best article i've seen on how l-dopa is absorbed and how that absorption can be affected by protein.
discusses potential affect in early and later stages and suggests things to try to improve absorption and lessen fluctuations.
didn't notice this initially but mentions fava having l-dopa in a different structure than synthetic?
" The beans are a natural food which contains L-dopa in a
physicochemical form different from that of tablet formulations
and may thus have some use in the management of Parkinsonian
motor fluctuations."

i assume old article, most recent literature citation was 1992 and doesn't mention stalevo or duodopa but interestingly does mention experimental IV and nasal tube delivery getting around the protein problem in the duodenum absorption but not the BBB.
i found this interesting, exactly why getting the l-dopa out of the stomach asap is important if you have on/off periods:
"L-Dopa is optimally absorbed from the duodenum and proximal
jejunum.[16] The drug is not absorbed across gastric mucosa,[17]
but oral doses are dependent on gastric emptying for access to
absorption sites. The rate of gastric emptying is chiefly
determined by the energy content of food and is inversely
proportional to the energy density of meal.[18] Thus fat will
retard gastric emptying to greater degree than either protein or
carbohydrate. Low gastric acidity slows emptying [19] although
routine administration of antacids to Parkinsonian patients does
not improve L-dopa absorption.[20] Some types of dietary fiber
increase food viscosity and slow gastric emptying.[21] The
gastric mucosa contains the enzyme dopa decarboxylase,[22] which
will catalyze unwanted conversion of L-dopa to dopamine,
reducing the amount of L-dopa available for subsequent
absorption from doses affected by delayed gastric emptying."



http://www.parkinsons-information-ex...chive/097.html