And by eating both raw and cooked foods, "you get the best of both worlds," said Jennifer Nelson, director of clinical dietetics at the Mayo Clinic and associate professor of nutrition at the Mayo Medical School in Rochester, Minn.
Overcooking and charring can be a problem. Boiling the life out of greens will indeed reduce the nutrient load. And charring meats and vegetables creates cancer-causing chemicals. The solution, however, is not to stop all cooking, but rather to steam, lightly sauté or stir-fry vegetables, and to make more soups.
Fermenting or juicing raw foods also can make some nutrients more available, but that shouldn't deter from the fact that cooking is an ancient craft that makes some foods more digestible and nutritious.
As for the concept of life energy in raw food, this is a spiritual belief beyond the realm of science, so debating its benefit, let alone existence, would be futile.
Misconception #2: Cooking destroys enzymes
This one is absolutely true, but it doesn't matter. Yes, heat destroys enzymes. But humans make their own digestive enzymes to break down large food molecules into smaller ones.
The raw-enzyme logic itself breaks down when you consider that most humans cook food and that most humans are digesting that food reasonably well.
Ironically for the raw vegan, most of the plant enzymes in raw food get destroyed anyway in the acid of the human gut. Only a few make it to the small intestine. Fermented foods such as sauerkraut can carry enzymes into the gut. Their contribution to digestion is not zero, but it does appear to be minimal. "I know of no importance of plant enzymes in human digestion," said McDougall.
The enzyme theory for raw foods dates back to Edward Howell, a physician who published a book on enzymes in the 1940s, primarily citing research from the 1920s and 30s. We now know, however, that almost all nutrients are absorbed in the small intestine and that digestion at that stage relies almost entirely on human-generated bile and pancreatic enzymes.
A corollary myth is that humans have a finite number of enzymes and that, once they are used up, these enzymes are gone. This idea, too, was hatched by Howell. But where would this packet of enzymes reside? Howell never said. But in reality, humans make new enzymes throughout their lifetimes.
Misconception #3: Raw foods are detoxifying
Dietary detoxification is an alternative medicine concept with little scientific credibility. Usually, two organs are cited as needing detoxification: the liver and the colon. In reality, toxins can accumulate anywhere in the body, particularly in fat and fatty tissue, but also in proteins and bone.
The colon is surprisingly low in toxins, however. As for the liver, the confusion is that this organ "filters" toxins and must therefore, the reasoning goes, be loaded with toxins. But the liver is more of a chemical-processing plant than a filter; it breaks down toxins as they pass through. That is, the liver doesn't have extra toxins by virtue of it being the body's natural toxin-neutralizer. [Wishful Thinking: 6 'Magic Bullet' Cures That Don't Exist]
Another argument is that burning fat — in this case, on a raw vegan diet — would release toxins from the body. But fat cells don't burn up, as if into ashes, liberating their contents. Fats cells merely get bigger or smaller, depending on the amount of fatwithin the cell that's used.