Serotonin precursor influenced by type of carbohydrate meal in healthy adults

Abstract

We compared the effects on the ratio of plasma tryptophan to large neutral amino acids (trp:LNAA) of two different carbohydrate meals (sucrose or starch, 120 g) and a contrasting meal of fat + protein given at breakfast to 10 healthy adults. Plasma glucose and insulin were also measured. The trp:LNAA ratio rose after both carbohydrate meals (p less than 0.001). Glucose and insulin peaks were higher after sucrose than starch, and trp:LNAA rose correspondingly higher (sucrose +34% and starch +20%, p less than 0.05). The ratio declined 45% after the fat + protein meal. At 180 min, absolute ratio values were twofold higher after carbohydrate (sucrose 0.133 and starch 0.127) than after fat + protein (0.057). Similar results were found with the same meals given in the evening. Our results suggest that high-carbohydrate meals have an influence on serotonin synthesis. We predict that carbohydrates with a high glycemic index would have a greater serotoninergic effect than carbohydrates with a low glycemic index.

Effects of Diet on Sleep Quality

“…In support of this, a correlation between plasma glucose and insulin, and peak Trp:LCNAA has been reported (36). Therefore, an HC diet, especially one with a high GI, would promote a higher Trp-to-LCNAA ratio and have a greater serotonergic effect (36). Moreover, it has been reported that the Trp-to-LCNAA ratio peaks between 2 and 4 h after the ingestion of an HC meal (36), which likely accounts for shorter SOL after the consumption of an HC or high-GI meal 4 h compared with 1 h before bedtime (23).…”

“…With the consumption of an HC diet, the resulting higher postprandial insulin enhances the Trp-to-LCNAA ratio by facilitating uptake of LCNAA by muscle, further promoting Trp entry into the brain and enabling serotonin production (23). In support of this, a correlation between plasma glucose and insulin, and peak Trp:LCNAA has been reported (36). Therefore, an HC diet, especially one with a high GI, would promote a higher Trp-to-LCNAA ratio and have a greater serotonergic effect (36).…”

“…When the concentration of Trp is higher than that of LCNAAs, its entry into the brain is favored and serotonin production is upregulated (34,35), which would promote sleep (24). Because the Trp-to-LCNAA ratio is affected by dietary carbohydrate intake (33,36), it is possible that changes in sleep architecture as a result of carbohydrate manipulation are mediated by the Trp-to-LCNAA ratio. An HC diet or meal would increase the Trp-to-LCNAA ratio and promote sleep through increased serotonin production (33,34).…”

“…Therefore, an HC diet, especially one with a high GI, would promote a higher Trp-to-LCNAA ratio and have a greater serotonergic effect (36). Moreover, it has been reported that the Trp-to-LCNAA ratio peaks between 2 and 4 h after the ingestion of an HC meal (36), which likely accounts for shorter SOL after the consumption of an HC or high-GI meal 4 h compared with 1 h before bedtime (23). This proposed mechanism must be explored further, however, because the Trp-to-LCNAA ratio was not measured in the studies reported in the current review.…”

Nutritional influences on cognitive function: mechanisms of susceptibility

“…On the other hand, TRP is scarce in most protein sources, and is readily metabolised on passage through the liver; thus, the plasma ratio of TRP to competing amino acids falls after a proteinrich meal (Schweiger et al 1986b;Yokogoshi & Wurtman, 1986;Christensen, 1993). Indeed, the protein-induced reduction in plasma TRP ratio often seems to be more marked than any carbohydrate-induced rise (Lieberman et al 1986;Lyons & Truswell, 1988;Wolever et al 1988;Christensen & Redig, 1993). Such effects also depend on the interval since, and nutrient content of, the last meal (Fernstrom & Fernstrom, 1995).…”