What are Sugars and What are Starches?

Hidden Sugar in foods

  Last update November 11, 2021, article reviewed & updated multiple times since April 4, 2001.

  What You Need to Know

  • Not everyone is clear on just what the words carbohydrate, sugar, and starch mean especially in relation to low-carb and keto diets.
  • Every single thing we eat, without exception, can be classified as one or a combination of only these five substances: carbohydrate, protein, fat, vitamin, or mineral.
  • All the things we eat are composed of one or combinations of some of the 100+ ‘basic elements’ that make up everything known to exist in the world.

The Truth About Carbohydrates

All of us living the Low Carb lifestyle use the words carbohydrate, sugar, and starch on a daily basis. But although we use the words freely, not everyone is clear on just what those words mean, how the substances relate to one another, or how they relate to other things we eat. So, let’s start at the very beginning, and build an understanding. Just take one sentence at a time, and I promise that you will be an expert when we reach the end.

First, it is important to understand two basic facts that lie beneath all discussions having to do with food.

Fact 1: Every single thing we eat, without exception, can be classified as one or a combination of only these five substances: carbohydrate, protein, fat, vitamin, or mineral.

Fact 2: All the things we eat (which are one or another of those five substances) are composed of one or combinations of some of the 100+ ‘basic elements’ that make up everything known to exist in the world, or in the universe, for that matter.

I’m certain that you are already familiar with many of these basic elements, although you might not have known that basic elements are what they are. For example, you already know the names carbon, oxygen, hydrogen, sodium, and calcium. If you want to know the names of the rest of the basic elements, look in any chemistry book for what is called “The Periodic Table of Elements.”

Periodic Table of Elements
2012rc, CC BY 3.0, via Wikimedia Commons

How Carbohydrates Are Digested

Now that we know the two basic facts, we can go on. The word carbohydrate means ‘a combination of carbon, hydrogen, and oxygen.’ We generally use the abbreviation ‘carb’ for carbohydrate, but you may also have seen it abbreviated as “CHO.” Those letters stand for carbon, hydrogen, and oxygen.

Let’s divide the word carbohydrate into its components. The “carbo-” part means carbon. Note that the “-hydrate” part of the word is like ‘dehydration’ or ‘hydrant,’ as in fire hydrant. These words relate to water; water is composed of hydrogen and oxygen. So, now we can understand that carbohydrate more specifically means “one of many different combinations of carbon, hydrogen, and oxygen, whose various sections join and break apart by taking on, or releasing water.” This explanation may seem a bit technical, but knowing it will help you understand what happens to sugar, as we go along.

Now we know what a carbohydrate is. The next question is: “What things are carbohydrates?” The answer is that carbohydrates are sugars, starches, dextrins, and gums. I’ll discuss dextrins and gums at another time. For now, we are going to focus on sugars and starches.

One of the important words that refers to sugars and starches is saccharide. (Think about the artificial sweetener, saccharin. They made up, deriving it from the word saccharide.) There are two types of saccharides that concern us here, the mono-saccharides (“mono-” means “one”), which are also called the simple sugars, and poly-saccharides (“poly-” means “many”), which are also called the complex sugars. Complex sugars are broken down in the human body by digestive process into simple sugars. They do this by coming apart at the water connections in a process called hydrolysis (“hydro-” means water; “-lysis” means breakdown).

What are Sugars

Sugar Cubes
david pacey from LEEDS, West yorkshire, CC BY 2.0, via Wikimedia Commons
The simple sugars in foods that are most important to human nutrition are called sucrose, fructose, lactose, and maltose. But the body wants the simple sugar called glucose, so these other simple sugars break apart in the body to become glucose. They do this by coming apart easily at the water connections.

Sucrose is table sugar. Sucrose is the form of sugar we are most familiar with. It is obtained from sugar cane, sugar beets, and the syrup from sugar maple trees. It is also naturally present in some amounts in most fruits and vegetables, along with higher amounts of other sugars. Whenever the word “sugar” is used in common conversation, it is usually sucrose that is being referred to. Two other names for sucrose are dextrose and saccharose.(Do not confuse saccharose with sucralose. Sucralose is the artificial sweetener, Splenda.)

Fructose is the form of sugar found in fruits, honey, and corn.It is sometimes called levulose. In recent decades, fructose has been super-refined to make the sweeteners known as corn syrup and high fructose corn syrup. Since fructose in those forms can be made to be very concentrated, and since it is much sweeter to our taste buds than sucrose, fructose is the poster child for economic success in the food industry. Pushers of fructose tell us that it is better to use it because “It is natural,” or “Since it is sweeter, you’ll use less of it than table sugar,” or even that foods containing it are “sugar-free.”

Yes, fructose is natural. So is sucrose, and so is arsenic, for that matter. Yes, it is sweeter to the taste, and you can use less of it, but even the lesser amount is too much. Yes, it is “sugar-free,” but that’s because there is a legal definition of “sugar” in the food industry. Under the legal definition, if a food product doesn’t contain sucrose, it may be called “sugar-free.” Governmental officials who make these stupid rules should read this article, and become informed as to what “sugar” actually means!

Lactose is the sugar found in milk and cottage cheese. Maltose is the sugar in grains. And, all four of the sugars we have been talking about break down easily into glucose in two simple, water-related steps.

You will notice that many sugar-related words end in the letters “-ose.” When you read ingredients on labels, consider every word that ends in “-ose” (or “-oses”) to be sugar. There are two notable exceptions: cellulose and sucralose. Cellulose, while it is a complex sugar, is not digested by our bodies, and therefore doesn’t enter into sugar considerations. Sucralose/Splenda does not provide usable carbohydrates in its pure form.

What are Starches

No More Flour & Corn Starch for Low-Carb Cooking
Now, let’s talk about starches. Starches include such foods as potatoes, cereals, wheat and other grains, and rice. A few paragraphs above, we talked about mono-saccharides and poly-saccharides. Mono-saccharides are the simple sugars. Poly-saccharides are complex sugars. Starches are complex sugars, and complex sugars break down into one of the simple sugars (maltose), and then to glucose by (you guessed it!) easily breaking apart at the water connections.

Since starches do not taste very sweet, they do not jump to mind when sugar is mentioned, but they quickly become the simple sugar maltose, and then the simple sugar glucose because the breakdown of starch from the complex sugar form to the simple sugar form is quick and easy. Essentially, starches are sugars that merely require a few more steps to make them into glucose, but they are no better for the low-carb diet than sugar.

Starches are often given names that end in the letters “-an,” such as glycan or mannan. When you read labels and see ingredients you don’t recognize, it is best to assume that any word that ends in “-an” (or “-ans”) is starch.

In Conclusion

So, there you have the straight skinny on starch and sugar. No matter what form you eat, it will become glucose once it is in your body.

Next time, we’ll talk about dietary fiber and how it relates to carbohydrates. We’ll also talk about the so-called glycemic index. Hope you’ll be here with me.

The Science of Low-Carb & Keto Diets
    The Science of Low-Carb & Keto Diets

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  • This article is number 1 of 24 articles describing The Science of Low-Carb & Keto Diets. Visit this link or click the above image for all of the articles in the series.
Article History

  • Last Update November 8, 2021
  • Updated January 4, 2018
  • Updated May 22, 2010
  • Updated July 29, 2003
  • Original Article April 4, 2001
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About Dr. Beth Gruber
Dr. Gruber is a graduate of the Southern California University of Health Sciences and has been in private chiropractic practice in Long Beach, California since 1964. She also received both a Bachelor’s Degree and a Master’s Degree from California State University at Long Beach. She has written on health-related subjects for over 30 years, for several different publications. She lives in Southern California with her husband of 33 years. Both she and her husband follow and live the low-carb lifestyle full time.

More Vital Information articles by Dr. Beth Gruber.

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  1. The concept of carbohydrates, sugars and starch has been explained in nice way. Sir kindly also explain about reducing and non reducing sugars and their significance

    • I am unaware of any research regarding reducing and non-reducing sugars vis a vis a carbohydrate-restricted diet, and certainly haven’t see the distinction made on any nutritional breakdown — they’ll list total carbohydrate, fiber, and sugars, but I’ve never seen a breakdown of sugars into reducing or non-reducing. Sorry to be of no help.

  2. I have been checking out Dr. Beth’s pages with a huge amount of interest over the past few days and find her material very easy to digest and quite conclusive. My mom is in hospital at the moment with gall stones and some disorder with her liver. She has been on a low fat (no fat diet) for ages now and i had begun to wonder some time back why there was discoloration in her eyes. I’ve been away from home for a few years and have arrived back recently and this is something that has struck me. So okay… we now know that the she has a kidney and gall bladder disorder :). A Bilary stent procedure was preformed yesterday and all is is well for the time being until the inflammation of the gall bladder returns to normal and they can operate to remove it. My question is this; can we during this time reintroduce small amounts of unrefined organic oils like olive, flax (linseed) and sesame used cold as dressing and the like and perhaps a half teaspoon with yogurt. Or, is it best during this time to refrain from using oils. You’re help is much appreciated, Dave from Ireland.

    • Hi Dave,
      So sorry to hear about your mom, but glad she is getting help. Dr. Beth isn’t currently writing for us, but I’ll do my best to find someone who can answer your questions.

      • Thanks Amy, you’re a star.
        My mom came home yesterday and is feeling much much better. I look forward to hearing back from you guys in time and thanks again.

  3. “Under the legal definition, if a food product doesn’t contain sucrose, it may be called “sugar-free.” Governmental officials who make these stupid rules should read this article, and become informed as to what “sugar” actually means!”

    This statement is false. It seemed fishy to me so I did some research.

    From the FDA Website:

    “Sugars: No daily reference value has been established for sugars because no recommendations have been made for the total amount to eat in a day. Keep in mind, the sugars listed on the Nutrition Facts label include naturally occurring sugars (like those in fruit and milk) as well as those added to a food or drink. Check the ingredient list for specifics on added sugars.”


    This is not a nit pick, but that is a glaring mistake and you are claiming that consumers cannot trust the nutrition labels when no evidence supports such a conclusion.

    • J Smith: I believe the article was referring to the claims on the front of a food label and to the ingredients part of the label as opposed to the nutritional panel. At least that’s the way I read it. I’ve seen things with HFCS as well as agave & other high fructose ingredients with a big Sugar Free label on the front of the food item. It’s happening less because people are starting to realize that those things are sugars too and affect the body the same way (or possibly worse) than straight sucrose, but it does seem to be allowed.

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