The Counterintuitive Physiology of Obesity

At the National Academy of Sciences yesterday, the Roundtable on Obesity Solutions got a bit of a jolt. It came in the form of an afternoon spent reflecting on the counterintuitive physiology of obesity. One roundtable member summed it up nicely. “This way of thinking about obesity just smashes our old models for solving the problem.”

We had four outstanding presentations – by Kevin Hall, Mark Hopkins, Lee Kaplan, and Lynn Goldman. We’ll keep this concise and focus on Kaplan’s overview.

Physiology That Drives Behavior

Most of our thinking about obesity flows from a single reference point – human behavior. Two behaviors – eating and physical activity – give rise to obesity, a state of too much adiposity. Because of that altered state, physiology changes and complications arise. It’s a long and familiar list: joint damage, diabetes, heart disease, liver disease, certain cancers.

But in a compelling presentation, Kaplan explained that this thinking is precisely backward.

It is physiology that drives the behaviors we associate with obesity. Many complex systems work together to protect stores of fat tissue. Just as it regulates body temperature, the body works to maintain a fixed level of fat stores. When levels of fat rise above that set point, the body works to burn off the excess. The brain suppresses appetite and thoughts about food.

Likewise, when fat stores drop below the set point, the body adapts. Appetite and hunger rise. Food that would ordinarily never appeal starts looking delicious. Metabolic function slows to conserve energy.

A Set Point for Fat Mass

Obesity is a disease where that set point gets altered. The body works to protect a level of adiposity that interferes with health and body functions. Just as we can hold our breath, we can alter our eating and physical activity patterns to try to suppress it. Some people can have a lot of success with doing this. But for most people, all that’s possible is a 5-10% reduction in weight.

Such modest outcomes can improve a person’s health. Unfortunately, though, it doesn’t reverse the underlying physiology. And they don’t reverse all the health problems that obesity causes. The physiology that drives the disease is still at work.

So if we want obesity solutions, we need to stop thinking we can simply nudge the population to behave itself better. Real solutions will require fixing what we’ve broken in the food chain and our physical environment that’s altering our physiology. We’ll need to remove sources of stress, distress, and pollution that disrupt metabolism. We must move away from using medicines that cause weight gain.

In other words, real solutions will come from correcting the problems that disturb our physiology. Not from downstream behaviors.

Click here for Kaplan’s presentation.

A Droplet Upside Down, photograph © Predi / flickr

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August 8, 2018