Dr. Robert Lustig, who became a YouTube sensation with his outstanding speech Sugar: The Bitter Truth, wrote an essay a few years ago titled Childhood obesity: behavioral aberration or biochemical drive? Reinterpreting the First Law of Thermodynamics. I’d try to summarize it, but it’s already so brief, I don’t think I can. So here it is:
Childhood obesity has become epidemic over the past 30 years. The First Law of Thermodynamics is routinely interpreted to imply that weight gain is secondary to increased caloric intake and/or decreased energy expenditure, two behaviors that have been documented during this interval; nonetheless, lifestyle interventions are notoriously ineffective at promoting weight loss.
Obesity is characterized by hyperinsulinemia. Although hyperinsulinemia is usually thought to be secondary to obesity, it can instead be primary, due to autonomic dysfunction. Obesity is also a state of leptin resistance, in which defective leptin signal transduction promotes excess energy intake, to maintain normal energy expenditure. Insulin and leptin share a common central signaling pathway, and it seems that insulin functions as an endogenous leptin antagonist.
Suppressing insulin ameliorates leptin resistance, with ensuing reduction of caloric intake, increased spontaneous activity, and improved quality of life. Hyperinsulinemia also interferes with dopamine clearance in the ventral tegmental area and nucleus accumbens, promoting increased food reward.
Accordingly, the First Law of Thermodynamics can be reinterpreted, such that the behaviors of increased caloric intake and decreased energy expenditure are secondary to obligate weight gain. This weight gain is driven by the hyperinsulinemic state, through three mechanisms: energy partitioning into adipose tissue; interference with leptin signal transduction; and interference with extinction of the hedonic response to food.
Notice that Lustig is calling for the First Law of Thermodynamics to be reinterpreted, not repealed. He isn’t denying that when kids gain weight, they’re taking in more calories than they’re expending. But as an endocrinologist who’s worked with a lot of obese kids, he knows better than to simply blame obesity on consuming too many calories and let it go at that. As he said in his first interview with Jimmy Moore, “No child chooses to be obese. The quality of life of an obese child is the same as a kid on cancer chemotherapy.”
Lustig also pointed out that there’s been a sharp rise recently in the number of obese six-month-olds. Are the obese six-month-olds taking in more calories than they’re expending? Yes, of course. But unless we’re going to start blaming babies for eating too much and exercising too little, the laws of thermodynamics don’t provide an explanation or a solution. Lustig knows that from experience.
Some years ago, he worked with a group of kids who had brain cancer. The cancer treatments were successful, but later the kids became obese. According to their parents, the kids had developed enormous appetites and become sedentary. As Lustig put it, they spent all day sleeping or sitting in front the of the TV and eating Doritos.
They were clearly consuming more calories than they were expending. But luckily for the kids, Dr. Lustig is blessed with the intelligence to distinguish between how we get fat and why we get fat. Consuming more energy than we expend is how. But the how doesn’t explain the why, any more than “your car is burning more gasoline per mile than it did a year ago” explains why you’re getting lousy mileage.
As an endocrinologist, Lustig understood that the change in behavior was being driven by a change in biochemistry. He suspected that as a side-effect of the cancer treatments, the kids were over-producing insulin. Tests confirmed his suspicion.
Now he knew why the kids were becoming obese, not just how. The high insulin was driving a disproportionate share of what the kids ate into their fat cells. With the energy being stored away instead of burned, they were hungry and tired all the time. So they ate more and sat around.
After recognzing the cause, Lustig gave the kids an insulin-suppressing drug. As he told Jimmy Moore:
“When we gave these kids this drug that blocked insulin secretion, they started losing weight. But more importantly, something that was even more amazing, these kids started exercising spontaneously. One kid became a competitive swimmer, two kids started lifting weights, one kid became the manager of his high school basketball team … Changing the kids’ insulin levels had an effect not just on their weight, not just on their appetites, but on their desire to engage in physical activity.”
Lustig didn’t tell the parents, “Well, it’s a simple matter of thermodynamics, so we must deal with imbalance between the calories in and the calories out. Tell your fat kid to eat less and move more.” And he didn’t (thank God) tell them, “Your kid is producing a high level of insulin, which according to an article I saw on the internet is actually a fabulous appetite suppressant, so don’t worry, he’ll start eating less any day now.”
Nope. Lustig recognized the actual cause of the problem, so that’s what he treated, not the symptom. When insulin was high, the kids stored too many calories as fat, so they ate more. When insulin was low, they burned more calories, so they ate less. You can correctly apply the laws of thermodynamics to either situation — but they won’t tell you anything useful.
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