Several studies have outlined the link between cancer and obesity. Although it is undetermined why obesity leads to an increased risk of cancer, it is believed to be due to the inflammation in visceral fat.

Obesity increases the risk of 13 different cancers, which make up 40% of all cancer cases diagnosed in the United States annually. The American Cancer Society reports excess body weight is responsible for about 11% of cancers in women and 5% of cancers in men in the United States, and about 7% of all cancer deaths.

The Link Between Cancer and Obesity

Several mechanisms explain the link between cancer and obesity. 

Insulin

Increased insulin levels in the blood are common in obese individuals. Elevated insulin levels facilitate the development of type 2 diabetes, a risk factor for cancer development. Increased levels of insulin and insulin-like growth factor-1 (IGF-1) have been linked to the development of colon, kidney, prostate, and endometrial cancers.

Inflammation

Obese individuals have chronic inflammation that can cause oxidative stress, which leads to DNA damage, increasing the risk of cancers. Similarly, visceral fat (fat around the organs, including the liver and intestines) triggers inflammation. 

The problem with excess visceral fat is that it affects specific processes in the body. Fat cells produce hormones that promote cell growth; the more often these cells divide, the more likely cancer will develop. Fat tissue can also produce proteins that cause conditions like chronic inflammation and insulin resistance, which can promote cell growth. 

When cells reproduce uncontrollably, the risk of cancer increases dramatically. The more cells divide and reproduce, the greater the chance a tumor will form.

Fat Cells

Obesity increases the prevalence of adipose (fatty) tissue in the body. Fat tissue produces high levels of estrogen, which has been linked to an increased risk of breast, endometrial, ovarian, and other cancers. 

Similarly, fat cells produce adipokines, hormones that stimulate or inhibit cell growth. Adiponectin, a type of adipokine hormone, helps with insulin sensitivity and managing inflammation. Adiponectin is less abundant in obese individuals and can increase the risk of developing cancer for the reasons mentioned above.

Prevalence of Cancers in Obese Individuals

As discussed above, there is a correlation between cancer and obesity. “The percentage of cancer cases attributed to excess body weight varied widely across cancer types and was as high as 51% for liver or gallbladder cancer, 49.2% for endometrial cancer in women, 48.8% for liver or gallbladder cancer, and 30.6% for esophageal adenocarcinoma in men.”  

• Endometrial Cancer: 7 times as likely in people with severe obesity, 
• Esophageal: 4.8 times as likely in people with severe obesity
• Gastric Cancer: 2 times as likely in people with obesity
• Liver Cancer: 2 times as likely in people with obesity or overweight
• Kidney Cancer: 2 times as likely in people with obesity or overweight
• Multiple myeloma: 1.1–1.2 times as likely in people with obesity or overweight
• Meningioma: 1.5 times as likely in people with obesity
• Pancreatic Cancer: 1.5 times as likely in people with obesity or overweight
• Colorectal Cancer: 1.3 times as likely in people with obesity
• Gallbladder Cancer: 1.6 times as likely in people with obesity
• Breast Cancer: 1.2–1.4 times as likely in people with obesity or overweight
• Ovarian Cancer: 1.1 times as likely for every 5-unit increase in BMI
• Thyroid Cancer: 1.3 times as likely in people with obesity

Can Bariatric Surgery Minimize Cancer Risk?

Patients who have had bariatric surgery appear to have lower obesity-related cancer risk than those who did not have weight loss surgery. Though bariatric surgery is more aggressive than lifestyle modifications, surgery may provide additional benefits, such as improved quality of life and decreased long-term health care costs. One study determined that the “odds of developing breast, esophageal, prostate, renal, and colorectal cancers [were] significantly lower in morbidly obese patients who under[went] bariatric surgery.”