Thermodynamics in nutrition

The law of conservation of energy states that energy cannot be created or destroyed. It can only be transformed from one form to another. This law also applies to nutrition. 
Calories in versus calories out.
Many experts disagree with the belief of counting calories as a method to lose bodyfat. 1 pound of bodyfat roughly equals 3500 calories. Therefore, eating 500 calories less everyday for 7 days straight would result in exactly 1 pound of loss in bodyfat. Several studies have proven this to be false solidifying the belief that counting calories does not work. This disparity can be explained.
Reasons.
1. Thermic effect of food: 1 calorie of protein is not the same as 1 calorie of carbohydrates or fats. The body requires energy to digest food. Fats require only 0-3% of the total energy from food to get digested. Carbohydrates require 5-10% of energy while proteins require 20-30% of energy. Therefore, the macronutrient profile (protein, carbohydrates and fats ratio) play an important role in weight loss.
2. NEAT: Non exercise activity thermogenesis or NEAT is the amount of energy a person uses during daily activities. Examples of NEAT include jittering, walking, brushing teeth and even writing. People generally feel weaker when they consume less calories so they tend to move less reducing NEAT.
3. Miscounting calories: Studies have shown that over 90% of the population underestimate their daily caloric consumption. 
Conclusion.
Ultimately, calories consumed versus calories spent will always hold true. In order to lose weight, one must consume less calories and move more.