William Harris, M.D. -- The Scientific Basis of Vegetarianism
Home | On Going Vegan | Questionnaire | Menu for starting out | Exercise | Water & Salt | Supplements
About Dr. Harris | Visitors | Labels | Pesticides | HippoSuction | Testimony | Computercide | F.L.A.K.E.
The Scientific Basis | Breast Cancer | Vegan Political Action | Health Discussion Board

July 16, 2000

Raw vs Cooked

(see graph at end)

Raw food enthusiasts have always been a part of the vegetarian/vegan scene. Their core idea is that enzymes are still active in raw food whereas they're denatured, hence inactive, in cooked food. No contest. Next question: So what? The theory is that all food should be eaten raw to avoid the destruction of the enzymes in the food itself which are held to be essential to proper digestion. One afficionado has stated that "enzymes present in raw foods take priority over secreted (digestive) enzymes."

Now Ganong's Physiology (1) lists 25 human gastrointestinal digestive enzymes from salivary glands, lingual glands, stomach, exocrine pancreas, intestinal mucosa, and the cytoplasm of mucosal cells. There are at least 11 polypeptide gastrointestinal hormones regulating the secretion of these digestive enzymes. If food, in fact, could digest itself for us, why would a parsimonious evolution (or an efficient God) have bothered installing these enzymes, hormones, and the segments of the GI tract that are set up specifically to process them and their respective food components?

Neither Ganong nor thousands of scientific writers on the subject of digestion make mention of any value of intrinsic food enzymes in human digestion. There is one exception: Prochaska LJ; Piekutowski On the synergistic effects of enzymes in food with enzymes in the human body. A literature survey and analytical report. Med Hypotheses (ENGLAND) Jun 1994. In this article the authors mostly repeat the well understood effects of heat in breaking down vitamins, amino acids, and producing undesirable cross-linkages in proteins, particularly in meat. They do not produce a surfeit of evidence in support of the "enzyme theory", although they do point out that cooking beans increases their digestibility by destroying the trypsin inhibitors therein and they cite this as evidence that these enzymes can survive the digestive enzymes at least long enough to cause negative effects. They also present tentative evidence that there is some degree of synergy between some food enzymes and human digestive enzymes, a concept that would at least seem plausible. However they admit: "In the absence of active enzymes in food, the foodstuffs are still able to be digested and the nutrient release from food still occurs, but not at maximum efficiency." This is a far cry from "the enzymes present in raw foods take priority over secreted enzymes."

A search of Medline and the American Journal of Clinical Nutrition, however, failed to turn up a single additional article in support of this thesis and four physiology, biochemistry, and nutrition textbooks, while elaborating on human digestive processes to the point of tedium, also did not mention any useful predigestion of food by the food's own enzymes.

A teleological mind-set is reflected in the idea that a benevolent nature designed foods to predigest themselves for the benefit of man. Amylase, protease, and lipase are used to mobilize stored carbohydrate, protein, and fat for the benefit of the food organism itself, be it plant or animal. Animals have additionally evolved large organs to synthesize and secrete other enzymes for digestion of food in whatever form it comes. This evolved machinery would not have been necessary if foods could adequately predigest themselves.

Cooking is a form of predigestion in which heat is used to hydrolyze nutrients which would otherwise be hydrolyzed at body temperature by digestive enzymes. The end result is the same, but one raw food author seems to obliquely suggest that another reason for leaving food enzymes intact is so they can be absorbed intact into the blood stream to continue their digestive work there. Such a process would be catastrophic as the absorbed enzymes would be peptide fragments and would be more likely to generate allergic and autoimmune reactions than robust good health..

Some of the pros and cons of the raw diet:

Pro: Humans are the only species on the planet who cook their food, so cooking is unnatural..

Con: We're also the only species that build computers and write treatises. That's unnatural, too.

Pro: We've only been cooking for a half million years so we're not well adapted to cooked food.

Con: On the other hand, one recent author suggested that the learned ability to cook raw tubers over a million years ago resulted in such an increase in dietary Calories that it reduced sexual dimorphism in the pre-humans who employed it, and that in turn led to the psychosexual bonding that gave rise to human families and civilization (2).

Pro: A raw vegan diet rather reliably leads to weight loss and that would be great for the 30% of Americans who are either overweight or obese.

Con: What happens to the people who are already raw fooders but continue to lose weight from reduced Calorie intake?

Further food limitations on a raw diet:

A raw diet places even further restrictions on the vegan diet. Among the first dietary restrictions would be grains. Human population growth since the agricultural revolution 12,000 years ago has been tied to grain cultivation and a 1994 Scientific American article underscored this, ascribing wide spread spinal defects in ancient female skeletal remains to the all-fours posture required to kneed grains to the point where they could be cooked and consumed (3 ). People have been pounding grains to insensibility as long as they've been around, to get rid of the nutritious but poorly digestible outer shell. American grocery shelves are not by accident stuffed with white breads as far as the eye can see; many people do not like or even tolerate whole grain bread. As example and according to a mid-30s apologist for white bread, the Germans, after over-running Belgium in WWI, decreed a 98% extraction rate for Belgian bread in a well-intentioned attempt to improve Belgian nutrition. However, Belgian tummies responded to the resulting German black bread with epidemic malabsorption problems and the incidence of tuberculosis went up. Whole grain bread may be good for most people but for a subset of new vegans the gluten content may unmask a previously unrecognized celiac syndrome.

Raw fooders respond to this by saying that grains should not be milled but sprouted and this usually does improve nutrient values and digestibility. On the other hand sprouted alfalfa contains a non-protein amino acid L-canavanine which is thought to trigger systemic lupus erythematosis (SLE), an auto-immune disease. Various other seed sprouts may harbor Salmonella and E. coli bacteria, although this probably reflects contamination during production and distribution, rather than intrinsic fault in the seeds.

On a raw diet, potatoes, a generally well tolerated staple, also go out. To counter that, it can be said that potatoes with green skin contain solanine, a toxic alkaloid that has been popularly, though not scientifically, incriminated in some arthritic conditions. But we could probably get along without potatoes, too.

Other casualties would be soy and many other beans. Raw soy contains trypsin inhibitors, goitrogens, and a laundry list of other allegedly adverse factors. If you have any doubt about the ability of raw beans in general to cause gastrointestinal disturbance, try eating some yourself. Even when cooked, fava beans, a Mediterranean species, win a place for themselves in medical textbooks under the heading "Hemolytic Anemias-Favism."

The raw food literature is rife with "life force", a metaphysical concept that dates back to ancient medical theory with more recent abuse at the hands of George Bernard Shaw (Man and Superman-1903), William Faulkner (Light in August-1932), and the red stripes in the present Uzbekistan national flag. However, the German chemist Friedrich Wohler by 1828 had carried out the first synthesis of an organic compound, urea, an achievement that began the decline of the vitalistic theory that had dominated organic chemistry and that had required the existence of a "life force" for organic synthesis. Modern biochemists synthesize vastly more complex molecules than urea without any recourse to "life force." Perhaps, as it has been suggested, metaphysics is for people too lazy to study physics, a field in which there are still enough unexplained mysteries in the fine structure to accommodate all the mysteries of life. It's not necessary to sweep all those mysteries under a metaphysical rug dubbed "life force."

Things that are alive exhibit metabolism, the combining of food, water, and oxygen through enzyme-catalyzed chemical reactions in order to obtain energy for functioning. They also exhibit such properties as growth, reproduction, movement, and response to stimuli. But pitching raw food on the basis that it is "alive" creates a semantic minefield for vegetarians.

Sure, the greens are alive until they have been cooked and the enzymes have been denatured, but then so is a piece of fresh beefsteak. The cells from both could be kept alive in tissue culture. Does that mean we should eat raw beef because it's "live food?" Does it mean the cow that the live steak was taken from is still alive? Does it mean that the dim consciousness that inhabited that primitive skull and presided over all the fear reactions that we also experience when faced with death is still there? Of course not; the cow had something the greens don't have, a nervous system, it's consciousness is gone forever, and that's what the whole ethical vegetarian case is about. "Live food" arguments really muddy the waters when you're trying to explain the ethics of vegetarianism to a meat eater.

All the foregoing sounds like a frontal assault on the raw fooders, but it's not. I agree with them that raw foods should be a major if not sole part of the diet but not for their reasons. Raw foods are not healthiest because they're "live food" or because of "life force", "living enzymes", "nerve energy", or "chi", but because the foods that can be eaten raw (mostly vegetables, fruits, nuts and seeds) coincidentally have enormously higher nutrient values than the foods that either have to be, or usually are, cooked. Here is a six-bar stacked and rotated graph assembled from Nutritionist IV data and Quattro Pro showing the amounts of six important nutrients in various foods with the RDA for the six nutrients at the bottom. It should be self-explanatory, but the foods that are usually cooked are shown in the upper part of the graph and the ones that can be eaten raw in the lower part. The nutrient values, expressed as "Percent of (Recommended Dietary Allowance [RDA] per Calorie)" are highest for the raw foods. Note that potato, brown rice, winter wheat, pasta, and 16 averaged breads don't even make it to the RDA (vertical light blue arrow). 96 averaged vegetables are beginning to look pretty good, however not all of the ones included can be eaten raw and included among the 96 were a few raw seeds and nuts which dragged down the nutrient indices considerably. Raw they may be but they are also high in fat.

There are at least forty essential nutrients in the human diet but Quattro can only show six at a time and RDAs have not been set for many of the others.

(V4 juice is just a tomato, a bunch of parsley, a carrot, and a stalk of celery run through a juicer.)

Summary: The Raw Fooders are probably right but maybe not for their stated reasons.


1. Ganong WF. Review of Medical Physiology. Appleton & Lange. Norwalk 1991. ISBN 08385-8418-7. p 438 p449.

2. Wrangham R, Jones JH, Laden G, Pilbeam D, and Conklin-Brittain, The Raw and the Stolen: Cooking and the Ecology of Human Origins. CURRENT ANTHROPOLOGY Volume 40, Number 5, December 1999

3. Molleson, T. The Eloquent Bones of Abu Hureyra: The daily grind in an early Near Eastern agricultural community left revealing marks on the skeletons of the inhabitants. Scientific American August 1994.