How your birthday affects your BMI — and what you can do about it

I’ve spoken about epigenetics quite a bit in the past. And I’ve explained how changes in gene expression may play a bigger role than we thought in a whole host of modern health crises — including the obesity epidemic.

But I recently came across a study that I thought was particularly interesting. It found that people born in the mid-20th century have stronger genetic ties to high BMI than older generations. And this discovery may shed a little new light on what, exactly, has been driving obesity rates up for the last 40 years.

We’ve been wrapped up in this epidemic so long that we can finally examine generational differences. (Sad, but terribly true.) And that’s just what this study set out to do. Researchers looked at how “fat genes” and actual BMI measurements shifted between older and younger people as our nation ballooned in size.

In both black and white participants, genetic obesity risk had strong ties to BMI. But when researchers accounted for birth year, they found that higher genetic risk ratcheted up BMI dramatically depending on the subject’s generation.

Having a higher genetic obesity risk more than doubled BMI differences in younger populations, compared to high-risk members of their parents’ generation. In other words, the same fat genes had a much bigger influence on the weight of people born after 1943 than they did on people who were born before 1924.

These results appeared in the Journal of the American Medical Association (JAMA). And they offer some of the clearest evidence to date that our environment is definitely changing us, inside and out.

It makes sense, if you think about it. Anyone born in the early 1900s was already older by the time the obesity epidemic took hold. But the younger population was practically raised in it, having lived the majority of their lives in an environment that promotes obesity.

The obesity epidemic officially started in the mid- to late-70s — an era that saw the rise in fast food, soda consumption, and the introduction of hormones and antibiotics into the food supply. (To say nothing of the other obesogens I’ve discussed here — pesticides, plastics, and so on — that have only become more common as the years pass.)

But it can work both ways. Yes, this study shows that genetic factors behind weight gain are more likely to take hold in obesogenic environments. But we also know that healthy environments result in low obesity rates.

We may live in an obesogenic world — but it doesn’t have to be a losing battle. This study proves that your genetics only dictate part of the story. The rest is up to you…

You don’t have to be fat, even if you come from an obese family. I’m living, breathing proof of that. My family may consider me a freak of nature — but the truth is, it’s nature that has allowed me to overcome this genetic predisposition.

I work hard to stay lean and healthy. You should too. And don’t ever let anyone tell you that you can’t succeed. Because with enough vigilance and dedication, you can… and you will.