[Retric]

Fat burns calories.

Generally, to maintain X pounds of weight loss you must consume ~10X fewer calories every day. In order to more quickly reach a new weight most people exceed that difference, but they can’t go back to old eating habits without regaining their original weight.

PS: Metabolism and exercise have real impact, but you can easily out eat any reasonable exercise plan.

[masonic]

  Fat burns calories.

Only brown fat (BAT) does, and humans have very little.

[Retric]

All cells require energy to survive.

On top of that strapping an extra 10+ pounds to your body and walking around would require extra energy for the same movements.