A calorie is a calorie as far as weight loss or gain is concerned, but not in the case of health.
from Lean Eating...pt 1
A Calorie Is Not A Calorie
While the gurus and pundits of the past believed that all calories were created equal, and while much of the current dietetics herd still believes it, I'm here to tell you why it just ain't true. To do so, I'll focus on three main arguments: the Thermic Effect of Feeding (TEF), cross-cultural studies, and the effects of isoenergetic diets using different foods.
The TEF, as I've said many times before, represents the additional caloric expenditure (above resting metabolism) that it takes to digest, absorb, and process the food you eat. Studies on the thermic effect of different foods have been important in describing the different effects of the macronutrients on metabolism.
The TEF lasts from between one to four hours after eating a meal. When adding up the thermic effects from each of your meals, this extra metabolism represents between 5% and 15% of your total daily energy expenditure. Therefore, if your daily energy expenditure is 3,000kcal, about 150 to 450kcal of that comes from the TEF. Interestingly, different macronutrients tend to have different effects on metabolism.