The main flaw: While some complex vitamins such as vitamins C and B benefit from minimal cooking, nutrients such as cancer-fighting lycopene need heat to be released. What’s more, heating foods to 118°F doesn’t “kill” protein or fiber, as raw food gurus suggest.   In fact, cooking makes them easier to digest, says Nelda Mercer, RD, a spokesperson for the American Dietetic Association. And the belief that cooked food ferments in your GI tract? “Total nonsense,” she says.