Weight and cancer risk: Just what the rats and mice predicted

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In my October 10 CTV blog posting, I pointed out that women could cut their lifetime risk of breast cancer by losing excess fat. It all had to do with decreasing the body’s fat cells that churn out estrogen, the hormone that drives the growth of many breast cancers. 

Just two weeks later, CTV’s Dr. Marla Shapiro wrote a similar blog reporting a study in the Archives of Internal Medicine that confirmed the link between post-menopausal weight gain and breast cancer.

Now, the American Institute for Cancer Research and the World Cancer Research Fund has upped the ante, warning that weight gain also increases the risk of developing cancers of the colon, kidney, esophagus, pancreas, and uterus (endometrium).

“This report is a real milestone in the fight against cancer, because its recommendations represent the most definitive advice on preventing cancer that has ever been available anywhere in the world,” said Prof. Martin Wiseman, project director of the report.

The study’s most important recommendation is to be “as lean as possible within the normal range of body weight”. 

Weight and cancer risk
Weight and cancer risk

Weight can increase your cancer risk

Sir Michael Marmot, chairman of the study panel, offered this advice: “We are recommending that people… avoid weight gain throughout adulthood. This might sound difficult, but this is what the science is telling us more clearly than ever before. The fact is that putting on weight can increase your cancer risk, even if you are still within the healthy range.”

If that isn’t enough, the report provided additional bad news: nightly cocktails, Sunday brunch and trips to the local steak house or McDonald’s might have to be cancelled or, at least, curtailed, as alcohol, bacon, red meat and (of course) fast foods are among the many substances implicated in increased cancer risk.

fat mice

What rat and mice has to say?

“Rats!” some of you may be exclaiming at this juncture… to which I would add: “Mice!” And you know what? We would be on to something.

For decades, laboratory studies have shown unequivocally that chronic underfeeding increases the lifespan of rodents by 40-60%, in part by decreasing the incidence of spontaneous cancers that, as in humans, spring up in ageing mice and rats. Those skinny rodents may be lean (and definitely aggressive and mean) but are they healthy!

As for their fatter, sleepy and oh-so-content but lumpy counterparts, call the oncologist!

Why does calorie restriction drop the risk of cancer in rodents and humans?

Weight loss, in addition to decreasing fat cells that make estrogen, implicated in breast and uterine (endometrial) cancer, also stops the body from overproducing a substance called insulin-like growth factor (IGF), a calorie-induced chemical that stimulates the development and growth of many different forms of cancer in the test-tube.

Experiments on mice and rats

Experiments in mice and rats show that when calories are restricted, blood levels of IGF plunge and so does the incidence of cancer. But when pure IGF is injected into skinny rodents, the rate of cancer climbs to the level found in their over-fed cousins.

The moral to the story is that research findings in laboratory animals often predict subsequent findings in humans and can also provide clues as to how diseases such as cancer occur. 


Don’t be surprised by the latest recommendations on diet and prevention of human cancer. The mice and rats have been telling us the same story for years.

Support the humane use of animals in medical research. Your health may depend on it!

Michael Richardson

Michael Richardson

I am a nutritionist and healthcare practitioner with over 10 years of experience. I am a medical article writer, blog writer. My passion is to help people. My favorite quote is:  “Let food be thy medicine and medicine be thy food.” ― Hippocrates

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