Where does the body get the majority of carbohydrates?

January 9, 2026 •

4 min read

According to health guidelines, 45% to 65% of an adult's daily calories should come from carbohydrates, largely from dietary intake. The body gets the majority of carbohydrates from a wide variety of plant-based foods that contain starches, sugars, and fiber.

Quick Summary

The body primarily obtains carbohydrates from plant-based foods rich in starches, such as grains and vegetables, which are broken down into glucose for energy.

Key Points

Majority Source: The body gets the majority of carbohydrates from dietary starches found in plant-based foods like grains, legumes, and starchy vegetables.
Metabolism for Energy: Carbohydrates are broken down into glucose, which is the body's primary fuel for supporting all bodily functions and physical activity.
Complex vs. Simple: Complex carbohydrates provide a slower, more sustained energy release, while simple carbohydrates offer a quicker burst but can lead to energy crashes.
Storage System: Excess glucose is stored as glycogen in the liver and muscles for future use, and any remaining surplus is converted into fat for long-term storage.
Undigested Fiber: Fiber, a complex carbohydrate, is not digested for energy but is crucial for digestive health, blood sugar regulation, and promoting fullness.
Dietary Recommendations: Health experts recommend that 45-65% of daily calories come from carbohydrates, prioritizing nutrient-dense, complex carb sources.

The Primary Sources: Starchy Foods

The majority of carbohydrates consumed and used for fuel come from starchy, plant-based foods. These complex carbohydrates, known as polysaccharides, are long chains of glucose molecules that the body slowly breaks down and absorbs. This gradual release of glucose into the bloodstream provides a steady supply of energy, avoiding the rapid spikes and crashes associated with simple sugars.

Some of the most significant contributors to the body's carbohydrate supply include:

Whole Grains: These are a cornerstone of many diets and include foods like brown rice, oats, whole-wheat bread, and quinoa. They provide a rich source of complex carbohydrates along with essential fiber, vitamins, and minerals.
Legumes: A diverse group including beans, lentils, and peas, legumes are excellent sources of complex carbs and fiber. They also offer protein, making them a highly nutritious energy source.
Root Vegetables and Starchy Vegetables: Potatoes, sweet potatoes, corn, and peas are packed with complex carbohydrates and other vital nutrients.

The Role of Simple Carbohydrates

While complex carbohydrates make up the bulk of healthy carb intake, simple carbohydrates also contribute, providing a faster source of energy due to their simpler chemical structure. Simple carbs are sugars, and they can be found naturally in many foods or added during processing.

Natural Sugars: Fructose in fruits and lactose in milk and dairy products are examples of naturally occurring simple carbohydrates. Fruits also provide fiber, vitamins, and antioxidants, making them a healthier source of sugar than processed options.
Added Sugars: Found in processed foods, sodas, and candies, these provide quick energy but lack the nutritional benefits of natural sources. It's recommended to consume these in moderation.

From Food to Fuel: The Digestion Process

Carbohydrate metabolism is the biochemical process that converts food into energy. The journey begins in the mouth and involves several enzymatic steps.

Digestion from Mouth to Small Intestine

Digestion starts in the mouth, where salivary amylase begins breaking down starches. The stomach's acid inactivates this enzyme, and little carbohydrate digestion occurs here. The majority of digestion happens in the small intestine, where pancreatic amylase and other enzymes break down remaining starches and disaccharides into monosaccharides (single sugars).

Absorption and Distribution

The resulting monosaccharides—primarily glucose, fructose, and galactose—are then absorbed through the wall of the small intestine into the bloodstream. From there, they are transported to the liver, where fructose and galactose are converted into glucose. Glucose is the primary fuel source that cells use for energy.

Storage for Later Use

When the body has more glucose than it needs for immediate energy, it stores the excess for later.

Glycogen Storage: Excess glucose is converted into glycogen and stored in the liver and muscles. This provides a readily available energy reserve for short, intense activities or for regulating blood sugar levels.
Fat Conversion: Once glycogen stores are full, any remaining excess glucose is converted into fat and stored in adipose tissue for long-term energy reserves.

Complex vs. Simple Carbohydrate Sources

This table provides a quick comparison of the two main types of carbohydrates.


Feature	Complex Carbohydrates	Simple Carbohydrates
Energy Release	Slow, sustained energy release.	Fast, rapid energy release.
Blood Sugar Impact	More stable blood sugar levels.	Rapid increase, followed by a sharp drop.
Food Sources	Whole grains, legumes, starchy vegetables.	Fruits, milk, sweets, juices.
Nutritional Value	Rich in fiber, vitamins, minerals.	Often lack other nutrients, especially added sugars.
Overall Health	Promotes stable energy and satiety.	Best consumed in moderation due to potential for weight gain and health issues.

The Indigestible Carbohydrate: Fiber

Fiber is a crucial complex carbohydrate that humans cannot digest. It passes through the digestive system largely intact but plays a vital role in health. Fiber aids digestion, promotes gut health by feeding beneficial bacteria, helps regulate blood sugar, and promotes feelings of fullness. It is found abundantly in plant-based foods like fruits, vegetables, whole grains, and legumes. A diet rich in fiber is associated with a lower risk of heart disease and digestive issues.

Conclusion: Fueling Your Body Wisely

In summary, the body gets the majority of carbohydrates from a balanced intake of plant-based foods, with complex carbohydrates from whole grains, vegetables, and legumes serving as the primary source of sustained energy. Simple carbs, found naturally in fruits and dairy, also play a role but should be consumed in moderation, especially added sugars. A well-rounded diet that emphasizes high-fiber, complex carb sources ensures a steady energy supply and supports overall health, from digestion to blood sugar management. Understanding these sources and how the body uses them is key to making informed dietary choices for optimal well-being. For more detailed information on healthy eating, you can refer to authoritative sources such as The Nutrition Source from Harvard T.H. Chan School of Public Health: https://nutritionsource.hsph.harvard.edu/carbohydrates/.

Frequently Asked Questions

The primary function of carbohydrates is to provide the body with glucose, which is the main source of energy for all bodily functions and physical activity.

No, carbohydrates come in different forms, including simple carbs (sugars), complex carbs (starches and fiber), and are digested differently. Healthy diets emphasize complex carbs.

Excess glucose from carbohydrate digestion is first stored as glycogen in the liver and muscles. If those stores are full, any remaining glucose is converted to and stored as fat.

Complex carbohydrates, such as starches, are broken down by enzymes like salivary and pancreatic amylase, primarily in the small intestine, into single sugar units (monosaccharides) that can be absorbed.

Natural sugars are found in whole foods like fruits and milk, which also provide other nutrients. Added sugars are put into processed foods and offer little nutritional value.

Yes, fiber is a complex carbohydrate. However, the human body cannot digest it for energy, though it supports digestive health and other bodily functions.

Excellent sources of complex carbohydrates include whole grains (brown rice, oats), legumes (beans, lentils), and starchy vegetables (potatoes, sweet potatoes).