Serotonin is a neurotransmitter in the brain that regulates mood, sleep, cognition, sexual behavior and appetite. Anti-depression drugs work by enhancing its availability, while medications that lower its level cause depression. Nutrition plays a role in the function of serotonin, which is made with the help of the essential amino acid tryptophan.
Serotonin as a Neurotransmitter
Nerve circuits in different parts of the brain control mood, memory, cognition and feelings. The nerve cells of these circuits do not touch; instead, neurotransmitters are released from one cell to another to transmit messages. A defect in connecting these cells leads to mood disorders and depression. Antidepressants increase serotonin concentration in the area between two nerves.
Diet can improve serotonin availability. Factors that affect the impact of nutrition include personal or family history of mood disorders, stress and genes.
Serotonin and Appetite
Serotonin plays a role in appetite, food selection and weight. Researchers at the UT Southwestern Medical Center found that serotonin activates the nerves that curb appetite while at the same time deactivates nerves that increase appetite.
In fact, fen-phen, a weight loss drug banned from U.S. markets in 2007 due to cardiac side effects, worked by increasing serotonin release between nerve cells of the brain.
Production of Serotonin
Tryptophan, the building block of serotonin, must enter the brain by crossing the blood-brain barrier. This barrier, made of brain capillary walls, prevents the passage of bacteria, viruses and some drugs while permitting glucose and some amino acids to pass through.
Tryptophan attaches to receptors on the barrier that also transport large neutral amino acids (LNAA). High blood concentration of LNAA competes with tryptophan, reducing its availability in the brain. A high tryptophan-to-LNAA ratio is more significant than total tryptophan. Meals that increase the ratio increase serotonin production and improve sleep and mood.
Carbohydrates, Proteins and Serotonin
When ingested, carbohydrates trigger insulin secretion, which transports LNAA to the muscles. This clears the way for tryptophan to cross the blood-brain barrier and make more serotonin.
While proteins supply the essential amino acid, a meal with as few as 5 percent of calories from protein lowers the tryptophan-to-LNAA ratio. Therefore, foods with a high tryptophan-to-LNAA ratio must be eaten alone or with concentrated carbohydrates, such as fruit, to affect serotonin. This explains why people crave carbohydrates with stress or mood disturbances.
Dietary Tryptophan
Foods with a high tryptophan-to-LNAA ratio are milk, sesame seeds, sunflower seeds, eggs, raw soybeans, Parmesan cheese, cheddar cheese, pasta, pork chops, caribou, potato chips and sweet potatoes.
The commercially available alpha-lactalbumin, a whey protein and the primary protein in human breast milk, has a high tryptophan-to-LNAA ratio. Protein powders made from whey protein concentrate or isolate have a high tryptophan-to-LNAA ratio as well.
Tryptophan Supplements
Tryptophan is available as a prescription drug and a non-prescription supplement. The supplement dose used in clinical studies is 2 to 4 g daily. Reported side effects are drowsiness, dry mouth, nausea and gastrointestinal symptoms.
Supplements trigger modest increases in serotonin production compared with antidepressants. The Canadian Network for Mood and Anxiety Treatments concluded in a 2009 report that evidence is not strong to support tryptophan supplements for depression treatment.
References
- "NeuroMolecular Medicine;" Dietary Amino Acids and Brain Serotonin Function: Implications for Stress-Related Affective Changes; C. Rob Markus; December 2008
- "American Journal of Clinical Nutrition;" Can Nutrient Supplements Modify Brain Function?; J.D. Fernstrom; June 2000
- "Journal of Affective Disorders;" Clinical guidelines for the management of major depressive disorder in adults; Arun V. Ravindran, et al; October 2009
