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What Happens to Protein at High Temperature?

A frequently asked question of those who consume protein supplements is “what happens to the protein at high temperature?”  In order for a meaningful explanation of this phenomenon, a few basics must be understood.  Proteins are complex molecules that consist of long chains of amino acids connected by peptide bonds.  The primary difference between the various sources of protein is the type of and sequence of amino acids.  There are 22 different types of amino acids, where only nine of them are considered essential because the body cannot synthesize these amino acids on its own: L-Tryptophan, L-Threonine, L-Isoleucine, L-Leucine, L-Lysine, L-Cystine, L-Tyrosine, L-Valine, and L-Histidine.  A protein containing all nine of these amino acids is considered a “complete protein” because all nine amino acids are present in the exact ratio necessary to support the dietary needs and biological functions of the human body.  

The best sources of complete proteins are animal foods derived from meat, fish, poultry, and milk.  While each type of protein derived from one of these sources contains the same ratio of essential amino acids, the overall absorbed protein content to your body will vary depending on how the protein is prepared before consumption.  The protein molecule has a three-dimensional shape that can be denatured by an external source such as a strong chemicals or heat.  The three-dimensional shape of this molecule affects the basic properties, in the case of cooking, by breaking the hydrogen bonds that form the 3-D shape without breaking the bonds between the amino acids within the protein chain.  Common examples of this effect include the hardening of an egg or the firming up of meat during the cooking process.  

A denatured protein does not mean the protein has lost its nutritive value, it simply means that the physical or chemical structure of a protein has been changed.  However, heat does alter the biological activity.  A large egg will still contain 6 grams of protein whether it is raw or cooked.  All commercial dairy products have limitations in preserving the full biological activity of the protein content.  During the pasteurization process of milk and pH regulation steps of cheese, immune and regenerative properties are lost along the way.  While it is not considered safe to consume raw sources of animal protein such as eggs or meat to get the full biological activity of each gram of protein consumed due to food borne bacteria, the end result of denatured protein is reduced solubility.  

The more soluble a protein is, the more easily the body can digest and break down the amino acids for the body’s dietary needs as well as supporting the growth of muscle.  However, cooked proteins, with varying degrees of solubility compared to raw proteins, will require more energy to digest therefore burning more calories during the digestion process.  Cooking protein is necessary to eliminate bacteria; though one should seek proteins with the highest possible biological value such a whey and soy protein to gain the most from each gram of protein consumed.