Obese peo- (19, 20). The risk increase is greater in weight gain or losing weight reduces ple who have bariatric surgery appear women than men. cancer risk comes from cohort and case- to have lower risks of obesity-related • : Many studies have shown control studies. These studies can be dif- cancers than obese people who do not that, in postmenopausal women, a higher ficult to interpret because people who lose have bariatric surgery (35). BMI is associated with a modest increase weight or avoid weight gain may differ Nevertheless, the follow-up study of in risk of breast cancer. For example, in other ways from people who do not. weight and breast cancer in the Women’s a 5-unit increase in BMI is associated Nevertheless, when the evidence Health Initiative (36) found that for with a 12% increase in risk (21). Among from multiple observational studies is women who were already overweight postmenopausal women, those who are consistent, the association is more likely or obese at baseline, weight change obese have a 20% to 40% increase in risk to be real. Many observational studies (either gain or loss) was not associated of developing breast cancer compared have provided consistent evidence that with breast cancer risk during follow- with normal-weight women (22). The people who have lower weight gain up. However, for women who were of higher risks are seen mainly in women during adulthood have lower risks of normal weight at baseline, gaining more who have never used menopausal hor- colon cancer, kidney cancer, and— than 5% of body weight was associated mone therapy and for tumors that express for postmenopausal women—breast, with increased breast cancer risk. hormone receptors. Obesity is also a risk endometrial, and ovarian cancers (34). factor for breast cancer in men (23). Stronger evidence for a relationship For the expanded article and references, • Ovarian cancer: Higher BMI is between weight loss and cancer risk please see the online version of this article. associated with a slight increase in the comes from studies of people who have risk of ovarian cancer, particularly in undergone bariatric surgery (surgery Source: National Cancer Insititute.

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