For the better part of the last century, the standard test to measure protein quality (ie: digestibility + bioavailability) was the Protein Efficiency Ratio (PER). In 1989, PER was supplanted by a new method developed by the United Nations Food & Agricultural Organization (FAO) together with the World Health Organization (WHO) called the Protein Digestibility Corrected Amino Acid Score (PDCAAS).  In recognition of certain limitations and biases inherent in PDCAAS, the FAO has now recommended, in a report released in February 2013, that PDCAAS be replaced by a newer, more precise method called the Digestible Indispensable Amino Acid Score (DIAAS).

The report indicates that, when evaluated with the DIAAS method, dairy protein appears to have a much higher bioavailability compared to plant proteins than was previously indicated through PDCAAS. The DIAAS score of whole milk powder was 10 to 30% higher than high grade soy isolate, double that of pea protein, and more than double wheat protein.

For a PDF facsimile of the entire report, click HERE.

The report could be construed as additional confirmation of something that most bodybuilders and other performance athletes already know -  milk proteins such as whey and casein are some of the very best protein sources for building a lean, muscular, and healthy physique. In light of the new findings, however, there may be additional implications for the supplement buyer.

Over the last few years, many people have lamented the relentless rise in price of their favorite protein powders. This rise has affected virtually all brands because the cost of raw bulk whey powder has doubled in the last two years. In an effort to keep prices down,  some supplement companies have resorted to substituting some of the whey protein with other, less expensive plant sources of protein. Supplement buyers generally look at the grams of protein per serving, or sometimes the percent of protein, but not as many will check the fine print on the label to see all the sources of protein in the product. Just because a product name says “Whey Protein”, it does not necessarily mean that 100% of the protein in the product is derived from that source. A company may start adding a bit of legume protein to cut costs, while retaining the same amount of protein per serving and protein percent in the product.

This practice has not become widespread, but may become more prevalent in the future, as predictions are that raw whey protein will become even more expensive. So check that label to know where the protein is coming from, and remember the old adage that “You get what you pay more”. High price in supplements is a generally a good indicator of quality, and when it comes to putting stuff into your body, you should care about quality.


Food And Agricultural Organization of The United Nations, Food and Nutrition Paper 92, Dietary protein quality evaluation in human nutrition. Report of an FAO Expert Consultation 31 March - 2 April, 2011, Auckland New Zealand.

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