Blog | Monday, November 26, 2012

Raw food diet hype is overheated

Raw food diets have emerged as a pop culture preoccupation. They seem to have considerable traction in the public psyche, as evidenced by the volume of websites they populate, and the coverage they command in print.

It is doubtful they have comparable traction at the dinner table, of course. We have enough trouble getting people to eat a reasonable amount of reasonable foods, and to renounce ingestibles that glow in the dark. In this context, it seems a bit far-fetched that we would shift, en masse, to a strict diet of raw, unprocessed foods.

But our appetites for the concept, and the claims made in its defense, seem insatiable. So let's chew on it.

In pure form, raw food eating is exactly as advertised: No foods are cooked. The diet is based overwhelmingly, if not exclusively, on plant foods. If it does include animal foods, they are consumed raw. If milk is consumed, it is consumed raw, which is to say, unpasteurized. Some versions are strictly vegan, and ban all animal products.

There are, to be sure, potential benefits of such a diet, or of many aspects of it. By placing an emphasis on plant foods, the diet is a rich source of the foods that are in turn the richest sources of valuable nutrients. The diet renounces most processed foods, and thus eliminates trans fat, and provides generally very low levels of saturated fat, sodium, and sugar, while providing nutrient-dense foods, rich in fiber. And because food choice is subject to rather strict constraints, calories are caged, making raw food diets an effective answer to the prevailing problems of weight control.

Many foods are, indeed, most nutritious when raw. Heat can destroy many nutrients, notably some water-soluble vitamins, many antioxidants, and unsaturated fats, including omega-3s. The beneficial effects of dietary fibers, both insoluble and soluble, may be altered, and at times reduced, by cooking.

And there are potential harms of cooking that raw foods sidestep. Cooking meat can lead to charring, which generates carcinogenic compounds known as heterocyclic amines. Cooking of carbohydrates can produce acrylamide, another potential carcinogen.

There is, however, a great leap of faith from some benefit in eating some foods raw some of the time, to raw is always and dramatically better.

There are claims, for instance, that raw food is better because cooking destroys enzymes in plants. Perhaps so, but so does digestion. Very few enzymes survive the hydrochloric acid they encounter in the stomach. Meaningful health effects of swallowing an enzyme that doesn't survive to see the duodenum are dubious at best.

Raw food advocacy ignores the fact that some foods are more nutritious when cooked. The nutrient lycopene makes tomatoes red. It is a potent carotenoid antioxidant, long thought to reduce prostate cancer risk, although that effect per se is in doubt. Lycopene is fat-soluble, and much more "bioavailable", that is to say, available for absorption and making contributions to our health, when tomatoes are heated in combination with an oil. Tomato sauces with olive oil are ideal, and raise blood lycopene levels far more effectively than eating raw tomatoes.

Eggs are a good source of biotin, a nutrient important in many ways, its contributions to healthy hair, skin, and bones noteworthy among them. Raw eggs contain a protein called avidin, which binds and inactivates biotin. Cooking denatures avidin, a term used when the shape of a protein is changed. Denatured avidin does not bind biotin, so cooked eggs are a good source of bioavailable biotin.

Even more important than the nutrients that cooking can "add" to food are the things it can take away, namely pathogenic bacteria. Cooking is the best and final defense against salmonella, E. coli, and other microscopic nasties that can hitch a ride on our foods. Raw milk has captured the modern imagination, but pasteurization took hold for good reason. Milk can be contaminated by bacteria, from the cows, the farmers, or farm equipment, and it makes a great growth medium. Pasteurization protects us from the attendant consequences, which were once fairly common.

And finally, there are some truly excellent foods that can't be eaten raw; beans and lentils come to mind. These are nutrition powerhouses, inexpensive, and rich enough in high-quality protein to make a good meat alternative. But they are all but indigestible unless cooked.

Some variations on the theme of raw food eating accommodate this concern, by allowing for cooking at low temperatures. But food cooked low and slow is not really raw, it's slow-cooked, and should call itself that. Cooking is always a product of heat intensity times duration, so when raw food expands to encompass slow cooking, the topic devolves to a debate about cooking methods.

Lastly, there is the notion that cooking is a form of food processing and thus "unnatural." Perhaps. But cooking, and freezing, have figured in humans' interactions with foods since long before the dawn of agriculture. So if cooking is "unnatural," everything about agriculture is even more so. To make it just as blunt as a stone hammer: We cooked meat long before we ever grew potatoes.

What we are left with, then, is a whole lot of hype that runs well ahead of any legitimate science.

All too often, opinions about nutrition are disseminated with religious zeal, as if gospel. I have argued before for the separation of church and plate, and reaffirm my own commitment to it here. I have my own opinions about nutrition. But when they are just opinions, I am careful to treat them as such.

At its best, nutrition is science. That doesn't make it perfect. Our scientific understanding is not perfect in any field, and nutrition is far from an exception. But all opinions about a science must at least run the gauntlet of what we do know. Those that cannot do so and survive are hearsay.

We tend to honor this implicitly in almost every science but nutrition. Unsubstantiated opinions about how to build a suspension bridge, perform neurosurgery, or accelerate atoms are of no particular interest. We recognize in these disciplines that expertise matters, and we differentiate the insights of those with such expertise, generally born of years of study, from the random inclinations of the rest of us riff-raff.

Somehow, though, we make an exception for nutrition. Perhaps the fact that everyone eats invites us to view everyone as comparably expert in the far-reaching implications of what we eat on physiology, pathophysiology, cell biology, and biochemistry. But of course, that just ain't so.

Cyberspace may be the perfect crock pot for haphazard food for thought. Everyone with an Internet connection gets to dish. And so while raw food advocacy has been around for 200 years, it has taken on a whole new prominence only rather recently.

The result of acting as if all food-related opinions are created equal is a whole lot of food for thought unsuitable for human consumption. Ingesting such opinions nonetheless leads to a state I am inclined to label "cognitive indigestion", a condition of unfounded convictions, misplaced trust, and/or perennial confusion.

Many foods can be eaten raw, and many foods are the better for it. An emphasis on eating mostly plants direct from nature is irrefutably good, be they raw or cooked. But as is true of so much in the realm where opinions about nutrition masquerade as gospel, the case for raw food eating is oversold, the rhetoric is overheated, and the claims of universal benefits, substantially overcooked.

David L. Katz, MD, FACP, MPH, FACPM, is an internationally renowned authority on nutrition, weight management, and the prevention of chronic disease, and an internationally recognized leader in integrative medicine and patient-centered care. He is a board certified specialist in both Internal Medicine, and Preventive Medicine/Public Health, and Associate Professor (adjunct) in Public Health Practice at the Yale University School of Medicine. He is the Director and founder (1998) of Yale University's Prevention Research Center; Director and founder of the Integrative Medicine Center at Griffin Hospital (2000) in Derby, Conn.; founder and president of the non-profit Turn the Tide Foundation; and formerly the Director of Medical Studies in Public Health at the Yale School of Medicine for eight years. This post originally appeared on his blog at The Huffington Post.