The harnessing of fire as a tool by humans led to the cooking of food, which stands in contradistinction to the eating habits of the rest of the animal kingdom. Cooking destroys disease-producing organisms (usually a consequence of animal agriculture), but are there any adverse effects on health?
"Raw foods" diets are trendy, but the arguments in favor of such diets by their advocates are often unscientific. Let us examine some of the claims.
Proponents claim health benefits that they often attribute to the preservation of enzyme activity, which is destroyed by heat. Exactly how these enzymes would affect health is unclear, because at least some enzymes would be destroyed by stomach acid. Even if they remained intact after exiting the stomach, enzymes, which are specialized proteins, would be mostly broken down by our body's own digestive enzymes in the small intestine and would therefore not be absorbed intact. Even if they were absorbed intact, however, there is no evidence they would confer any health benefits.
Some claim that the preparation or mastication of raw plant foods activates autolytic enzymes, which help in the digestive process, thereby reducing the burden on the body's own digestive enzymes. The implication is that the process helps prevent the exhaustion of our body's ability to produce digestive enzymes over time. There is no evidence that this is true, however. There is some evidence, in fact, that if we don't utilize certain enzymes, their activity will decrease over time. For example, people who don't consume dairy products might be more likely to develop reduced amounts of lactase, the intestinal enzyme that breaks down lactose, or milk sugar.
Finally, some raw foods enthusiasts imbue enzymes with a kind of spirituality, the embodiment of a kind of life force. As stated earlier, enzymes are simply specialized proteins whose production is dictated by the DNA in our cells, and their job is to act as a catalyst in the chemical reactions that take place in the body. They are chemical compounds, nothing more.
Therefore, the arguments put forth to explain the biochemical basis for any health benefits accruing from the consumption of a raw foods diet represent pseudoscience. Nevertheless, people who engage in erroneous thinking sometimes turn out to be correct in the position they advocate, and that may well be true in this instance. There is a growing body of evidence that cooking foods more lightly or not at all may be beneficial to health.
First, cooking destroys nutrients, especially vitamin C and some of the B-vitamins. However, the effect is not always in the negative direction. For example, although carotenoids like beta-carotene, lycopene, and lutein are destroyed to a minor degree by cooking, the process results in changes that allow them to be absorbed much more readily.
Another disadvantage of cooking is that it produces carcinogens (cancer-causing chemicals): grilling of meat is a frequently cited example.
With regard to the destruction of enzymes by cooking, there actually are some ways in which the preservation of enzyme function by not cooking is potentially beneficial. When certain raw foods are crushed (as with eating) or cut, some enzymes are indeed activated and may promote health by mechanisms other than aiding digestion. For example, activation of the enzyme alliinase in garlic converts alliin to allicin, a phytochemical that may have anticarcinogenic (cancer preventive) properties. Similarly, activation of the myrosinase enzyme in cruciferous vegetables results in the formation of compounds that induce the production of the liver's phase 2 enzymes that inhibit carcinogenesis and that may help prevent chronic diseases. Whether consuming a higher proportion of raw foods would actually prevent cancer remains to be determined because the studies performed to date have been small, but the possibility and potential are there.
Still another disadvantage of cooking (especially at high temperatures and for long periods) is that it causes the formation of advanced glycoxidation end products (AGEs), which are felt to promote aging and diabetic complications.
Because uncooked foods are bulkier than cooked foods, they may promote the intake of fewer calories per day. Consuming foods of lower energy density, such as bulky foods, has been shown to promote satiety (sensation of fullness) equal to that of foods of higher energy density and with higher total caloric content. Intake of fewer calories per day not only promotes weight loss in overweight individuals but may have significant health benefits to all of us (see page on Dietary Restriction).
Although few of us are willing to give up cooking foods entirely, increasing the percentage of food cooked in the raw state and cooking foods as lightly as possible, e.g., avoiding toasting of bread and browning of other foods, would seem prudent, and I consider this concept to be an important part of an optimal diet.