Markus C R, Olivier B, Panhuysen G E, Van Der Gugten J, Alles M S, Tuiten A, Westenberg H G, Fekkes D, Koppeschaar H F, de Haan E E
TNO Nutrition and Food Research Institute, Zeist, The Netherlands.
Am J Clin Nutr. 2000 Jun;71(6):1536-44. doi: 10.1093/ajcn/71.6.1536.
Increased brain serotonin may improve the ability to cope with stress, whereas a decline in serotonin activity is involved in depressive mood. The uptake of the serotonin precursor, tryptophan, into the brain is dependent on nutrients that influence the cerebral availability of tryptophan via a change in the ratio of plasma tryptophan to the sum of the other large neutral amino acids (Trp-LNAA ratio). Therefore, a diet-induced increase in tryptophan availability may increase brain serotonin synthesis and improve coping and mood, particularly in stress-vulnerable subjects.
We tested whether alpha-lactalbumin, a whey protein with a high tryptophan content, may increase the plasma Trp-LNAA ratio and reduce depressive mood and cortisol concentrations in stress-vulnerable subjects under acute stress.
Twenty-nine highly stress-vulnerable subjects and 29 relatively stress-invulnerable subjects participated in a double-blind, placebo-controlled study. Subjects were exposed to experimental stress after the intake of a diet enriched with either alpha-lactalbumin or sodium-caseinate. Diet-induced changes in the plasma Trp-LNAA ratio and prolactin were measured. Changes in mood, pulse rate, skin conductance, and cortisol concentrations were assessed before and after the stressor.
The plasma Trp-LNAA ratio was 48% higher after the alpha-lactalbumin diet than after the casein diet (P = 0.0001). In stress-vulnerable subjects this was accompanied by higher prolactin concentrations (P = 0.001), a decrease in cortisol (P = 0.036), and reduced depressive feelings (P = 0.007) under stress.
Consumption of a dietary protein enriched in tryptophan increased the plasma Trp-LNAA ratio and, in stress-vulnerable subjects, improved coping ability, probably through alterations in brain serotonin.
脑内血清素水平升高可能会提高应对压力的能力，而血清素活性下降则与抑郁情绪有关。血清素前体色氨酸进入大脑的过程取决于营养物质，这些营养物质通过改变血浆色氨酸与其他大型中性氨基酸总和的比例（色氨酸-大型中性氨基酸比例）来影响色氨酸在大脑中的可利用性。因此，饮食诱导的色氨酸可利用性增加可能会提高脑内血清素的合成，并改善应对能力和情绪，尤其是在应激易感人群中。
我们测试了富含色氨酸的乳清蛋白α-乳白蛋白是否能提高应激易感人群在急性应激下的血浆色氨酸-大型中性氨基酸比例，并降低其抑郁情绪和皮质醇浓度。
29名高度应激易感受试者和29名相对应激不易感受试者参与了一项双盲、安慰剂对照研究。受试者在摄入富含α-乳白蛋白或酪蛋白酸钠的饮食后接受实验性应激。测量饮食诱导的血浆色氨酸-大型中性氨基酸比例和催乳素的变化。在应激源前后评估情绪、脉搏率、皮肤电导率和皮质醇浓度的变化。
摄入α-乳白蛋白饮食后，血浆色氨酸-大型中性氨基酸比例比摄入酪蛋白饮食后高48%（P = 0.0001）。在应激易感受试者中，这伴随着应激状态下催乳素浓度升高（P = 0.001）、皮质醇降低（P = 0.036）和抑郁情绪减轻（P = 0.007）。
食用富含色氨酸的膳食蛋白质可提高血浆色氨酸-大型中性氨基酸比例，并且在应激易感人群中，可能通过改变脑内血清素水平来提高应对能力。
