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Originally posted by Starman

Edge::What do you believe to be true but cannot prove?

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Originally posted by furshur

I have never seen a satisfactory explanation as to why your pee stinks after eating asparagus.

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Originally posted by astropin

I believe there is other life in our universe, not necessarily intelligent.

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Monty Python:
So remember when you're feeling very small and insecure
How amazingly unlikely is your birth
And pray that there is intelligent life somewhere up in space
Cause there is bugger-all down here on Earth

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Originally posted by furshur

I have never seen a satisfactory explanation as to why your pee stinks after eating asparagus.

...well I haven't...

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In February we discussed beeturia. Now we will cover two more food idiosyncrasies: why urine becomes malodorous after the ingestion of asparagus, and why water tastes sweet after the ingestion of artichoke.
The ingestion of asparagus is associated with the production of malodorous (described as "rotten or boiling cabbage" or "vegetable soup") urine. This occurs in approximately 40-43% of people (a figure of 79% was observed in the United States) within an hour after eating only a few spears of asparagus.
It has been shown to remain with individuals for virtually a lifetime. Those who produce this odor assume that everyone does, and those who do not produce it have no idea of its potential olfactory consequences.1,2,3,4,5

Why does this occur?
This phenomena has been regarded as either the result of an inborn error of metabolism or an inherited (autosomal dominant) trait.5,6

But this appears to be not true. The urinary excretion of a pungent odorous substance after asparagus is eaten appears to be universal and the variable is the ability to detect the related odor. The detection of the odor constitutes a specific smell hypersensitivity. Those who can smell the odor in their own urine would thus be able to smell it in the urine of anyone who has eaten asparagus, whether or not that person was able to smell it himself. It is possible that this odor sensitivity is a genetic hypersensitivity or general hyperosmia rather than an inborn error of metabolism. Studies have suggested that it is a genetically determined specific hypersensitivity (controlled by a single autosomal dominant gene).6,7

What is evident is that there also appears to exist a specific hyposmia (hyposphresia) or anosmia, wherein certain individuals are unable to smell the odor even from the most fetid urines. A later study suggested that both phenomena coexist. Some people are excretors while others are nonexcretors; some people are perceivers (able to smell the odor) while others are nonperceivers (do not smell it). But this still needs further investigation.7

Several metabolites have been found present in the urine after ingesting asparagus and at least two different ones have been held responsible for the characteristic odor. Specifically six discrete sulphur-containing alkyl compounds have been identified, namely methanethiol, dimethyl sulphide, dimethyl disulphide, bis-(methylthio)methane, dimethyl sulphoxide and dimethyl sulphone. But other have also been found present.4,7,8

One study has indicated that a substance, namely methylmercaptan, appeared in the urine of 40% of the subjects and suggested that its excretion was an expression of an autosomal dominant gene.7

S-methyl thioacrylate and its methanethiol addition product S-methyl-3 (methylthio) thiopropionate have been postulated to be the odor-causing compounds in most studies that have been performed, but the metabolic pathway leading to their formation has not been identified.2,3,7,9

The isolation of sulfur-containing compounds from the urine after asparagus ingestion is, however, no indication that they themselves contribute to the odor, as they may be insufficiently volatile. Due to many queries about the methods used, more investigations are needed.7,8

...

1. Mitchell SC. Asparagus and malodorous urine. Br J Clin Pharmacol 1989 May;27(5):641-2.
2. Richer C, Decker N, Belin J, Imbs JL, Montastruc JL, Giudicelli JF. Odorous urine in man after asparagus. Br J Clin Pharmacol 1989 May;27(5):640-1.
3. White RH. Occurrence of S-methyl thioesters in urines of humans after they have eaten asparagus. Science 1975 Sep 5;189(4205):810-11.
4. Mitchell SC. Food idiosyncrasies: beetroot and asparagus. Drug Metab Dispos 2001;29:539-43.
5. Mitchell SC, Waring RH, Land D, Thorpe WV. Odorous urine following asparagus ingestion in man. Experientia 1987 Apr 15;43(4):382-3.
6. Hoffenberg L. A note on polymorphism: the ability to smell urinary metabolites of asparagus. Diastema 1983;11:37-8.
7. Lison M, Blondheim SH, Melmed RN. A polymorphism of the ability to smell urinary metabolites of asparagus. Br Med J 1980 Dec 20-27;281(6256):1676-8.
8. Waring RH, Mitchell SC, Fenwick GR. The chemical nature of the urinary odour produced by man after asparagus ingestion. Xenobiotica 1987 Nov;17(11):1363-71.

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Originally posted by BigPapaSmurf
I think were way off topic here, we are listing what is not known instead of "What science cannot explain"

Science is everything, what is not is what science cannot explain. Our failure in understanding has no bearing on the actual science involved.

We will never have a scientific proof of imagination so anything therein cannot be properly tested.

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