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(Looking at the Science on Raw vs. Cooked Foods--continued, Part 2A)

Does Cooked Food Contain Less Nutrition?

In this part, we'll investigate whether raw food is or is not more nutritious than cooked food. This will involve the following considerations:

Effects of cooking on digestibility


It is known that starch gelatinization--a change of structure into a form that resembles gelatin--results from cooking at temperatures higher than 70°C (158°F), which improves digestibility [Holm et al. 1988, Lee et al. 1985]. Cooking also neutralizes the anti-amylases (in grains and seeds, and also some tubers).

On the other hand, some resistant (indigestible) starch is formed by cooking. Resistant starch is present [Englyst 1985] in smaller amounts in (dehulled, rolled, steamed) oats than in cornflakes or white bread. However, about 94% of the carbohydrates are digested. Uncooked oats don't contain resistant starch, so their starch is totally digestible if left long enough in test tubes, but in practical terms it is less digestible than in cooked form. (Any reader not convinced of that should try two comparison meals for themselves, both consisting of 200 grams of oats, one raw and the other cooked.)

Experimental results show cooked starch to be 2 to 12 times more digestible than raw starch. Kataria and Chauhan [1988] provide a direct comparison of starch digestibility in raw vs. cooked mung beans. Here, starch digestibility was measured in milligrams (mg) of maltose released per gram of food. The data from this study indicate that digestion of mung beans soaked 12 hours yields 25.3 mg maltose/gm, mung beans sprouted 24 hours yield 75.0, mung beans soaked and subjected to ordinary cooking yield 138, while mung beans soaked and pressure-cooked (for 5 minutes) yield 305 [Kataria and Chauhan 1988, Tables 1-3, pp. 54-56]. This is solid evidence that the starch in cooked mung beans is much more readily digested than the starch in soaked or sprouted beans, by a factor ranging from about 1.8 (i.e., 138 ÷ 75.0) to 12 times more efficient (305 ÷ 25.3), depending on differences in methods of preparing raw vs. cooked starch. We thus conclude here that overall, certainly at least in the case of mung beans, cooking greatly improves starch digestibility.

One final point regarding starch digestion needs discussion. Some raw advocates claim that their ability to digest raw starch increases when raw starches are a regular part of the diet. This assertion is based on close examination by the raw vegan of his/her stools (fecal matter; a topic of intense interest for some rawists). While there are reasons to believe that the human digestive system adapts, to a certain degree, to the diet eaten, it appears that there are no studies or experiments to quantify the degree of adaptation in comparisons of raw vs. cooked starch digestion. Furthermore, the limited qualitative anecdotal evidence available does not support a claim that the human digestive system can become 1.8 to as much as 12 times more effective in digesting raw starch--i.e., the magnitude of the effect seen from cooking of mung beans, as seen in the above-cited research.


We won't try to be exhaustive here, but our intention is to show by means of examples that, depending on the food and on the temperature and duration of cooking, a food can become more, or less, digestible, so that no general rule can be inferred.

Cooking followed by increased protein digestibility

From Oste [1991], many foods benefit from cooking:

Of course, other treatments, such as germination, can improve digestibility as well (at least for some of these foods).

Processing conditions may also alter the food structure on a cellular level, enabling digestive-tract enzymes to gain physical access to the protein.

Some native legume proteins resist proteolysis (breakdown of proteins into smaller components), but are degraded after heating.

Destruction of antinutrients of primary importance. But perhaps the major reason for the improved digestibility that can result from cooking is the destruction of antinutrients, such as protease inhibitors, polyphenols (including tannins and saponins), hemagglutinins, phytates, and dietary fiber. Polyphenols and phytates are, however, not reduced by heat alone. (For instance, soaking, sprouting, and fermentation also reduce phytates.)

From Bradbury [1984], the protein digestibility of the aleurone layer and grain coat from raw rice was only 25%, but increased to 65% from cooked rice, due to the disruption of the cellulose cell walls at 100°C (212°F), which was shown by electron microscopy.

Cooking followed by reduced protein digestibility

From Bach Knudsen et al. [1988], protein utilization and digestibility are decreased by cooking in some varieties of sorghum. In contrast, protein digestibility of pearl millet and corn (maize) decreases only very little (not significantly) after cooking [Ejeta et al. 1987].

From Oste [1991], heating (above 100°C, or 212°F) decreases meat protein digestibility. Frying chickpeas, oven-heating winged beans, or roasting cereals at 200-280°C (392-536°F) reduces protein digestibility.

Seidler [1987] studied the effects of heating on the digestibility of the protein in hake, a type of fish. Fish meat heated for 10 minutes at 130°C (266°F), showed a 1.5% decrease in protein digestibility. Similar heating of hake meat in the presence of potato starch, soy oil, and salt caused a 6% decrease in amino acid content.


(Do "Food Enzymes" Significantly Enhance Digestive Efficiency and Longevity?)

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GO TO PART 1 - Is Cooked Food "Toxic"?

GO TO PART 2 - Does Cooked Food Contain Less Nutrition?

GO TO PART 3 - Discussion: 100% Raw vs. Predominantly Raw

Back to Research-Based Appraisals of Alternative Diet Lore

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