system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible to be genetically fat?

What I mean by this question is that one argument given by overweight people is that they've tried all the diets under the sun and they are still fat and thus blame genetics.

Other people give a similar argument that certain medical conditions make it impossible to eat a healthy diet.

But wouldn't the laws of thermodynamics still be relevant, ie calorie intake < calorie usage = weight loss?
gpt
The answer is 'kind of'. Metabolism is determined by the genetic makeup. Still, weight gain and loss is, for every one of us, the sum of calories absorbed and calories spent. 

 Some ethnicities are on average more prone to gaining weight as a result of being adapted to diets low in fats and sugars. Many tribes from the American continents, for instance, have experienced a very negative impact from suddenly being introduced to western food products rich in fats and sugar. 

 With very few exceptions to the rule, a carefully planned diet combined with adequate exercise works for everyone.