Raffinose and Gas: The Sugar Your Body Can't Digest
Raffinose is a naturally occurring sugar found in beans, cabbage, and whole grains that the human body simply cannot break down — making it one of the most reliable triggers of intestinal gas.
What Is Raffinose?
Raffinose is a complex carbohydrate known as an oligosaccharide, built from three simple sugars: galactose, glucose, and fructose. It belongs to a group called the raffinose-family oligosaccharides, or RFOs, which also includes stachyose, made of four sugars, and verbascose, made of five. These molecules are especially abundant in legumes such as beans, lentils, and chickpeas, in cruciferous vegetables like cabbage, broccoli, and Brussels sprouts, and in whole grains and asparagus. Plants use raffinose as a storage carbohydrate and as a protectant that helps their seeds survive freezing and drying. The defining feature of raffinose is the chemical bond linking its galactose unit, an alpha-1,6-galactosidic bond, which turns out to be the very reason it causes so much trouble in the human digestive tract.
Why Humans Can't Digest It
The human small intestine produces a wide array of digestive enzymes, but it lacks one crucial one: alpha-galactosidase. This enzyme is required to cleave the alpha-1,6 bond that attaches the galactose unit to the rest of the raffinose molecule. Without it, raffinose cannot be broken into absorbable single sugars, so it travels intact through the stomach and small intestine without providing any calories or nutrition. Humans are far from unique in this limitation, because most mammals lack the enzyme as well. When raffinose finally reaches the large intestine, it arrives essentially untouched, still carrying all of its fermentable energy. There it meets the trillions of bacteria that make up the gut microbiome, many of which possess exactly the enzyme that humans do not, setting the stage for vigorous fermentation.
Fermentation and Gas Production
In the colon, gas-producing bacteria such as species of Bacteroides and Clostridium happily consume raffinose because they carry alpha-galactosidase. As they ferment the sugar, they release a mixture of gases including hydrogen, carbon dioxide, and, in people who host methanogenic archaea, methane. This is the direct source of the bloating and flatulence associated with a plate of beans. Because raffinose is osmotically active, it can also draw water into the colon, contributing to a sense of fullness and occasionally loose stools. The amount of gas produced varies dramatically from person to person, depending on the makeup of an individual's microbiome, how quickly food transits the gut, and how much raffinose-rich food was eaten. Some bacteria even consume the hydrogen produced by others, which is one reason gas output differs so widely between people.
How to Reduce Raffinose Gas
Several practical strategies can lower the gas load from raffinose-rich foods. Soaking dried beans for several hours and discarding the water removes a portion of the water-soluble oligosaccharides before cooking, and long, thorough cooking helps further. Sprouting seeds and fermenting foods, as in tempeh, miso, or sauerkraut, allows enzymes and microbes to pre-digest much of the raffinose. The most direct solution is a supplement of alpha-galactosidase, sold under brand names such as Beano, which supplies the missing enzyme so that raffinose is broken down in the small intestine before bacteria can reach it. Finally, eating high-raffinose foods regularly and in gradually increasing amounts allows the gut microbiome to adapt over weeks, often reducing symptoms as the community of bacteria shifts toward a more balanced fermentation.
Did You Know?
- Raffinose provides no usable calories to humans because we cannot digest it at all.
- The anti-gas supplement Beano is simply the enzyme alpha-galactosidase, produced by a mold called Aspergillus niger.
- Plants load their seeds with raffinose partly to protect them from damage during freezing and drought.
- Stachyose, raffinose's larger cousin, is often present in even greater amounts in soybeans.
Fun Fact
The raffinose in a single serving of baked beans can keep colon bacteria fermenting for hours, which is why the gassy effects of a bean-heavy meal are famously delayed rather than immediate.
Sources
- Rackis, J.J., Flatulence Caused by Soya and Its Control Through Processing, Journal of the American Oil Chemists' Society, 1981
- Suarez, F.L. et al., Gas Production in Humans Ingesting a Soybean Flour, American Journal of Clinical Nutrition, 1999
- Elango, D. et al., Raffinose Family Oligosaccharides: Friend or Foe for Human and Plant Health, Frontiers in Plant Science, 2022