Obesity and Inactivity: The Evolutionary Perspective

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AICR’s expert report concluded that carrying excess body fat is a convincing cause of six different cancers (colorectal, postmenopausal breast, esophageal, endometrial, kidney and pancreatic) and a probable cause of gallbladder cancer as well.  That means that in the US alone, obesity is responsible for over 100,000 cancer cases every year.

And as obesity figures continue to rise, that number is likely to grow even larger.

How did we get here?

Last week, at the 3rd International Congress on Physical Activity and Public Health, many researchers presented data tracking recent trends in the amount of leisure-time physical activity we’re getting, nowadays. But one of the keynote speakers, Dr. William Leonard of Northwestern University, presented an intriguing talk that took the long view.

The very long view.

Like, hundreds of thousands of years long.

Dr. Leonard is an  anthropologist, you see.  He talked about how humans evolved, specifically how how changes in our diet and activity level changed our body type.

Basically, said Dr. Leonard, as our brains got bigger, they placed larger demands on our metabolism, and our diets became more nutrient- and calorie-dense to support them.

Leonard proposed that the recent and much-talked about uptick in the calorie-density of our foods over the past few decades (higher fat content, larger portion sizes) is simply an extension of what’s been happening to us, on an evolutionary scale, for millions of years.  But the difference is key: dietary changes that used to to take thousands and thousands of years to occur have happened within a single lifetime.

Even so, he suggested that we might be missing the real story by focusing so much on the increase in calories in our diets.  In fact, he notes, while calorie content of the diet in the developed world has increased since the fifties, that increase leveled off in the 80s.  Yet obesity rates continued, and continue, to rise.

To explain this, he suggests that it’s decreased calorie expenditure that plays a larger role in obesity than caloric intake.

Throughout our evolution, our caloric intake increased to match greater and greater needs we placed upon our bodies – hunting calorie-dense animals is more demanding than gathering low-calorie-dense crops. But this eon-old trend toward increased calorie-burning is now experiencing a dramatic reversal: Our jobs have become much more sedentary since the 80s and the advent of the computer.

Our bodies have evolved over millions of years to actively and effectively meet our caloric needs from the environment. But now we’re suddenly accelerating the trend toward more calories – and by changing the physical environment to make things easier, we’re reversing the evolutionary trend toward burning more calories.

The net effect: we’re upsetting an equilibrium our species has managed to maintain for thousands and thousands of years.

Stairs for Cancer Prevention?

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Blogging from a conference of the Society of Public Health Educators (SOPHE)

What are Public Health Educators talking about?

As at many health related conferences, the talk is about developing environments in neighborhoods, workplaces and schools to promote good health.  That is – encourage more physical activity and access to healthy food. Just about every researcher and practitioner is talking about how to engage the community and neighborhood to help drive these changes.  This may seem obvious, but it hasn’t always been done.  Read about AICR’s Policy Report Policy and Action for Cancer Prevention, which includes recommendations for government, schools, industry, health professionals and others.

Interesting research tidbit: One of the speakers today mentioned a simple initiative of posting signs and prompts around the workplace to encourage more use of stairs in the building.  This has shown moderate effectiveness with anywhere from 2-9% increase in stair use.  While not a huge change in behavior, it’s an easy intervention for inspiring some change.  And an easy way to incorporate more physical activity – which lowers risk for cancer  – into your day.

Do you choose stairs or elevators when given the choice?

“A Sea-Change in How the US Approaches Disease Prevention”

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Great short piece on America Public Media’s Marketplace Morning Report on a story that hasn’t gotten the attention it should:  How the new healthcare legislation broadens our national approach to diseases like cancer by placing an unprecedented amount of focus on prevention. Take a listen.

Understand: More and better prevention efforts are sorely needed and long overdue.  But if there’s one thing our policy report made clear, it’s that government can’t do it alone.  All levels of society – industry, schools, health professionals, the media, individuals – helped get us to where we are now, and must play a role in the kind of sweeping societal changes needed to make it easier for everyone to make healthy, cancer protective choices.

How are our policy report’s 49 recommendations addressed in the new legislation?  What, exactly, remains to be done?  It’ll take some time to tease out those answers.

In the meantime, count on the American Institute for Cancer Research for practical everyday advice that’s based on research your generosity makes possible — research that reveals how you can help protect yourself from cancer.