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 selection, 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 (approximately 52 yr old) nonobese subjects. In more advanced obesity, ie 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.
D000293:Adolescent; D000328:Adult; D000368:Aged; D000596:Amino Acids / Q000097:blood; D001923:Brain Chemistry; D003920:Diabetes Mellitus / Q000097:blood / Q000378:metabolism*; D005951:Glucose Tolerance Test; D006801:Humans; D007328:Insulin / Q000097:blood; D008875:Middle Aged; D009765:Obesity / Q000097:blood / Q000378:metabolism*; D012701:Serotonin / Q000096:biosynthesis*; D014364:Tryptophan / Q000097:blood
D000596:Amino Acids; D007328:Insulin; D012701:Serotonin; D014364:Tryptophan