Question

During prolonged fasting, in what sequence are the following organic compounds used up by the body: -
A. First carbohydrates, next fats, and lastly proteins
B. First fats, next carbohydrates, and lastly proteins
C. First carbohydrates, next proteins, and lastly lipids
D. First proteins, next lipids, and lastly carbohydrates

Answer 1

Prolonged fasting infers no food being eaten for a long time. Periods of fasting are counteracted by our body by tapping on to the stored energy reserves. Stored energy reserves can be carbohydrates that are stored as glycogen, fats which are stored as fatty acid chains in the adipose tissue, and protein that are present in muscles.

Complete answer:
Our body has evolved several mechanisms by which we can remain functioning even during prolonged periods of fasting or not having food. Generally, our body utilizes the food that we eat to function, and if excess energy is produced it is stored as either glycogen or fatty acids.
-It is only when we stop eating does our body begin to utilize our glycogen reserves. Glycogen is a complex polysaccharide made of amylopectin stored primarily in the liver but is also stored in individual cells. The metabolic reactions convert the glycogen into glucose and utilize it for energy to maintain basic metabolic function and organ function.
-Once our glycogen reserves have been depleted, our body taps into the fat reserves. Fatty acids stored in the adipose tissue are converted into acetyl CoA molecules in a process called beta-oxidation, where the fatty acids are oxidized to form these compounds. The acetyl CoA then goes into the Krebs cycle and produces ATP and other ketone bodies as byproducts, this stage within the body is known as ketosis.
-After the fat reserves have been tapped out our body goes for the proteins in our muscles. The protein is converted to pyruvate through the metabolic pathway of gluconeogenesis. This pyruvate is then used to produce energy. Once the maximum amount of protein from muscles has been utilized proteins from organs are taken, mainly the heart as it’s a muscular organ. And once this occurs it is immediately followed by organ failure and other disorders and ultimately leads to death.
Therefore, the correct option is A.

Note: Glycogen reserves are very small within the body when compared to fats and proteins. This is because our body cannot store glycogen for long periods as it’s a complex molecule. Whereas fats can be stored perpetually in our adipose tissue in large amounts. This is the same in the case of proteins.