Straight Dope on the fat gene?

Factual Questions
1

During Thanksgiving my sister tells one of her sons to enjoy being able to eat like a pig now, before the family fat gene kicks in and he gains a bunch of weight. If earned a glare from her with a side of smirk from my nephew when I pointed out this gene seems to only have affected her and my other sister. Our parents were quite trim, ditto our grandparents. Both her sons are quite fit, and so are me and my brother. Of our twenty-some cousins, only one is overweight and he’s been overweight since we were kids, unlike my sisters.

She countered that none of that precludes her and her sister from havinghe fate gene.

My query: how would she know? How does anyone? I’ve seen Cecil’s article and others estimating the percentage of the population that has the gene, but nothing indicating there’s a test to let people like my sisters know it’s genetics rather than their insanely sednetary lifestyles combined with overeating (for Thanksgiving they made a couuntry ham and 20lb turkey - there were six of us).

2

The idea of it all coming down to one gene is wrong. Eye color doesn’t even come down to one gene. High school biology is a poor way of understanding how genetics actually works.

The idea that genetics can predispose you to being fat is correct, but the idea that genetics is destiny is also wrong, because genes can’t magically create calories.

3

Of course, there’s also the possibility that those individuals’ weight is largely influenced by the attitude that you should “enjoy pigging out”.

4

And here we get down to nature vs nurture, also known as the difficulty of disentangling culture from genetics when it comes to what humans do.

5

How old is the son? It could be a humorous way of telling him to enjoy the high metabolism of youth while he still has it.

6

If there’s a fat gene then it appeared in the late 70s and early 80s, because that’s when the American obesity epidemic started.

7

The fat gene is formed by large quantities of ingested junk food.

I caught it in my mid 20s and it has been hard to manage.

8

So is it more a case of people having certain markers that would show up in a screening? And does anyone bother screening for it since, as you point out, simply the presence of the gene wouldn’t make someone obese? The Straight Dope article said people with the gene were only 7lbs. heavier on average.

9

Obesity is like intelligence, there are hundreds of genes that all play a minor role.

Also genetics haven’t changed much in the last 50 years, but obesity rates have skyrocketed starting around 1980. Epigenetics play a role, the environment we live in will change how genes are expressed.

However obesity rates do get higher among adults vs adolescents. I’m not sure of all the reasons why, but changes in level of endocrine hormones probably plays a role.