Brandel France de Bravo, MPH, Noy Birger, Shahmir Ali, and Ealena Callender, MD, MPH, Cancer Prevention and Treatment Fund
There are many reasons why being overweight is bad for our health, but most people
don’t realize that cancer is one of them. Of course, excess body weight can contribute
to serious medical conditions such as heart disease and type II diabetes. Still, more
recent research shows that excess body fat also increases the risk of developing certain
types of cancer.
Researchers estimate that more than 481,000 of newly-diagnosed cancer cases
worldwide in 2012 were due to overweight or obesity.  An estimated 111,000 cancer
cases in North America are caused by being overweight or obese. This represents 23%
of total global cancer cases – the highest of any region. In addition, three cancers
accounted for 73% of all obesity-related cancers among women globally: endometrial
cancer, postmenopausal breast cancer, and colon cancer. For men, kidney and colon
cancers accounted for 66% of all obesity-related cancers. Other cancers associated
with overweight and obesity include prostate cancer, several gastrointestinal cancers,
and non-Hodgkin’s lymphoma.
In 2018, American Cancer Society researchers concluded that each year from 2011 to
2015, approximately 37,700 cancer cases in men in the U.S. and 74,700 cancer cases
in women aged 30 years or older were attributable to excess body weight.  Among men,
the excess cancers ranged from 3.9% in Montana to 6.0% in Texas. In women, the
excess risk of cancer was almost twice as high as for men, ranging from 7.1% in Hawaii
to 11.4% in Washington, DC. The highest number of weight-related cancers were
primarily found in southern and midwestern states, as well as Alaska and Washington,
D.C. Overall, cancers attributable to excess body weight account for at least 1 in 17 of
all cancers in each state.
The good news is that a large 2014 study showed that with a healthy diet and regular
exercise, postmenopausal women may significantly reduce their cancer risk.  In the
study, researchers defined a healthy diet as one that limits red meat and processed
meat, emphasizes whole grains over refined grains, and includes two and a half cups of
vegetables and fruits daily. In addition, regular exercise involves at least 150 minutes of
moderate-intensity physical activity or 75 minutes of vigorous-intensity physical activity
every week. Those with the healthiest diets and most active lifestyles saw their chance
of getting breast cancer drop by 22%, their likelihood of colon cancer drop by 52%, and
their overall chance of dying during the 12-year study drop by 27%. While all the women
who ate better and exercised more lowered their chances of developing cancer, non-
white women seemed to benefit the most.
A 2020 study of more than 8,000 Black and White men and women also found that
exercise helps lower the likelihood of dying from cancer. The study found that inactive
people (whether couch potatoes or sitting at a desk all day) were more likely to die from
cancer. At the same time, those who engaged in light to moderate physical activity were
less likely to die from cancer. 
In 2022, a study of adults aged 59 to 82 found that those who were as physically active
as was recommended by the Physical Activity Guidelines for Americans were less likely
to die of cancer than those who were less active.  All men and women in the study
who were at least moderately active were less likely to die from cancer or
cardiovascular disease than those who were not active at all. In addition, when
researchers evaluated the type and intensity of activity, the activity that seemed most
likely to reduce the chance of dying from cancer was running, followed by other aerobic
exercise, swimming, and cycling.
How does obesity increase the risk of developing cancer?
Excess body weight results in extra body fat – which has unique features that can make
it more likely for an obese person to get cancer.  Body fat, also known as adipose
tissue, contains an abundance of cells that cause chronic inflammation and make it
easier for tumors to grow.
Chronic inflammation in individuals with excess body fat may also contribute to insulin
resistance.  Insulin is a hormone that helps our cells use glucose – a type of sugar
found in the foods we eat – to make energy. Insulin resistance means our bodies can’t
respond properly to insulin, and the glucose we need for energy stays in our blood,
where it can’t be used. Too much glucose in our blood – also referred to as high blood
sugar levels or hyperglycemia – increases the likelihood of getting and dying from
cancer.  Elevated blood sugar levels lead to an increase in insulin and similar hormones
that cause tumors to grow. The higher the insulin level of a breast cancer patient, the
greater the chance of death.  For example, one study of non-diabetic women with early-
stage breast cancer found that women with the highest fasting insulin levels had three
times the risk of recurrence and death compared with women with the lowest insulin
levels. High insulin levels may also interfere with the way certain cancer drugs work,
making treatments less effective. 
Researchers think the danger of excess weight is partly due to hormones secreted by
fat tissues, such as estrogen. In women, estrogen comes from a different source before
and after menopause. Before menopause, a woman’s ovaries secrete estrogen. After
menopause, estrogen comes from other tissues in the body. For obese postmenopausal
women, most estrogen comes from body fat, which can encourage the growth of cancer
cells. [11,12] Increased estrogen and increased body fat increase the likelihood of
developing postmenopausal breast cancer and endometrial cancer (also called cancer
of the uterus) in women. [11,12]
The location of body fat also may be important. Fat tissue deep inside your body
wrapped around your organs may increase the risk of developing cancer. For example,
one study followed 3,086 men and women for up to seven years and used medical
imaging scans and physical exams to assess the location of excess fat deposits.  After
statistically controlling for the effects of age, exercise habits, BMI, and eating habits,
researchers concluded that those with more fat deep inside the body, compared to
those with fat mostly just beneath the skin, were more likely to develop heart disease
How new is this news?
Researchers have documented the link between obesity and cancer
for many years. In 2003, based on a study of more than 900,000 adults, researchers
estimated that 90,000 cancer deaths could be avoided if adults maintained a normal
body weight.  Of all deaths from cancer in Americans over age 50, as many as 14% in
men and 20% in women may be attributable to overweight and obesity. 
Every additional study helps to explain how it is that fat fuels tumor growth. Renehan et
al.’s 2012 study, which seemed to be groundbreaking at the time, is based in part on an
earlier meta-analysis (a type of statistical analysis that combines many studies) in which
many of the same authors analyzed more than 200 comparable data gathered from
different countries around the world.  The meta-analysis found that excess weight in
men was most strongly associated with cancer of the esophagus, thyroid, colon, and
kidneys. According to the meta-analysis, being overweight did not appear to increase a
man’s risk of prostate cancer. On the other hand, one U.S. study found that an
overweight man with prostate cancer is more likely to die of it than a man with prostate
cancer who is not overweight. 
According to the meta-analysis, excess weight in women increases the chances of
developing endometrial cancer, cancer of the gallbladder, esophagus, and kidneys. A
few other cancers were also associated with being overweight for both men and
women, including leukemia, multiple myeloma, and non-Hodgkin’s lymphoma, but the
link was weaker. In men, rectal cancer and malignant melanoma also seemed related to
weight. In women, those with a higher BMI were slightly more likely to be diagnosed
with post-menopausal breast cancer, cancers of the pancreas and thyroid, and colon
Additional studies have come to similar conclusions. For example, the American
Institute for Cancer Research (AICR) estimated that excess body fat is responsible for
49% of endometrial cancers; 35% of esophageal cancers; 28% of pancreatic cancers;
24% of kidney cancers; 21% of gallbladder cancers; 17% of breast cancers; and 9% of
colon cancers.  In addition, AICR estimates that over 100,000 new cases of cancer
each year are due to excess body fat, which is similar to estimates from the 2018
American Cancer Society study.
Neuhouser’s study, conducted at 40 U.S. clinical centers, of women ages 50 to 79
followed for about 13 years, showed that women who gained more than 5% of their
baseline weight during the study’s follow-up period had a modest increase in their
chance of getting breast cancer.  The risk was most significant for women with a body
mass index (BMI) over 35 — they were 60% more likely to develop breast cancer than
women of normal weight. Keep in mind that a BMI of 30 or higher is considered obese.
A 2016 study found that the link between obesity and cancer is more robust in some
countries than others.  Middle Eastern countries have the highest proportion of
overweight and obesity in the world and a high proportion of obesity-related cancer.  In contrast, countries in sub-Saharan Africa and Asia have only seen a limited increase in
BMI over the last 30 years. Likewise, North America and Europe have a large proportion
of obesity-related cancers, while countries in sub-Saharan Africa and Asia have a
smaller proportion of obesity-related cancer.
Several studies show that high dietary fat intake increases the risk of post-menopausal
breast cancer,  prostate cancer,  and pancreatic cancer.  Researchers have also
found that high-fat diets may increase the likelihood of death from cancer, while low-fat
diets reduce the chances of cancer recurrence.  It is unclear whether weight or diet is a
stronger predictor of increased cancer risk, although red meat and processed meat
have been found to increase the risk of some cancers. For more information, see our
articles entitled “Red Meat: The News is Not Good” and “Are Processed Meats More
Dangerous Than Other Red Meats?”
Does losing weight reduce your risk of cancer?
Can losing weight help prevent you from getting cancer? The evidence is clear for some
cancers but not for others. For example, postmenopausal women who lose weight may
reduce their chance of getting breast cancer.  Also, weight loss may reduce the
likelihood of gastroesophageal reflux – which may be linked to esophageal cancer. In
addition, some studies have found an association between weight loss and decreased
chance of getting prostate cancer.
Men and women who experience significant weight loss after bariatric surgery may
decrease their likelihood of getting cancer. Bariatric surgery, also called weight-loss
surgery, is generally associated with a decrease in body weight of 20% to 35%.  A
2022 study of 30,318 men and women compared the incidence of cancer and cancer-
related death between obese patients who had bariatric surgery and those who did not.
The incidence of most types of cancer and cancer-related death was lower in the
surgical weight loss group. This difference was most significant for endometrial cancer –
the cancer most strongly associated with obesity.
Other studies of obese patients who intentionally lost weight found a decrease in certain
factors in the blood that encourage tumor growth. Called tumor growth factors, these
markers represent chronic inflammation and create a setting that makes it easier for cancer cells to grow. [27,28] Estrogen – a hormone associated with postmenopausal breast cancer and endometrial cancer – also decreased in women who intentionally lost weight.  The study found that women who experienced just a 10% weight loss saw their blood estrogen levels decrease by at least 33%. Overall, researchers have not reached a conclusion about the association between weight loss and postmenopausal breast cancer. Although one study showed a decreased likelihood when the weight loss occurs after age 30 but before menopause,  other studies have found no impact at all. 
What we know and don’t know
Decreasing the likelihood of getting cancer is one of the many benefits of achieving and
maintaining a healthy body weight. However, we still do not fully understand how a
person’s weight, diet, level of physical activity, and genes all work together to determine
one’s cancer risk.
After giving up tobacco, watching your weight and staying active are your best forms of
health insurance. For guidelines and tips on living a healthy lifestyle, read Eating Habits
That Improve Health and Help with Weight Loss and BMI. 
All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.
The National Center for Health Research is a nonprofit, nonpartisan research, education and advocacy organization that analyzes and explains the latest medical research and speaks out on policies and programs. We do not accept funding from pharmaceutical companies or medical device manufacturers. Find out how you can support us here.
- Arnold M, Pandeya N, Byrnes G, et al. Global burden of cancer attributable to high
body-mass index in 2012: a population-based study. The Lancet Oncology.
- Islami F, Goding Sauer A, Gapstur SM, Jemal A. Proportion of Cancer Cases
Attributable to Excess Body Weight by US State, 2011-2015. JAMA Oncology.
- Thomson CA, McCullough ML, Wertheim BC, et al. Nutrition and Physical Activity
Cancer Prevention Guidelines, Cancer Risk, and Mortality in the Women’s Health
Initiative. Cancer Prevention Research. 2014;7(1):42-53. doi:10.1158/1940-
- Gilchrist SC, Howard VJ, Akinyemiju T, et al. Association of Sedentary Behavior
With Cancer Mortality in Middle-aged and Older US Adults. JAMA Oncol.
- Watts EL, Matthews CE, Freeman JR, et al. Association of Leisure Time Physical
Activity Types and Risks of All-Cause, Cardiovascular, and Cancer Mortality Among
Older Adults. JAMA Network Open. 2022;5(8):e2228510.
- Khanna D, Khanna S, Khanna P, Kahar P, Patel BM. Obesity: A Chronic Low-Grade
Inflammation and Its Markers. Cureus. Published online February 28, 2022.
- Gutierrez DA, Puglisi MJ, Hasty AH. Impact of increased adipose tissue mass on
inflammation, insulin resistance, and dyslipidemia. Curr Diab Rep. 2009;9(1):26-32.
- Stocks T, Rapp K, Bjørge T, et al. Blood Glucose and Risk of Incident and Fatal
Cancer in the Metabolic Syndrome and Cancer Project (Me-Can): Analysis of Six
Prospective Cohorts. Wareham NJ, ed. PLoS Med. 2009;6(12):e1000201.
- Hede K. Doctors Seek To Prevent Breast Cancer Recurrence by Lowering Insulin
Levels. JNCI Journal of the National Cancer Institute. 2008;100(8):530-532.
- Boyd DB. Insulin and Cancer. Integr Cancer Ther. 2003;2(4):315-329.
- Cleary MP, Grossmann ME. Obesity and Breast Cancer: The Estrogen Connection.
Endocrinology. 2009;150(6):2537-2542. doi:10.1210/en.2009-0070
- Kaaks R, Lukanova A, Kurzer MS. Obesity, Endogenous Hormones, and
Endometrial Cancer Risk: A Synthetic Review1. Cancer Epidemiology, Biomarkers
& Prevention. 2002;11(12):1531-1543. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4142485/
- Britton KA, Massaro JM, Murabito JM, Kreger BE, Hoffmann U, Fox CS. Body Fat
Distribution, Incident Cardiovascular Disease, Cancer, and All-Cause Mortality.
Journal of the American College of Cardiology. 2013;62(10):921-925.
- Calle EE, Rodriguez C, Walker-Thurmond K, Thun MJ. Overweight, Obesity, and
Mortality from Cancer in a Prospectively Studied Cohort of U.S. Adults. N Engl J
Med. 2003;348(17):1625-1638. doi:10.1056/NEJMoa021423
- NCI. Home | Cancer Trends Progress Report. Published March 2020. Accessed
January 10, 2023. https://progressreport.cancer.gov/
- Renehan AG, Tyson M, Egger M, Heller RF, Zwahlen M. Body-mass index and
incidence of cancer: a systematic review and meta-analysis of prospective
observational studies. The Lancet. 2008;371(9612):569-578. doi:10.1016/S0140-
- Wright ME, Chang SC, Schatzkin A, et al. Prospective study of adiposity and weight
change in relation to prostate cancer incidence and mortality. Cancer.
- Nelson M. Large study finds (again) obesity links to many cancers. American
Institute for Cancer Research. Published March 1, 2017. Accessed January 10,
- Neuhouser ML, Aragaki AK, Prentice RL, et al. Overweight, Obesity, and
Postmenopausal Invasive Breast Cancer Risk: A Secondary Analysis of the
Women’s Health Initiative Randomized Clinical Trials. JAMA Oncol. 2015;1(5):611.
- Arnold M, Leitzmann M, Freisling H, et al. Obesity and cancer: An update of the
global impact. Cancer Epidemiology. 2016;41:8-15.
- Wynder EL, Cohen LA, Muscat JE, Winters B, Dwyer JT, Blackburn G. Breast
Cancer: Weighing the Evidence for a Promoting Role of Dietary Fat. JNCI Journal of
the National Cancer Institute. 1997;89(11):766-775. doi:10.1093/jnci/89.11.766
- Giovannucci E, Rimm EB, Colditz GA, et al. A Prospective Study of Dietary Fat and
Risk of Prostate Cancer. JNCI Journal of the National Cancer Institute.
- Thiébaut ACM, Jiao L, Silverman DT, et al. Dietary Fatty Acids and Pancreatic
Cancer in the NIH-AARP Diet and Health Study. JNCI: Journal of the National
Cancer Institute. 2009;101(14):1001-1011. doi:10.1093/jnci/djp168
- Chlebowski R. Lifestyle Change Including Dietary Fat Reduction and Breast Cancer
Outcome. The Journal of Nutrition. 2007;137(1):233S-235S.
- Wolin KY, Colditz GA. Can weight loss prevent cancer? Br J Cancer.
- Aminian A, Wilson R, Al-Kurd A, et al. Association of Bariatric Surgery With Cancer
Risk and Mortality in Adults With Obesity. JAMA. 2022;327(24):2423.
- Byers T, Sedjo RL. Does intentional weight loss reduce cancer risk? Diabetes,
Obesity and Metabolism. 2011;13(12):1063-1072. doi:10.1111/j.1463-
- Harvie M, Howell A, Vierkant RA, et al. Association of Gain and Loss of Weight
before and after Menopause with Risk of Postmenopausal Breast Cancer in theIowa Women’s Health Study. Cancer Epidemiology, Biomarkers & Prevention.
- Teras LR, Goodman M, Patel AV, Ryan Diver W, Dana Flanders W, Feigelson HS. Weight loss and postmenopausal breast cancer in a prospective cohort of overweight and obese US women. Cancer Causes Control. 2011;22(4):573-579. doi:10.1007/s10552-011-9730-y
- Dudley S, Pederson S, Kennedy C, Rosseau N. Eating Habits That Improve Health and Help with Weight Loss and BMI. National Center for Health Research. Published March 29, 2010. Accessed January 10, 2023. https://www.center4research.org/eating-habits-improve-health-help-weight-loss-bmi/