Macronutrients 101: Carbohydrates

Our survival depends on the consumption of three essential macronutrients- carbohydrates, lipids, and proteins. The diet industry has distorted our perception of macronutrients through extreme diets. From Atkins to no fat, people jump unto these fads without a solid understanding of individual macronutrients. Hence, I thought I’d write a series of posts to explain these poor misunderstood nutrients. I’ll start off with carbohydrates as they are the essence of our metabolic pathways.

Carbohydrates (aka saccharides) are originally created by plants via photosynthesis. The plants than utilize these carbs as an energy source or a structural scaffold. The left over carbs are stored by plants as starch which eventually become consumed by us or other animals.

Photosynthesis reactions

A good way to think of carbs is as “carb”-o”hydrates” as they are fundamentally made up of carbon, oxygen and hydrogen atoms. Additionally, carbs are cyclic molecules meaning that they form into ring-like structures. These rings can exist on their own like as monosaccharides, linked with another sugar ring as disaccharides or in large polymer chains called polysaccharides.

The best known monosaccharide is glucose. It is a simple 6-member ring structure and is a readily available energy source. Other monosaccharides examples include 5-member ring structures like a fruit sugar called fructose or ribose and deoxyribose which form the backbone of DNA and RNA, respectively.

Disaccharides form when two monosaccharides form a bond while losing 1 water molecule. This bond can then be broken by the addition of water and generally a specific enzyme. Examples of disaccharides include sucrose, lactose, and maltose. Healthy humans have enzymes in the digestive tract that break down these disaccharides into their components to be used as energy sources. However, if one has insufficient quantities of these enzymes then they will be unable to digest these disaccharides. A common example of such issue is in individuals who lack lactase and are thus unable to break down lactose.

For longer storage or structural purposes, glucose molecules can form large polymers called polysaccharides. Common examples of polysaccharides include glycogen, starch, and cellulose. The way that glucose molecules form bonds give the polysaccharides their distinct properties.

Glycogen is the way humans store glucose in the liver and muscles. Our bodies are in a constant equilibrium with enzymes building and breaking down glycogen based on blood glucose levels. The way that glucose molecules are bound in glycogen is somewhat disorganized and gives them a branched pattern. I’d say glycogen looks kind of like the root of a tree. This arrangement allows enzymes easy access to glycogen branches to rapidly release glucose in case of unexpected exercise.

Another important polysaccharide is starch (amylose and amylopectin) which is the plant’s version of fat or energy storage. This carb is easily broken down into glucose by the enzyme amylose found in our saliva. This makes starch easy to digest and makes it a quick energy source.

Nevertheless, our bodies cannot digest all carbs. Plant fiber (cellulose) is a prime example of that. Cellulose like amylose is simply a chain of linked glucose molecules which comprises the plant cell wall. However, the glucose bonds are  slightly different and our bodies do not possess the enzyme necessary to break them. That’s why vegetables are so low in calories! We simply cannot digest their fibers and get no energy out of them.

There it is, a brief overview of some common carbohydrates. See, they’re not scary at all 🙂 Our bodies were meant to digest things like starches. The only caveat is that you should not consume excess amounts of carbs. Yet, almost anything in excess is bad 😉

In the next few posts I will similarly go over the basics of lipids and proteins so stay tuned!


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s