Nutrition Diet: Why Are Starches Called Complex Carbs?

November 4, 2025 •

4 min read

According to the Cleveland Clinic, a food's chemical structure and how quickly your body digests it determines whether a carbohydrate is complex or simple. This foundational principle is why starches are called complex carbs, and understanding it is key to making better nutritional choices that support long-term health and energy.

Quick Summary

Starches are known as complex carbs due to their chemical structure of long, complex chains of sugar molecules. This structure causes slower digestion, providing a gradual energy release, sustained energy, and stable blood sugar levels compared to simple sugars, which are broken down quickly.

Key Points

Complex Chemical Structure: Starches are polysaccharides, meaning they are long chains of many sugar molecules bonded together, which is why they are called 'complex'.
Slow Digestion for Sustained Energy: The body takes longer to break down these complex chains, leading to a slow, steady release of glucose into the bloodstream.
Stable Blood Sugar: This gradual absorption prevents the rapid spikes and crashes in blood sugar levels caused by simple sugars.
Enhanced Satiety: Foods rich in complex carbs, especially those with fiber, help you feel fuller for longer, which can assist in weight management.
Prioritize Whole-Food Sources: The health benefits are highest in unprocessed starches like whole grains, legumes, and starchy vegetables that retain their natural fiber and nutrients.
Processing Changes Digestion Speed: Refining starches (like in white flour) removes fiber, causing them to be digested much faster and act more like simple carbs.

The Chemical Basis for 'Complex'

At its core, the reason why starches are called complex carbs lies in their chemical structure. While all carbohydrates are made of sugar units, the difference between simple and complex carbs is the length of their molecular chains.

Polysaccharides: The term for a complex carbohydrate is a 'polysaccharide,' with 'poly' meaning 'many' and 'saccharide' referring to a sugar unit. Starches are large polysaccharide molecules, meaning they are built from hundreds or even thousands of simple sugar units, like glucose, bonded together.
Amylose and Amylopectin: Starch is composed of two main types of glucose polymers: amylose, which forms a linear, unbranched chain, and amylopectin, which is highly branched. This intricate, interwoven structure is what makes starch physically and chemically 'complex' and challenging for the body to break down quickly.
Contrast with Simple Carbs: Simple carbohydrates, or monosaccharides and disaccharides, consist of only one or two sugar units linked together. Their simple structure allows for rapid digestion and absorption. Examples include the fructose in fruit or the sucrose in table sugar.

The Digestion Process: A Crucial Difference

The slow and steady digestion of starches is a major reason they are considered the healthier carbohydrate option. When you eat starchy foods, your body's digestive enzymes must work to break apart the many bonds holding the long glucose chains together.

Sustained Energy: This slow, gradual breakdown process results in a steady release of glucose into your bloodstream over a longer period. This provides your body and brain with a stable, prolonged source of energy, preventing the sharp energy spikes and subsequent crashes often associated with simple sugars.
Blood Sugar Regulation: Because the glucose from starches is absorbed slowly, it helps to regulate blood sugar levels, which is particularly beneficial for managing and preventing conditions like type 2 diabetes. In contrast, simple sugars cause a rapid spike in blood sugar, triggering a larger insulin response.

Health Benefits of Complex Carbohydrates

Including healthy, unrefined complex carbs in your diet provides a host of benefits beyond just sustained energy:

Increased Satiety: Starchy foods, particularly whole-grain varieties rich in fiber, promote a feeling of fullness. This can aid in weight management by reducing overeating and snacking between meals.
Improved Digestion: Dietary fiber, also a complex carbohydrate, is crucial for digestive health. It adds bulk to stool, preventing constipation and supporting a healthy gut microbiome.
Higher Nutrient Density: Many whole-food sources of complex carbs are packed with essential vitamins, minerals, and antioxidants that are vital for overall health. Examples include B vitamins, iron, and magnesium found in whole grains.
Heart Health: The fiber in complex carbohydrates can help lower bad (LDL) cholesterol, contributing to better cardiovascular health.

Simple vs. Complex Carbohydrate Comparison


Feature	Simple Carbohydrates	Complex Carbohydrates (Starches)
Chemical Structure	1-2 sugar units (monosaccharides/disaccharides)	Many sugar units bonded together (polysaccharides)
Digestion Speed	Very fast; broken down easily	Slow; body takes longer to break down
Energy Release	Rapid burst, followed by an energy crash	Sustained and gradual release
Blood Sugar Impact	Causes sharp spikes and drops	Leads to more stable and regulated levels
Nutrient Content	Often low in nutrients, fiber, and vitamins (empty calories)	Often rich in fiber, vitamins, and minerals
Food Examples	Sugary cereals, candy, sodas, fruit juice	Whole grains, legumes, starchy vegetables

The Impact of Processing on Starches

It's important to recognize that not all starchy foods are equal in their nutritional impact, largely due to how they are processed. Refined grains, like white rice or white bread, have been stripped of their bran and germ, which removes much of the fiber and other vital nutrients. This refining process makes the starch more accessible to the body's enzymes, causing it to be digested much faster—closer to a simple carbohydrate than a whole-grain starch.

Conversely, whole grains, such as brown rice and whole-wheat pasta, retain their fiber and nutrients. The fiber helps slow down digestion further, reinforcing the benefits of complex carbohydrates. Some cooking methods can even increase the amount of resistant starch (a type of complex carb that resists digestion) in food, like cooking and then cooling potatoes or rice.

Incorporating Healthy Starches Into Your Diet

Making smart choices about your carbohydrate intake is a cornerstone of a healthy diet. Focus on swapping refined options for whole-food alternatives to maximize the benefits of starches.

Breakfast: Choose oatmeal or a slice of whole-grain toast instead of a sugary breakfast cereal or refined pastry.
Lunch: Opt for a salad topped with legumes like chickpeas or lentils, or make a brown rice bowl with vegetables.
Dinner: Substitute white pasta or white rice with whole-wheat pasta, brown rice, or quinoa. Serve meals with nutrient-dense starchy vegetables like sweet potatoes or corn.
Snacks: Snack on whole fruits, nuts, or even air-popped popcorn for a healthy source of complex carbs and fiber.

Conclusion

Starches are called complex carbohydrates because their lengthy, intricate chemical structure of multiple bonded sugar units requires more time and effort for your body to break down. This slower digestion process is the source of their key benefits: a sustained release of energy, better blood sugar control, and prolonged satiety. By prioritizing unprocessed, whole-food sources of starches over refined versions, you can harness the power of complex carbs for a more stable and nutritious diet. Making informed choices about your carbohydrates is a simple yet powerful step towards improving your overall health and well-being.

For more information on the types of carbohydrates and their roles in a healthy diet, you can refer to authoritative sources like the American Heart Association.

Frequently Asked Questions

Simple carbohydrates consist of one or two sugar units, known as monosaccharides or disaccharides. Complex carbohydrates, like starches, are much larger molecules called polysaccharides, made of long, intricate chains of many sugar units bonded together.

Slower digestion means a more gradual release of glucose into the bloodstream. This provides sustained energy, prevents drastic blood sugar spikes and crashes, and promotes a feeling of fullness, which can aid in weight management.

While most starches are complex carbs, their health impact depends on how they are processed. Refined starches, like white rice and white bread, have been stripped of fiber and nutrients, causing faster digestion. Whole-food starches, like brown rice and lentils, are the healthiest options.

Yes, pasta is primarily a complex carbohydrate made from starch molecules. While white pasta is refined, its fundamental starch chains still require more time to digest than simple sugars. Whole-wheat pasta, with its added fiber, offers an even slower release of energy.

Yes, all carbohydrates, including starches, are broken down into glucose, which raises blood sugar. However, healthy complex carbs do so at a slower, more stable rate. Highly refined starches can cause a faster spike, similar to simple sugars.

Fiber slows down the digestion and absorption of carbohydrates. When a starchy food is rich in fiber (like whole grains or potatoes with skin), it provides an even more gradual energy release and stable blood sugar levels.

Excellent sources include whole grains (brown rice, quinoa, oats), legumes (beans, lentils, chickpeas), starchy vegetables (sweet potatoes, corn, peas), and most fruits and vegetables.