Answer: Ghrelin
Explanation: Ghrelin is the hormone found in the body that acts as hunger hormone .The functioning of this hormones is based impact of consumption of food, growth hormones, fat percentage etc. It gets produced and released through stomach .
This hormone is also responsible for breaking down the deposited fat in the body and produce muscles.
According to the case ,Troy is also facing the obstruction from effects of ghrelin as he is not able to lose fat even after exercising which makes him thinks its due to genetic reason..