Proteins are essential to the human body. In fact, they’re often considered building blocks of life. Our bodies make some proteins, but they are regularly broken down and need to be replaced. Because of this, we need to consume protein to obtain the essential amino acids that help to replace those lost proteins.
Twenty amino acids join together in different combinations to form different proteins. Our bodies can’t create some of those amino acids, thus making them essential for consumption. A complete protein, sometimes called high-quality protein, is one that contains all these amino acids, according to the Centers for Disease Control and Prevention. Proteins that come from animals, such as beef, chicken, milk and eggs, generally provide all the needed amino acids and for this reason are considered complete proteins. An incomplete protein, on the other hand, is missing some of those amino acids. Those foods include beans, rice and tofu.
Casein is one of two proteins found in milk. Like whey, the other milk protein, casein is a complete protein. Casein also contains calcium and phosphorous, two important minerals the body needs. A "Journal of Sports Science and Medicine" review article says milk proteins are significantly important to the body's ability to absorb nutrients and vitamins.
Greek yogurt has grown in popularity over the last few years, primarily because of its protein content, Susan Bowerman, assistant director of the UCLA Center for Human Nutrition, told the "Los Angeles Times." As much as 4 pounds of raw milk are used to make Greek yogurt. One pound of the yogurt is a highly concentrated source of protein.
Amino Acids in Proteins
Medline Plus classifies amino acids in three categories – essential, nonessential and conditional. Since our bodies can’t make nine amino acids in particular, they fall into the essential category and must be obtained through diet. Those are histidine, isoleucine, leucine, lycine, methionine, phenylalanine, threonine, tryptophan and valine. Medline Plus notes that you just need to get these amino acids over the course of a day from a variety of foods and not necessarily all in one meal.
Nonessential amino acids are those that our bodies can make in the normal process of breaking down protein. Alanine, asparagine, aspartic acid and glutamic acid are nonessential amino acids.
Conditional amino acids are needed in times of illness and stress, not necessarily at other times, Medline Plus notes. Those are arginine, cysteine, glutamine, glycine, ornithine, proline, serine and tyrosine.
Medline Plus notes that proteins are no longer considered complete or incomplete.
Bodybuilders often use casein powder to pack an added punch of proteins in their diets. "Men’s Fitness" magazine cited a Baylor University study that found men who drank a casein protein shake blended with whey gained more muscle mass than men who drank a whey protein shake. In that same article, registered dietitian Sarah Currie, a personal trainer in New York, said protein supplementation is not usually necessary, because most people get enough protein in their diets.
Lucy D'Berry has been a writer for nearly 30 years, specializing in nutrition and health issues, as well as in education and government. She has written for daily newspapers and edits a national magazine. She has earned both a bachelor's degree and a master's degree in the communications field.