Effect of hydrolysed egg protein on brain tryptophan availability

Abstract

Serotonin synthesis critically depends on plasma levels of tryptophan (TRP). Earlier studies have shown that for mood and cognitive benefits to occur, the ratio between TRP and other large neutral amino acids (LNAA) has to be increased by approximately 40%. The present study investigated the dose-dependent effects of a TRP-rich hydrolysed protein (egg-protein hydrolysate, EPH) on the plasma TRP:LNAA. Moreover, it was investigated whether EPH could increase TRP:LNAA in the presence of 2g of milk protein (MP). In a randomised double-blind crossover design, plasma amino acids were measured every 30min for 3·5h after ingestion of a drink containing either three different doses of 4, 8 and 12g EPH containing 270, 560 or 800mg of TRP, respectively, the combination of 4g EPH and 2g MP (74mg TRP), or 4g MP (148mg TRP) in twenty healthy subjects with a mean age of 52 years. All three EPH doses caused significant increases of TRP:LNAA above 40% at 30, 60 and 90min after consumption in a dose-dependent manner. Compared with the 4g EPH, the increase in TRP:LNAA in the 4g EPH with 2g MP condition was significantly lower at 60min (63 v. 44%, P<0·001) and did not differ significantly at 90min (58 v. 53%, P>0·05). The present study showed that a low dose of 4g EPH with even the addition of 2g MP was sufficient to increase the ratio of TRP:LNAA above 40%. Thus, EPH offers a viable ingredient to increase TRP availability.