A big myth that is still at it's height right now is the idea, put forth by raw food proponents, that raw foods contain "living enzymes" that are integral to their nutritional value. These enzymes contained in "living foods" are said to facilitate their digestion. When we cook food, it is claimed, these enzymes are destroyed causing the body to have to compensate by producing enzymes (like from the pancreas) in order to digest the food.
In reality the enzymes present in foods are proteins and they are subject to the same digestive process as any other protein, meaning they will not make it past the acidic environment of the stomach…they will be "destroyed". They had a role in the plant or animals biologic processes but they have no role in our digestion. Instead, they are just a part of the protein make up and provide amino acids just like any other protein.
ALL Nutrients are Destroyed by Cooking
To go along with this is the oft-stated, completely ignorant, claim that ALL nutrients are destroyed by heat. This is not true. Some nutrients are heat sensitive and some are not. Some nutrients, in fact, become more available by cooking.
"Denatured" Proteins from Cooking
Related to the above myth is the idea that cooking denatures proteins and denatured proteins are "useless" to the body. Cooking absolutely denatures proteins but it makes no difference to the body whatsoever. A protein will be broken down into peptides and single aminos and absorbed by the gut regardless of it's having been denatured. In fact, some proteins, by cooking and thus being denatured, become MORE digestible and thus more available.
One of the most popular questions on the bodybuilding forums, as you all know, is about raw eggs. Trainees want to know whether it is okay for them to drink a bunch of raw eggs, Rocky style, for convenience. The invariable answer is that it is okay and that it is even better, you'll get more protein. In fact, the opposite is true. Cooked egg whites are much more digestible and you'll get LESS protein from eating raw egg whites. Because of avidin binding, in fact, raw egg white diets can induce biotin deficiency and this binding CANNOT be released by the gastrointestinal tract. So, in this case, cooked eggs make more protein available to the body and uncooked eggs mean LESS nutrients, in the form of biotin. Nothing is simple and pat.
A major player in the "living food" scene is raw milk.