When you consume a meal that's heavy in carbohydrates, your body responds by releasing insulin. Insulin is a hormone that, when released into the blood stream, lowers the concentration of most amino acids. The one amino acid that doesn't decrease in response to insulin is tryptophan, which is converted in the brain to serotonin. When insulin lowers the concentrations of other amino acids, tryptophan is able to pass into the brain more readily. Via this mechanism, the consumption of carbohydrates can prompt serotonin production, according to Columbia University's Health Q&A Internet Service.
Simple Carbohydrates
Simple carbohydrates have the strongest effect on serotonin levels, but that doesn't mean all simple carbohydrates are necessarily desirable from a health perspective. The Franklin Institute likens the effect of eating simple carbohydrates to receiving an injection of sugar. Simple carbohydrates are short-chain sugar molecules that are rapidly metabolized. Foods such as candy, corn syrup, fruit juice and honey belong to this food group. Fruits and milk products contain simple carbohydrates, too. The elevation in serotonin levels following consumption of simple carbohydrates typically wears off after just one or two hours.
Complex Carbohydrates
Complex carbohydrates are broken down in the body more gradually than simple carbohydrates, and their sugar content enters the bloodstream more slowly. This type of carbohydrate is made up of long chain sugar molecules. The liver must break them down into smaller molecules in order for the brain to be able to use them for fuel. The cell walls of plant foods containing complex carbohydrates consist of cellulose. The fibrous nature of cellulose makes it resistant to digestion, and thus the presence of these fibrous cell walls further slows the release of sugar into the blood stream and the subsequent release of insulin. The Franklin Institute suggests brown rice, cottage cheese, meat, peanuts and sesame seeds as excellent dietary sources of tryptophan.
The Role of Protein
Since tryptophan, the precursor to serotonin, competes with other amino acids for transport across the blood brain barrier, the consumption of proteins may inhibit serotonin production. Columbia University notes that many protein rich foods often contain tryptophan. If you find yourself feeling sleepy after eating carbohydrate rich lunches, you may find that adding some protein to your meal helps you stay alert in the afternoon.
