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Meal composition and plasma amino acid ratios: Effect of various proteins or carbohydrates, and of various protein concentrationsThe effects of meals containing various proteins and carbohydrates, and of those containing various proportions of protein (0 percent to 20 percent of a meal, by weight) or of carbohydrate (0 percent to 75 percent), on plasma levels of certain large neutral amino acids (LNAA) in rats previously fasted for 19 hours were examined. Also the plasma tryptophan ratios (the ratio of the plasma trytophan concentration to the summed concentrations of the other large neutral amino acids) and other plasma amino acid ratios were calculated. (The plasma tryptophan ratio has been shown to determine brain tryptophan levels and, thereby, to affect the synthesis and release of the neurotransmitter serotonin). A meal containing 70 percent to 75 percent of an insulin-secreting carbohydrate (dextrose or dextrin) increased plasma insulin levels and the tryptophan ratio; those containing 0 percent or 25 percent carbohydrate failed to do so. Addition of as little as 5 percent casein to a 70 percent carbohydrate meal fully blocked the increase in the plasma tryptophan ratio without affecting the secretion of insulin - probably by contributing much larger quantities of the other LNAA than of tryptophan to the blood. Dietary proteins differed in their ability to suppress the carbohydrate-induced rise in the plasma tryptophan ratio. Addition of 10 percent casein, peanut meal, or gelatin fully blocked this increase, but lactalbumin failed to do so, and egg white did so only partially. (Consumption of the 10 percent gelatin meal also produced a major reduction in the plasma tyrosine ratio, and may thereby have affected brain tyrosine levels and catecholamine synthesis.) These observations suggest that serotonin-releasing neurons in brains of fasted rats are capable of distinguishing (by their metabolic effects) between meals poor in protein but rich in carbohydrates that elicit insulin secretion, and all other meals. The changes in brain serotonin caused by carbohydrate-rich, protein-poor meals may affect subsequent food choice and various serotonin-mediated behaviors.
Document ID
19930074626
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Yokogoshi, Hidehiko
(Massachusetts Inst. of Tech. Cambridge, MA, United States)
Wurtman, Richard J.
(Massachusetts Inst. of Tech. Cambridge, MA, United States)
Date Acquired
August 16, 2013
Publication Date
September 1, 1986
Subject Category
Aerospace Medicine
Report/Patent Number
NAS 1.26:192874
NASA-CR-192874
REPT-670
Accession Number
93N72073
Funding Number(s)
CONTRACT_GRANT: NAG2-210
Distribution Limits
Public
Copyright
Public Use Permitted.
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