During prolonged fastings, in what sequence are the following organic compounds used up by the body ?

Step-by-step solution

During prolonged fasting, first carbohydrates are used up then fats and proteins are used last. Carbohydrate and fat metabolism can produce energy more easily than protein and they follow a more or less simple pathway to enter into TCA cycle. When all carbohydrates of the body are used up then fats are converted into carbohydrates and when all fats are used up then ultimately proteins of the body are converted into carbohydrates to be used up by the body.