Obesity and Cancer

We’ve all heard about the obesity epidemic but what does it really mean. Obesity is a medical term used to describe individuals whose BMI is greater than 30. On average that would mean if you were 5’4″ you would weigh more than 172 pounds. There is much evidence on the relation between obesity, in particular abdominal obesity, and increased cancer risk.

Large epidemiologic studies have linked being overweight or obese with greater risk of developing certain malignancies such as postmenopausal breast, endometrial, esophageal, colon, Kidney, liver, pancreatic, and gallbladder cancers. Other studies showed that obesity is associated with developing more aggressive forms of prostate and breast cancer and those extra pounds are linked to poor outcomes for many tumors. Women who are obese have nearly tripled the risk of developing endometrial cancer than those of normal weight. Obesity increases the risk of their developing postmenopausal breast cancer by 40%. Obese men have about a 24% higher risk of Colon cancer. What is the cause? Most animal, laboratory and clinical studies suggest insulinemia (high levels of insulin or hyperinsulinemia), excess production of sex hormones (estrogen and Testosterone) and inflammation.

Excess abdominal fat causes high blood levels of insulin and type II diabetes. This is part of the cascade for inducing several malignancies including breast, colon, Pancreatic, prostate and postmenopausal breast cancers. High serum insulin levels induced production and activity of insulin like growth factor (IGF)-1. IGF-1 stimulates cell proliferation (over growth) and decreases natural cell death (apoptosis) through biochemical pathways known to cause growth and spread of various tumors. High insulin levels cause greater availability of the sex hormones estrogen, testosterone and androgens which are known to trigger many tumors, especially breast, prostate, and endometrial cancer. Fat tissue can also produce it’s own estrogen through an enzyme aromatase pathway which converts androgens into estrogens. This local estrogen production increases estrogen levels in breast tumors >8-10 times higher than that found in the circulation. This is why postmenopausal women who are obese tend to have breast cancers that are estrogen receptor-positive.

In addition, inflammatory cytokins are released by fat cells, which also induced high insulin blood levels. This boosts the activity of the tumor growth factor IGF-1 and increase the production of aromatase which increases estrogen levels. Fat tissue can cause cancer or its progression, by releasing excessive amounts of tumor necrosis factor (TNF) and IL-6. These inflammatory cytokines are thought to activate tumor promoting transcription factors and lead to higher overall cancer death rate. Fat tissue also releases the enzymes tumors use to invade other tissues and metastasize such as matrix metalloproteinase.

Obesity heightens the risk of esophageal, pancreatic, colorectal, postmenopausal breast, endometrial, gallbladder and kidney cancers. Since elevated levels of insulin (hyperinsulinemia) is thought to be secondary to obesity and directly linked to type II diabetes drugs that combat hyperinsulinemia like Metformin, has been shown to improve cancer survival.

The current obesity epidemic, affecting both children and adults in this country, may evolve into a cancer epidemic if nothing is done to stop it. Approximately 2/3 of adults and close to 25% of children in the United States is overweight or obese placing them at increased risk for cancer. We discussed with our patients their risk of developing heart disease and diabetes because of their weight however the more ominous feature we should discuss with our patient’s is the risk of cancer.

Efforts to lower your BMI under 25 and increase activity have both been shown to lower insulin levels which are thought to precipitate the development of fat. Dietary efforts should include avoiding foods that induced insulin secretion (carbohydrates) and consuming more foods that do not involve insulin for their metabolism such as vegetables and proteins.