Nutrition Science and Everyday Application - beta v 0.1

180 ALICE CALLAHAN, PHD, HEATHER LEONARD, MED, RDN, AND TAMBERLY POWELL, MS, RDN
valuable nutrients. We also find refined starch—such as corn starch—as an ingredient in
many processed foods, because it serves as a good thickener.
2 – Glycogen
Glycogen is structurally similar to amylopectin, but it’s the storage form of carbohydrate in
animals, humans included. It’s made up of highly branched chains of glucose, and it’s stored
in the liver and skeletal muscle. The branched structure of glycogen makes it easier to break
down quickly to release glucose to serve as fuel when needed on short notice.
Liver glycogen is broken down to glucose, which is released into the bloodstream and can
be used by cells around the body. Muscle glycogen provides energy only for muscle, to fuel
activity. That can come in handy if you’re being chased by a lion, or sprinting to make your
bus! Both liver and muscle glycogen serve as relatively short-term forms of energy storage;
together, they can only provide enough glucose to last for about 24 hours in a person fasting
or eating a very low carbohydrate diet.
Even though glycogen is stored in the liver and muscles of animals, we don’t find it in
meat, because it’s broken down soon after slaughter. Thus, glycogen is not found in our food.
Instead, we have to make it in our liver and muscle from glucose.
Here’s a beautiful depiction of glycogen.
Figure 4.6. Glycogen is made from long, branching chains of glucose, radiating around a central
protein.
3 – Fiber
Fiber includes carbohydrates and other structural substances in plants that are indigestible
to human enzymes. Fiber is made by plants to provide protection and structural support.