How are proteins classified?
Proteins can be classified in many ways and in the same manner for some protein is just protein. Protein comes from a specific source or category (e.g. animal or plant), but when it comes to evaluating its nutritional quality several steps have been taken.
First of all there are 12 essential or indispensable amino acids, that means that our body can’t synthesize or produce them in our metabolism. Therefore we require to get these indispensable amino acids in sufficient content from our food. The current recommendations are listed in the table.
Six other amino acids are considered conditionally essential in the human diet, meaning their synthesis can be limited under special conditions, such as premature infants.
The recommended daily intakes for children aged three years and older is 10% to 20% higher than adult levels and those for infants can be as much as 150% higher in the first year of life.
So the presence of these indispensable amino acids gives food to the signal ‘complete’ protein. This however doesn’t state on the amount present.
In the past Protein Efficiency Ratio (looking at weight gain due to protein consumption) and Biological Value of a protein (absorbed protein from a food based on nitrogen excreted in the stool) were the first attempts on classifying the efficacy of the protein consumed.
The most dominant way of scoring or evaluating the quality of protein is a variant of these above: amino acids that have passed the ileum in the body, will be assumed to be not synthesized by the body. This PDCAAS (Protein Digestibility-corrected Amino Acid Score) does have some flaws. As we know now that there are also so-called anti-nutrional factors, which limit the absorption of certain foods and the fact that we don’t know where proteins actually are being digested makes that in 2013 another variant is introduced called DIAAS (Digestible Indispensable Amino Acid Score). This method looks to the amount of amino acids absorbed by the body at the end of the small intestine. This is more accurate compared to PDCAAS as this has the tendency to overestimate the amino acids absorbed.
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