What Sugar Breaks Down Into Fructose? A Complete Guide

December 26, 2025 •

4 min read

Sucrose, the scientific name for common table sugar, is a disaccharide uniquely composed of one molecule of glucose and one molecule of fructose. This sweet compound is the most common example of a sugar that your body breaks down into fructose during the digestive process.

Quick Summary

Sucrose, or table sugar, is enzymatically broken down into its monosaccharide components, glucose and fructose, during digestion in the small intestine. High-fructose corn syrup is also made by converting glucose into fructose via a catalyzed isomerization process.

Key Points

Sucrose is the key sugar: Sucrose, or table sugar, is the primary sugar that breaks down into fructose in the body during digestion.
Enzymatic hydrolysis: The breakdown of sucrose is facilitated by the enzyme sucrase in the small intestine through a process called hydrolysis.
HFCS is produced differently: High-fructose corn syrup is made by converting glucose into fructose using enzymes in a laboratory setting, not through natural digestion.
Source matters for health: While both sucrose and HFCS provide fructose, the source (e.g., concentrated added sugars vs. whole fruit) significantly impacts metabolic health.
Metabolic implications: Excess fructose is primarily processed by the liver and can contribute to fat synthesis, non-alcoholic fatty liver disease (NAFLD), and insulin resistance.

Sucrose: The Digestive Pathway to Fructose

Sucrose, the simple table sugar derived from sugarcane or sugar beets, is a key dietary source of fructose. Unlike simple sugars (monosaccharides) like glucose, which are absorbed directly, sucrose is a complex sugar (disaccharide) that must be broken down first. This digestion process is a vital step in how your body accesses the fructose locked within.

The Role of the Enzyme Sucrase

The breakdown of sucrose into fructose and glucose begins in the small intestine. The lining of the small intestine produces a specific enzyme called sucrase. This enzyme's sole job is to catalyze the hydrolysis of sucrose. Hydrolysis is a chemical reaction in which water is used to split a larger molecule into smaller, more digestible components. In this case, one molecule of sucrose is broken apart by a water molecule into its two constituent monosaccharides: one molecule of glucose and one molecule of fructose.

Once broken down, these simple sugars are absorbed through the intestinal wall into the bloodstream. From there, they travel to the liver for metabolism. While glucose is used by cells throughout the body for immediate energy, fructose is processed almost exclusively by the liver, which has significant metabolic implications.

High-Fructose Corn Syrup: An Industrial Conversion

Beyond sucrose, another major source of fructose in the modern diet is high-fructose corn syrup (HFCS). However, the way HFCS is produced differs significantly from how your body breaks down sucrose. HFCS is not a naturally occurring compound but rather a manufactured sweetener made from cornstarch.

The Isomerization Process

The production of HFCS is a multi-step industrial process:

Cornstarch Breakdown: Corn is first milled to produce cornstarch, which is a long chain of glucose molecules.
Corn Syrup Production: The cornstarch is then broken down into individual glucose molecules using enzymes, which results in corn syrup (essentially 100% glucose).
Enzyme-Catalyzed Conversion: To create HFCS, a separate enzyme called glucose isomerase (or D-xylose isomerase) is added. This enzyme catalyzes the conversion of some of the glucose into fructose through a process called isomerization. This is a chemical reaction that rearranges the atoms within a molecule, converting an aldose (glucose) into a ketose (fructose).

HFCS is available in different compositions, most commonly HFCS-42 (42% fructose) and HFCS-55 (55% fructose), which are used in various processed foods and beverages.

The Health Context of Fructose

While both sucrose and HFCS supply the body with a mixture of glucose and fructose, the health implications of excessive fructose consumption are a topic of significant research. This is largely due to the liver's role in processing large amounts of fructose, which can overwhelm its metabolic capacity.

Excessive fructose intake can lead to a process called de novo lipogenesis, where the liver converts excess fructose into fat. This can contribute to several metabolic issues, including non-alcoholic fatty liver disease (NAFLD), insulin resistance, and elevated triglycerides. In contrast, the fructose in whole fruits is consumed alongside fiber, which slows absorption and provides other nutrients, making it far less metabolically impactful than the large, concentrated doses of fructose found in added sugars.

For more detailed information on fructose metabolism and its effects on health, the National Institutes of Health (NIH) is an excellent resource, with several articles summarizing the latest research. Learn more about fructose metabolism and its health effects here.

Comparison of Sucrose vs. High-Fructose Corn Syrup


Feature	Sucrose (Table Sugar)	High-Fructose Corn Syrup (HFCS)
Composition	50% glucose, 50% fructose	Typically 42% or 55% fructose, rest is glucose and other sugars
Source	Extracted and refined from sugarcane or sugar beets	Industrially produced from cornstarch
Breakdown Mechanism (in the body)	Hydrolysis by the enzyme sucrase during digestion	Already a mixture of free glucose and fructose, so no breakdown of a bond is required
State	Solid, granulated crystals	Liquid
Molecular Bond	Glucose and fructose are chemically bonded	Glucose and fructose are not bonded; they exist as free molecules

Conclusion

In summary, the sugar that breaks down into fructose in the human body is primarily sucrose, which is common table sugar. This natural digestive process relies on the enzyme sucrase in the small intestine to split sucrose into equal parts glucose and fructose. Industrially, high-fructose corn syrup is produced by a different method, using enzymes to convert glucose from cornstarch into fructose through isomerization. While both sucrose and HFCS provide the body with fructose, the source and process of obtaining it are different. Understanding this distinction is crucial for making informed decisions about dietary sugar intake, particularly concerning the health implications of excessive consumption of added fructose from processed foods compared to the fructose naturally found in fruits.

Frequently Asked Questions

Sucrose is the only disaccharide commonly known as "sugar" that is broken down into fructose and glucose by the body during digestion. Other complex carbohydrates like starches are broken down into glucose, but not fructose.

The enzyme responsible for breaking down sucrose into glucose and fructose is called sucrase, or invertase. It is produced by the cells lining the small intestine.

High-fructose corn syrup is already a mixture of free glucose and free fructose, so it does not need to be broken down during digestion like sucrose does. It is absorbed directly into the bloodstream.

Once fructose and glucose are separated from sucrose, the body handles them in the same way as it does the free fructose and glucose in HFCS. However, the rate of absorption can differ, as the free sugars in HFCS are absorbed faster than the bonded sugars in sucrose.

Unlike glucose, which can be used by nearly all cells for energy, fructose is metabolized almost entirely by the liver. Excessive amounts can overload the liver, leading to the conversion of fructose into fat, a process linked to fatty liver and insulin resistance.

Sucrose is a naturally occurring carbohydrate found in many fruits, vegetables, and grains, most notably in high concentrations in sugar cane and sugar beets.

High-fructose corn syrup is produced commercially by first breaking cornstarch down into glucose syrup. The enzyme glucose isomerase is then added to convert some of the glucose into fructose.