Before I answer this question, let me first explain what are carbohydrates are:
In short:
Basically, carbohydrates are a bunch of Carbon, Hydrogen, and Oxygen molecules: CarbOHydrates, also known as CHO. Carbohydrates are made of glucose molecules. Glucose has the molecular formula of C6H12O6 and is used by the cells in our bodies for energy, in fact, it is the preferred fuel source because it is so quickly digested, absorbed and utilized. Essentially: Carbs = Fuel
They are found in many foods including:
Grains
Beans & legumes
Starchy vegetables
Non-starchy vegetables
Fruit
Dairy
Nuts & seeds
In Depth:
Carbohydrates are one of the 3 main macronutrients, which are nutrients human bodies need in larger quantities. These are carbohydrates, fats, and proteins. Each has a different function in the body, but I will focus on carbs today.
Function
As stated above, the primary function of carbohydrates in the body is fuel. This is partially why the amount of carbs needed varies day to day and is different for each individual. Someone competing in triathlons requires a much different carbohydrate intake than someone like me who sits at a desk multiple days a week -- but I still need some to perform my best!
The body generally uses carbs and fats for fuel, but carbs are its favorite. The ideal, though, is to be able to switch fluidly between carbs and fats depending on macronutrient intake and activity type. Generally, high intense activity requires more glucose, while lower/steady state activity will use more fats.
However, carbohydrates have other functions as well:
Preserve muscle mass
Help regulate digestion
Do we need carbohydrates?
You may have heard that our body doesn’t actually need carbs, though.
Technically, this is true. BUT, that does NOT mean it is ideal! Carbohydrate consumption is important for OPTIMAL function and energy production. This is the unfortunate fact I learned studying biochemistry while simultaneously discovering low-carb paleo and bulletproof coffee and that all I needed to do was eat fats and eventually I’d be a fat burning machine! Right? Wrong. Very, very wrong.
Anyway, no, technically we don’t need carbohydrates to survive, however, to thrive, we definitely do. We will survive because without the presence of this preferred fuel source, our bodies will either make glucose through a process called gluconeogenesis, or provide fuel through the production of ketone bodies.
Gluconeogenesis
Gluco (glucose) + neo (new) + genesis (generate) = new glucose is generated from non-carbohydrate substrates, typically amino acids. This process either turns dietary amino acids or muscle protein into glucose to be used as energy.
Gluconeogenesis is a survival mechanism, which means our bodies don’t prefer it, but juuust in case there happened to be no carbohydrate sources around: no fruit trees, or tubers in the ground, or perhaps an oreo bush (nope, those aren’t real), we would not die of starvation. Because our bodies are amazing!
Ketone Bodies
There are three ketone bodies, also known as ketones: acetone, acetoacetate, and 3-hydroxybutyrate. They are produced by the liver and used as an energy source when glucose is low. They are always present in the blood and increase, again, as a survival mechanism, during fasting and prolonged exercise when glucose is no longer available. This process is a bit different than using fats as a fuel source.
Photo source: Researchgate
The body will break down fats to ketone bodies, but without enough glucose, the body does not break fats down completely into carbon dioxide and hydrogen in the citric acid cycle (also known as the krebs cycle and tricarboxylic acid cycle [TCA]). Hydrogen then goes on to be used in oxidative phosphorylation, where the most energy, or ATP, is produced. ATP = Adenosine TriphosPhate, the type of energy used to fuel the cells in our body, which can be created by each macronutrient.
This is because fat burns in the flame of carbohydrates, or rather, oxaloacetate.
Why oxaloacetate is needed to burn fat efficiently
Alright, ready to dive into some biochemistry? No? That’s okay, you can skip this part and continue reading about types of carbohydrates in part II, but for those of you who are curious, let’s jump in, shall we?
When we consume carbohydrates, they break down into glucose (which I will explain a bit later on), and glucose fuels one of the main metabolic systems called glycolysis, a product of which is pyruvate. Glycolysis has many steps, but this image illustrates it simply:
Now, pyruvate, then goes on to produce acetylCoA (acetyl coenzyme A: delivers acetyl group to the citric acid cycle) and oxaloacetate. AcetylCoA is also produced by fats. AcetylCoA and oxaloacetate both fuel the citric acid cycle, but oxaloacetate initiates the first steps.
Source: SlidePlayer
Thus, without carbohydrates, there is no pyruvate, no oxaloactate, and no complete use of acetylCoA. Why is this important? The citric acid cycle produces energy precursors for oxidative phosphorylation (also called the electron transport chain), which ultimately produces the most energy (or ATP) from the original macronutrients.
For more information read: https://www.namrata.co/fats-burn-in-the-flame-of-carbohydrates/
To put this into a little perspective, 1 glucose molecule will produce only 2 ATP from glycolysis, but 30-45 ATP from oxidative phosphorylation.
Does that make sense? If not, read more about it here:
On to part II!
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