Soy oligosaccharides: effect on our health

Soybeans contain raffinose (0.7%) and stachyose (3%), which are oligosaccharides with powerful prebiotic properties. But what are oligosaccharides and prebiotic sugars?
Oligosaccharides are large molecules consisting of 3 or more sugar units. They taste less sweet than monosaccharides, such as glucose or fructose, and disaccharides, such as saccharose. Prebiotic compounds are defined as nondigestible food ingredients that have beneficially effects in the host by selectively stimulating the growth and activity of health promoting bacteria, such as bifidobacteria and lactic acid bacteria, in their colon. Why would you buy expensive probiotic yoghurts, such as Yacult or Activia, when consuming soy products will achieve better effects in a more natural way.

Does soy give you gas?

Oligosaccharides from soybeans, but also from other foods such as chickpeas, sunflower seeds, onions, cabbage and other beans, are known to cause flatulence in sensitive individuals. Flatulence is not unhealthy, but passing gas in the wrong place at the wrong time can cause social embarrassment. Consuming soy products does not always give you gas, if you consume soy on a regular basis you may even experience less faltulence production, because your colon bacteria will adapt and digest the oligosaccharides into lactic acid, without gas formation. Fermented soy products, such as tempeh, soy sauce and miso, are likely to give less gas than unfermented soy products such as tofu and soy milk. If you make your own soy milk you can reduce the level of oligosaccharides in the soy milk by increasing the soaking time of the soybeans. And what does science tell us? Fabrizis Suarez and co-workers investigated the effect of soy ingestion on gas formation in 20 healthy persons (1). They found that the intake of 34 g soy meal had no influence on either the severity of symptoms nor flatus frequency, but consuming 80 g soy meal (which is quite a lot) doubled the flatus frequency. The scientists also tested a special soybeans naturally low in oligosaccharides and found that it produced little flatulence, significantly less than that associated with conventional soy.

Health benefits of soy oligosaccharides

Our body cannot digest raffinose and stachyose very well, but "good" gut bacteria thrive on them on are responsible for many health benefits, which include:

• Stimulation of the growth of bifidobacteria, which suppress the activity of putefactivebacteria, such as Clostridium in the colon.
• Preventing constipation due to the production of short-chain fatty acids.
• Production of vitamins by increased activity of healthy gut bacteria.
• Protection of liver by reducing the production of toxic metabolites.
• Improving absorption of calcium and other minerals.
• Reducing the risk of colon cancer.

References

(1) Suarez FL et al. Gas production in human ingesting a soybean flour derived from beans naturally low in oligosaccharides. Am J Clin Nutr. 1999 Jan;69(1):135-9.