Obesity-Cancer Risks

"At this point, I think the oncology community believes there's a link between obesity and [the] risk for most cancers. And they believe that obesity contributes to the outcomes for many cancers."
"Every major study supported this [weight gain's impact on cancer] being an important factor. I think there's enough evidence to be really concerned and to have spent my whole career focusing on this area."
"We think losing as little as 5 percent will lead to physiological changes that may improve health outcomes as well as breast cancer outcomes. [The Breast Cancer Weight Loss study [BWEL] will give us the proof we need not only to show it's causal but to show it's reversible."
Dr. Pamela Goodwin, Oncologist, head, breast cancer program, Mount Sinai Hospital, Toronto

"It [the link between obesity and cancer] has gained much broader attention in the last few years. [However], there has been a lack of understanding among physicians but even more in the general population."
"We know that women who are overweight or obese when they're diagnosed with breast cancer have a higher risk of breast cancer recurrence compared to lean women. We're really interested in seeing if we can change that by helping women lose weight after they've been diagnosed with breast cancer."
Dr. Jennifer Ligibel, breast cancer physician, scientist, Harvard University

How might body weight affect cancer risk?

Excess body weight may affect cancer risk through a number of mechanisms, some of which might be specific to certain cancer types. Excess body fat might affect:

• Immune system function and inflammation
• Levels of certain hormones, such as insulin and estrogen
• Factors that regulate cell growth, such as insulin-like growth factor-1 (IGF-1)
• Proteins that influence how the body uses certain hormones, such as sex hormone-binding globulin

In the early 1990s, Dr. Goodwin became increasingly aware of suspected links between obesity and cancer. Three decades later, those who failed to share her theory are now prepared to, since evidence  is seen as sufficiently persuasive to the medical community that associating obesity with over a dozen forms of cancer is justified. A panel of the St.Galen International Breast Cancer Conference -- which occurs twice yearly whose purpose is to aid in determination of best practices internationally -- recommended weight loss and exercise as prescriptive parts of a preventive package against cancer onset.

As far as Dr. Goodwin is concerned, it is a link whose time has come to be presented as real and problematical, desperately awaiting a solution. According to several large studies, cancer risks emanating from the influence of excess weight in all probability rivals the proven risks of heart attacks stemming from obesity. Determining that such links exist, and influencing people's lifestyles through education in hopes that the problems can be ameliorated has, however, proven to be less than effective.

Massive public health efforts to persuade people to alter their lifestyles to make themselves less susceptible to wholesale weight gains with all the health impacts involving heart, diabetes and cancer have been for nought in the realization that obesity rates have continued relentlessly to soar among American adults in the past ten years, according to most recent studies. An unfortunate fact of life that is seen echoed in Canadian rates.

While involved in a fellowship at Princess Margaret Hospital twenty-five years ago, Dr. Goodwin came across a number of studies she read that appear to have bypassed the notice of most physicians and researchers who, if they heard of the theory, simply dismissed the possibility of a potential link between obesity and cancer. More latterly, a research paper published in the Journal of the American Medical Association points out that 40 percent of the U.S. adult population is now classified as obese.

Dr. Ligibel points out that an analysis by the World Health Organization dating from 2016, of studies that examined obesity and cancer development indicated at least thirteen types of cancer were associated with excess weight. Both Drs. Goodwin and Ligibel, though acknowledging a lack of scientific proof linking obesity with cancer, cite the reality that overwhelming evidence does exist that obesity represents a significant factor in cancer onset.

Both doctors are determined to find that "causal" link and to that end have undertaken a large-scale study, conducted in both Canada and the United States, focusing on the effects of a weight-loss program on recurrence of breast cancer in obese women. The study known as BWEL -- Breast Cancer Weight Loss study -- is in its initial stages, and is destined to track several thousand patients over a ten-year period.

Patients will be divided into two groups, with both receiving standard breast cancer treatments and weight-loss advice. One of the two, however, will be enlisted in a two-year diet and exercise program. According to Dr. Goodwin, exercise represents a dual weapon for obese individuals
against cancer, where it helps to rid the body of risky fat, while producing its own disease-fighting effects.

As an example, a higher exercise-gained muscle mass counters properties created in fat tissue which boosts cancer. As well, physical activity aids in lowering levels of some hormones known to aid tumour growth.