Levodopa belongs to a class of drugs used to treat neurodegenerative diseases and is commonly prescribed for Parkinson’s disease. In patients taking levodopa, the type of protein eaten and the timing of meals that contain protein become important because a significant drug-nutrient interaction often causes decreased absorption, metabolism and excretion of the drug.
Levodopa is a derivative of the amino acid tyrosine and a psychoactive agent – it functions in the brain. It is important in the treatment of Parkinson’s because of its ability to cross through the blood-brain barrier that separates blood circulating throughout the body from the brain and prevents certain compounds from directly reaching the brain and central nervous system. Dopamine is deficient in the brains of people of Parkinson’s disease and cannot cross the blood-brain barrier. However, levodopa is able to cross this barrier and breakdown to dopamine.
Protein and Levodopa Compete for Absorption
Dietary proteins are broken down into smaller molecules called amino acids. Once in the small intestine, they are transported across the small intestine into the bloodstream via specific carriers. Levodopa uses these same carriers to gain entry into the bloodstream. Managing dietary protein intake is effective in maximizing levodopa absorption to maximize its therapeutic benefits in patients with Parkinson's disease.
Branched-Chain Amino Acids
Amino acids referred to as branched-chain, or BCAA, directly interfere with levodopa absorption. Leucine, isoleucine and valine are the three branched-chain amino acids that inhibit levodopa absorption more than other amino acids obtained from protein. Foods high in BCAAs include red meat, dairy, chicken, fish, poultry and eggs. Protein powders and whey supplements, a high-quality source of protein produced during the making of cheese, are also rich-sources of BCAAs.
Managing Levodopa and Protein Interactions
Levodopa should be regimented with respect to meal times and patients should have a tightly controlled dietary protein intake. Limiting meat products and avoiding whey-based protein supplements often decreases interference. One nutritional therapy strategy involves limiting protein intake during the day and having the majority of protein in the evening or right before bed. Patients may also benefit from a high-carbohydrate, low-protein diet.