>- a good way to prepare foods to preserve the nutrients
Cooking inactivates many enzymes, principally by denaturing them through the application of heat itself.
Enzymes are very important in the function of the body and denatured enzymes are basically useless unless completely digested and then reassembled. This is why raw is important but it is not necessary to go completely raw.
Both cooked foods and raw foods have their benefits. An example is brocolli which should be eaten both raw and cooked. Some of the active sulphoraphanes are actually better absorbed from cooked brocolli while some of the other ones are denatured so as to be made inactive. Eating cooked and raw brocolli provides the best of both forms.
Another example is tomatos which contain a number of important nutrients. Cooking tomatos increases the amount and the absorbability of lycopene but at the same time reduces and denatures some of the other carotenes that are also important.