Tuesday 7 November 2006

Pic of the day: "If you waste food, divine retribution will fall upon you." At least my body seems to have taken this to heart...

Day-after-salad taste

Yesterday I had salad for breakfast. Actually there were no salad leaves in it: The basis was cooked maize (corn to my American readers) with some pasta, egg, cheese and red onion. It is pretty tasty and agrees well with my digestion, which is otherwise rather picky.

Today at roughly the same time, I could taste the salad again, except it tasted slightly different. Recognizable though. I had not eaten anything like it in a day, and had even brushed my teeth. Clearly the vague taste did not come from my mouth but rather from my bloodstream.

Food spends usually around three days passing through the human digestive tract, by far most of this in the large intestine. (Which is probably why it is larger...) Some simple substances are absorbed already in the stomach, and most in the small intestine. Starches (now converted to sugars), proteins and even fats largely are absorbed here. Only the "tough customers" are passed on to the large intestine: In a normal diet mostly cellulose from plants, but also various other substances like the complex starches from beans and legumes, and animal fibers from meat. There are also "leftovers" since absorption in the small intestine is not perfect. The resulting mass is left to "fermentation" by gut bacteria. (I will not get into how these bacteria got there in the first place, let us just say we are not born with them.)

The bacteria live a hectic but short life. As a by-product of the fermentation they release organic compounds that are absorbed by the intestinal walls and converted in the liver into ordinary fuel for the body. The liver also destroys moderately toxic by-products, changing them into harmless compounds that are secreted by the kidneys. The bacteria themselves are eventually digested furher downstream, at least some of them and to some degree, thus giving us one last serving of the food we ate two days ago. What happens after that should be familiar enough.

So when I could taste some of the flavors from the food I ate yesterday, it was no doubt because some of the volatile substances that gave them flavor were also absorbed by the intestines together with the volatile fatty acids from the cellulose fermentation. Yay. The system works, for now at least.

(You may wonder why the bacteria selflessly give away the volatile fatty acids and later their lives. Well, they don't really have a choice. The intestine is patrolled by representatives from the human immune system, and any attempt at a takeover would be forcibly flushed from the system. As long as they play by the rules, however, the bacteria can rest assured that their descendants will live as long as their host, barring some disaster like antibiotics, after which the population has to be rebuilt. I leave that as an exercise for the reader. Bon appetit!)