Oligosaccharides are a type of carbohydrate, or prebiotic fiber, composed of three to ten simple sugar units linked together. Because humans lack the necessary digestive enzymes, these compounds pass undigested into the large intestine, where they are fermented by beneficial bacteria like Bifidobacterium and Lactobacillus. This process makes oligosaccharides essential for supporting a healthy gut microbiome.
Natural Plant Sources
Legumes and Grains
Legumes are among the richest sources of naturally occurring oligosaccharides, particularly those from the raffinose family. These include raffinose, stachyose, and verbascose, which are composed of glucose, galactose, and fructose units. Common legume sources include:
- Lentils
- Chickpeas
- Soybeans
- Peas
- Kidney beans
Many grains, especially whole-grain products, also contain significant amounts of oligosaccharides like fructooligosaccharides (FOS), inulin, and arabinoxylan oligosaccharides (AXOS). Good grain sources include wheat, rye, barley, and oat. Soaking and cooking can sometimes alter the content of these sugars in legumes.
Vegetables
Many common vegetables are excellent sources of oligosaccharides, primarily FOS and inulin. Inulin is a fructan chain widely distributed in plants and often extracted from chicory root for use as a food ingredient. Key vegetables include:
- Onions and garlic
- Leeks and scallions
- Asparagus
- Jerusalem artichoke
- Chicory root
- Cabbage (red and green)
- Broccoli
- Beets and fennel
Fruits
While typically associated with simple sugars, many fruits contain moderate amounts of oligosaccharides. The specific content and type can vary depending on ripeness. Notable sources include:
- Bananas (especially unripe)
- Watermelon
- Nectarines
- Grapefruit
- Berries (blueberries, raspberries)
- Dates and prunes
Other Sources
Human Milk Oligosaccharides (HMOs)
Human breast milk is a uniquely abundant source of oligosaccharides, containing over 200 different complex sugars known as HMOs. These are not a source of nutrition for the infant but are crucial for shaping the infant's gut microbiome by selectively feeding beneficial bacteria like Bifidobacteria. HMOs also act as anti-adhesive agents, preventing harmful pathogens from attaching to the gut wall. Some infant formulas now add specific HMOs, like 2'-fucosyllactose (2'-FL), to replicate some of these benefits.
Fermented Foods and Supplements
Fermented foods and certain dairy products can contain various oligosaccharides. For example, miso, sake, and soy sauce contain isomaltooligosaccharides (IMOs). Galactooligosaccharides (GOS) are found naturally in milk and soybeans, and some versions can be synthesized from lactose to add to foods like infant formula. Beyond food, concentrated forms of FOS, GOS, and inulin are sold as nutritional supplements.
Comparison of Oligosaccharide Sources
| Source Type | Primary Oligosaccharides | Key Food Examples | Best For |
|---|---|---|---|
| Plant-based Foods | Fructans (FOS, Inulin), Raffinose family (Stachyose, Raffinose) | Onions, garlic, legumes, wheat, rye, Jerusalem artichoke, asparagus | Incorporating into a regular diet for general prebiotic benefits |
| Human Breast Milk | Human Milk Oligosaccharides (HMOs), such as 2'-FL | Exclusively from human breast milk | Infant immune system development and establishing a healthy gut microbiome |
| Manufactured Sources | FOS, GOS, Inulin, IMO | Infant formula, supplements, functional foods (bars, cereals) | Supplementation, specialized dietary needs |
| Fermented Foods | Isomaltooligosaccharides (IMO) | Miso, soy sauce, sake | Specific dietary intake of IMO |
How the body utilizes oligosaccharides
Unlike simple sugars that are digested and absorbed in the small intestine, oligosaccharides are designed to resist human digestive enzymes. This allows them to pass into the large intestine intact, where they are consumed by gut bacteria through fermentation. This process produces short-chain fatty acids (SCFAs), which have numerous health-promoting effects, such as reducing the pH of the colon, improving mineral absorption, and maintaining the intestinal barrier. The indigestible nature of these fibers is key to their prebiotic function.
Health Benefits
Beyond their role as a prebiotic, the consumption of oligosaccharides offers several potential health benefits:
- Improved Digestion: By supporting the growth of beneficial bacteria, they help maintain a healthy balance of gut microbiota and can aid with issues like constipation and diarrhea.
- Enhanced Immunity: A healthy gut microbiome supported by oligosaccharides can positively influence the immune system, particularly in infants.
- Better Mineral Absorption: Fermentation of oligosaccharides can improve the absorption of minerals like calcium, magnesium, and iron.
- Support for Heart Health: Some studies suggest that regular intake can help lower cholesterol and triglyceride levels.
- Weight Management: They may help reduce appetite by stimulating fullness hormones.
Conclusion
Oligosaccharides are crucial prebiotic carbohydrates, with widespread presence in natural foods, from the legumes and vegetables in our kitchens to the unique composition of human breast milk. Their ability to escape human digestion and selectively nourish beneficial gut bacteria makes them a vital component for fostering a healthy microbiome and supporting overall well-being. Understanding these diverse sources allows for more informed dietary choices, promoting better digestive and immune health.
Visit the National Institutes of Health for more research on the human gut microbiome
