Not surprisingly, Pianko, now 54, has a slew of weight-​related health problems: high blood pressure, diabetes, knee joints that are bone on bone. By 2009, she had to give up a nursing career and go on disability. When she reached a BMI (body mass index) of 52, she knew she had to do something, partly because she worried a cancer diagnosis could be her next health battle.
A BMI of 30 and above (considered to be obese and just 30 extra pounds for the average woman who is 5' 4") is predicted to soon outpace tobacco use as the No. 1 preventable cause of cancer in the U.S. Pianko is not alone in her struggle with weight but is unusual for recognizing it as a risk factor for cancer.
"If you ask anyone about lung cancer, they know well that smoking increases your risk. But if you ask someone about obesity, they wouldn't usually associate it with cancer," notes registered dietitian Edith Nault of Excela Health's Well-​Being Center.
The list of weight-​related cancers from the National Cancer Institute (NCI) includes postmenopausal breast cancer, endometrial (uterine lining) cancer, colorectal cancer, esophageal cancer, kidney cancer and pancreatic cancer. Being overweight or obese also raises the risk of dying from cancer — more so for women. An estimated 20 percent of all cancer deaths in women (14 percent in men) could be blamed on excess weight, according to an often-​cited paper published in 2003 in the New England Journal of Medicine.
Our bodies, especially women's, are designed to easily store unspent fuel as fat deposits, explains UPMC's Dr. Edwards. In ancient times, when we dealt with periods of deprivation, this propensity gave women an edge up on carrying and delivering a healthy baby.
But fat tissue is not just a repository for excess calories; it creates the perfect environment for cancer cell growth. Adipose (fat storage) tissue is highly metabolically active and pumps out an astounding array of hormones, growth factors and signaling molecules, according to the NCI. Most, if not all, of the molecules being studied as potential mediators between obesity and cancer are not cancer-​causing but rather cancer-​promoting: They don't cause the mutations that turn a normal cell into a cancerous one but feed the growth and proliferation of malignant cells.
Other research shows that weight-​loss (bariatric) surgery, which often helps a woman lose and keep off as much as 100 pounds, can reverse precancerous conditions in the uterus lining.
Pianko lost more than 100 pounds in 2015 without having to resort to weight-​loss surgery. She credits regular exercise and her Excela Health dietitian, Nault, for helping her make changes that finally made a dent. Pianko is still considered to be obese but her BMI is now in the low 40s. After Nault had her write down everything she ate, Pianko realized her diet was heavy in carbs and her frequent dining out meant large portion sizes.
Fat tissue is not just a repository for excess calories; it creates the perfect environment for cancer cell growth.
Here's a snapshot of a recent talk Dr. Willett gave at the National Cancer Institute that explores four paradigms related to diet and cancer over the past half century.
"There was never any strong evidence for this idea but it was repeated so often that it became dogma in the 1980s and 1990s," Willet says. This idea was buried after researchers followed thousands of women on low-​fat diets over many years. What still holds true? While healthy fats (nuts, olive oil, avocados) are good for us, there is a positive association between animal fat and red meat consumption and risk of colon cancer.
"This paradigm, also referred to as positive energy balance, is here to stay," Willett says. "Very clearly, there is a relationship that has been supported in dozens and dozens of studies done across many countries over the past 15 years. This paradigm is not totally new, he adds, if we look back at studies done in the 1930s, it was noted that when animals gained weight they were more likely to develop cancer. Back then, though, this finding was considered to be a nuisance rather than a starting point for scrutiny.