So what is 200 calories?

We often hear people talk about calories, but what exactly are calories? In fact, a calorie is a unit of measurement for the thermal energy of food, 1 calorie being the thermal energy required to raise the temperature of 1 gram of water by 1 degree Celsius. So how much energy is contained in all sorts of food? And how much and which foods are more conducive to maintaining good health? According to the book "Energy and Protein Requirements" published by the World Health Organization, a healthy adult woman needs to consume daily...