How Tryptophan and Glucose Affect Mood
Tryptophan is an amino acid, one of those “building blocks of protein.” Glucose, the end product of carbohydrate metabolism, is the sugar that circulates in your blood, the basic fuel on which your body runs. Milk and cookies, a classic calming combo, owe their power to the tryptophan/glucose team.
Start with the fact that the neurotransmitters dopamine, norepinephrine, and serotonin are made from the amino acids tyrosine and tryptophan, which are found in protein foods (like milk). Tyrosine is the most important ingredient in dopamine and norepinephrine, the alertness neurotransmitters. Tryptophan is the most important ingredient in serotonin, the calming neurotransmitter.
All amino acids ride into your brain on chemical pathways, but your brain makes way for the bouncy tyrosine first and the soothing tryptophan last. That’s why a high-protein meal heightens your alertness.
To move the tryptophan along faster, you need glucose, and that means carbohydrate foods (like those cookies). When you eat carbs, your pancreas releases insulin, a hormone that enables you to metabolize the carbs and produce glucose. The insulin also keeps tyrosine and other amino acids circulating in your blood so that tryptophan travels on plenty of open paths to the brain. With more tryptophan coming in, your brain can increase its production of soothing serotonin. That’s why a meal of starchy pasta (starch is composed of chains of glucose molecules) makes you feel calm and cool.
The effects of simple sugars, such as sucrose (table sugar), are more complicated. If you eat simple sugars on an empty stomach, the sugars are absorbed rapidly, triggering an equally rapid increase in the secretion of insulin, a hormone needed to digest carbohydrates. The result is a rapid decrease in the amount of sugar circulating in your blood, a condition known as hypoglycemia (hypo = low; glycemia = sugar in the blood) that can make you feel temporarily jumpy rather than calm.
However, when eaten on a full stomach — dessert after a full meal — simple sugars are absorbed more slowly and may exert the calming effect usually linked to complex carbohydrates (starchy foods).
Obvious conclusion: Some foods, such as meat, fish, and poultry, make you more alert. Others, such as pasta, bread, potatoes, rice, and other grains, calm you down. The effect of the food depends on its ability to alter the amount of serotonin available to your brain.
Fascinating factoid: Even though turkey is high in protein, it’s also high in tryptophan, the precursor of (that is, the chemical that leads to the creation of) serotonin, which may explain why so many people nod off after Thanksgiving dinner.