Serine: An amino acid, one of the 20 building blocks of protein. A dietary nonessential amino acid, serine is present in many proteins participates in the synthesis of purines and pyrimidines, and is in the active sites of many enzymes. Symbol: Ser. QUESTION According to the USDA, there is no difference between a “portion” and a “serving.” See Answer From Nutrition and Healthy Eating Resources Foods That Fight InflammationGood and Bad Foods for PsoriasisHow to Eat Smarter (and Healthier) When You Have EPI Featured Centers Good and Bad Foods for PsoriasisVideo: Getting Personal on Life With MS Health Solutions From Our Sponsors Shot-Free MS Treatment Your Child and COVID-19