Biological value measures how well an organism can absorb and use a given protein. Eggs have a higher biological value than white flour. There are two scales used in measurement, and nitrogen concentration is used to measure biological value, although this method has weaknesses.
Biological value is a term applied to specific proteins that describes the degree to which an organism can absorb and use a given protein. When protein is absorbed from food, the body breaks it down and uses it to make more protein. The proteins in some foods can be broken down and used to a much greater degree than the protein in other foods. Eggs, for example, contain significantly more protein than white flour, so they have a higher biological value. People looking to build muscle require a significant amount of protein in their diets; They often consider the biological value of the foods they choose to eat.
There are two different scales used in the measurement of biological value. The first is simply a scale based on percentages; a protein that is completely absorbed would be given a value of 100%, while a protein that is only half absorbed would be given a value of 50%. The other scale sets some particular protein as the 100 mark (percentage signs are usually omitted on this scale) and measures other proteins based on that. Eggs are often assigned a value of 100 on this scale, as they have a high biological value. A protein that is absorbed to a greater degree, then, could have a value greater than 100.
Proteins are usually the main source of nitrogen in an individual’s diet, so nitrogen concentration is used to measure biological value. The amount of nitrogen in the proteins of a given food is measured, as is the amount of nitrogen that the body ultimately excretes. With this method of measurement, it is assumed that protein is, in fact, the only source of nitrogen in the diet. It follows, then, that the amount of protein can be calculated from the difference between the amount of nitrogen in the initial protein and the amount of excreted nitrogen. Non-excreted nitrogen belongs to proteins, which are broken down and used to build other proteins in the body.
This method of measuring biological value has its weaknesses. Age, weight, gender, general physical condition, and many other factors can affect the degree to which protein is absorbed in the body. As such, studies involving biological value are usually quite rigorous; test subjects tend to follow strict diets and do not engage in strenuous activities that could result in the use of protein as an energy source. Such precautions generally result in relatively accurate results.
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