Eating potatoes with the skin on raises questions about what happens to that outer layer. Unlike the fleshy, starchy interior, the skin is a complex biological structure. Whether potato skins are digested depends on the difference between the skin’s durable components and the limitations of human digestive enzymes. The skin is not absorbed but travels through the digestive tract, providing unique physiological benefits.
The Structural Makeup of Potato Skins
The potato skin (periderm) is primarily composed of structural carbohydrates that protect the vegetable. Unlike the soft interior, which is mainly digestible starch, the skin is a concentrated source of dietary fiber, including both soluble and insoluble types.
The bulk of this fiber includes complex carbohydrates like cellulose and hemicellulose. Cellulose forms the rigid structure of the plant cell walls. The skin also contains lignin and pectin, which contributes to soluble fiber. This composition makes the skin more nutritionally dense than the flesh, containing a greater concentration of fiber, minerals, and vitamins.
How the Body Processes Insoluble Fiber
When potato skins are consumed, the body’s digestive system cannot break down structural components like cellulose and lignin. Human digestive enzymes, such as amylase, dismantle starch bonds but are inert to the bonds holding cellulose together. Therefore, the majority of the potato skin passes through the stomach and small intestine without chemical digestion.
The undigested matter moves into the large intestine, encountering the gut microbiota. These microbes possess enzymes that humans lack, allowing them to ferment some fiber components, such as hemicelluloses and resistant starches. This fermentation yields beneficial compounds like short-chain fatty acids, which support gut health. However, the most durable parts of the skin, particularly cellulose, resist microbial breakdown and remain largely intact.
Potato skins are not digested like fats, proteins, or starches absorbed into the bloodstream. Instead, the insoluble fiber moves through the gastrointestinal tract, acting as non-digestible bulk. This material is eventually excreted, fulfilling a mechanical role rather than nutritional absorption.
The Health Function of Undigested Matter
The fact that potato skin fiber is largely undigested offers significant health benefits. The insoluble fiber adds considerable bulk and softness to the stool by attracting water into the intestine. This increased volume promotes healthy bowel movements and helps prevent constipation.
The mechanical action of this bulk assists in regulating intestinal transit time, ensuring waste moves through the colon efficiently. The physical presence of fiber also contributes to satiety, helping a person feel fuller after a meal. By slowing the overall digestion rate, this undigested matter helps stabilize blood sugar levels, preventing rapid spikes in glucose.