Some people are very prone to gain weight, while others find it very difficult to gain weight. Although the calories taken from foods and how much of these calories are taken from fats, carbohydrates and proteins are important, our daily activity and metabolic rate are also important factors in the regulation of body fat. If our metabolism rate is high, our body fat amount will be less. It has been proven that the metabolic rate of people who exercise for a long time is higher than that of sedentary (non-exercise) people.. The sum of the energy we spend with basal energy and daily activity gives the amount of calories we spend per day. Basal energy refers to the energy our body spends when we lie down without moving for 24 hours to maintain its vital functions. Although the metabolic rate varies according to the individual’s exercise status, gender and age, the metabolic rate slows down as the age progresses. Various scientific formulas have been developed to calculate how much energy we spend per day by calculating our basal energy. According to Harris – Benedict equation, basal metabolism energy needs for women = 655 + 9.6 x (weight, kg) + 1.8 x (height, cm) – 4.7 x (age), for men = 66 + 13.7 x (weight, kg) + 5 x (height, cm) – 6.8 x (Age). Multiplying the result by 1.4 if you are sedentary, by 1.7 if you are a moderate athlete, by 2 if you are a very active athlete gives you the approximate energy you spend daily. For example, a 30-year-old, 170 cm tall, 55 kilogram, moderately active athlete female has a basal energy of approximately = 655 + (9.6 x 55) + (1.8 x 170) – (4.7 x 30) = 1348 kilocalories. The energy she will spend on a non-exercise day is approximately = 1348 x 1.7 = 2291.6 kilocalories.