Nutrasweet - problem and a solution (?)

Andrew Ray aray at emory.edu
Tue Dec 5 00:01:53 EST 1995


In article <41728.robin073 at maroon.tc.umn.edu>, "Alan J. Robinson" 
<robin073 at maroon.tc.umn.edu> writes:

>I picked up some of the basic references on aspartame and brain 
>monoamines at the med school library because the whole subject of 
>aspartame safety appears to tie in with some other important recent 
>developments in medicine.
>
>Just a couple of minutes of thumbing through these books was enough to 
>convince me that the problem is so simple and straightforward it 
>is a wonder it wasn't resolved a long time ago.  In fact aspartame is 
>a very good demonstration of the problems associated with 
>administering a single psychotropic agent by itself.
>
>Many neurotransmitters are derived, directly or indirectly, from the 
>amino acids in food proteins.  It's a wonder we don't go crazy each 
>time we have a meal because of the sudden changes in plasma levels 
>of neurotrasnmitter precursors, but apparently the body can handle a 
>simultaneous increase of the 20 different amino acids in food.  What 
>it can't handle is an increase in just one - evolution never had to 
>deal with the problem of an animal consuming massive quantities of 
>just one of the amino acids.
>
--other stuff deleted for space--

That isn't exactly true - don't forget, your brain is priveledged tissue - what 
goes on in the plasma rarely affects the brain, except in certain cases such as 
CO2 changes, glucose deprivation, etc.  Your neurotransmitter biosynthetic 
pathways are EXTREMELY tightly controlled.  Any increases of precursors in the 
plasma are usually only weakly mirrored in NT levels.  The enzymes running the 
biosynthetic pathways are controlled through various feedback mechanisms, so 
you don't need to control plasma precursor levels as much.  True, you will see 
very weak increases in some NT levels (depends on the NT), but NT release will 
not be affected.  While evolution never had to deal with our bizarre diet, your 
brain is designed to be set off quite a bit from your diet.  The only way that 
weak increases in NT synthesis would affect brain function would be if you were 
concurrently taking amphetamines or other drugs which specifically cause 
release of newly synthesized NT.  If someone had a genetically caused problem 
with any of these biosynthetic feedback mechanisms (goes to genetic 
susceptibility issue), it would show up at every meal, not just if they had 
aspartame.  
     Think of it this way - fish contain large amounts of DMAE, an 
acetylcholine precursor.  If your theory were true, eating a plate of fish 
would load your plasma with DMAE.  This would be converted to Acetylcholine, 
and you would get a large dose of ACh in a short time.  This would lead to 
convultions and other neuromuscular problems - you'd be in bad shape until the 
ACh surge ended.  This is peripheral also - the central nervous system is much 
more priveledged than the peripheral nerves.  Since that doesn't happen, it is 
pretty clear there must be something preventing it.  There's good reason to 
assume that something would also function for the other NT's, since a balance 
is what is needed for normal function.  And in fact, that something does exist 
- as negative feedback mechanisms and the blood-brain-barrier.

Andrew Ray
Emory University Neuroscience Program
aray at emory.edu



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