A question about the effects of freezing prompts us to probe the purported benefits of enzymes in raw foods
by Craig Weatherby
We believe it’s wise to enjoy foods as close to their whole, natural state as possible.
For one thing, humans and their predecessors evolved eating whole foods, which represent unique, irreproducible, synergistic blends of myriad natural constituents.
And the results of most nutrition research award whole foods clear advantages over processed/refined foods and—with notable exceptions such as vitamin D—single-nutrient dietary supplements.
- The active enzymes found in raw, uncooked foods appear superfluous to maintaining human health.
- The central claims made for raw food-oriented diets and against healthfully composed raw+cooked food diets lack scientific support.
- There are pros and cons to eating foods raw or cooked, depending on the food, the cooking method, and one’s personal health status.
- Compared with prudent diets that blend raw foods and safely cooked foods, diets consisting largely or entirely of raw foods do not appear add significantly to human health.
- Exceptions to this rule relate to possible therapeutic effects in certain diseases, and uncommon personal health characteristics.
But there are distinctions among whole foods, and a query submitted to our Web site recently gives us an opportunity to explore a controversial question.
And that question is, "Do the enzymes found in raw foods—which are partially or fully inactivated by cooking—aid digestion of the foods containing them and offer strong health benefits?"
Clearly, people range widely in their bodies’ responses to various diets. Some thrive while eating little or no cooked foods, and inflammation-related medical conditions (e.g., arthritis, allergies) sometimes respond well to certain allergen-free raw food diets.
So-called “raw food” diets usually consist largely of fruits and vegetables (fresh or fermented). They may include sprouted beans and grains, as well as unpasteurized dairy products (raw milk, yogurt, cheeses).
Celebrities like Barbra Streisand, Angela Bassett, Robin Williams, and Steve Jobs have dabbled in raw food, and former “Cheers” star Woody Harrelson may be Hollywood's most prominent raw food fan.
Let’s explore this controversial topic, with the following customer query forming a good introduction our inquiry:
Dear Vital Choice,
I have a question. Does the process of freezing your blueberries result in the enzymes being stripped from them?
Please let me know. Thanks.
Answer to a “food enzyme” question raises nutrition and evolution questions
The following, expanded version of our answer to Rachel’s question allows us to delve more deeply into two controversial ideas advocated by raw-food advocates:
First things first: Rachel asked whether freezing inactivates (“denatures”) some of the enzymes in berries.
The answer is “yes”, but it is impossible to say what percentage become denatured, as this depends on the specific batch of fruit and precise conditions of freezing.
The downside of browning
Concerns about the safety of cooking meat and fish over high, dry heat relate to the creation of two kinds of potentially carcinogenic compounds during high-heat cooking: polycyclic aromatic hydrocarbons (PAHs) and heterocyclic amines (HCAs).
PAHs form when fat drips onto a flame, heating element, or hot coals. PAHs rise with the smoke and are deposited on the food. They can also form directly on the food when it is charred.
Heterocyclic amines (HCAs) can form in grilled, broiled and pan-fried meats and fish. HCAs are by-products of the Maillard (browning) reaction … which gives grilled meat or fish some of its characteristic flavor. The hotter the temperature and the more well done the meat or fish, the more HCAs get formed.
In addition to HCAs, browning of animal foods or baked goods creates compounds called advanced glycation end products (AGEs), which, once consumed, generate cell-damaging free radicals, stiffen collagen (creating wrinkles), and promote unhealthful “silent” inflammation.
But there is no evidence that low-to-moderate consumption of cooked foods containing these heart-related chemicals presents serious health risks. You can reduce formation of these compounds during grilling, broiling, and pan-frying by keeping meat, poultry, and fish moist (e.g., use marinades), and by removing any charred parts from poultry and fish.
And the negative impacts of grilled, broiled or pan-fried meats and fish can be mitigated very considerably by enjoying them with antioxidant-rich fruits, herbs, and vegetables. In addition to any free-radical-quenching effects, the antioxidants in produce tend to switch off the body’s gene-controlled inflammatory response to dietary free radicals and AGEs.
Our berries are flash-frozen: a process that produces no other significant chemical changes in the fruits, and preserves their fresh-picked flavors, colors, and vitamin content. (The University of Minnesota Extension Service offers an overview of the subject here. As they say, “Freezing, when properly done, is the method of food preservation which may potentially preserve the greatest quantity of nutrients.”)
We presume that Rachel’s question relates to the hypothesis that the enzymes in raw foods contribute to the digestion of these foods, and may offer other health benefits.
Raw foods offer some advantages, in that cooking certain foods in certain ways can degrade their nutritional value and/or generate carcinogenic, oxidizing, and/or pro-inflammatory chemicals (See our sidebar titled “‘High-and-dry’ cooking: the downside of browning”).
On the other hand, cooking makes many plant foods more digestible and enjoyable, and makes their nutrients more available and absorbable.
While certain kinds of cooking raise real health concerns, some folks avoid cooking in favor of eating raw, uncooked foods.
Raw foodism and food enzymes: A persistent hypothesis in search of proof
The increasingly popular “raw-foodist” stance is often based in part on a belief in the digestive and overall health value of raw foods’ inherent enzymes. (Many raw foodists are vegetarian, but some include raw dairy and fish, and meats and fish cured at low temperatures, in their raw regimens.)
Raw-foodists also believe that the enzymes in a raw food assist in its own absorption and digestion.
Enzymes are a special class of proteins, needed for many critical bodily processes at the molecular level. Heating food above 140° F (60° C) inactivates (denatures) most enzymes in food, while some denature at about 113° F (45°C).
In the 1920’s, Edward Howell, M.D. who noted that cooked foods contain fewer enzymes than raw foods.
Dr. Howell hypothesized that the enzymes in raw foods help us to break down these same foods and reduce the need to produced enzymes internally. And he claimed that the internal manufacture of enzymes taxes the body's limited energy stores.
But healthy people have no difficulty synthesizing enzymes, provided the body gets enough protein and other essential nutrients. Healthy human bodies experience no shortage of digestive enzymes, and no difficulty digesting frozen or cooked foods.
The only substantial exception to this general rule is that cooking foods at temperatures in excess of the boiling point (212° F / 100° C) renders their proteins somewhat harder to absorb.
In brief, there is simply no evidence for Howell’s core claims, which were largely based on limited, unpersuasive research conducted in the 1920's and 1930's.
Today, raw-food proponents point to enzyme-related research conducted in recent years. But very little of it has proven more persuasive, as the "Beyond Vegetarianism" Web site mentioned below documents in exhaustive detail.
Nor is there any evidence for Dr. Howell's claim that diets high in cooked foods tax the body's digestion or overall metabolism, promote disease, or accelerate aging.
Food enzyme advocates lack persuasive evidence
There are several major problems with Dr. Howell’s hypothesis.
Almost all of the enzymes present in raw foods are broken down into their components (amino acids) by our own digestive processes.
And the enzymes present in food are not equipped to act as digestive enzymes. Nor does it matter whether or not people eat enzymes, provided the body has an adequate supply of the food nutrients needed to construct enzymes internally.
Voluntary contributors to a remarkable Web site called Beyond Vegetarianism present a detailed scientific critique of Dr. Howell’s claims here. The site’s founders and chief contributors include practicing vegetarians and raw foodists of long standing, who seem bent on presenting scientifically sound information on various raw, vegetarian, or otherwise restricted diets.
Their exhaustive critique of Dr. Howell’s various raw food hypotheses is but one section in a series of private research papers concerning the pros and cons of raw and cooked foods, which starts here.
(Many of the Web site’s articles are well-referenced. The authors include paleolithic diet researcher Professor Loren Cordain, Ph.D., of Colorado State University, and Steven Bratman, M.D., editor of the respected Natural Pharmacist book series and Web encyclopedia.)
You can find related material at Columbia University.
Let’s take a look at archaeology to test the credibility of the idea that early humans and their ancestors evolved on largely raw-food diets. If true, this would indicate that raw-food diets are the healthiest choices for modern humans.
Did early humans and their ancestors cook foods?
Some raw food advocates say that because it takes thousands of years for humans to adapt to diet changes, the fact that proof of human cooking dates back no more than 50,000 years proves that humans are not adapted to cooked foods.
There are two problems with this claim.
First, paleo-anthropological research proves that major evolutionary adaptations—notably, lactose tolerance among cow-herding cultures in Northern Europe—have occurred within periods as brief as 1,200 years.
Second, most archaeologists date widespread human use of cooking to about 250,000 years ago, when hearths, earth ovens, burnt animal bones, and flint appeared across Europe and the Middle East. There is also evidence that early humans cooked tubers, which turns some of these plants’ near-indigestible starches into sugars and other digestible carbohydrates.
And according to recent finds in Africa, humans were cooking shellfish at least 164,000 years ago. See “Omega-3 Brain Evolution Theory Gets a Boost.” We did not mention that the shellfish in question seem to have been steam-cooked (Borenstein S 2007).
The most conservative estimates—which some raw foodists cite—place the earliest provable date for the beginning of cooking by humans at about 50,000 BC. But even if we use that date, the example (among others) of northern European cow-herders’ rapid, 1,200-year-long adaptation to dietary lactose suggests that it is reasonable to hypothesize that modern people are by now well adapted to routine consumption of cooked foods.
It is worth quoting here from an evidence review by anthropologists from Harvard University (Wrangham R, Conklin-Brittain N 2003):
- “No human foragers have been recorded as living without cooking, and people who choose a 'raw-foodist' life-style experience low energy and impaired reproductive function. This suggests that cooking may be obligatory for humans.”
“The possibility that cooking is obligatory is supported by calculations suggesting that a diet of raw food could not supply sufficient calories for a normal hunter-gatherer lifestyle. In particular, many plant foods are too fiber-rich when raw, while most raw meat appears too tough to allow easy chewing.”
“If cooking is indeed obligatory for humans but not for other apes, this means that human biology must have adapted to the ingestion of cooked food (i.e. food that is tender and low in fiber) in ways that no longer allow efficient processing of raw foods. Cooking has been practiced for ample time to allow the evolution of such adaptations.”
Interestingly, a study published earlier this month by a team from Harvard and Germany’s Max Planck Institute found that in general, great apes prefer cooked over raw foods (Wobber V et al. 2008).
Another of their studies, published last year, indicates that eating cooked foods takes less energy than eating raw foods… a small but possibly significant survival advantage in terms of calorie conservation (Boback SM et al. 2007).
Modern hunter-gatherers combine raw and cooked foods to healthful effect
Studies of modern hunter-gatherer societies indicate two things:
- They cook about half their food, which invariably includes some animal foods (meat, fish, insects), albeit much less meat than Americans and Europeans eat.
- They enjoy low rates of the chronic degenerative diseases that plague Western countries and are rising among developing countries as well: cancer, diabetes, heart disease, and dementia.
Together, these findings suggest that the prevalence of cooked versus raw foods probably plays a minor part in people’s overall health and their risk of developing the major degenerative diseases associated with Western civilization.
The negative impact of diets rich in fatty red meats is another matter. The evidence is now overwhelming that meaty, American-style diets raise the risk of cancer, diabetes, heart disease, and dementia.
However, these risks do not appear to apply to hunter-gatherer diets that feature lean meats, as explained by Australian anthropologists from RMIT University in Melbourne:
- “A study of human and pre-human diet history shows that for a period of at least 2 million years the human ancestral line had been consuming increasing quantities of meat… This meat was wild game meat, low in total and saturated fat and relatively rich in polyunsaturated fatty acids...”
- “In our own studies, we have shown evidence that diets high in lean red meat can actually lower [blood] cholesterol [levels], contribute significantly to tissue omega-3 fatty acid [levels] and provide a good source of iron, zinc and vitamin B12.”
For now, we’ll keep cooking fish – while savoring salads, fruits, and sushi
We believe strongly in the value of whole, natural foods: a stance increasingly supported by research (see our newsletter articles here and here.
But until persuaded by hard evidence, we must remain skeptical of Howell’s food enzyme concept.
To our surprise, the leaders of the Weston A. Price Foundation—which debunks modern dietary myths and advocates for time-tested traditional diets—appear to accept the Howell hypothesis rather uncritically.
Their stance on this issue may stem from the fact that Dr. Howell’s belief in a “life force” proffered by food enzymes fits with the Foundation’s (scientifically sound) advocacy of “live” (i.e., bacterially colonized) fermented foods, which enhance people’s intestinal flora and contribute bacteria-produced nutritional factors, including B vitamins (You can read their views on Howell here).
However, we see little evidence that the enzymes in fermented foods—which produce beneficial changes in cultured foods—offer significant benefits, post-consumption.
While lactobacilli and other food-fermenting bacteria use enzymes to digest the components of foods such as milk and cabbage, these enzymes, like almost all food enzymes, are broken into amino acids in the human digestive tract.
Clearly, people can survive and thrive eating only raw foods, albeit with a bit more planning and care than required for folks who observe a more conventional diet.
The devil, as always, lies in the details.
There is credible evidence that certain cooking methods degrade the healthfulness of certain foods.
But cooking also enhances some foods, and we see no evidence that cooked foods are generally unhealthful.
- Boback SM, Cox CL, Ott BD, Carmody R, Wrangham RW, Secor SM. Cooking and grinding reduces the cost of meat digestion. Comp Biochem Physiol A Mol Integr Physiol. 2007 Nov;148(3):651-6. Epub 2007 Aug 16.
- Borenstein S. Life was a beach for early humans: Archaeologists see signs of clambake and makeup from 164,000 years ago. Associated Press. Oct. 17, 2007. Accessed online May 27, 2008 at http://www.msnbc.msn.com/id/21347464/
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