Breakfast meal composition influences plasma tryptophan to large neutral amino acid ratios of healthy lean young men.

The effect of a carbohydrate, a 20% protein, or a carbohydrate +0.3% tryptophan TRP breakfast on plasma large neutral amino acid ratios was studied in 6 healthy men. The carbohydrate-rich meal produced shifts in plasma amino acid concentrations such that plasma TRP/LNAA ratios increased from 0.13 to 0.15 (p less than 0.04) and the protein meal decreased the ratio from 0.14 to 0.11 (p less than 0.04) after 1 hour. Addition of 0.3% TRP to the carbohydrate-rich meal increased plasma TRP/LNAA ratios more than 2-fold. The TRP containing meal was thus the only one likely to influence brain 5-HT synthesis, although the difference between the plasma TRP/LNAA ratios after carbohydrate and protein breakfasts suggests that the brain may distinguish, by synthesizing more or less 5-HT, the composition of breakfast meals.