Exploring Nutrition: Which Forms of Carbohydrates Are Digestible?

November 3, 2025 •

3 min read

Carbohydrates are the body's main source of fuel, but not all of them can be broken down for energy. To make informed dietary choices, it's essential to understand which forms of carbohydrates are digestible, how your body processes them, and what happens to the ones it can't.

Quick Summary

An examination of the carbohydrates humans can digest for energy, focusing on simple sugars like glucose and fructose, and complex starches. It explains the enzymatic process required for digestion and contrasts these with indigestible dietary fibers.

Key Points

Digestible Carbohydrates: Include simple sugars (monosaccharides and disaccharides) and complex starches, which are broken down into monosaccharides for absorption.
Enzymatic Role: Specific enzymes like amylase, sucrase, lactase, and maltase are required for carbohydrate digestion in the mouth and small intestine.
Simple vs. Complex: Simple carbs are digested quickly for immediate energy, while complex starches are digested slowly, providing sustained energy.
Indigestible Fiber: The human body lacks the enzymes to break down dietary fiber, which instead promotes gut health through fermentation.
Healthy Choices: Prioritize complex, high-fiber carbohydrates from whole foods over refined and added sugars for better blood sugar control and sustained energy.

The Basics of Carbohydrate Digestion

Carbohydrates are a crucial macronutrient, providing the body with its primary source of energy. Found in a wide array of foods, from fruits and grains to vegetables and dairy, carbohydrates must be broken down into their most basic units—monosaccharides—before they can be absorbed into the bloodstream. The human digestive system is uniquely equipped to break down specific types of carbohydrates through mechanical and enzymatic processes. The structure of the carbohydrate determines whether your body can digest it or if it will pass through largely unchanged.

Simple Digestible Carbohydrates: Quick Energy

Simple carbohydrates, also known as sugars, are the easiest and fastest for the body to digest. They consist of one or two sugar molecules, which require minimal breakdown. Digestible simple carbs include monosaccharides (glucose, fructose, galactose) and disaccharides (sucrose, lactose, maltose). Enzymes like sucrase, lactase, and maltase are needed to break down disaccharides.

Complex Digestible Carbohydrates: Sustained Energy

Complex carbohydrates, or starches, are longer chains of sugar molecules that take more time for the body to digest. Starches are a major dietary source of glucose and are found in foods like whole grains, legumes, and starchy vegetables. The digestion of starch starts in the mouth with salivary amylase and is completed in the small intestine by pancreatic amylase and brush border enzymes, breaking it down into glucose units for absorption.

The Role of Enzymes in Carbohydrate Digestion

The body’s ability to digest carbohydrates relies on specialized enzymes. Digestion begins in the mouth with salivary amylase for starches. The majority of digestion occurs in the small intestine, where pancreatic amylase continues starch breakdown, and enzymes like maltase, sucrase, and lactase break down disaccharides into monosaccharides. These monosaccharides are then absorbed into the bloodstream.

Non-Digestible Carbohydrates: Dietary Fiber

Dietary fiber is a complex carbohydrate that the human body cannot break down due to lacking the necessary enzymes. Fiber passes to the large intestine where it is fermented by bacteria, producing beneficial short-chain fatty acids. Found in plant-based foods, fiber promotes gut health and helps regulate blood sugar.

Comparison of Digestible vs. Non-Digestible Carbohydrates


Feature	Digestible Carbohydrates (Simple & Starch)	Non-Digestible Carbohydrates (Fiber)
Molecular Structure	Simple sugars or long chains of glucose.	Complex polysaccharides like cellulose.
Enzymes Required	Yes; includes amylase, sucrase, lactase, and maltase.	No; humans lack the enzymes.
Energy Yield	Provides 4 calories per gram.	Very little to no energy.
Absorption Site	Small intestine.	Large intestine.
Effects on Blood Sugar	Rapid or gradual increase.	Helps regulate and slow absorption.
Primary Function	Immediate and sustained energy.	Promotes digestive health and satiety.

Making Healthy Carbohydrate Choices

Prioritize complex, nutrient-dense carbohydrates like whole grains, legumes, and vegetables for sustained energy and fiber. Choose whole fruits over juices to benefit from fiber which moderates sugar release. Limit refined and added sugars found in candy and sugary drinks, as they provide empty calories and can cause rapid blood sugar spikes.

Conclusion

Understanding which forms of carbohydrates are digestible is fundamental to making smart nutritional choices. Simple sugars and starches are broken down by enzymes to provide energy, while fiber remains undigested but is vital for gut health. By choosing a balance of complex, fiber-rich carbohydrates from whole foods, you can support consistent energy and overall well-being. For more information, the American Diabetes Association offers guidance on carbohydrate counting.

American Diabetes Association (ADA) - Types of Carbohydrates

Frequently Asked Questions

No, not all carbohydrates are digestible. The human body can digest simple sugars and starches into glucose for energy, but it lacks the enzymes to break down dietary fiber, which passes through the digestive system largely intact.

Simple carbohydrates are made of one or two sugar molecules and are digested quickly for immediate energy. Complex carbohydrates, or starches, are long chains of sugar molecules that take longer to digest, providing a more sustained and stable release of energy.

The digestion of carbohydrates requires several enzymes, including salivary and pancreatic amylase to break down starches, and brush border enzymes like sucrase, lactase, and maltase to break down disaccharides.

Digestible carbohydrates are found in many foods, including whole grains (bread, rice, pasta), starchy vegetables (potatoes, corn), legumes, fruits, and dairy products like milk and yogurt.

Humans cannot digest fiber because we do not produce the necessary enzymes to break the chemical bonds within its complex structure. Instead, fiber passes through the system and is fermented by gut bacteria.

If you cannot digest certain carbohydrates (e.g., lactose due to lactase deficiency), they pass undigested into the large intestine. Here, bacteria ferment them, which can cause gastrointestinal symptoms like bloating, gas, and diarrhea.

Cooking generally increases the digestibility of starchy carbohydrates. Heat and moisture break down the protective structures of the food, making the starch more accessible to digestive enzymes like amylase.