Are Your Genes Making You Fat?

How many times have you heard someone complain that she’s overweight because she has “bad genes”? Or that heart disease “runs in his family”?

The truth is that genes account for a lot less of what happens in our life than most people believe. And the good news is that you may have a lot more control over what you’re genes “do” or “don’t do” than you might think.

Let’s say you’re a scientist and you want to know the effect of a certain gene—let’s call it Gene X . You have a hypothesis—Gene X has something to do with the feeling of fear. You suspect that those who have a copy of this gene are likely to be much more fearful than those without it, so you decide to test your theory using mice.

The first thing you do is you see what happens with mice that don’t have Gene X. Do they behave differently at baseline? Are they just as fearful when they see a cat? (If so, then there goes your hypothesis. If not, you might be on to something- you can go talk to CNN and say “more research is needed” and you’ll be right.)

But how do you find such mice, mice who don’t have a copy of this gene you want to study? Simple. You create them. Through some miraculous biochemical wizardry, you actually remove Gene X from a bunch of mice and you breed them with each other. This is done all the time—the resultant strain of mice are called the “Knockout” mice because you have literally “knocked out” the gene you’re trying to study.

Next, you take another group of mice who already have the “fear gene” (Gene X), but, just for good measure, you give them an extra copy of it. Now you have two strains of mice—the knockout mice (who have no “fear gene”) and the “enriched” mice (who have two copies of it).

Keeping everything else in their environment identical, you run your tests and see which mice are more fearful—and by how much.

How do you measure fear in mice? Simple. Mice are nocturnal—they naturally

prefer the dark. Under normal circumstances, they’ll hang out in dark corners and

avoid the light. So you take some delicious mouse food—the mouse equivalent

of Crème brûlée—and you put it on a plate in the middle of a brightly lit cage.

Naturally fearful mice won’t venture out to touch it, no matter how good it looks or

smells. Less fearful mice will check left and right, then sprint for the food and

gobble it down.

So what do you think happens?

The knockout mice—no Gene X “fear gene”– run out into the light and grab the food while the mice with the double dose of Gene X nervously hide in the dark.

Sounds like an open and shut case for the power of genes, don’t you think?

Not so fast.

Let’s suppose—as Robert Sapolsky did in his brilliant analysis of the gene paradox in his Wall Street Journal column—that the lab down the street now wants to test the hypothesis. “This sounds great!”, they say, “we want to duplicate the results and add some tests of our own!”. So they get themselves a bunch of the knockout mice and a bunch of the “double fear gene” mice and they run the same experiment.

Except… they get a different result. This time there’s a difference between the “fear gene” mice and the “knockout” mice—but it’s insignificant.

Then another lab decides to try the experiment—and they get the opposite result—this time the “fear” mice actually seem more likely to run out and get the food!

A fourth lab does the experiment—and they get the same results as the original lab!

What’s going on here?

What’s happening can be explained by the emerging and fascinating science of epigenetics, and its close cousin, nutrigenomics.

See, genes, don’t just sit there making things happen. Most genes are “turned on”, or “turned off” by things in the environment, things you actually have control of. Maybe the lab down the street used different mouse chow, which could affect digestion, hormones, even neurotransmitter production. Maybe the temperature of the lab was different, which could affect thyroid levels. Maybe the people handling the mice in the lab down the street were a lot rougher and louder, scaring the mice and changing the levels of their stress hormones- which affect many aspects of behavior and metabolism. Maybe the lab down the street was darker—or lighter—or used a disinfectant which altered chemicals in the brain.

Epigentics is the science of how the environment acts on genes to change what they do (or tell them not to do it in the first place). Genes are like light switches, wired to turn on certain lamps. If you flick the switch, it will predictably turn on the associated lamps, but if you don’t flick the switch, you’ll be sitting in darkness.

When genes are “turned on” they’re said to be expressed. Epigenetics is the science that looks at how life and your environment turns on and off the genetic light switches, telling your genes to either express themselves or shut up.

And ”nutrigenomics” is the science of how nutrition does the exact same thing.

What’s most important to remember is that genes aren’t fixed quantities that determine behavior no matter what. What happens—what you eat, what you do, where you live, who you hang out with, what chemicals you’re exposed to, what exercises you do, just about everything you can think of— can have a profound effect on whether those genes get called up to get in the game, or whether they sit there warming the bench.

Genes may make it more (or less) likely that something will happen. But with very few exceptions, having a particular gene practically never guarantees that you will get a particular disease.

Take obesity, for example, or diabetes. There is no “gene” for obesity, but there are many genes that, taken together, increase the probability that in a certain food environment, you are going to be someone who gains a lot of weight.

But if you don’t go into that food environment, those genes may never be “expressed”, (or “turned on”, like the abovementioned light switch.) In the presence of certain conditions (like high sugar food) your genetic make-up can in fact make it much more likely that you will get fat than, say, your lean neighbor who has a different set of genes.

You may not be able to change the genetic hand you were dealt, at least not yet.

But you are able – in some small or large way— to change, control, or modify your environment and your behavior. YOU have that power.

And those things have a lot more to do with how things turn out for you than your genes ever did.



1 Comment

  1. Joe

    Johnny. I am your biggest fan of low carb living. I have strayed and put on some weight and essentially by increasing carbs over the holiday. I think I switched my genes on by doing that. I am in the processs of regaining control. Thanks for all you visionar, excellent work in this field


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