Carbohydrate Lowers Serotonin from Exercise

Also see:
Sugar (Sucrose) Restrains the Stress Response
Gelatin > Whey
Serotonin, Fatigue, Training, and Performance
Thyroid peroxidase activity is inhibited by amino acids
Whey, Tryptophan, & Serotonin
Protective Glycine
Carbohydrate Lowers Exercise Induced Stress
Exercise Induced Stress

J Sports Sci. 1995 Summer;13 Spec No:S49-53.
Central and peripheral factors in fatigue.
Davis JM.
The causes of fatigue during muscular exercise include factors that reside in the brain (central mechanisms) as well as the muscles themselves (peripheral mechanisms). Central fatigue is largely unexplored, but there is increasing evidence that increased brain serotonin (5-HT) can lead to central (mental) fatigue, thereby causing a deterioration in sport and exercise performance. Although there are also strong theoretical grounds for a beneficial role of nutrition in delaying central fatigue, the data are much more tenuous. Dietary supplementation with branched-chain amino acids (BCAA) in low doses produces small and probably inconsequential effects on peripheral markers of brain 5-HT synthesis (plasma free tryptophan/BCAA), whereas larger doses are likely to be unpalatable, reduce the absorption of water in the gut, and may increase potentially toxic ammonia concentrations in the plasma. Alternatively, carbohydrate supplementation results in large reductions in plasma free tryptophan/BCAA and exercise time to fatigue is significantly longer, but it is difficult to distinguish between the effects of carbohydrate feedings on central fatigue mechanisms and the well-established beneficial effects of carbohydrate supplements on the contracting muscle. These data support the exciting possibility that relationships exist among nutrition, brain neurochemistry and sport performance. However, while the evidence is intriguing and makes good intuitive sense, our knowledge in this area is rudimentary at best.

Am J Clin Nutr. 2000 Aug;72(2 Suppl):573S-8S.
Serotonin and central nervous system fatigue: nutritional considerations.
Davis JM, Alderson NL, Welsh RS.
Fatigue from voluntary muscular effort is a complex phenomenon involving the central nervous system (CNS) and muscle. An understanding of the mechanisms within muscle that cause fatigue has led to the development of nutritional strategies to enhance performance. Until recently, little was known about CNS mechanisms of fatigue, even though the inability or unwillingness to generate and maintain central activation of muscle is the most likely explanation of fatigue for most people during normal daily activities. A possible role of nutrition in central fatigue is receiving more attention with the development of theories that provide a clue to its biological mechanisms. The focus is on the neurotransmitter serotonin [5-hydroxytryptamine (5-HT)] because of its role in depression, sensory perception, sleepiness, and mood. Nutritional strategies have been designed to alter the metabolism of brain 5-HT by affecting the availability of its amino acid precursor. Increases in brain 5-HT concentration and overall activity have been associated with increased physical and perhaps mental fatigue during endurance exercise. Carbohydrate (CHO) or branched-chain amino acid (BCAA) feedings may attenuate increases in 5-HT and improve performance. However, it is difficult to distinguish between the effects of CHO on the brain and those on the muscles themselves, and most studies involving BCAA show no performance benefits. It appears that important relations exist between brain 5-HT and central fatigue. Good theoretical rationale and data exist to support a beneficial role of CHO and BCAA on brain 5-HT and central fatigue, but the strength of evidence is presently weak.

Acta Physiol Scand. 2002 Sep;176(1):65-9.
Evidence that brain glucose availability influences exercise-enhanced extracellular 5-HT level in hippocampus: a microdialysis study in exercising rats.
Béquet F, Gomez-Merino D, Berthelot M, Guezennec CY.
The relationship between brain glucose and serotonin is still unclear and no direct evidence of an action of brain glucose on serotonergic metabolism in central fatigue phenomena has been shown yet. In order to determine whether or not brain glucose could influence the brain 5-hydroxytryptamine (5-HT) system, we have monitored in microdialysis the effects of a direct injection of glucose in rat brain hippocampus on serotonergic metabolism [i.e. 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) and tryptophan (TRP)], during high intensive treadmill running. The injection was performed just before and after exercise. We have shown that glucose induced a decrease of brain 5-HT levels to a minimum of 73.0 +/- 3.5% of baseline after the first injection (P < 0.01) and to 68.5 +/- 5.5% of baseline after the second injection (P < 0.01) and consequently prevented the exercise-induced 5-HT enhanced levels. We have observed the same phenomenon concerning the 5-HIAA, but brain TRP levels were not decreased by the injections. In conclusion, this study demonstrates that brain glucose can act on serotonergic metabolism and thus can prevent exercise-induced increase of 5-HT levels. The results also suggest that extracellular brain glucose does not act on the synthesis way of 5-HT, but probably on the release/reuptake system.