TV and Obesity, A Novel Hypothesis

It won't exactly be a surprise to anyone who's read an article or two about what's become known as "the obesity crisis" to say that watching a lot of television is associated with weight gain, a basic fact borne out by zillions of studies of kids' TV watching. The conventional, obvious, and intuitive explanation for this is that sitting around and eating potato chips instead of playing outside will make kids fat. This is just, well, "common sense," and like most "common sense" is seen as something that doesn't need to be tested. There's lots of evidence, however, that the relationship between TV and weight gain is not common-sensical at all, and that the reason kids who watch lots of television put on weight has less to do with sitting on the couch than with the brain's reaction to watching flickering images.

A really interesting data point on this comes as something of a byproduct of what we've learned from looking at the effects of psychotropic drugs. It's very hard to make people gain weight by making them eat more, but it's easy to do it with medication. Pretty much any anti-psychotic--Zyprexa was a well publicized one--will do it. This is not an accident. Most modern antipsychotics block a receptor in the brain for the neurotransmitter serotonin called the 5-HT2A receptor. Blocking it stops delusions and hallucinations, and most likely reduced anxiety as well. But for reasons that are as yet unclear, this also makes people gain a lot of weight.

Two things are scary about this. One is that blocking the 5-HT2A receptor is associated with especially big weight gains in children and teenagers, so it's particularly relevant to the whole obesity question.

But it's the other thing that's really worrying: you don't need to fiddle with psychotropic drugs to affect the 5-HT2A receptors in the brain. The receptors appear to be a key step in the brain's response to outside inputs. And when confronted with constant sensory stimulation the brain may do exactly what antipsychotic drugs do, which is to desensitize 5-HT2A receptors. That would protect the brain from a barrage of stimulation that would otherwise set off a dangerous fireworks of signals in the prefrontal cortex, something that is closely associated with epilepsy--the one illness characterized by attacks that we can say with certainty can be set off by television.

Exactly how much stimulation, and of what sort, could cause the "down-regulation" of 5-HT2A receptors that is linked to weight gain is an open question, but the 5-HT2A receptors provide a mechanism for a much stronger link between TV and obesity than the common "potato chips and lying on the couch" hypothesis. There's some strong evidence from studies of mice that implies that sensory stimulation affects the sensitivity of these receptors, but I haven't seen human research that would be conclusive, or any work that looks specifically at 5-HT2A receptors and TV viewing. If it's out there, I hope someone sends it to me. If it's not, I hope someone does it, because all the indirect evidence is already there. Though if I had a kid of my own, I'd wouldn't be rushing to volunteer him for the study.