A high quality protein is also known as a complete protein because it contains all of the essential amino acids. Meat and dairy provide the majority of high quality proteins. Eggs are the highest quality proteins. Soybeans and quinoa are both plant and complete proteins.
Lower quality proteins, in contrast, are called incomplete proteins because they lack one or more of the essential amino acids. Plant protein and lower quality protein are one and the same, comprising all starch (such as grains, potatoes, legumes) and vegetables. With low quality proteins, we may receive all of the essential amino acids by combining two different types of food products. This is the only way to accomplish protein synthesis, for without all of the essential amino acids the synthesis will not take place. For this reason, there were those who worried about the need to combine sources of plant protein in order to verify that amino acids were being consumed at appropriate levels. Nonetheless, as the number of vegans and vegetarians has increased without any evidence of mass protein deficiency appearing, this anxiety has since been allayed.
Extra dietary proteins are not stored as protein, but as fat. Whenever we consume more protein than we need, those amino acids are catabolized and either become components for energy or are converted into triglycerides and then stored as fat. Consuming a large amount of protein, therefore, will contribute to excess body fat.
Dietary requirements for protein assume that one’s energy needs are met. If these needs are not met, then amino acids are used for energy. In addition, these requirements also assume that one has consumed a sufficient amount of carbohydrates. If not, then amino acids will be relied upon to make glucose through gluconeogenesis. Although protein requirements are based mainly on the content of lean tissue in the person, body weight is used more conventionally. If someone has a higher than average amount of body fat, then the “ideal” body weight for that person should be used. For a healthy adult, the protein required is about 0.8 g/kg.
Although the protein requirements for athletes may be slightly higher than for non-athletes, the literature on this subject is far from clear. Since the percentage of lean tissue in athletes is higher than in non-athletes, a larger requirement is possible. Yet many of the athletes who participated in these studies were college-aged males. Their protein intake may have been higher as a consequence of not being fully formed. Meanwhile, different food sources can yield different results.
In the event that there is a requirement for extra protein, it should be consumed shortly after an intensive workout, forty-five minutes being the typical window. During this period, muscle enzymes take amino acids from the diet up into the muscle tissue, thereby replenishing them. For an athlete, the typical requirement of proteins is thought to be about 1.2 to 1.6 g/kg.
When energy levels are adequate, but protein intake is low, especially when it is abruptly lowered, say, during a famine, then one can develop kwashiorkor. Kwashiorkor results in stunted growth, skin lesions, and decreased plasma albumin. In young children, it typically presents itself as a swollen belly on an otherwise emaciated body. A lack of protein, which prevents fluid from being balanced, causes the swelling.