Chemical substance that composes the basic structure of proteins. Proteins are key to numerous functions that take place within cells, including the synthesis (manufacture) of many substances essential for life. Although there are only about 20 amino acids, they can form into nearly countless structures through the ways in which they align and configure themselves. The body can manufacture 12 amino acids from compounds that exist within it. These are called the nonessential amino acids. The body must acquire the remaining eight amino acids through the diet. Dietary proteins from animal sources, such as meats and dairy products, supply all eight of these amino acids. Dietary proteins from nonanimal sources vegetables, fruits, grains, nuts, legumes, and beans supply some of them. Combining different plant-based foods can provide the full range of essential amino acids. Nearly all body processes require amino acids, so it is important to meet the body’s dietary needs for them.
Amino acids are digested and absorbed into the bloodstream through the small intestine. The mechanics of this process limit the amounts of amino acids that the body can absorb in the normal length of time it takes for food to move through the digestive system. All amino acids that enter the body, regardless of source, compete for digestion and absorption. lEvodopa, the cornerstone of anti-parkinson’s medication therapy, is an amino acid that, once within the body, becomes metabolized into dopamine.
Because levodopa is taken orally and absorbed into the bloodstream through the intestines, it too competes for absorption. When levodopa doses are relatively small, typically the case early in the course of the disease, this is not so much a problem. When doses increase as symptoms intensify, however, dietary amino acids can crowd out levodopa, with the result that less of it enters the bloodstream than the dose would suggest. This of course affects levodopa’s effectiveness. Typically this results in raising the dose as an attempt to get more levodopa into the body. If dietary protein consumption is high, however, this strategy becomes counterproductive. It is more effective to separate levodopa doses from eating protein to limit the competition for absorption.