Metabolism Image Gallery. (Images description from left to right.)
1 – Metabolism. Carbohydrate and Fat.
The two major fuels for energy: carbohydrate and fat. A critical characteristic of human metabolism is that, with a few exceptions, it cannot make glucose from fat.
See – Carbohydrate | Fat | glucose
2 – Metabolism. Fat (triacylglycerol; TAG) structure.
Typical fatty acids have 20 or so carbon atoms. Fat cells continually break down and resynthesize TAG from fatty acids and glycerol.
3 – Metabolism. Keeping ketosis under control.
Ketogenesis is regulated by a feedback loop (light blue arrows in the figure): low glucose ➛ insulin falls ➛ lipolysis goes up ➛ high fatty acids ➛ ketone bodies ➛ insulin increases ➛ lipolysis is inhibited ➛ lower fatty acids ➛ ketogenesis shuts off ➛ cells use glucose ➛ glucose falls ➛ insulin falls, etc. The bottom line is that a ketogenic diet does not have a risk of ketoacidosis.
4 – Metabolism. Metabolic function and ketosis.
Two fuels (CHO and fat), supplied by dietary or stored macromolecules, are sources of energy from oxidation to carbon dioxide and water. A third fuel, ketone bodies, can be synthesized when glucose is low. Glucose can be stored in glycogen or converted to fat, but the key feature of metabolism is that you can’t convert fat to glucose. Protein can supply glucose, but in starvation, it will be body protein, and in this context, ketone bodies are “protein sparing” and can be oxidized as an alternative fuel, keeping the demand for GNG.
5 – Metabolism. Interaction of metabolic components.
Fat (TAG) can supply fatty acids for fuel, but this can also give us ketone bodies. To keep things from running away (too much fat breakdown, too many ketone bodies) ketone bodies stimulate insulin, which acts as negative feedback.
6 – Summary of metabolism.
The two fuels from the diet, carbohydrate and fat, and the ketone bodies that appear in response to carbohydrate restriction can be oxidized for energy (orange arrows). The fatty acid-TAG cycle and the glucose-glycogen cycle are regulated by insulin (which inhibits breakdown and favors storage) and by glucagon (which favors breakdown). Insulin itself regulates glucagon.
7 – Metabolism. What goes in & what goes out. (Infographic.)
8 – Metabolism. Energy & Human Life. (Infographic.)