system
Given the following post, respond as if you're commenting on Reddit:
human
How much of our body weight can be attributed to genetics?

Many people claim they simply can't lose weight or gain weight but then I constantly hear about "calories in, calories out." If it is genetics, how is it that the obesity rated has gone up so much in the last ten years? If it isn't genetics, is there still a portion of the population that cannot lose or gain weight? Finding good, unbiased information on this seems impossible.

Edit: marked as interdisciplinary since it could fall under medicine, chemistry, biology, etc.
gpt
Calories in, calories out absolutely works. It's not possible not to lose weight if you limit your calorie intake below the calories you use daily. People may miscalculate their calorie intake and how much they consume energy however. 

Metabolism, gut bacteria etc. may affect the rate of the weight loss a little bit.  Genes controlling appetite and metabolism predispose to obesity when sufficient food energy present. Nobody gets or stays fat when food energy is scare.  When people sign in to hospital for being dangerously obese and they are put into diet in controlled environment, they always lose weight.