EVIDENCE FOR DIMINISHED BRAIN 5-HYDROXYTRYPTAMINE BIOSYNTHESIS IN OBESE DIABETIC AND NON-DIABETIC HUMANS

Obese persons are often reported to have marked cravings for simple carbohydrate-rich foods. Because of the proposed relationships between protein/carbohydrate seletion, plasma tryptophan (TRP) to large neutral amino acids (LNAA) ratios, and brain 5-hydroxytryptamine (5-HT) neurotransmission, we examined the plasma TRP/LNAA ratios in four categories of obese subjects, before and 120 min after oral glucose tolerance test (GTT). Plasma TRP/LNAA ratios were reduced in obese, non-diabetics by 18%, the same extent as for older (.apprx. 52 yr old) nonobese subjects. In more advance obesity, i.e., obesity associated either with glucose intolerance, hyperinsulinemia or hypoinsulinemia, plasma TRP/LNAA ratios were reduced by 25%. One hundred twenty minutes after a 100 g glucose load plasma TRP/LNAA had not been normalized. Based on animal data, these results suggest there may be diminished 5-HT neurotransmission in obese diabetics. The implications of these findings for the cravings of obese for carbohydrate-rich foods is discussed.