If you haven't guessed already it is protein!
'How does it do that?'
1) Protein will help fill you up (therefore will help with portions)
2) Protein will help grow and maintain muscle mass ( more muscle means a higher calorie burn at rest)
3) Building muscle over time will burn more calories which in turn will help with fat loss.
The picture shows these men are both the same weight.
Very big difference in shape.
A larger amount of lean muscle will overtime will change your body shape.
Protein is one of the biggest things that can help with this along with a better overall eating habit and good sleep.