Our second gut

The prime candidate for the most impressive piece of plumbing in the human body has to be the gastrointestinal tract. From mouth to anus it offers an 8-metre-long journey with staging points including the oesophagus, stomach and small and large intestines. En route the fare we have consumed is processed, nutrients are extracted and the waste is neatly packaged ready for disposal.

The working of the small intestine has, however, long been a bit of a mystery. This is mainly due to its exasperatingly inaccessible position between the stomach and large intestine. Said small intestine has a diameter of just 3 cm, half that of the colon, and is coiled up in the abdomen like a hurriedly rolled up hose pipe. It comprises three parts, being the duodenum, where bile and digestive enzymes break down molecules, the jejunum which is the main venue for the absorption of nutrients into the bloodstream, and the ileum, whose tasks include mopping up remaining nutrients and bile before the remainder continues on its merry way to the colon or large intestine.

But now, techniques have been developed for inserting tubes in selected places in the small intestine to gain more data on what exactly is going on there while the digestive system gets on with its daily business.

It is becoming increasingly clear that the small intestine does other vital work besides processing food, such as preserving metabolic health and maintaining a healthy gut microbiome. Further, after the stomach has emptied each day the valves between the small and large intestine close and the then partially digested food accumulates in the ileum which starts to act like a small second stomach. It was also previously believed that fibre passed through the small intestine unscathed, but new techniques have shown this to be untrue.

Examinations at a Japanese university of the highly effective drug metformin, offered to help people with type 2 diabetes, surprisingly led to the discovery that such patients excrete large amounts of glucose into the jejunum in the small intestine, with the drug almost quadrupling the flux. Hence the effect, with lower blood sugar levels as a happy consequence with the excretion of glucose out of the blood stream.  

Our small intestine also controls metabolism by releasing appetite-suppressing hormones in response to food. It was previously believed that this was exclusively done by the colon. The spotlight is now being turned onto how to optimise the release of appetite-supressing drugs in the ileum to tackle obesity.

It may well be wise to give a little more consideration to our small intestine microbiome. The bacteria happily dwelling there are particularly partial to the two fibre molecules raffinose and stachyose, which are both abundant in legumes.