Why do some foods make your urine smell strange?

We posed this Question to Glenys Jones from the MRC Human Nutirion Research Unit in Cambridge...

Glenys - High sugar containing cereals could make urine smell, either because they contain a compound in there when it's metabolised that has an odour or it could actually be that there's so much sugar in there, it's beyond our renal capability. Diana - So the kidneys might not be able to process all of that sugar which could lead to microbes, breeding and then creating an interesting smell. But this is quite unusual. So where else do we encounter smelly wee. Glenys - Lots of foods are known to make our urine smell. So for example, something like asparagus contains a sulphur-containing compound methyl mercaptan and another compound called asparagine and when these are metabolised in the digestive track, they release a very typical odour that people who eat asparagus will often say, that their urine smells in a particular way. Diana - But not everyone is affected by the asparagus phenomenon. Glenys - Now, whether it's because there's only half the population who contain a gene to break this down or the only half does contain a gene that can actually smell it would also explain why only a percentage of the population actually can smell this specific urinous of smell when we eat asparagus. So it might be that you can eat asparagus and produce urine that smells, but you can't smell it or it could be vice versa. Similar foods I think like cheese, garlic, eggs, and beer, they're also known to make the urine smell quite particular. The compound that is found in asparagus is also actually found in skunk secretions, so the smell that you think of with the skunk, it's the same smell that releases when you eat asparagus.