Carbs 101: Boost your carb IQ

Making smart food choices starts with knowing what’s in your food

This sweet stuff isn’t the only sugar on the block. Photo by Ben White on Unsplash

Regardless of whether you are a low-carb Lucy or a high-carb Hannah, knowing your starches from your sugars, and your milk sugars from your fruit sugars, can help you hit your goals. For the record, you can call me carb-Agnostic Chana.

This article serves as a foundation for other articles about carbohydrates and health, by answering several basic questions:

- What is a carbohydrate? 
- What are sugars?
- What are starches and how are they different than sugars?
- Which types of carbs (sugars) are in my food?
- How does fiber fit in?
- How do artificial sweeteners fit in?

What is a carbohydrate?

  • A carbohydrate is a naturally occurring molecule made from various combinations of three "simple sugars": fructose, glucose, and galactose.
  • Different types of carbohydrates vary in how long their chains are, and how their units are attached.
  • The simple sugar building blocks are all made of carbon, hydrogen, and oxygen.

What are sugars?

Sugars (aka ‘simple carbohydrates’ or ‘short-chain sugars’) are short chains (one or two units long) of the basic carb building blocks. Fructose, glucose, and galactose hook up in various ways to form ‘couples’ or disaccharides. (see image)

What are starches and how do they differ from sugars?

Starches are very long, mostly straight, chains of glucose, with a few ‘branches’. Plants use starches to store energy the same way that animals use glycogen. They differ only in their bonding and branching patterns (and relative amounts).

Less common carbohydrates

In addition to short and long chains (starches) of simple sugars, mother nature also serves up several mid-length chains such as raffinose and stachyose. These three-unit sugars are similar to dairy milk in that they contain galactose. They are found in potatoes, beans, and beets.

Nerd note: raffinose = galactose + glucose + fructose ; stachyose = fructose + glucose + 2 galactose.

Which types of carbs (sugars) are in my food?

Fruits contain roughly equal parts of fructose and glucose, as well as ample fiber (zero calorie but big benefits!). This is because they contain a mix of singles (fructose and glucose) and sucrose (fructose+glucose). Each fruit has its own mix of these sugar types, with some ‘starchier’ ones, like bananas, providing more glucose, and others providing more fructose (e.g. apples and pears).

Grains and starchy vegetables (like potatoes) contain lots of glucose but very little to no fructose, along with plenty of fiber. This is because they tend to be rich in starches (long chains of glucose).

The graph below show this information in more detail. Sugar types are shown after digestion: starches are 100% glucose, and sucrose (table sugar) is 50% fructose and 50% glucose.

Breakdown of sugar type in various vegetables and fruits. Source USDA database.
  • Dairy products are unique in that they contain lactose: glucose+galactose. Human and cow milk both contain lactose.

Fun Fact: Lactose intolerance is caused by not making enough of the enzyme that helps ‘divorce’ glucose from galactose. This enzyme is called lactase.

  • Malt products (including beer) and some cereals contain maltose: (glucose+glucose).

How does fiber fit in?

Dietary fiber (e.g. cellulose) found in plants, is also a long, straight chain of glucose, with no branching. However, the glucose units are attached in a different way, one that your body can’t break apart. Thus, plant fibers do not provide any energy (or calories). They do, however, play a critical role in your health by providing bulk that aides in digestion and movement of food through the GI track, and fuels the bugs in your microbiome. [more to come on this topic!]

How do artificial sweeteners fit in?

Artificial sweeteners (such as Stevia and Equal) and zero-calorie plant-based sweeteners (such as Stevia) ‘tickle’ your sweet tastebuds because they fit the lock that is your tastebud. However, they provide little to no energy to your body, thus have far fewer calories than sugars.

  • Learn more artificial sweeteners in my upcoming article: Unlocking the Secrets of Sweetness.

You are now well equipped to not only make informed choices about your body’s fuel, but also to understand the complex relationship between carbohydrates and health.

Stay tuned for more!

About Me

My mission is to give people the information and tools they need to be smarter, healthier consumers.

Learn more at

Scientist (PhD Genetics @Stanford) * Mother * Passionate about science-based healthy choices * Lifelong learner * Founder: Fueled by Science