- Fructooligosaccharides (FOS) are a class of short-chain carbohydrates composed of fructose units linked together, often with a terminal glucose residue. They typically consist of 2 to 10 monosaccharide units, with the general structure Glc–(Fru)ₙ, where glucose is linked to a chain of fructose molecules via β-(2→1) glycosidic bonds.
- Common examples include 1-kestose (GF₂), nystose (GF₃), and fructofuranosylnystose (GF₄). Naturally, FOS are found in a wide variety of plants, including onions, garlic, asparagus, bananas, artichokes, wheat, and chicory root (the richest commercial source).
- Biologically, FOS serve as storage carbohydrates in plants, where they contribute to energy reserves and stress tolerance, especially under drought or cold conditions. They belong to the broader group of fructans, which are fructose-based polysaccharides. In plants, their solubility and flexibility make them useful for maintaining osmotic balance and protecting cellular structures during water stress.
- In human nutrition, FOS are categorized as prebiotic dietary fibers, since they are not digested in the upper gastrointestinal tract due to the absence of enzymes capable of breaking β-(2→1) linkages. Instead, they reach the colon intact, where they are selectively fermented by beneficial gut microbiota such as Bifidobacteria and Lactobacilli. This fermentation process produces short-chain fatty acids (SCFAs) like acetate, propionate, and butyrate, which improve colonic health, enhance mineral absorption, and support immune modulation. Because of these properties, FOS are widely recognized for their role in promoting gut health, improving bowel regularity, and reducing the risk of gastrointestinal disorders.
- From an industrial perspective, FOS are used as functional food ingredients and sweeteners. They provide mild sweetness (about 30–50% as sweet as sucrose) without contributing significant calories, making them suitable for low-calorie and diabetic-friendly products. Their stability under heat and acidity also makes them useful in processed foods, dairy products, beverages, and baked goods. Furthermore, FOS are utilized in nutraceuticals and infant formulas to mimic the prebiotic effects of human milk oligosaccharides.
- In addition to gastrointestinal benefits, ongoing research suggests that FOS may contribute to immune regulation, lipid metabolism, and glycemic control. By altering the gut microbiome and enhancing SCFA production, they may help reduce inflammation, improve cholesterol profiles, and lower postprandial glucose levels. However, excessive intake can sometimes lead to bloating, gas, or abdominal discomfort due to rapid fermentation in the colon, which is why moderation is advised.
