In order to understand why nutrition is important to treating diabetes, we need to talk about metabolism.
Since our bodies cannot synthesize their own source of energy like plants do, we need to ingest the fuel that allows our cells to live and function. The food we eat contains 3 metabolic fuels: proteins, carbohydrates, and lipids (commonly referred to as fats). Most foods have some combination of these fuels, as shown in the Venn diagram below.
I highly recommend watching the 15 minute Crashcourse video below that explains more about metabolic fuels. It’s very entertaining and succinctly explains what these fuels are made of.
Digestion of metabolic fuels
When we eat, Metabolic fuels are digested in the stomach and small intestine into their smallest components (called monomers), then are absorbed from the small intestine into the bloodstream. Once in the bloodstream, the fuel flows to all the cells in the body. The fuel either is used by the cells for energy, or stored for later use.
Glucose is the cell’s preferred metabolic fuel
All cells need a constant source of molecules called ATP. ATP is made by enzymes whose reactions are powered by extracting energy from metabolic fuel molecules. Under normal circumstances, the primary metabolic fuel used by cells is glucose, which is a carbohydrate. You may faintly recall the terms “glycolysis” and “Citric Acid Cycle” from your primary school biology classes. (Don’t worry, we’re just reviewing the highlights).
- Inside the cell, glucose undergoes Glycolysis. Glycolysis is the first step in extracting energy from glucose, and involves enzymes converting glucose into pyruvate.
- Pyruvate is converted into Acetyl-CoA by the enzyme pyruvate dehydrogenase.
- Acetyl-CoA is oxidized by critical series of enzymes we call the Citric Acid Cycle cycle (AKA Krebs Cycle). The Citric Acid Cycle is an important crossroads in metabolism, as it can accept Acetyl-CoA generated from other sources of metabolic fuel (protein and lipids. More on that later) During the oxidation steps of the Citric Acid Cycle, electrons in the form of NADH and FADH2 are generated.
- The electrons generated by the Citric Acid Cycle are then used by the electron transport chain (ETC). The ETC is a series of enzymes that use electrons to power an enzyme called ATP synthase to synthesize ATP. In the end, each glucose molecule can create 38 ATP molecules.
Here are the diagrams for the different steps converting glucose to ATP, if you’re interested.
What about protein?
Proteins are digested in the stomach and intestines into their smallest component, amino acids. Amino acids are absorbed into the bloodstream and imported into cells. Most amino acids are used by the cells to create proteins that the cell uses. The cell would rather use protein as a building block than a source of energy.
Under normal circumstance, about 10% of total body energy production comes from amino acids.
There are 20 different amino acids, and all of them have ways of entering the Citric Acid Cycle (see the figure below) to generate energy.
Of note, once in the Citric Acid Cycle, amino acids can be diverted into alternate pathways. One is called gluconeogenesis which converts the amino acid into glucose. The other diversion pathway is ketogenesis, some amino acids can be converted into ketone bodies.
What about lipids?