Obesity: The Final Answer

I recently found myself in a friendly argument over the origins of the obesity epidemic. It (the argument, not the epidemic) started with a post on my Facebook page (scroll down to January 2), which itself came from this article on weight loss in the New York Times Magazine.

The argument was over how much of the rise in obesity can be attributed to genetics vs. environment. Anoop Balachandran, a fitness professional studying for his Ph.D. in exercise science, argues that it’s virtually all genetics, and makes his case on his blog in this post and this one. His biggest point is that the people who are obese today are the people who would’ve been obese anyway, and what we call an epidemic is a rise in their weight, not an overall fattening of the entire population.

No one in my position wants to accept genetics as the final answer. To paraphrase Lt. Aldo Raine, “We ain’t in the excuse-makin’ business. We in the killin’-fat business. And cousin, business is a-boomin’.”

In the past I’ve worked hard to show that genes are part of the problem (in this Men’s Fitness article from 2005 I’m on the record saying it’s 40 percent), but that environment and lifestyle choices still matter. And, for a variety of reasons, our environment has become substantially more fattening since the late 1970s.

For example, take a look at this picture of my siblings and me from the 1970s, and guess how many people in that photo have struggled with their weight. (The answer: five.) Now guess how many ended up obese. (Three.) What do you see in that photo that suggests any of those fit, tanned, and healthy-looking people will end up gaining substantial amounts of weight that they will subsequently struggle to lose? That’s my own family, where everyone played sports, everyone worked out, and everyone has gone through life with a higher-than-average concern about his or her personal health.

But here’s the wild card: Our father (as I’ve mentioned in almost every book and several magazine articles) was extremely fat for his generation. If he was in a room, chances are he was the fattest guy there. Our mom was the opposite: skinny and so focused on weight that several of us worry when our kids are within earshot. She’s said terrible things about some of them, including my son when he was a roly-poly infant whose entire diet consisted of breast milk. What were we supposed to do, deny him the left breast so he’d learn to settle for whatever he could get from the right?

As I said, five of my siblings have inherited my father’s predisposition to easy weight gain, while for two of us, weight control has been relatively easy. Was it all just the luck of the draw? Or was there a range of possibilities for each of us?

Thanks to this paper from a journal called Disease Models & Mechanisms, we have an answer. (Huge thanks to Mike Nelson for the heads-up.) The authors are an international who’s who of veteran weight-loss researchers. Their goal was to explain why conventional explanations of obesity, like the set-point theory, are flawed, and what might provide a more durable model.

If obesity is all or mostly a genetic phenomenon, then the set-point theory would explain it. We all have a weight and a body-fat percentage that our bodies want to maintain, and any challenge to that set point will trigger mechanisms that make weight loss impossible to sustain. There might be a small range — perhaps 5 to 10 percent of body weight — that we can control. The rest was genetically determined at conception, more or less.

The authors poke these holes in that argument:

Why are the most affluent members of poor societies, but the poorest members of affluent societies, most prone to obesity? Why are children who watch more TV most susceptible? Why do people gain weight in specific circumstances (college, marriage, or upon moving from Asia to the U.S.)? I love this quote:

If the set point changes in response to our social class, our marital status, or whether or not we watch TV, then it is not a ‘set’ point.

To replace set-point theory, the authors offer the dual intervention point model. Each of us has an upper and lower intervention point. Your body won’t allow your weight to sink below the latter, or rise above the former. The range between my floor and ceiling seems to be relatively small, which is why my weight rarely goes below my current 180 pounds or above 190. But for someone else, it might be huge.

To quote the authors:

Within the gap between upper and lower intervention points is the space where environmental effects on energy balance hold sway. … More broadly, the model can explain the obesity epidemic as a consequence of increased food supplies driving up food intake, while also explaining why only some people become overweight and obese in this obesogenic environment.

So how much of your weight is determined by genes? According to the authors, our current best guess is 65 percent. The rest depends on the life you live and the choices you make.

Tags: Tags: body fat, dual intervention point model, energy balance, fat loss, genetics, lifestyle, obesity, set point theory, Weight Loss