What substances in plant foods are not digested the stomach or small intestine?

Plant foods contain various substances that are not digested in the stomach or small intestine. Some of these substances include:

Dietary fiber: Dietary fiber, also known as roughage, is a type of carbohydrate that cannot be broken down by human digestive enzymes. It is found in the cell walls of plants and includes compounds such as cellulose, hemicellulose, and lignin. Dietary fiber passes through the digestive tract largely intact and contributes to stool bulk.

Resistant starch: Resistant starch is a type of starch that resists digestion in the small intestine. It can be found in certain plant foods, such as unripe bananas, beans, legumes, and whole grains. Resistant starch acts similarly to soluble fiber and contributes to gut health by nourishing beneficial gut bacteria.

Polyphenols: Polyphenols are a diverse group of antioxidants found in many plant foods, including fruits, vegetables, tea, and coffee. While some polyphenols can be absorbed and metabolized in the small intestine, others can reach the large intestine undigested.

Lignans: Lignans are plant compounds with antioxidant and estrogen-like properties. They are found in foods such as flaxseeds, sesame seeds, and whole grains. Lignans are poorly absorbed in the small intestine and undergo bacterial metabolism in the large intestine.

Oligosaccharides: Oligosaccharides are short chains of sugars that are resistant to digestion by human enzymes in the small intestine. They are found in various plant foods, such as beans, onions, garlic, and legumes. Oligosaccharides can reach the large intestine where they are fermented by gut bacteria, potentially causing digestive discomfort such as gas and bloating.

Inulin: Inulin is a type of soluble fiber that is found in foods like chicory root, artichokes, and Jerusalem artichokes. It passes undigested through the small intestine and acts as a prebiotic, supporting the growth of beneficial bacteria in the large intestine.

These undigested substances play important roles in maintaining gut health, promoting regularity, feeding beneficial gut bacteria, and potentially reducing the risk of certain chronic diseases.