2 replies to this topic

[mrak1979]

Does anyone know if it is possible to cause malabsorption by taking too many supplements? or at once?

[zoolander]

Yes.

With some amino acids their is a competitive inhibition to cross the blood brain barrier if they are taken together.

For example:

Inhibition of neutral amino acid transport across the human blood-brain barrier by phenylalanine.

Shulkin BL, Betz AL, Koeppe RA, Agranoff BW.

Department of Internal Medicine (Division of Nuclear Medicine), University of Michigan Medical School, Ann Arbor.

The delivery of large neutral amino acids (LNAAs) to brain across the blood-brain barrier (BBB) is mediated by the L-type neutral amino acid transporter present in the membranes of the brain capillary endothelial cell. In experimental animals, the L-system transporter is saturated under normal conditions, and therefore an elevation in the plasma concentration of one LNAA will reduce brain uptake of others. In this study, we used positron emission tomography (PET) to determine the effect of elevated plasma phenylalanine concentrations on the uptake of an artificial neutral amino acid, [11C]-aminocyclohexanecarboxylate ([11C]ACHC), in human brain. PET scans were performed on six normal male subjects after an overnight fast and again 60 min after oral administration of 100 mg/kg of phenylalanine. The plasma phenylalanine concentration increased by an average of 11-fold between the first and second scans. This increase produced a reduction in [11C]ACHC uptake in all brain regions but not in scalp. The mean +/- SD influx rate constant for whole brain decreased after phenylalanine ingestion from 0.036 +/- 0.002 to 0.019 +/- 0.004 ml/g/min. Kinetic analysis of the effect of plasma phenylalanine concentration on the rate of [11C]ACHC uptake is compatible with a model of competitive inhibition so that large increases in the concentration of one LNAA in plasma will reduce the brain uptake of other LNAAs across the human BBB.

PMID: 7861158 [PubMed - indexed for MEDLINE]

In short....amino acids travel accross the blood brain barrier via a transporter. These transporters carry different amino acids but they can only carrier one amino acid at a time. Large Neutral Amino acids (LNAA) were mentioned above. The LNAAs are: phenylalanine, tyrosine, tryptophan, threonine, isoleucine, leucine, valine, methionine, and histidine. These amino acids compete with one another for access into the brain.

Also, you might want to look into the effects of phytates and oxalates with mineral absorption

[xanadu]

That's a very complex subject and I'm not the expert on it. I do know that some minerals or substances will block absorbtion of other minerals or substances. For example, oxalic acid in spinach makes it hard to absorb iron. Generally, people take supplements with food but a few are better taken on an empty stomach.