In the wonderful world of nutrition and supplements, protein is at the top of the list for evidence base, efficacy and popularity. The reasons for this are aplenty, in part because of the role protein plays in clinical recovery from illness i.e. hospitals prescribe protein drinks pre and post-surgery in order to encourage repair and recovery, and also in people who are undernourished and in need of this key macronutrient. Proteins popularity has boomed in recent times though, and this is because of the rise and rise of the exercise, health and fitness industry! As much as consumers are becoming more and more aware of what they are consuming, there remains many who are oblivious to what they should be having and yet, consume any protein supplement regardless. Those who have a good understanding of protein and the need to consume a good quality source will be familiar with different protein sources, protein availability to the body and which types of protein are the best quality. Terms such as Biological Value (BV) and Net Protein Utilisation (NPU) may or may not be familiar to you, if they are then great, if they’re not then read on to familiarise yourself.
Considering the proteins quality
There are a few ways that the quality of protein is measured and validated, the main two are Biological value (BV) and Net Protein Utilisation (NPU). The BV of protein is often used by avid consumers to gauge which protein is best utilised by their body, and it is one of the main measurements used by protein manufacturers. The BV is determined according to how certain types of protein are retained by an animal (usually rats). It is calculated by measuring the amount of nitrogen used for protein synthesis (muscle growth for example), and then dividing it by the amount of oxygen that is absorbed from the diet. This figure will give the manufacturers the amount of nitrogen absorbed during digestion, which is actually retained by the body.
But wait… why are they looking at nitrogen when it’s protein that we’re interested in? Well, the nitrogen atom is abundant in protein, consequently when protein is broken down it becomes traceable in the blood. Because protein is high in nitrogen, and yet low in carbohydrate and fat, free nitrogen levels make for an ideal marker of where the dietary protein consumed is used within the body. If after the consumption of protein, no nitrogen is present in the urine, the organism that consumed the protein is deemed to have utilised and absorbed all of the protein.
The BV score
Based on the amount of nitrogen passed out with urine, a BV score is assigned to a protein source. If no nitrogen is present in urine after consuming protein, the BV score is 100 (as a percent of utilisation), and it was the humble egg that this score of 100 was based on. However, a score of 100 was surpassed by a particular, very popular, source of protein…Whey protein. This led to the introduction of a BV score of 104, this is because the benchmark had already been set to egg (BV 100), but research suggested that whey protein was actually better utilised than egg, hence a figure of 104.
Net Protein Utilisation (NPU)
The NPU method of determining the quality of a protein is also based on a proteins capacity to be utilised by the body. The difference between BV and NPU is that BV looks at the amount of protein absorbed, whereas NPU considers the total amount of protein ingested, meaning it gauges the amount of ingested protein retained by the body. This is different from BV in that BV looks at absorbed protein retained (so doesn’t consider total protein consumed, only that absorbed), whereas NPU measures the number pf protein ingested relative to protein retained.
The process of measuring NPU compared to BV is a little different. NPU assessment is deemed to be a little less humane (at least during the testing stages) because the organism (often a rat) that consumed the protein may be sacrificed to get an absolute accurate measurement. More humane methods, i.e. methods that can be practiced in humans, involve nitrogen balance testing that look at values similar to the BV of 0- 100. A value of 0 suggests that none of the protein consumed was utilised by the body for protein synthesis (growth), whereas a value of 100 indicates 100% utilisation of the protein (nitrogen).
Llewellyn, W. (2009). Sport Supplement Reference Guide. Molecular Nutrition.