Most diets fail and any weight loss is followed by an equal and sometimes greater weight gain. This is because when calories are restricted it causes chemicals to be released that eventually trigger your appetite to increase. You can fight this for awhile, but usually it overpowers even the most determined dieter. Research is emerging that indicates eating more protein may help curb your appetite when calories are restricted. This study took dieters that had lost 5-10% of their body weight and randomized them to a control group (15% protein) or a high-protein group (18% protein). Weight was monitored over a 6 month period. During this 6 month period, the control group gained back 7 pounds and the protein group only 2 pounds of the weight loss. Not only was weight regain less in the protein group, they also gained only muscle, not fat. One reason for the better weight maintenance in the protein group was because of enhanced satiety, that is, the protein group was less hungry. Just bumping up protein a little (for example, one serving of a protein shake) may be effective at maintaining weight loss compared to a normal protein diet.

Lejeune MP, Kovacs EM, Westerterp-Plantenga MS. Additional protein intake limits weight regain after weight loss in humans. Br J Nutr. 2005 Feb;93(2):281-9.