What are Calories?

Calorie is a measuring unit for energy. In the context of weight loss, food and exercise, Net Calorie Intake [Calories In (diet) - Calories Out (exercise + metaboic calorie loss)] predicts if you will lose weight or gain weight and the rate of weight loss or gain.
Basic calorie components of any food are fats, proteins and carbohydrates where

• 1 gm of fat = 9 calories
• 1 gm of protein = 4 calories
• 1 gm of carbohydrate = 4 calories

1 kg of weigth is equal to 7700 Calories - hence to lose 1 kg your net calorie intake should be -7700 Calories. As an example if your net intake is about -500 calories per day, you will lose 1 kg in 15 days