Carbs: What Are They?

Written by: Not a professional


A picture of potatoes, a food that is copious in carbohydrates

Credit: Scott Bauer, USDA ARS


Carbs (or carbohydrates) are a type of biological molecule that are associated with calories and foods such as potatoes and breads. It's ubiquitous in the average American diet with about 50% of their calories stemming from this delicious molecule.

The common types of dietary carbs you encounter are:

While there are many other types of dietary carbs I did not mentions, these should be the main forms of carbohydrates you will encounter.

The goal of this website is to inform you about what dietary carbs are, what they're made of, how they're digested, and extra information for those curious. The more complicated information and extra information will be below the general synopsis in an attempt to be able to also teach the more complicated topics without prior knowledge.

A side note: I will be calling small carbohydrates like fructose and sucrose sugars because they usually taste sweet.

Types of Carbohydrates

What's the difference between starches and sugars (like table sugar)?

The answer is the two are structurally different despite its building blocks being the same. To understand why their structures are different, I need to give you a review on the building blocks of carbohydrates, the monosaccharide.

You may have heard of one already - its name is glucose.

However there are other kinds of monosaccharides similar to glucose; in fact, there are tons of monosaccharides but some of the important ones to note are:

It's likely that you've heard of the first two but the last monosaccharide may seem like it's out of left field. That's because galactose is not as sweet as glucose or fructose and its main role in nutrition is forming lactose, the sugar found in milk.

Now with these three building blocks, we can talk about larger carbohydrates and why starch is different from your table sugar.

As previously mentioned, lactose (a disaccharide) is formed from galactose but it's also bonded to glucose. If you remember high school chemistry, you know that this forms something new and so it's called lactose.

We can bond many different kinds of monosaccharides together but the main types of bonded monosaccharides found in your food are listed in this table

Carb Name Components Type of Saccharide
Lactose Glucose and Galactose Disaccharide
Sucrose Glucose and Fructose Disaccharide
Maltose Glucose and Glucose Disaccharide
Starch Many glucose molecules Polysaccharide
Glycogen Many glucose molecules Polysaccharide
Cellulose Many glucose molecules Polysaccharide

While I won't get into the specifics of glycogen, starch, and cellulose (at least not yet), I will say that cellulose is commonly referred to as fiber and a long string of monosaccharides bonded together is called a polysaccharide.

In summary, the difference between your potato and a packet of table sugar is that your potato is made from a long string of one monosaccharide, glucose, while your packet of sugar is composed of small pairs of glucose and fructose molecules bonded together.

How they are digested

A quick note on enzymes: They are special molecules in your body that work many functions. In the case of digestion they work to break down these components.

The digestion process is a simple and here is the step-by-step process:

  1. An enzyme called amylase work to break down the complicated starches in your mouth and create smaller, more managable polysaccharides.
  2. After passing through the stomach, your pancreas releases more amylase producing even smaller saccharides which are almost ready to be absorbed.
  3. Your small intestine produces 4 more enzymes that completely break down all carbohydrates into glucose, fructose, and galactose.
  4. Now that it's broken down, your intestine absorbs these nutrients into your bloodstream.
  5. Any carbohydrates that cannot be broken down is instead passed through your body until it leaves. This is what we call dietary fiber.

This process is generally true unless you're lactose intolerant. In this case, your body no longer produces the enzyme lactase resulting in lactose -the sugar found in dairy products- passing into your large intestine and giving a large feast for bacteria in your gut which release gas after finishing their meal.

People who do frequent blood checks may also note that the sugars are absorbed into the bloodstream and is why your doctor requires a fasting period before blood is drawn. While it is possible to avoid the fasting period, measurements are much less precise and have a much wider range of error due to the wildly varying diets available.

Fun Facts

The favicon is a chair! (Technically, it's a chair conformation)

If you have heard about the keto diet, then you might know that the only real rule is that you should not consume carbs at all. This is because your body does not need you to eat carbs to survive. If your body does not receive enough carbohydrates from your food, then they will undergo a process called gluconeogenesis. The basic premise is that your body uses fats and proteins from your body and sort of "molds" them either into sugars or components of the TCA (Kreb's) cycle. The downside is that your body is originally accustomed to high levels of carbs from your diet and so needs a period to ramp up gluconeogenesis, leaving your cells initially deprived from the normal amount of sugar; this is the fatigue caused by keto you may have read about online. If you want to learn more and have a strong background in both chemistry and biology, then you can read the wikipedia article here.

A food that is high in galactose is celery! Who would've thought!

Saccharin, an artificial sweetener, has no calories because it cannot be digested by your body! Even though your tongue receptors think it's a sugar (a really really really sweet sugar), your body thinks otherwise.

Sorbitol, another artificial sweetener, does actually have a caloric value but is digested slowly in your body unless you leave it in your mouth where bacteria can cause tooth decay (fun).

While I covered how your body deals with pure carbohydrates, chemistry allows these carbs to be attached to basically anything! If you've know about DNA then you already know a modified carbohydrate. That's right, DNA has a monosaccharide called deoxyribose (a slightly modified version of ribose, a legit sugar) that is only part of the incredibly complex system known as your genome.

Your body regulates the amount of sugar in your blood using the pancreas. While its brother insulin gets most of the attention, glucagon also does a role in regulating your blood sugar levels. Insulin's job is to store sugar from your blood into cells while glucagon's role is to release sugar from the cells into the blood.

Extra Details

This section will be full of nit-picky and detailed information about the article in general. If you have not taken AP Biology and Chemistry or General Biology and Chemistry, then you should probably skip this section.

Although I talk about starch as one polysaccharide, it is actually two separate polysaccharides, amylose and amylopectin. The only difference between the two is are the branches in amylopectin as a result of additional a-1,6 links on the main glucose chain.

Something else I don't mention is the existance of trioses, pentoses, and hexoses because I didn't feel like it was really necessary because glucose, galactose, and fructose are all hexoses (ribose is a pentose).

I also don't mention oligosaccharides because they don't appear often enough to mention them.

Epimers are not mentioned because nobody likes stereochemistry. Even general isomers like structural and enantiomers are beyond the scope of this article.

The types of bonds are not mentioned for the same reasons as epimers: it's not vital to the article and would introduce more confusion than information. Even though they are all glycosidic, the anomeric carbon allows for there to be two types of the same sugar depending on how the ring is formed (I'm not talking about enantiomers or different ring conformations): Alpha and Beta. Its importance appears when the glycosidic linkages occur as the alpha and beta varieties provide different structures and challanges. The clearest example is cellulose and amylose. Both are long chains of glucose but because our body expects a-1,4-linked glucose instead of b-1,4-linked glucose, it's impossible for cellulose to be digested by amylase.

Funnily enough, glycogen and amylopectin are pretty similar in that both branch out but glycogen is synthesized in animals while amylopectin is synthesized in plants, leading to some peculiarities.

I do mention amylase but that's in the mouth with its formal name being salivary a-amylase because the pancreas produces a similar enzyme called a-amylase which breaks down larger polysaccharides than what salivary a-amylase does. Other enzymes are glucoamylase, maltase, isomaltase, sucrase, and lactase.

Absorption of the sugars is also skimmed because I don't feel like explaining membrane rafts, symport, diffusion gradient, transport proteins, and ATPase (another enzyme).

Do note that I am not a professional and that this information should not be taken verbatim.

About the Author

This is where I get exposed.

While I could give more information about myself, I think it's more interesting that this is for Google Code-in, a really cool program/competition/opportunity that allows people to take on tasks requested by companies. It's kind of like mercenary work except it occurs over Winter Break so I can do something besides be a pile of laundry.

As for my credentials regarding this topic...

I have taken AP Bio, Gen Chem 1, and self taught AP Chem, Orgo 1, and some strange mish-mash of Bioc 1 and 2 (Although mainly leaning towards Bioc 2).


So this isn't going to be like a "Works Cited" page in MLA format because I'm lazy.

The main source of information is from a book called:

The reason why I can't give a clear answer to the level of biochemistry I'm learning is because this book is designed for the USML test which focuses more on the biochemistry of humans, something I'm not complaining about. The problem is that there is no real way for me to judge how the contents I'm learning translate to university level classes because the target audience is way, way, way past university.

I also used that one picture of a potato and some other stuff that's from Wikipedia.