Ur-ine trouble if you've been eating asparagus

I was reading last week in Hugh Fearnley-Whittingstall's delightful food column that asparagus is in season again. I really enjoy this whole eating in-season produce and being eco-responsible lark (despite it being so fashionable it almost makes you cringe). It's great; you get to eat really fresh food which is also quite cheap, since there's loads of it around.

Asparagus stalks in the wild

So I've been tucking in to the zingy spears all week and have been loving it. I was surprised to learn from a friend who had been similarly glutting-out on asparagus, that he also always enjoys eating asparagus, since 'it always makes my wee smell all mental.' I was surprised by this as I had experienced no real bathroom shocks, asparagus-related or otherwise, over the past few days.

But enough of this cheap toilet humour. As usual I needed to quench my insatiable thirst for scientific knowledge (or something) so I set about finding out what causes these magic odours which some people can smell and some can't.

First off, it is clear that a chemical of some sort is responsible. Scientists generally agree the one causing the grievance in this case is methyl mercaptan.

As an interesting aside though, unlike our other senses, smell is not really that well understood by scientists. We know how things like vision, touch and hearing work in quite a lot of detail, but smell remains something of an enigma.

We do know that there are various receptors in our noses, and it seems obvious that these mediate smell in some way. So far though, it has proved difficult for scientists to work out their exact structures. (Conversely, we do know the structures of lots of other proteins, for example opsin, as shown in the recent benchtwentyone article on retinal). To add to the confusion several molecules which have similar structures have wildly different scents. Conversely, molecules of vastly different sizes and shapes can sometimes smell very similar (figure 1). As a result of this confusion, there have been several not-widely-accepted theories of smelling even relatively lately [1].

Most receptors in the body are large proteins. These mediate everything from the digestion of food to the degradation of neurotransmitters and work on the theory of 'lock and key'. This means the cleft in the center of the protein has a specific shape and size which binds only a particular guest. But if this is the case for odourants, we would expect similar molecules to smell the same - which is not always the case.

Figure 1

Methyl mercaptan (the guilty party derrived from asparagus) and ethane dithiol are both sulfurous compounds which smell awful; like rotten eggs. Acetophenone has a relatively small methyl group compared to benzophenone which is much larger. They both smell similar though - people tend to describe the odour as a lot like burnt almonds.

To get back to asparagus though, it seems there are two possible explanations for the discrepancy between mine and my friend's post-asparagus wee. The first option is that one of us has a particular enzyme or bacteria in our intestinal tract which breaks down a compound present in asparagus to methyl mercaptan and the other doesn't. This might make quite good sense, as naturally occurring amino acids which contain sulfur (such as methionine) are known to be broken down in the mouth to methyl mercaptan by bacteria [2], causing bad breath. The alternative is that we both have the compound in our urine, but I don't have the correct receptors in my nose to smell it.

Stopping short of inviting my contact into a slightly too close for comfort wee smelling investigation, I consuted the British Medical Journal and found that the experiment had already been done by the professionals [3]. The researchers in question found that the chemical was present in the urine of all the 203 asparagus-fed volunteers they investigated. Also, when presented with samples of an 'unknown liquid' (the researchers obviously felt it wouldn't be proper to reveal it's true identity) the volunteers who could smell the guilty chemical in their own urine could smell it also in everyone else's.

So like it or not, if you're like me and have been chowing down on asparagus all week, you're going to have some seriously funky bathroom smells sometime soon.

[1] L. Turin, Chem. Senses., 1995, 773 - 790

[2] T. Koga etal., Infection and Immunity, 2000, 68 (12), 6912-6916.

[3] M. Lison, S. H. Blondheim and R. N. Melmed, British Medical Journal, 1980, 281, 20 - 27.

Paradigm shifts

Some scientists like to think that they pressume nothing, and have the cold pursuit of facts as their only rule. In fact this is largely nonsense. If we really stop to think about it we realise that all knowledge is based on certain assumptions and approximations. In lots of cases (most, even) these assumptions are reliable and good, but what happens when something occurs which contradicts all our percieved limitations?

A few years back a man called Thomas Kuhn demonstrated what can happen by cheekily constructing a deck of playing cards in which the suits of hearts and diamonds were coloured black and the clubs and spades were red - this of course going against the whole mind set you automatically take on as soon as you glimpse a pack of small cards with that characteristic pattern on their backs. Kuhn conducted an experiment where he quickly flashed random cards at his subjects, who he asked to try and identify them. He found most people identified the black cards as either spades or clubs automatically, even though they weren't, but displayed some degree of brow-furrowing. The second time round people were utterly confused and some even became angry. He even cited one of his subjects as crying and screaming hysterically, such was her distress at realising that somehow everything she thought she knew about cards was suddenly and inexplicably wrong with no apparent explanantion.

Kuhn conducted this experiment in order to try and illustrate his theory of 'paradigm shifts' and wrote it up in his 1962 book The Structure of Scientific Revoloutions. A historian by trade, Kuhn believed that scientists (like all of us) make a set of assumptions about their field of research. This could be based on the previous work done, where and by whom you have been taught or just on random prejudices. Generally this set of rules is shared by the majority of informed people in a field and forms what Kuhn dubbed a paradigm. A paradigm then, is like a window, the assumptions we make about things like the sills which frame the view. A paradigm shift is what happens when suddenly someone finds out something which they can't explain using the current scientifc theories - the window frame shifts to make room for new ideas.

Paradigm shifts have occured on a global scale lots of times in history as Kuhn expertly details in his book. For example it must have been one heck of a shock when one day a bloke called Nicolaus Copernicus came along and told everyone that in fact it was not the earth which was at the centre of the universe, but the sun (of course, we now know that's not exactly the full picture either). Equally, when scientists such as Bohr, Einstein and Planck started observing that the laws of nature which work for very large objects (like footballs and planets) didn't work for very small objects (like electrons and atoms) they found they needed new laws to explain what they were seeing. We now call that quantum mechanics.

Some argue that we are currently moving from a modern to a post-modern era and this is a form of cultural paradigm shift. Modernism was characterised by the formation of large, characterless conglomerations and as a result the making of large sums of money. Post-modernism is rather the opposite: a distrust of organised bodies of all kinds (especially the government and especially the financial systems) and a search for a more personal and resonant meaning and truth.

There are paradigm shifts going on all over the place. Now you know what they are you can try and spot one and tell someone else. You'll make yourself look very intellectual. Either that or just appear wierd and alienate yourself a little.