Oligosaccharides are prebiotics – non-digestible food ingredients that selectively stimulate the growth of prebiotic bacteria in the colon. We cannot digest and absorb oligosaccharides ourselves as we lack the enzymes needed to break them down. Similarly, they cannot be used as a food source by other, less desirable bowel bacteria, including E. coli. This means that oligosaccharides selective stimulate the growth and division of beneficial probiotic bacteria, especially strains of Bifidobacteria.
Fructooligosaccharides versus galactooligosaccharides
Oligosaccharides are naturally sweet as they consist of short chains of two to 10 sugars. Longer chains of sugars are known as polysaccharides.
The most important dietary oligosaccharides are fructo-oligosaccharides (FOS) and galactooligosaccharides (GOS).
Fructooligosaccharides are composed of short chains of two to ten fructose sugars.
Galactooligosaccharides consist of short chains of two to ten galactose sugars.
What do oligosaccharides do
Oligosaccharides are best known for their ability to improve the balance of bacteria in the large bowel and to help normalise bowel motions. Oligosaccharides act as an exclusive food source for beneficial Bifidobacteria strains and, to a lesser extent, Lactobacilli. These probiotic bacteria ferment oligosaccharides to produce short chain fatty acids and other metabolites that play an important role in regulating healthy bowel function.
The short chain fatty acids (eg butyrate, propionate) produced by bacterial fermentation of oligosaccharides act as a food source for bowel lining cells (colonocytes) and butyrate may offer some protection against ulcerative inflammatory bowel disease. Propionate is also absorbed and travels directly to the liver, where it has beneficial effects on liver metabolism to improve cholesterol balance and glucose control.
Oligosaccharides also have beneficial effects on calcium absorption, immunity and inflammation. Latest research suggests oligosaccharides also promote the secretion of substances that influence our mood, food choices, feelings of hunger or satiety and weight.
Oligosaccharides may be used alone, to stimulate growth and multiplication of the probiotic bacteria already present in your gut, with beneficial effects usually seen within seven days.
Oligosaccharides can also be combined with probiotic supplements to effectively ‘feed’ them and improve their health benefits and their ability to colonise and remain in the bowel. The combined use of probiotics and prebiotics is sometimes referred to as synbiotics – a term invented by microbiologist Professor Glenn Gibson.
Oligosaccharides are added to food products and infant formulas as a prebiotic to stimulate the growth of beneficial digestive bacteria. For every gram of fibre added to the diet, the weight of bowel motions increases by around 5g due to increased bacterial growth, and absorption of fluid. This bulking stimulates healthy bowel movements and can overcome both diarrhoea and constipation.
Galacto-oligosaccharides (GOS) are produced by enzymatic conversion of the milk sugar, lactose (a disaccharide consisting of two sugars bound together: galactose and glucose). The enzymatic conversion removes the glucose and connects the galactose units into chains to form galactooligosaccharides. The types of GOS produced depend on the specific enzymes used.
The most effective supplements use a b-galactosidase enzyme derived from probiotic Bifidobacteria strains, and these generate galactooligosaccharides (B-GOS) that preferentially stimulate the growth of Bifidobacteria (eg B. bifidum, B. longum infantis) to produce unique digestive health benefits.
Although made from lactose, GOS are not associated with lactose intolerance as their structure is very different.
Galactooligosaccharides and metabolic syndrome
Galactooligosaccharides (B-GOS) were assessed against placebo in 45 overweight adults with metabolic syndrome – which is associated with various combinations of central obesity, raised triglycerides, cholesterol imbalances and high blood pressure. When taking the B-GOS supplements, the number of faecal bifidobacteria increased, along with increases in protective antibodies (secretory IgA) and decreases in inflammatory markers, insulin, total cholesterol, triglycerides and a rise in ‘good’ HDL-cholesterol. This suggests that galactoligosaccharides can improve the markers of metabolic syndrome.
Galactooligosaccharides and immunity
The stress of exams is associated with intestinal symptoms such as diarrhoea, indigestion, heartburn and abdominal pain. Stress also reduces immunity and increases the risk of developing a common cold or ‘flu symptoms. A clinical trial involving 427 university students found that galactooligosaccharides significantly improved intestinal symptoms of diarrhoea, constipation, abdominal pain and indigestion. Those taking GOS also had up to 40% fewer days with cold or flu symptoms.
Galactooligosaccharides and asthma
Gut bacteria are increasingly recognised as playing a role in immune function, allergic sensitisation and inflammation. Taking prebiotic galactooligosaccharides (B-GOS) for 3 weeks significantly reduced airway hyper-responsiveness, bronchoconstriction and markers of airway inflammation compared with placebo.
Galactooligosaccharides and traveller’s diarrhoea
By stimulating the growth of Bifidobacteria, prebiotics can increasing resistance to infection and traveller’s gastroenteritis. A study involving 159 healthy volunteers, who travelled abroad for a minimum of 2 weeks found that those taking galactooligosaccharides (B-GOS) for one week before the holiday, and during travels, had significantly fewer episodes and duration of diarrhoea, or abdominal pain, compared with placebo. The supplements helped to preventing the incidence and symptoms of travellers’ diarrhoea.
Galactooligosaccharides and Irritable Bowel Syndrome
Some people with irritable bowel syndrome find their symptoms improve by following a low FODMAP diet, which involves avoiding foods and supplements containing Fermentable Oligosaccharides, Disaccharides, Monosaccharides And Polyols (FODMAPs). When following a low FODMAP diet, you are advised to avoid fructooligosaccharides. However galactooligosaccharides (B-GOS) produce significantly less gas when fermented than fructooligosaccharides (FOS) and do not contribute to flatulence and gastrointestinal discomfort at recommended doses. You may notice a few initial intestinal symptoms (I noticed some interesting fluttering sensations in the abdomen) but these diminish over a period of 3 weeks as bowel symptoms improve.
Galactooligosaccharide supplements (B-GOS) have been shown to reduce symptoms associated with irritable bowel syndrome such as pain, bloating, diarrhoea and constipation. In 44 people with IBS, taking galactooligosaccharide supplements (B-GOS 3.5g daily) for 12 weeks significantly increased gut levels of Bifidobacteria and improved stool consistency, flatulence and bloating compared with placebo. Higher doses (7g per day) also significantly improved anxiety scores.
Fructo-oligosaccharides are mainly produced from chicory root which, when dried, consist of up to 20% inulin. Inulin is a plant energy storage carbohydrate that is a rich source of fructooligosaccharides (FOS) as well as longer linear polysaccharides with chains of 60 or more fructose sugars linked together.
Fructooligosaccharides are less popular than galacto-oligosaccharides for people with irritable bowel syndrome as FOS fermentation in the bowel can increase gas formation. As a result, symptoms of irritable bowel syndrome (IBS) can worsen initially when taking FOS. However FOS is an excellent treatment for functional constipation that is not associated with pain as in IBS.
FOS and constipation
A clinical trial involving 100 constipated women assessed the effects of combining fructooligosaccharides with Lactobacillus and Bifidobacterium strains, against placebo, for 30 days.
Those receiving the active treatment recorded increased frequency of evacuation, improved stool consistency and shape compared than the placebo group, with significant benefits noted during the second and third weeks.
FOS and glucose control
The combination of 2g fructooligosaccharides and probiotic bacteria (100 million Lactobacillus acidophilus plus 100 million Bifidobacterium bifidum) was assessed in 20 people with type 2 diabetes who took either the active supplements or placebo for 30 days.
Those taking the FOS and probiotics showed as significant improvement in cholesterol balance with increased ‘good’ HDL cholesterol, as well as a significant reduction in fasting glucose levels, compared with placebo.
Best prebiotic supplements
The best prebiotic supplements for constipation are those containing inulin, fructooligosaccharides or galactooligosaccharides.
The best prebiotic supplements for irritable bowel syndrome and for preventing travellers’ diarrhoea are those containing B-GOS – galactooligosaccharides produced by specific Bifidobacteria enzymes.
List prebiotic foods
Oligosaccharides are found naturally in plant foods such as artichokes (Jerusalem artichokes and globe artichokes), asparagus, bananas, barley, blueberries, garlic, honey, leeks, legumes/beans, nectarines, oats, onions, pears, scallions/spring onions, tomatoes, watermelon and wheat.