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Metabolism. 1988 Jul;37(7):672-6.

Plasma amino acids and insulin levels in obesity: response to carbohydrate intake and tryptophan supplements.

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Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge 02142.


We assessed the plasma amino acids, glucose, and insulin responses of obese and lean control subjects to midafternoon carbohydrate snacks. After a standard 400 kcal lunch, eight lean and nine obese subjects received, at 2PM, a 30 g sucrose snack; blood samples were obtained at hourly intervals until 6 PM. Each subject participated in four similar studies in which the carbohydrate snack was consumed alone or with 250, 500, or 1,000 mg of L-tryptophan (Trp), offered as a capsule. The obese group exhibited elevated plasma levels of the branched-chain amino acids, phenylalanine and tyrosine, and the levels of these amino acids declined much less in response to carbohydrate intake than in lean controls. As a consequence, the plasma ratio of Trp:large neutral amino acids (Trp/LNAA ratio), which normally rises after carbohydrate consumption, showed virtually no change in the obese group. The plasma Trp/LNAA response of this group did not reach control values even when carbohydrate intake was increased to 50 or 75 g. Peak plasma Trp concentrations and Trp/LNAA ratios after 250, 500, and 1,000 mg Trp doses were also significantly lower in the obese. Since brain Trp uptake is strongly correlated with the plasma Trp/LNAA ratio, which in turn determines the rate of brain serotonin synthesis, the blunted Trp/LNAA response to carbohydrate intake in the obese could contribute to alterations in the serotonin-mediated regulation of food intake.

[Indexed for MEDLINE]

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