Whey has the highest biological value (BV) of any known protein. According to wikipedia, Biological value (BV) is defined as a measure of the proportion of absorbed protein from a food which becomes incorporated into the proteins of the organism’s body. It summarises how readily the broken down protein can be used in protein synthesis in the cells of the organism.
Biological value is determined based on this formula.[4][5]
BV = ( Nr / Na ) * 100
Where:
Na = nitrogen absorbed in proteins on the test diet
Nr = nitrogen incorporated into the body on the test diet
However direct measurement of Nr is essentially impossible. It will typically be measured indirectly from nitrogen excretion in urine.[6] Faecal excretion of nitrogen must also be taken into account - this protein is not absorbed by the body and so not included in the calculation of BV.
BV = ( ( Ni - Ne(f) - Ne(u) - Nb ) / Ni - Ne(f) ) * 100
Where:
Ni = nitrogen intake in proteins on the test diet
Ne(f) = nitrogen excreted in faeces whilst on the test diet
Ne(u) = nitrogen excreted in urine whilst on the test diet
Nb = nitrogen excreted on a protein free diet
Note:
Nr = Ni - Ne(f) - Ne(u) - Nb
Na = Ni - Ne(f)
This can take any value of 100 or less, including negative. A BV of 100% indicates complete utilization of a dietary protein, ie. 100% of the protein ingested and absorbed is incorporated into proteins into the body. Negative values are possible if excretion of nitrogen exceeds intake in proteins. All non-nitrogen containing diets have negative BV. The value of 100% is an absolute maximum, no more than 100% of the protein ingested can be utilized (in the equation above Ne(u), Ne(f) and Nb cannot go negative, setting 100% as the maximum BV).
[edit] Relative utilization
Due to experimental limitations BV is often measured relative to an easily utilizable protein. Normally egg protein is assumed to be the most readily utilizable protein and given a BV of 100. For example:
Two tests of BV are carried out on the same person; one with the test protein source and one with a reference protein (egg protein).
relative BV = ( BV(test) / BV(egg) ) * 100
Where:
BV(test) = percentage BV of the test diet for that individual
BV(egg) = percentage BV of the reference (egg) diet for that individual
This is not restricted to values of less than 100. The percentage BV of egg protein is only 93.7% which allows other proteins with true percentage BV between 93.7% and 100% to take a relative BV of over 100. For example, whey protein takes a relative BV of 104, while its percentage BV is under 100%.
The principal advantage of measuring BV relative to another protein diet is accuracy; it helps account for some of the metabolic variability between individuals. In a simplistic sense the egg diet is testing the maximum efficiency the individual can take up protein, the BV is then provided as a percentage taking this as the maximum.
[edit] Conversion
Providing it is known which protein measurements were made relative to it is simple to convert from relative BV to percentage BV:
BV(percentage) = ( BV(relative) / BV(reference) ) * 100
BV(relative) = ( BV(percentage) / 100 ) * BV(reference)
Where:
BV(relative) = relative BV of the test protein
BV(reference) = percentage BV of reference protein (typically egg: 93.7%).
BV(percentage) = percentage BV of the test protein.
Sorry to jump in there Thibs but, I figured since you were on honeymoon you might appreciate the extra time:-) Hope that helps guys.