The obesity-cancer connection


Approximately 25% of men and 26% of women in New Zealand are obese[i]. Although obesity has been long associated with diabetes and heart conditions, it is also increasingly linked to cancer, as recent findings have shown. Today’s post explores the implications and reasons behind the numbers.

The World Health Organisation defines obesity as having a Body Mass Index (BMI)[ii] of 30 or more[iii]. In New Zealand, approximately 25% of men and 26% of women are obese[iv].

Around the world, obesity rates have doubled since 1980[v] and, although long associated with diabetes and heart conditions, a recent report now shows a clear connection between obesity and cancer. The report, released at the annual meeting of the American Society of Clinical Oncology in Chicago this past May 29, reveals two major findings:

  • 1 in 5 cancer deaths is caused by obesity
  • obesity will replace smoking as the largest preventable cause of cancer in the western world within the next ten years[vi].

The obesity-cancer connection

According Cancer Research UK, not only does excess fat alter the level of certain hormones, such as oestrogen, testosterone and insulin, in the body, which can increase cancer risk, but fat cells themselves can also generate “chemical messengers” which affect our body’s functioning.

Acknowledging that the obesity-cancer connection has yet to be completely understood, the American Cancer Society maintains that being overweight or obese is the main factor behind 1 in 5 cancer-related deaths. The organisation considers that obesity has a more influential role in certain cancers, such as breast and colon, than it does in others, yet indicates that excess belly fat, regardless of total weight has been associated with increased risk of some cancers. There is also research suggesting that the age when weight gain occurs may play a role in increasing cancer risk[vii].

The American Society of Clinical Oncology also notes that, in addition to being a preventable cause of cancer, obesity can also lead to worse outcomes for cancer sufferers, including increased risk of recurrence[viii].

Understanding the risks

The report findings are making headlines in the medical community and in national healthcare planning, yet the ramifications of obesity still need to make their way to the general public. Part of the reason is that, when we think of obesity, we tend to think of numerous health risks, but not cancer. Indeed, in discussing the report findings, Dr Jennifer Ligibel of the Dana Farber Cancer Institute at Harvard University echoes this common misconception about obesity as a health risk:

“I think people are aware that being overweight increases the risk of heart disease and diabetes but not that it increases the risk of cancer and their risk of dying from cancer[ix].”

The health risks of obesity are many, and Best Doctors encourages our blog readers and members to maintain a healthy weight, and to discuss healthy and sensible weight loss programmes with your doctor. People who are trying to quit smoking should also consult their doctor about effective options that reduce the risk of weight gain whilst quitting.


[i] World Map of Obesity (2014) World Obesity Federation. Retrieved from:

[ii] The WHO defines Body Mass Index as weight in kilograms divided by square height in meters (kg/m2). See note iii for reference.

[iii] World Health Organisation (2015) Obesity and overweight. Retrieved from:

[iv] See note i

[v] see note ii

[vi] Press Association (May 29th 2015) Obesity ‘causes one in five cancer deaths’. Retrieved from:

[vii] American Cancer Society (April 24th 2015) Body weight and cancer risk. Retrieved from:

[viii] American Society of Clinical Oncology (2015) Obesity and cancer. Retrieved from:

[ix] see note vii

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