Biological value (BV) is one of the most commonly used criteria for assessing the quality of proteins. The protein's biological value index (BC) is calculated as the ratio of the amount of nitrogen remaining in the body to the amount of nitrogen obtained from this protein, t. its digestibility is taken into account.

BC = (nitrogen remaining in the body / nitrogen derived from the protein) x100 The biological value equal to 100 will thus reflect 100% utilization of the body's protein, t. all consumed protein remains in the body without losses.

To determine the biological value, subjects are usually put on a protein-free diet to pre-measure the baseline (under normal conditions) of nitrogen loss by the body. Thereafter, the test protein at different doses (usually 0.6, 0.5, 0.4 and 0.3 g / kg of weight) is given a test protein, and then the nitrogen balance. Some researchers used more or less long periods of pre-fasting, which also affects the accuracy of measurements. For example, in a study often referred to in advertising by producers of whey protein hydrolyzate, the nitrogen balance was measured in rats after a three-day fast (which corresponds to a longer period of fasting in humans). The results of this study showed that whey protein hydrolyzate had a better ability to retain nitrogen in the body and stimulated muscle growth more than other tested proteins. But the researchers "forgot" to mention that fasting changes the ability of the body to retain protein, which leads to overestimated indicators of biological value. Conclusion:

this study is of little interest to a person who regularly consumes a large amount of protein.

Although the methodology for estimating the nitrogen balance has several drawbacks, it can be used as a rather crude indicator of how well this protein meets the needs of the organism. If the given amount of protein (or more precisely, this amount of nitrogen) maintains zero (or positive) nitrogen balance of the body, we can say that the quality of the protein is sufficient to maintain protein stores of the body.

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