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Will losing excess weight reduce my cancer risk?

Obesity and cancer is in the news again. Two major reports linking obesity to cancer have appeared in the last month, and they make for scary reading. One report says excess weight could bring an increased risk of developing up to 13 different types of cancer, while the other suggests the longer you are overweight the more this risk grows.

I can practically feel the panic rising as I read them.  So I want to know, once and for all, does losing excess weight actually reduce cancer risk?

Obesity and cancer

Obesity is a hot topic in cancer research. At Worldwide Cancer Research we’ve funded at least four projects in the last 4 years alone, all directly investigating just how obesity and cancer are connected. And in the wider world, at least two heavyweight reports studying obesity and cancer have recently been in the media.

Obesity now linked to 13 different types of cancer

The first study, published by the IARC (International Agency for Research on Cancer) at the end of August reported that excess body weight can now be linked to an increased risk of developing cancer in as many as 13 different areas of the body. It sounds alarming, but dig deeper and a more balanced, more hopeful message comes through.

This study is not new research, it’s actually more of an overview of past research. The authors of the report (a group of 21 international cancer experts) evaluated the findings of over 1000 different studies. Rather than hyping-up the potential implications this might have for people who are overweight or obese, the experts carefully stated that they believe there is now “sufficient evidence in humans [which shows] that the absence of excess body fatness reduces the risk of cancers of the gastric cardia (a type of stomach cancer), liver, gallbladder, pancreas, ovary, thyroid, meningioma, and multiple myeloma.”

“This comprehensive evaluation reinforces the benefits of maintaining a healthy body weight in order to reduce the risk of several different types of cancer,” said Dr Béatrice Lauby-Secretan, lead author of the article.

This report actually builds on the findings of an earlier IARC report, published in 2002, which found “sufficient evidence in humans for a cancer-preventive effect of avoidance of weight gain” [and physical activity] for a number of cancers, including breast and bowel cancer.

Note the specific wording. What the experts are saying in a very careful way, is that based on the data they have reviewed, being obese or overweight can be a risk factor for developing cancer in these areas of the body. It doesn’t mean an obese person will always develop cancer, and it doesn’t mean a non-obese person will never develop cancer. This is patently untrue. It just means that, like smoking, it can be another factor which might alter an individual’s overall chances of developing cancer.

This comprehensive evaluation reinforces the benefits of maintaining a healthy body weight in order to reduce the risk of several different types of cancer

The most positive, and I think most important thing to come out of this report is the message that by reducing excess body fat, that is by intentionally losing weight (and by doing exercise), I can potentially reduce one of my own personal cancer risk factors. This is good news and pretty motivational to get out and about.

Duration of obesity and cancer risk

A second report, this time published in the open-access journal PLOS  by US and Israel-based researchers, followed 70,000 overweight and obese women over a number of years. This study gained some truly lurid headlines, brilliantly addressed by NHS choices.

The researchers used various observational methods to chart each participant’s weight over a number of decades along with whether or not they developed cancer. They found that for each decade of being overweight a person’s risk of developing an obesity-related cancer increased by 7%, with endometrial cancer (cancer of the lining of the womb) incurring the greatest risk.

But- their data also suggested that the degree of increased risk was linked to the duration and extent of obesity. And again this provides a positive message. A message that I can do something about my potentially weight-related cancer risk.

So it seems it doesn’t matter for how long I’ve been lugging round that extra body fat, the minute I start to lose weight and live healthier is the minute I potentially start to reduce my risk of developing some cancers.

But what does this really mean for me?

Both of the studies I’ve mentioned above have limitations to them, but the overall message really seems to be coming through loud and clear now. Obesity can be counted as another cancer risk factor for some people and for some cancers. The good news is that like smoking, it also seems to be a risk factor I can do something about.

"The minute I start to lose weight and live healthier is the minute I potentially start to reduce my risk of developing some cancers.”

What are Worldwide Cancer Research doing about obesity and cancer?

In four of our most recent projects, Professor Tony Tiganis in Australia and Professor Manolis Pasparakis in Germany have both independently studied how obesity is linked to liver cancer, Professor Stella Knight at Imperial College London used her funding to understand how obesity, the immune system, and bowel cancer might all interact, and Dr Michelle Hill in Australia investigated the link between obesity, cholesterol and prostate cancer.

And in a brand new project Dr Hector Peinado Selgas in Spain is investigating how being very overweight might increase the risk of some types of cancer spreading.

Further information

If you’re interested in living healthier NHS choices has a 12-week diet and exercise plan that’s free to download.

You can read more about our latest projects, including our projects tackling obesity and cancer here.

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