The Musical Fruit

No discussion of digestable and indigestable sugars would be complete without a foray into the ones that cause flatulence. It’s a topic that every food writer has in their repertoire, in the same way that every bar band knows the song Mustang Sally. Playing it is in one sense a show of poor taste. But on the other hand it’s pretty fun too. So what they hey? It’s Friday is it not?

If you remember my first lengthy post from yesterday, I briefly discussed a family of carbohydrates called oligosaccharides. These are short-chain sugars (three, four, or five glucose molecules long) that generally belong to plants. When we come along and eat those plants, they become ours. It’s the kind of take-no-prisoners game survival is.

Now humans have a wide variety of enzymes in our digestive systems that allow us to break complicated sugars down into simpler ones. We have quite a few for oligosaccharides, though we don’t have enzymes for all of them. Which means that some of the plant sugars we eat proceed down the digestive tract untouched, at least by us. But then we aren’t the only players in the digestion game, even where our own bodies are concerned. There are billions upon billions of so-called “friendly” flora and fauna that inhabit the warm, wet environment that is our intestines, just waiting for their turn at the buffet. Many possess just the right enzymes for breaking oligosaccharides down into usable fuel.

And so the little microbes have at it, gobbling down sugars and extracting their energy in a process that we know as fermentation. The main by-product of fermentation, other than heat, is gas (mostly carbon dioxide) which goes on to exit our bodies in a rather, um…conspicuous fashion.

Interestingly, there are some plant sugars that are even too much for our microbiological partners to handle. These include long-chain carbohydrates like cellulose and lignin which plants produce not for energy storage, but for building material. Cellulose is the major structural component of plant stems. It’s also found in abundance in the tough outer husks of seeds, which in the case wheat and oat grains are known as bran.