Researchers devise a new method to assess protein utilization through stable isotopes


Researchers at St. John’s Research Institute, Bengaluru have enabled better characterization of amino acid availability of various food types through dual-tracer method.

Proteins are important dietary components that contribute energy as well as amino acid building blocks and nitrogen for synthesis of biomolecules like DNA. Dietary proteins can be categorized based on their amino acid content. Of the 20 amino acids that we need, our body cannot synthesize nine and therefore it is necessary to include them in daily diet. Dietary proteins containing all the nine ‘indispensable amino acids’ are called ‘complete proteins’; proteins lacking one or more of them are called ‘incomplete proteins.’ Dietary proteins also differ based on how easily the body digests and absorbs them.

Characterization of dietary protein quality and digestibility is important for nutrition scientists to make protein intake recommendations tailored to age, health, and availability of various food items. A bottleneck is the inability to accurately measure the amino acid content of a food item that is actually utilized by the body. The research team devised a new method to assess protein utilization using stable isotopes.

Margdarshi Fellow Professor Anura Kurpad and colleagues used Spirulina, a well-studied blue green algae and dietary supplement and labeled it with the stable isotope of carbon (13C) . It was fed in combination with amino acids labeled with the stable isotope of hydrogen (2H) to six healthy individuals. In addition, chickpea and mung bean using water labeled with (2H) were also grown. The digestibility and absorption of the proteins were compared with that of Spirulina.

The average digestability of IAA in spirulina protein was 85.2%. The average IAA digestability of intrinsically 2H-labelled chicpea and mung bean protein was 56.6% and 57.7%, respectively. Dehulling of mung bean before ingestion increased the average IAA digestibility by 9.9% in comparison to whole bean digestibility. 

Thus, researchers have found out that better characterization of amino acid availability of various food types can be achieved using the dual-tracer method. The findings are relevant in regions where high quality protein foods are not commonly consumed.

The dual tracer method could be instrumental in optimizing protein nutrition in growing young children and individuals suffering from chronic infections and illnesses.

 The research is published in The American Journal of Clinical Nutrition.

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