Weight loss or weight gain all boils down to energy. You have to find the appropriate balance to achieve the desired outcome. In general if energy consumed exceeds energy expended then we gain weight. Conversely, when the goal is to create a caloric deficit, where calories expended exceed calories consumed, weight loss will occur. Energy expended can be divided into basal metabolic rate(60%, determined by lean body mass), the thermic effect of food(10-15%), and activity thermogenesis(15-50%, depending on person)

The thermic effect of food accounts for 10-15 percent of calories expended in a given day.  Essentially eating, digesting and processing and food requires energy. Protein has a greater thermic effect than other macronutrients, followed by carbohydrates, and then fats, which have very little thermic effect.  Just by upping the proportion of protein in your diet you can metabolize more fat. See a Registered Dietitian for adequate ranges for your specific needs. These may change for health conditions, disease status, athletic ability, age and gender; however, general guidelines for protein consumption are .8-1 gram per kilogram of body weight. (10-15% of daily total calories).