Obesity is linked to several forms of cancer. Now researchers believe they have uncovered how extra fat causes malignancies.

Recently published statistics show that 5.4 percent of cancers in women and 1.9 percent in men are associated with obesity, or having a body mass index of 30 or more. A BMI of 25 or more indicates being overweight, while 30 or is consider obese.

Obesity is particularly linked with cancers of the esophagus, bowel, kidneys, and pancreas and -- in women -- the gallbladder, ovaries, uterus, breast, said Dr. Alexandra Kautzky-Wille, an endocrinologist at the Comprehensive Cancer Center in Vienna, Austria.

Excess abdominal fat increases cancer risk because it changes the balance of sex hormones  by spurring production of estrogen, which encourages the growth of breast and endometrial cancers.

Excess fat also results in increased insulin production, which can act as a growth-stimulating hormone, encouraging cell division and tumor growth. In addition, fat causes inflammation in the abdominal region, which fuels cancer development, she said.

"The positive thing is that you can do something about this risk by losing weight or keeping an eye on your weight from the outset. Many types of cancer could be easily avoided in this way; a Mediterranean diet and exercise also helps, said Dr. Kautzky-Wille.