In the story I discuss how Tarzan’s body metabolizes the different kinds of foods he eats. Here is a little more detail on those processes (keep in mind that this is greatly simplified):

Dietary Fat

The fat we eat is first broken down into its constituent fatty acids and absorbed into the walls of the intestines. There the fatty acids are formed into “triglycerides” (three fatty acids attached to a glycerol backbone). The triglycerides are then packed up together and placed on these life rafts called “chylomicrons” which can move through the bloodstream and carry the triglycerides to fat cells for storage. Fats are also used to build structures, including cell membranes. When glucose is low, some fatty acids will be broken down by the liver and used to create something called “ketone bodies” (or “ketones”), which most tissues can burn for fuel in place of glucose.

Protein

Protein is broken down into its constituent amino acids. These amino acids are used to effect tissue repair and growth, and to build other structures needed by our cells. Amino acids can be burned as fuel by our cells if needed, and excess amino acids can be converted by the liver into glucose or fats.

Carbohydrates

Carbohydrates come in three main forms:

Starch: Starch is a long string of glucose molecules bound together.

When we eat starch it is broken down into individual glucose molecules. How quickly that happens is affected by how tightly the starch is bound up by fiber (starches bound up with fiber result in a slower and lower glucose rise in the blood).

Fiber: Fiber comes in two forms, which work together to slow digestion of starch.

• Insoluble fiber (does not absorb water): We do not digest insoluble fiber. It passes into the gut, and on out of the body.
• Soluble fiber (does absorb water): It turns into a gel and helps to slow digestion of starches. The soluble fiber can be eaten by the microorganisms in our gut.

Sugars:

The sugars that concern us here are:

Fructose:

This is the sweetest sugar, which is found in fruits and in lesser amounts in vegetables. Some fructose is converted to glucose in our intestines, and the rest is sent to the liver. There it can be burned for fuel, converted to glucose and stored as glycogen (glycogen is a long string of glucose molecules that can be quickly broken down to glucose when needed), or converted to fat. The fat is formed into triglycerides, packed on life rafts called “Very Low-Density Lipoproteins” (VLDL) which can carry them to fat cells for storage. (The VLDL particles also carry cholesterol to cells. As the cargo is dropped off, the VLDL particles become LDL (Low-Density Lipoproteins).

Glucose:

This is the most common sugar. The starch in grains and vegetables is broken down into glucose molecules. Every cell in our bodies can burn glucose and there is a small subset of cells that can only burn glucose. Glucose can be burned for fuel, stored as glycogen, or converted to fat in the liver. This fat is also packaged into triglycerides and loaded onto VLDL particles for transport to the fat cells. Muscles also store glucose as glycogen for use in a pinch.

NOTE: Table sugar is a combination of fructose and glucose known as “sucrose”; when we eat it, the fructose and glucose are separated and metabolized as described above. Our bodies handle high-fructose corn syrup the same way.

Lactose:

This is a sugar found in milk and is made of glucose and galactose. The glucose and galactose are separated, and then the galactose is converted to glucose.

NOTE: The triglyceride number on your lab report is greatly affected by how much fructose and glucose your liver is converting to fat.