Why do lipids generate Twice as much Energy than Carbohydrates?

Why do fats store more energy than carbohydrates? What is the chemistry science behind it? This article attempts to answer all of that.

Introduction:

The question “Why do fats store more energy than carbohydrates” is pretty common in young students of chemistry hence the topic of this article. To better understand the answer to this question, let’s first review all the related concepts to this question.

What are Fats, Lipids, and Carbohydrates?

Fats and lipids are almost identical terms but are not the same. Lipids are a broad term that includes many compounds including oils, phospholipids, fats, steroids, and more. While fats come under the lipids bracket and are made up of fatty acids and glycerol.

As mentioned before lipids are a broad class of similar compounds. One of which is fat made of fatty acids and glycerol. Fatty acids have long chains in which there is a carboxyl group (COOH) at one end and carbon atoms in between.

The second component is glycerol which acts as a backbone for the molecular structure of fat. It is composed of a three-carbon alcohol molecule in which a carbon atom is bound to a hydroxyl group. In animal tissues, fats are stored as triglycerides, which is an arrangement of these fatty acids and glycerol. In this arrangement, three fatty acid molecules are esterified to three hydroxyl groups of glycerol.

Carbohydrates on the other hand are one of the macronutrients required by our body to supply energy for human metabolic processes. Made up of carbon, hydrogen, and oxygen atoms, these compounds are typically bonded in a ratio of 1:2:1 and are prime sources of energy in our muscles and brain.

How do Lipids Store Energy?

As mentioned before, the fat (one type of lipid) is converted and stored in the body tissues in the form of triglycerides. The body does that in the case of excess energy extracted from the food sources in a process called lipogenesis. These triglycerides are produced by the body by special cells called (adipocytes) which do the task of converting excess energy into triglycerides. This form of lipids is stored for long-term storage and later used as a backup. So, in short, lipids store energy in the form of triglycerides.

This stored fat is then used back to give energy when needed. For that, special enzymes called lipases break down these triglycerides (lipolysis) by hydrolyzing the ester bonds between fatty acids and glycerol. These broken chains are then released into the bloodstream. These chains arrive at the cells (especially muscles) where they are needed.

Fatty acids from these broken chains are processed in the mitochondria of cells to produce ATP (adenosine triphosphate). This is the pure form of energy usable by our body cells often regarded as body energy currency.

How do Carbs store Energy?

They store energy in the form of glycogen in the case of excess glucose through a process called glycogenesis. This form of glucose is primarily stored in the liver and muscles of our bodies and can be broken back through a process called glycogenolysis.

During this process, this stored glucose in the form of glycogen is broken down into glucose-1-phosphate and later converted into glucose-6-phosphate finally ending up as glucose in blood bloodstream. It is then used by our cells for normal metabolic processes.

Why do Fats store more Energy than Carbohydrates?

The core reason for that is that fats (lipids) are composed of a long chain of hydrocarbons with a higher proportion of carbon and hydrogen atoms. These longer chains and a higher proportion of C and H atoms give them less oxygen content compared to carbohydrates.

The hydrogen-carbon bonds are not just linkages but energy linkages. When they break, energy is available for the cells to use in metabolic processes. Fat has much longer chains of such C-H bonds giving them much higher energy storage capacity as compared to carbs which have more oxygen content in them.

Glycogen also contains a high concentration of water molecules to bind with glucose molecules. This leads to significant additional weight in the molecule which doesn’t provide additional energy. On the other hand, fats have much less water content giving them higher energy storage per unit of weight.

All the above-mentioned reason gives lipids about 9 Kcal of energy per gram as compared to 4 Kcal of energy per gram. This significant difference in energy density indicates almost double the energy-storing capacity of lipids (fats) as compared to carbs.

Conclusion:

To conclude the answer to the question “Why do fats store more energy than carbohydrates” can be stated that fats do so because of their higher C-H bonds and less water content in their molecular structure as compared to carbohydrates.