Thermodynamics is only involved at the simplest levels. Hunger and satiation are regulated primarily with leptin, not thermodynamics. Fat storage is controlled primarily with insulin which is itself regulated by various endocrine system components. Thermodynamics is only involved at a level far below complex systems control dynamics.
A Pound is 3,600 calories. I can easily eat 1,800 calories over my maintenance requirement.
Do you think in one year I am going to gain 180 pounds or .5 pounds per day?