An essential amino acid (one the body must obtain from outside sources) that is a serotonin precursor (a substance the brain requires to produce the neurotransmitter serotonin). Serotonin is important for neuron communication related to mood and emotion; below-normal levels of serotonin cause depression and anxiety and contribute to psychosis. The body obtains tryptophan from dietary proteins such as meats, dairy products, whole grains and whole grain products, soy-based foods, and legumes. There are also dietary supplement products that deliver this amino acid in the form of L-tryptophan.
People who have Parkinson’s disease, particularly middle and late stage, often do not obtain enough tryptophan from their diet because of protein restrictions. Dietary protein competes with lev-odopa, also a protein, for absorption from the intestines into the bloodstream. When it becomes necessary to take higher dosages of levodopa to mitigate the symptoms of Parkinson’s, this competition becomes a problem. The solution is to eat meals high in carbohydrates during the day, to aid in levodopa’s absorption, and to consume the daily protein requirement with the evening meal when the levodopa dosage is smaller. For many people, however, this is hard to do, and as a result they do not receive adequate protein. Compounding the situation are the symptoms of Parkinson’s that affect the ability to chew and swallow, which make eating meat, the most common source of protein in the U.S. diet, difficult. People with advanced Parkinson’s disease and weight loss or other signs of low protein intake should probably consider nutritional supplements that include L-tryptophan to attempt to meet the body’s needs for this essential amino acid. It is important to avoid taking such supplements at the same time as levodopa dosages and to consult the doctor before beginning such supplements as they may contain other ingredients that can interact with anti-parkinson’s medications or therapeutic reasons for not taking them. A nutritionist’s consultation may also be helpful in making this decision.