Oligosaccharides are short-chain carbohydrates composed of 3 to 10 monosaccharide units, but they are not digestible by human enzymes in the small intestine. Instead, they travel to the colon, where they are fermented by the gut microbiota, promoting the growth of beneficial bacteria like Bifidobacteria and Lactobacilli. This prebiotic function is responsible for many of the health benefits associated with these compounds. Understanding the different types and their sources can help you make informed dietary choices.
Fructooligosaccharides (FOS)
Fructooligosaccharides, or FOS, are naturally occurring carbohydrates composed of fructose units. They are one of the most common and well-researched types of oligosaccharides, prized for their prebiotic effects.
Characteristics and sources
- Structure: FOS consists of linear chains of fructose units, often terminating in a glucose unit.
- Digestion: They are non-digestible and pass through the digestive system to the colon unchanged.
- Sources: FOS is found naturally in many plants, including garlic, onions, leeks, asparagus, bananas, and chicory root. Inulin is a long-chain fructan that is also considered a type of FOS.
- Health Benefits: FOS is known to improve mineral absorption and promote the growth of beneficial gut bacteria. It is also used as a low-calorie, non-cariogenic sweetener in food manufacturing.
Galactooligosaccharides (GOS)
Galactooligosaccharides, or GOS, are another crucial group of prebiotics. They are produced from lactose and feature a chain of galactose units.
Characteristics and sources
- Structure: GOS is composed of galactose-containing oligosaccharides linked together.
- Digestion: Like FOS, GOS is resistant to digestion in the small intestine.
- Sources: GOS is naturally present in some dairy products, beans, and root vegetables. In food manufacturing, they are often added to infant formulas, dairy products, and beverages.
- Health Benefits: GOS is known to promote the selective proliferation of Bifidobacteria and Lactobacilli in the gut. It has also been shown to help prevent eczema in infants at risk for allergies.
Human Milk Oligosaccharides (HMOs)
Human Milk Oligosaccharides, or HMOs, are a highly diverse class of complex carbohydrates found in human breast milk. They are the third most abundant solid component in human milk, after lactose and lipids.
Characteristics and sources
- Structure: Over 200 distinct HMOs have been identified, each made up of various monosaccharides. The most abundant HMO is 2'-Fucosyllactose (2'-FL).
- Digestion: Infants cannot digest HMOs; they serve as food for beneficial gut bacteria.
- Sources: Naturally present exclusively in human breast milk, though some infant formulas now contain bio-identical HMOs like 2'-FL.
- Health Benefits: HMOs play a critical role in establishing a healthy gut microbiome, supporting the immune system, and acting as decoys to prevent pathogens from binding to the gut wall. They also support brain development.
Raffinose Family Oligosaccharides (RFOs)
The Raffinose Family Oligosaccharides, or RFOs, are a group of oligosaccharides found extensively in plants, especially legumes. They include raffinose, stachyose, and verbascose.
Characteristics and sources
- Structure: RFOs are composed of galactose units attached to a sucrose moiety.
- Digestion: Humans lack the enzyme alpha-galactosidase to digest RFOs in the small intestine, leading to fermentation by gut bacteria in the colon, which can cause flatulence and bloating.
- Sources: Legumes (beans, peas, lentils), cabbage, broccoli, and Brussels sprouts are common sources of RFOs.
- Health Benefits: Despite causing some digestive discomfort, RFOs have prebiotic potential by promoting the growth of beneficial gut bacteria. In plants, they are crucial for stress tolerance and seed germination.
Comparison of Primary Oligosaccharides
| Feature | Fructooligosaccharides (FOS) | Galactooligosaccharides (GOS) | Human Milk Oligosaccharides (HMOs) | Raffinose Family Oligosaccharides (RFOs) |
|---|---|---|---|---|
| Composition | Short chains of fructose units | Chains of galactose units | Complex, diverse mix of multiple monosaccharides | Galactose units attached to a sucrose core |
| Primary Sources | Chicory root, garlic, onions, asparagus, banana | Dairy products, legumes, root vegetables | Human breast milk | Legumes, beans, cabbage, broccoli |
| Digestibility in Humans | Not digestible in small intestine; fermented in colon | Not digestible in small intestine; fermented in colon | Not digestible by infants; fermented by infant gut bacteria | Not digestible in small intestine; fermented in colon leading to gas |
| Main Prebiotic Function | Stimulates Bifidobacteria and produces SCFAs | Promotes Bifidobacteria and Lactobacilli growth | Supports Bifidobacteria growth in infants and pathogen defense | Promotes growth of beneficial bacteria; can cause gas in humans |
| Other Health Benefits | Low-calorie sweetener, improves mineral absorption, aids digestion | May reduce eczema risk in infants and help with lactose intolerance | Crucial for infant immune system and brain development; protects against infection | Can provide energy for plants and aid seed survival |
How oligosaccharides act as prebiotics
The core function of oligosaccharides as prebiotics is based on their resistance to human digestion. This allows them to pass into the large intestine, where they are selectively fermented by certain beneficial bacteria. This process produces short-chain fatty acids (SCFAs), which are crucial for maintaining a healthy gut environment. These SCFAs, such as butyrate, acetate, and propionate, nourish the cells lining the colon, lower the gut's pH to inhibit pathogenic bacteria, and have systemic anti-inflammatory effects. The structure and composition of different oligosaccharides influence which types of beneficial bacteria they promote, making diversity in prebiotic consumption important.
Role in food industry
The unique properties of oligosaccharides have led to their increasing use in the food industry as functional ingredients. Their low sweetness, non-digestibility, and prebiotic effects make them attractive alternatives to traditional sweeteners. They are commonly added to infant formulas, dairy products like yogurt, beverages, and baked goods to improve taste, texture, and nutritional value. Some, like FOS and inulin, are also used as fat replacers. The market for functional oligosaccharides continues to grow due to the increasing consumer demand for products that support gut health.
Conclusion
In summary, the primary oligosaccharides—Fructooligosaccharides, Galactooligosaccharides, Human Milk Oligosaccharides, and Raffinose Family Oligosaccharides—are important functional carbohydrates that play significant roles in both nutrition and food science. Their primary function as prebiotics directly impacts gut health by promoting beneficial bacteria and producing important metabolites like short-chain fatty acids. While they share many core functions, differences in their structure, sources, and specific biological effects exist. From supporting infant immunity and development to serving as functional ingredients in foods, oligosaccharides are a versatile and beneficial class of compounds. Recognizing these primary types can help individuals better understand their dietary intake and the profound impact these carbohydrates have on overall health and the gut microbiome.
- Fructooligosaccharides (FOS): Primarily derived from plants like chicory and onions, FOS are well-known prebiotics that promote beneficial gut bacteria and can function as low-calorie sweeteners.
- Galactooligosaccharides (GOS): Sourced from dairy and legumes, GOS are valuable prebiotics that stimulate the growth of Bifidobacteria and can be added to infant formulas.
- Human Milk Oligosaccharides (HMOs): Found exclusively in breast milk, HMOs are unique and complex oligosaccharides vital for establishing a healthy infant gut microbiome and supporting immune function.
- Raffinose Family Oligosaccharides (RFOs): Present in legumes and cruciferous vegetables, RFOs possess prebiotic properties but can also cause gastrointestinal discomfort due to gas production.
- Prebiotic Function: All primary oligosaccharides serve as prebiotics by resisting digestion and being fermented by gut bacteria, producing beneficial short-chain fatty acids.
