Carbohydrate digestion is one of the most misunderstood processes in nutrition. Many people think carbs simply “turn into sugar” the moment they’re eaten, but the reality is much more complex. Carbs go through multiple stages of digestion, each involving specific enzymes, gut organs, and even your microbiome. Understanding this process helps explain why not all carbs are created equal and why fibre plays such a critical role in long-term health.
Step 1: The Mouth
Carb digestion begins as soon as food enters the mouth. Chewing increases the surface area of food particles, while salivary amylase breaks down starch into shorter chains. This early step kickstarts the process, making later digestion more efficient.
Step 2: The Stomach
Once food reaches the stomach, mechanical mixing continues. However, chemical digestion pauses here — stomach acid (HCl) inactivates salivary amylase. At this point, carbs remain largely intact until they pass into the small intestine.
Step 3: The Small Intestine
The small intestine is where most carbohydrate digestion and absorption occur. Pancreatic amylase and brush-border enzymes break starch into simple sugars (glucose, fructose, galactose). These sugars are absorbed into the bloodstream and delivered to tissues for energy use or storage.
Step 4: The Large Intestine
Not all carbohydrates are digested. Fibre and resistant starch reach the colon, where they’re fermented by gut bacteria. This fermentation produces short-chain fatty acids (SCFAs), compounds that fuel colon cells, regulate inflammation, and support metabolic health. The remaining undigested fibre is excreted as waste.
Why This Matters
Carbohydrates aren’t just “good” or “bad.” Their impact depends on the type, structure, timing, and how your body digests them. Some carbs quickly deliver glucose for energy, while others, like fibre, primarily nourish gut microbes. This dual role highlights why carbs are more than fuel, they’re essential for both performance and long-term health.
If you want to move beyond carb myths and learn how to tailor your nutrition for performance, physique, and long-term health, our 1:1 coaching offers evidence-based strategies designed for your goals. Reach out below!