How Excess Weight Raises Cancer Risk — and What New Research Says About Lowering It
- Obesity contributes to roughly 10% of all new U.S. cancer diagnoses each year, and up to 50% of endometrial and hepatobiliary cancers, according to new findings published in JAMA.
- Excess adipose (fat) tissue drives cancer development through chronic inflammation, hormonal disruption, immune suppression, oxidative stress, and changes in the gut microbiome, all of which create conditions that support tumor growth.
- “Extra energy – in the form of free fatty acids in the bloodstream – causes stress in our body known as oxidative stress, and that’s what causes DNA damage… if there’s enough DNA damage, that can lead to just the right type of mutation in an otherwise normal cell that can lead to a cancer mutation,” Dr. Neil Iyengar at Emory Winship Cancer Institute tells SurvivorNet.
- Weight loss of more than 10%—whether through bariatric surgery (procedures that reduce stomach size) or GLP‑1 medications like Wegovy or Ozempic—has been linked to modest reductions in obesity‑related cancer risk, though researchers say more randomized clinical trials are still needed to confirm the effect.
- “Preliminary data suggest significant weight loss, perhaps with the help of GLP1 receptor agonists, may help reduce these risks. In terms of prostate cancer, we see clear links between obesity and aggressive prostate cancer, progression after treatment, and death from prostate cancer. The impact of lifestyle interventions and ultimately weight loss to reduce these risks is ongoing,” Dr. Stephen Freedland, at Cedars-Sinai Medical Center, explains.
A growing body of research is sharpening the picture of how excess body weight helps fuel cancer — and why meaningful weight loss may help reduce that risk.
A new study published in JAMA adds fresh evidence to a long‑standing concern: obesity can be linked to roughly 10% of all new cancer diagnoses in the United States each year, and for certain cancers, it may account for up to half of all cases. Read More
- Endometrial
- Esophageal
- Gastric
- Renal
- Colorectal
- Liver, gallbladder, and bile duct (hepatobiliary cancers)
- Pancreatic
- Prostate
- Postmenopausal breast
- Ovarian
- Thyroid
- Multiple myeloma
The researchers estimate that overweight and obesity contribute to 10% of new cancer diagnoses annually, and up to 50% of endometrial and hepatobiliary cancers, such as liver, gallbladder, and bile ducts.
Research published in the journal “Cancers” says that “Obesity also increases the risk of dying from cancer and may influence the treatment choices. About 4–8% of all cancers are attributed to obesity.”
WATCH: Obesity and Cancer Risk
To learn more about your ideal healthy weight, determine your body mass index (BMI).
Body weight that exceeds what the body mass index deems appropriate for your weight and height can help determine body fat content. Although your BMI can help you learn if you are at a healthy weight, underweight, overweight, or obese, other factors may contribute to your overall health.
The National Cancer Institute analyzed several studies to observe the impact of physical activity on overall cancer risk. The NCI says that “higher levels of physical activity are linked to lower risk of several types of cancer.”
Regular exercise, a balanced diet, and managing stress are some ways people can practice leading a healthy life. For cancer survivors, a healthier lifestyle alongside getting regular checks for recurrence may improve their quality of life.
“Excess weight is one of the most important causes of cancer, second only to smoking, which it may even overtake in the coming years,” Dr. Graham Colditz, Director, Division of Public Health Sciences at WashU Medicine and Siteman Cancer Center.
“As rates of overweight and obesity continue to rise, we need to invest in effective systemic changes to help prevent weight gain and to help with weight loss. This can include better infrastructure that promotes activity, better access to affordable, healthy foods, and insurance that covers weight and diet counseling,” Dr. Colditz adds.
How Excess Weight Fuels Tumor Growth
The study outlines several interconnected biological pathways that help explain why obesity increases cancer risk. They involve inflammation, hormone changes, immune suppression, and shifts in the gut microbiome.
The study outlines several interconnected biological pathways that help explain why obesity increases cancer risk, including inflammation, hormone changes, immune suppression, and shifts in the gut microbiome. Dr. Iyengar says these processes begin with the way excess fat tissue disrupts the body’s normal balance.
“In the setting of obesity, the environment in a person’s body is just ripe for the growth of tumors and cancer. When you have excess adipose (fat) tissue, the normal function of fat tissue is to store energy and maintain energy homeostasis… When we have too much fat tissue, the fat tissue can no longer function properly.”
- Inflammation and Hormone Disruption
- Excess adipose (fat) tissue becomes biologically active, producing inflammatory molecules and altering hormone levels. This includes:
– Increased estrogen and leptin
– Decreased adiponectin
– Elevated inflammatory mediators such as prostaglandin E2, IL‑1β, IL‑6, and TNF‑α - These changes can directly stimulate tumor growth or indirectly promote cancers that are sensitive to hormones, such as breast, ovarian, and endometrial cancers.
- Excess adipose (fat) tissue becomes biologically active, producing inflammatory molecules and altering hormone levels. This includes:
- Immune System Suppression
- Obesity is linked to the accumulation of myeloid-derived suppressor cells, which weaken the body’s ability to detect and destroy emerging cancer cells. At the same time, the function of cytotoxic T cells and natural killer cells — the immune system’s frontline defenders — is reduced.
- Genomic Instability and Oxidative Stress
- Chronic inflammation and excess free fatty acids create oxidative stress, which can damage DNA and impair the body’s ability to repair it. This increases the likelihood of gene mutations that can lead to cancer development.
“Dysfunctional fat tissue can cause inflammation,” Dr. Iyengar explains.
As that tissue becomes dysfunctional, he explains, it releases energy in the form of free fatty acids into the bloodstream—fuel that cancer cells can readily use. Those circulating fatty acids also trigger insulin resistance, creating even more metabolic stress.
“Extra energy causes stress in our body known as oxidative stress, and that’s what causes DNA damage… if there’s enough DNA damage, that can lead to just the right type of mutation in a cell that is a cancer mutation,” Dr. Iyengar explained.
- Gut Microbiome Disruption
- Obesity is associated with a loss of beneficial gut bacteria (such as Akkermansia muciniphila) and an overgrowth of species linked to inflammation and cancer development (such as Bilophila). These shifts further heighten inflammation and oxidative stress.
“We know that obesity changes the types of bacteria that live in our gut… what you see in the gut bacteria of people with obesity is that it’s bacteria that create more inflammation,” Dr. Iyengar said.
Can Weight Loss Reduce Cancer Risk?
The study suggests that meaningful weight loss — more than 10% of body weight — may help lower cancer risk, but the effect varies by cancer type.
Evidence comes from large observational groups:
Bariatric surgery patients (n = 30,318). These patients underwent some form of minimally invasive (laparoscopic/robotic) weight-loss surgery that reduced their stomach size.
People using GLP‑1 receptor agonists such as semaglutide or tirzepatide (n = 1,651,452)
Across these groups, cancer incidence dropped by 0.02% to 0.5%, respectively, indicating a measurable but not dramatic reduction.
Researchers emphasize that randomized clinical trials are still needed to confirm whether weight loss directly reduces cancer risk or whether other factors contribute.
“There is no one single mechanism, but likely many mechanisms that can explain these links between cancer and obesity,” said Dr. Stephen Freedland, Director of the Center for Integrated Research in Cancer and Lifestyle, Co-Director of the Cancer Genetics and Prevention Program, and Associate Director for Faculty Development at the Samuel Oschin Comprehensive Cancer Institute at Cedars-Sinai.
“Preliminary data suggest significant weight loss, perhaps with the help of GLP1 receptor agonists, may help reduce these risks. In terms of prostate cancer, we see clear links between obesity and aggressive prostate cancer, progression after treatment, and death from prostate cancer. The impact of lifestyle interventions and ultimately weight loss to reduce these risks is ongoing,” Dr. Freedland continued.
What This Means for Patients
The findings reinforce a growing consensus: obesity is not just a metabolic condition — it is a major cancer risk factor.
As obesity rates continue to rise, the study underscores the urgency of prevention strategies, early detection, and broader access to effective weight‑loss interventions.
WATCH: NYU’s Dr. Holly Lofton explains what we do know about GLP-1RAs and cancer risk
At the same time, experts caution that weight loss is not a guaranteed cancer‑prevention tool. The biological pathways linking obesity and cancer are complex, and reducing risk likely requires a combination of lifestyle changes, medical support, and continued research.
That complexity also shapes how newer weight‑loss medications, such as GLP‑1 receptor agonists, should be used — especially for people who already have a cancer diagnosis.
How GLP‑1 Drugs May Affect Cancer Patients: Weighing Potential Benefits Against Important Risks
“It’s a different story for people who have been diagnosed with cancer and the use of GLP‑1s. That’s because we have far less evidence or data about the use of GLP‑1s after a cancer diagnosis. We also have little to no data about interactions with cancer therapy. What I would say about that is this is essentially a risk‑benefit analysis that every patient with cancer should discuss with their oncologist,” Dr. Iyengar explained.
Early observational studies offer some encouraging signals, particularly for survivors whose biggest risks after treatment are cardiometabolic diseases.
“We have some smaller observational studies that suggest that GLP‑1 receptor agonists combined with hormone therapy for breast cancer, for example, appear to be safe. You may have a little less weight loss.”
Still, Dr. Iyengar notes that the picture is far from complete, and potential interactions with certain cancer therapies remain a concern.
“The GLP‑1 receptor agonist is likely to be helpful by improving overall survival and reducing cardio‑metabolic risk, and may even improve the risk of recurrence of that cancer. Now… there’s also some data to suggest — this is all very early — that for some immune‑mediated cancers there might be a different story… the GLP‑1 receptor agonists may interact with immune therapy in a negative way. And I also worry that if the side effects from the GLP‑1 receptor agonist make the side effects of chemotherapy worse, that may lead to dose reductions and pauses of the chemotherapy.”
Because of these uncertainties, he says decisions should be individualized based on the type of cancer therapy a patient is receiving. Ultimately, more research and randomized controlled clinical trials are needed before GLP‑1s can be fully integrated into cancer‑risk‑reduction strategies.
Semaglutide works by impacting the glucagon-like peptide-1 (GLP) GLP-1 hormone.
Integral to blood sugar control, GLP-1 is a hormone released by the gut in response to food. It causes the pancreas to release insulin. A rising blood insulin level causes all body tissues to absorb glucose (blood sugar) from the bloodstream, lowering blood glucose levels.
GLP-1 also prevents the release of glucagon, a hormone that raises blood sugar levels by stimulating liver cells to release glucose, and helps people feel full for longer. These effects can also cause people to lose weight.
Early data from Truveta, a data aggregator that is comprised of 30 U.S. Health Systems shows that many people who haven’t previously used GLP-1 medications are now getting prescriptions for the Wegovy pill directly from their primary care providers.
“GLPs are amazing medications. They change people’s lives in terms of cardiac risk and diabetes. They have widespread benefits,” Dr. Samantha Newman, at Memorial Sloan Kettering Cancer Center, tells SurvivorNet.
The FDA approved the oral version in December 2025, and uptake has been swift. Tens of thousands have already started the medication, which not only supports weight loss but also reduces the risk of diabetes and several cancers.
“Some of the benefits for using GLP-1 agonists can be weight loss, improvement in glycemic control or blood glucose, decreased risk of weight-related conditions such as various cancers, like breast cancer, endometrial cancer, colon cancer, liver disease,” Dr. Holly Lofton, director of the Medical Weight Management Program at NYU Langone in Manhattan, tells SurvivorNet.
Injectable GLP-1 therapies like semaglutide and tirzepatide have shown significant benefits for weight loss and overall health, but for many people interested in taking advantage of the weight loss drug, have often been shaped by practical barriers—how the drug is administered via an injection, whether patients can access it, how well they tolerate it, and what their insurance will cover.
The oral form of the weight loss drug may help lower some of those barriers by offering a non-injectable option that can be prescribed and managed across a wider range of clinical settings.
Side Effects of Semaglutide
Some of the possible side effects include:
- inflammation of your pancreas (pancreatitis)
- changes in vision
- low blood sugar, kidney problems
- kidney failure
- serious allergic reactions
Tips to Live a Healthier Life
Dr. Ken Miller, the director of outpatient oncology at the University of Maryland Greenebaum Cancer Center, recommends these four things for cancer survivors to do to try to avoid another cancer diagnosis:
- Exercise at least two hours a week; walking counts
- Eat a low-fat diet
- Eat a colorful diet with lots of fruits and vegetables; doctors recommend two to three cups a day
- Maintain a healthy weight
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