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.

The Fitness Factor

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A lot of this issue’s Cancer Research Update focuses on the benefits of physical activity for cancer prevention, which is a relatively new area of study.

It’s clear that being physically active helps us lose and/or control weight. Weight control is the obvious reason to be active, now that research shows excess body fat causes seven different cancers.

Less is known about exactly how physical activity helps fight cancer independent of weight.  Studies show that it does, but can physical activity reduce cancer risk regardless of the number on the scale?

To learn more, read the full story in CRU.

And if you want a mental health boost as well as a physical one, try exercising outside. A new study in Environmental Science & Technology found that just five minutes of “green exercise” per day improves mood and self -esteem. Green exercise is any activity that takes place outdoors, such as a backyard garden or walk in a park.

With warmer weather, there are precious few excuses not to add some fun activity into your day. AICR has plenty of “Moving More” strategies here. If you have a fitness tip of your own, please share.

Serve Up a Healthy Weight

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Forget serving bowls.  If you’re trying to cut back to lose some weight, a simple strategy may help in a big way.

According to a Cornell University study titled “Serve Here; Eat There,” if you leave the serving dishes off the table you may eat less.

The researchers studied the amount of food 78 adults ate under different conditions.  They served some meals from the kitchen (“plated the food”) and allowed serving dishes to be on the table at other meals.

They found that people refilled their plates fewer times if food was served from the kitchen.  Overall, people ate 20% fewer calories (men ate about 29% less) when serving dishes were absent from the table.

Finding healthy ways to reduce extra body fat could help Americans reduce cancer cases by 100,000 every year according to AICR.  Learning to eat smaller portions and limiting “seconds” is one strategy experts say works.

So to lower your risk for cancer and other chronic disease, try this at home: Serve the food in the kitchen and leave the serving dishes off the table – with one exception.  Leave vegetable serving bowls on the table.  You may find you and your family emptying the vegetable bowl rather than filling up on pasta or meat.

How do you serve your meals?