Our body tries to keep a constant weight in response to over or underfeeding by changing its metabolic rate.
An interesting study from the Pennington Biomedical Research Center in Baton Rouge, Louisiana found out that energy expenditure resulting from overfeeding was higher in people eating a high-protein diet. Participants were overfed for 56 days by consuming 40% more calories than usually. The increase in energy expenditure from overfeeding was connected to the protein content of the diet but not to the excess calories. People gained weight consistently during the study and there was no evidence of adapting the metabolic rate.