More weight around your middle appears to increase cancer risk.

Obesity Causes Disease

I recently read an article from Nutrition Action Newsletter that highlighted cancer being linked to obesity[1].  I am absolutely certain that most Americans have heard the tie or link between obesity, metabolic syndrome, heart disease, and diabetes type 2.  You cannot walk through your local grocery store without seeing a magazine trumpeting these risks.  What you do not see is a lot of them talking about obesity being linked to cancer[2].  The fact is that we know that obesity is tied to nearly every cancer thus an increased risk of contracting and dying of said cancer.  

Why would excess body weight put me at risk for cancer?  

Obesity causes a lot of problems in your body.  It not only causes your body to wear out quicker but it also creates inflammation.  Low-level inflammation may reduce your ability to defend yourself against cancer and infection.  Being overweight causes pressure in your belly and induces gastroesophageal reflux.  Reflux with inflammation increases your risk of stomach and esophageal cancer.  Obesity also causes men and women to produce and store more estrogen.  Estrogen predisposes both men and women to breast cancer.  Estrogen increases a female’s risk of ovarian and uterine cancers.  Basically, these cancers are fueled by high levels of the hormone estrogen.  Also, obesity puts stress on the body and increases insulin and insulin resistance which appears to increase the risk of breast, pancreatic, colon, and kidney cancers [3],[4].  These are just a few examples of why excess weight increases the risk for cancer.  There are many more. 

So which cancers have an increased risk in obese patients?

Obesity Causes Cancer

Nearly all studies that have been performed before this date have shown an increased risk of cancer in those that are obese, and there is consistent evidence across both animal and human trials to support a link[5].  In fact, the evidence linking obesity to cancer risk is exceptionally strong.  I will illustrate this with some prior completed studies.  In fact, the evidence linking obesity to cancer risk is exceptionally strong.  I will illustrate this with some prior completed studies.  Many of these studies I found on PUBMED and National Cancer Institute or Cancer.gov.  The studies I will use will be mostly large cohort studies which are observational studies.  There are not a lot of randomized placebo-controlled trials on this topic because it is unethical to try to cause cancer or to purposely make people obese knowing the risk to humans.  It is important to notice that you cannot interpret a finding from an observational study as being a cause because correlation is not equal to causation.  This fact being true, there are plenty of animal studies to show causation, and we can assume human studies would produce similar results.  

The 13 cancers linked to obesity:

1. Breast Cancer: Obesity is a well establish risk for developing breast cancer, and this is especially true in post-menopausal women.  Obese females that have an elevated BMI have elevated estrogen levels that a higher risk of breast cancer than lean women[6].  Estrogen is stored in fat deposits and leaches out over time.  This elevation in estrogen increases their risk for breast cancer.  This risk increase persists in the elderly with and without hormone replacement[7],[2],[4].  Contrary to popular belief, this risk is not only in women and is also found in obese males[8].  Not only does elevated body fat increase the risk of heart disease, but it also increases the risk that the patient will not respond to treatment once the cancer is found[2].
2. 

   Cancers associated with obesity infographic

   Colorectal cancer: Colorectal cancer rates not only rise as we increase our fat intake and lower our fiber intake, but it also increases as people become more obese.  That being said, it appears even though fat intake increased the risk of colon cancer, fat from nuts does not[9].  The obese are slightly more likely to develop colorectal cancer than normal-weight people[10],[11],[12].  Obesity and a higher BMI is associated with increased risks of colon and rectal cancers in both men and in women, but the increases are higher in men than in women[11].  Also, surgical removal of the cancer is less successful, and lymph node harvesting for staging is less successful[13].

3. Endometrial cancer: As with breast cancer, obese and overweight women are more likely than normal-weight women to develop endometrial cancer (cancer of the inside surface of the uterus).  The endometrium is the surface of the uterus that is slothed off every month during menses.  Endometrial cancer is caused by abnormal over-proliferation of the lining of the uterus.  Because obese women have higher estrogen levels, they are more likely to acquire this form of cancer.   Adult obesity is one of the strongest risks for developing this type of cancer[14].  In fact, the research shows that the aggressive and higher risk tumors are more common in obese females[15].
4. Esophageal adenocarcinoma: Esophageal cancer is more commonly seen in subjects who have gastroesophageal reflux disease (GERD), smoke, drink alcohol, have gallbladder disease, and are obese.  People who are overweight or obese are more likely than the non-overweight to develop a type of esophageal cancer named esophageal adenocarcinoma.  People who are extremely obese are more than four times as likely.  In fact, obesity is an independent risk factor without smoking and without an elevated body weight[16].  In fact, obesity and elevated BMI are associated with poorer prognosis in esophageal cancer[17].
5. Gallbladder cancer: This type of cancer is exceptionally rare in the United States with less than 1 per 100,000 in the United States.  Regardless, compared with normal-weight people, people who are obese and overweight have an increase in the risk of gallbladder cancer[18],[19].  The article from cancer.gov states there is a 20% and 60% increased risk for the overweight and obese respectively[20].  The risk increase is greater in women than men[21].  
6. Stomach cancer: Upper stomach or gastric cardia cancer has been tied to increased body fat.  Per cancer.gov, people who are obese are near twice the risk of normal-weight people to develop cancer in the upper part of the stomach or gastric cardia[22],[23].  Although not all gastric cancers are increased with obesity, these are.   
7. Liver cancer: Being overweight or obese doubles your risk for liver cancer when compared to healthy normal weight individuals.  The liver is the bodies detoxification center so the bigger you are, the more stress it puts on your liver.  It only makes sense that it would increase your risk for liver cancer.  People who are overweight or obese are up to twice as likely as normal-weight people to develop liver cancer.  The association between overweight/obesity and liver cancer is stronger in men than women[24],[25].
8. 

   Tummy and Tape Measure

   Kidney cancer: Being overweight or obese increases your risk for kidney cancer[26].  Part of this is due to insulin and insulin resistance, but it is also due to the increased stress on the kidneys caused by the increased body weight.  The kidneys detoxify the blood and clear toxins into the urine.    Increased body weight increases the toxin load in the blood and the demand upon the kidneys to clear toxins.  Although higher blood pressure is associated with higher body weight and also with kidney cancer, the association of renal cell cancer with obesity is independent of its association with high blood pressure[27].  Renal cell carcinoma has an elevated mortality that has increases with elevations in BMI[28].  

9. Multiple Myeloma: Obesity is a risk for multiple myeloma[29],[30].  Compared with normal-weight individuals, overweight and obese individuals have a higher risk of developing multiple myeloma[31].  
10. Meningioma: Brain cancer is scary.  A growing mass inside your skull quickly builds up the pressure and reduces your faculties.  Meningioma is a relatively rare but severe cancer, but the risk is higher in obesity[18].  Any cancer in the skull is of high risk just because it increases the pressure on the brain.  Meningioma is a slow-growing brain tumor that arises in the membranes surrounding the brain and the spinal cord.  Since it is in the skull, it is dangerous.  Even if a tumor in the skull does not metastasize, they can result in blindness just be increasing pressure in the skull.  Adiposity or obesity is related to enhanced risk for meningioma[32].
11. Ovarian cancer: Prior research has shown a tie to ovarian cancer and excess estrogen so it makes sense that obesity would also increase this risk.  Higher BMI has been associated with an increase in the risk of ovarian cancer.  This risk is particularly higher in women who have never used menopausal hormone therapy or had babies[33].  For example, an elevated BMI is associated with a 3% increase in ovarian cancer incidence per decade despite never using hormone replacement therapy[33].
12. Pancreatic cancer: After our prior discussion of estrogen and cancer risk, it only makes sense that obesity is tied to pancreatic cancer.  Obesity put a stress on the pancreas so obesity should increase the risk of pancreatic cancer, but pancreatic cancer is a diverse group cancer, so it is not so clear.  Based on research, obese people, as marked by BMI and waist-hip ratios, are more likely to develop pancreatic cancer than normal-weight people[34].
13. Thyroid cancer: Higher BMIs are associated with an increase in the risk of thyroid cancer[34],[35],[36],[37].  It appears that the risk is tied to insulin resistance[35],[38].  It only makes sense that obesity puts a stress on the thyroid and increases thyroid cancer risk.  

The bottom line:  Extra pounds means an increase cancer risk.   There is a strong link between obesity and cancer, but you cannot interpret this as a cause.  Data from observational studies cannot definitively establish that obesity causes cancer.  Obese or overweight people may differ from lean people in ways other than their body fat, so one of the other differences may actually be the cause.  I would use this with the other risks tied to obesity as motivation to lose weight.  The absence of excess body fatness lowers the risk of most cancers, so it makes sense that losing weight would be a good idea.