Sucrose, glucose, and fructose explained

Sucrose is another name for plain white table sugar. It’s made up of two other sugars: glucose and fructose.

Glucose, fructose, and sucrose all contain the same amount of energy per gram. 

Each of these sugars occurs naturally in certain foods. But manufacturers also add them to many processed foods and drinks.

Rather than focusing on which types of sugar to eat or avoid, you can make more of a difference to your health by checking for added sugars.

At ZOE, our research has shown that a one-size-fits-all approach to nutrition doesn’t work. Our personalized program gives you advice based on an analysis of your gut bacteria, blood sugar responses, and blood fat responses.

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What are the differences?

Sugars can be either monosaccharides and disaccharides.

"Monosaccharide" means "one saccharide," or sugar unit. These units are the building blocks of carbohydrates. Disaccharides have two monosaccharides joined together.

Your body digests and metabolizes these sugars differently.

Sucrose

Sucrose — or table sugar — is a disaccharide composed of one glucose and one fructose unit. Manufacturers create it by processing sugar cane and sugar beets.

Because sucrose is a disaccharide, your body has to break it down into monosaccharides before it’s absorbed into your bloodstream.

Glucose

Glucose is a monosaccharide in grains, nuts, and vegetables. It also occurs in starchy foods like potatoes and rice. 

However, glucose is also present in disaccharides, like sucrose or lactose, which is the sugar in milk.

Dextrose has the same structure as glucose, and it’s common in food manufacturing. You might see it in ingredients lists for baked goods, corn syrup, and other processed foods.

When you eat foods containing glucose, your body will use what it needs and store the rest as glycogen in your liver or muscles. 

The hormone insulin tightly controls glucose levels in your blood.

Fructose

Like glucose, fructose is a monosaccharide. It occurs naturally in fruits, honey, and many root vegetables.

When manufacturers add fructose to products, you may see it as “high fructose corn syrup” on packaging. It tends to be in sauces, sugary drinks, fast food, and flavored yogurt.

Your liver needs to convert fructose into glucose before your body can use it as fuel.

Absorption and digestion

Your body digests and absorbs different types of sugars in different ways. For instance, you absorb monosaccharides straight into your bloodstream. 

But you need enzymes to break down disaccharides into monosaccharides before these get absorbed.

Sucrose

Your body must break down sucrose into glucose and fructose monosaccharides before you can absorb these sugars into your blood. 

The process begins in your mouth, but most of the work occurs in your small intestine.

Glucose

Your body doesn't have to break down glucose before it absorbs it.

This is why glucose can raise your blood sugar more quickly than other, more complex sugars.

Once glucose enters your blood, it triggers the release of insulin. This helps glucose move from your bloodstream into your cells. It reduces the level of glucose in your blood.

Fructose

Because fructose is a monosaccharide like glucose, it’s absorbed directly into your bloodstream. 

However, your body can’t use fructose as energy. As a result, your liver has to convert it into glucose. Because of this extra step, fructose doesn’t stimulate the release of insulin.

Research suggests that it may play a role in metabolic diseases, like obesity and non-alcoholic fatty liver disease. 

This may be because consuming too much fructose causes fat to build up in your liver. 

However, scientists still don’t fully understand the links, and research is ongoing.

This is thanks to the other components of these plants: Their water and fiber cause you to absorb fructose into your blood at a slower rate. 

Also, the wide range of health benefits associated with eating fruit and vegetables offset any harm that their fructose might cause.

Added sugars and processed foods

Added sugars are any sugars that a manufacturer has added to their product.

On labels, added sucrose, fructose, and glucose can go by many names.

Look out for ingredients such as: 

• high fructose corn syrup

• dextrose

• maltodextrin

• agave syrup

• raw sugar 

We’ve put together a more extensive list in our article on added sugars.

Where to find added sugars

Soda is one of the biggest sources of added sugar.

The American Heart Association explains that sweetened drinks make up almost half of the sources of added sugar in people’s diets. Sports drinks, flavored coffees, and sweet teas also fall into this category.

Because these drinks contain no fiber, you absorb the sugar into your bloodstream quickly.

Low-fat products also often contain added sugars. Manufacturers add sugars to replace the taste lost when they remove fat. 

Health effects of added sugar

Eating too much sugar can negatively affect your dental health. 

Research has also shown an association between eating lots of sugar and cardiometabolic diseases, such as:

• cardiovascular disease

• obesity and metabolic disease

• fatty liver disease

In addition, research suggests that too much added sugar could have an unfavorable effect on your long-term mental health.

Which of these sugars is healthiest?

Overall, no type of sugar is the most or least healthy. 

We typically eat sugar in meals and drinks, and these are what we should focus on.

If we’re singling out added sugars, fructose might have the most harmful effects, though scientists are still investigating.

ZOE runs the largest nutrition science study in the world. We know that our blood sugar rises after we eat certain foods and falls again afterward in a way that’s unique to each of us.

Using our at-home test, you can learn how different foods will affect your blood sugar and blood fat levels. You’ll also discover how healthy your gut is.

Take our free quiz to find out how it works.

How to limit your added sugar intake

Limiting natural sugars (from fruits, vegetables, and other whole foods) isn’t necessary for most people. 

Whole foods contain many beneficial compounds, like fiber, vitamins, minerals, and polyphenols.

“Free sugars” typically refers to added sugars plus the natural sugars in juiced or pureed fruit and veggies, though the definition can vary. 

When you juice or puree these plants, it breaks down their structure, freeing the sugars from the plants’ cells. This makes it easier for your body to absorb the sugars.

No foods should be completely off-limits, but eating more whole foods and cutting back on ultra-processed foods is the best way to reduce your added sugar intake.

This can slow the rate at which you absorb the sugar, reducing the risk of a large blood sugar rise.

Eating meals with higher amounts of fiber, protein, and non-sugary carbs also means you're less likely to have a significant blood sugar dip afterward. These dips can cause food cravings for some people. 

But it’s worth noting that not everyone experiences blood sugar dips.

Our article on how to stop eating sugar has more detailed advice and information about reducing your sugar intake.

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Summary

Experts agree: There’s no need for most people to limit their intake of sugar from natural sources, like fruits and vegetables. 

Looking out for added and free sugars is the best way to reduce your sugar intake and support your health.

Overall, fructose might have the most harmful effects — when it’s an added sugar and you have large quantities.

A healthy diet contains lots of whole foods, which slow your absorption of sugar. It’s also a good idea to keep an eye on how much added sugar is in the processed foods you’re consuming.