Chemical messengers called neurotransmitters bridge the synaptic gaps between nerve cells in the brain so that information can be conveyed to the appropriate target. Different neurotransmitters serve different purposes. Serotonin is a neurotransmitter that has received a lot of scientific scrutiny for its ability to affect mood, hunger and sleep. The blood-brain barrier determines which chemicals are able to entire the brain. Serotonin is not able to pass through the blood brain barrier, but its precursor, tryptophan, is. A number of natural foods contain tryptophan.
Poultry
It's a popular misconception that the sleepiness that follows a Thanksgiving binge is due to the presence of tryptophan in turkey. It is true that turkey and other forms of poultry contain amounts of tryptophan, but this amount is not especially high. EurekAlert! notes that other foods such as pork and Swiss cheese contain higher levels of tryptophan. The tryptophan found in poultry is not easily absorbed through the blood brain barrier. The trouble with trying to use a high protein food source such as poultry to increase serotonin levels in the brain is that protein is made up of building blocks called amino acids. Turkey contains many types of amino acids. Tryptophan is one of them, but it is in low concentrations compared to the other amino acids found in protein foods. When you eat a high protein food, all of its amino acids compete for passage through the blood brain barrier. With so many other competitors vying for entry into the brain, relatively little tryptophan is able to pass through and become serotonin.
Whole Grains
Carbohydrates are a good source of tryptophan, according to the "American Journal of Clinical Nutrition," but you'll want to skip simple carbohydrates such as those found in sugary candies and baked goods. Opt instead for the complex carbohydrates found in natural whole grains. Carbohydrates are a good nutritional source for the type of tryptophan that will more readily pass through the blood brain barrier, and high carbohydrate protein-free diets have been shown to increase the ratio of tryptophan to other amino acids in the blood. Complex carbohydrates are digested more slowly than simple carbohydrates, thus they deliver less of a sudden spike in blood glucose levels and are healthier overall.
Fruit
Simple carbohydrates can sometimes be healthy food choices, as long as they are selected from the produce aisle and not the candy store. Simple carbohydrates are also found in fruits, many of which are known to contain tryptophan. The Kentucky State University Cooperative Extension Program states that an average-size banana provides 12 mg of tryptophan. An orange and a pawpaw each clock in at slightly lower levels, with 9 mg each.
References
- "American Journal of Clinical Nutrition": Effects of Normal Meals Rich in Carbohydrates or Proteins on Plasma Tryptophan and Tyrosine Ratios
- Go Ask Alice!: Serotonin and Foods
- Kentucky State Cooperative Extension Program: Pawpaw Description and Nutritional Information
- Middle Tennessee State University: Food, Mood and Neurotransmitters
- MedlinePlus: Tryptophan
- EurekAlert! Medical Myths Even Doctors Believe
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