Genetic testing for weight

[Halloweenshock]

I have one teen child who is very over weight, the other two are are not. The overweight child shares the looks of the heavy side of her relations, the other teens do not. The all eat around the same amount.

I suspect they have some sort of genetic predisposition to gaining weight. How do we find this out though? I would love to know if there is anything we could be doing to help. The GP just says diet and exercise, whereas the the child does lots of exercise and eats healthily.

any suggestions welcome.

I am not sure what this would achieve for you in the end.
I would suspect that genetics are at play. My friend has non-identical twins in their late teens - one is slim and the other noticably overweight. They eat the same food, similar portions, both are very sporty. Neither has a secret eating disorder. Their body types have evolved since very early childhood.
Maybe it would put your mind at rest knowing genetics are at play?

There was a threat about two housemates who eat the same, wfh etc yet one was not putting any weight on.
After digging it turned out that the other one goes for run, jiggles a lot, and the weight one one had occasionally extra little snack.

It's often the little things people don't even realise until they look for them.

Even if there is a genetic predisposition, the key to dealing with it is still calorie intake and activity levels. The only thing knowing the cause will do is make you and the child complacent (in a "there's nothing we can do, it's genetic" way).

They think that you only have to eat the equivalent of a Mars bar a day to end up with a weight problem.

With it being that finely balanced I am not sure you can draw any conclusions that it must be genetic.

activity levels
These van make quite difference.
Even if 2 people are both "sporty" each sport burns different levels and builds different level of muscle.
Eg - training for marathon will most likely burn more than kayaking. Also build muacles completely differently.
Now if bot people eat 3 exactly same meals but one does activity burning (made up numbers) 500cal and the second one 300cal, there is a considerable difference even before taking the muscle mass into account.