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


Effects of cooking on vitamins


Vitamin loss can be induced by a number of factors. Obviously, losses of vitamins depend on cooking time, temperature, and cooking method. Some vitamins are quite heat-stable, whereas others are heat-labile. From textbooks in nutrition, such as Kreutler et al. [1987], many other factors than heat can destroy (some) vitamins, such as: solubility in water, exposure to air (oxidation), exposure to light (UVs), heat, acid and alkaline solutions, storage losses, etc. Here is a tabular summary:

FACTORS THAT CAN INDUCE
VITAMIN LOSS


Nutritional Element

Is substance susceptible to losses
under given condition?

Soluble
in Water

Exposure
to Air

Exposure
to Light

Exposure
to Heat

Vitamin A

no

partially

partially

relatively stable

Vitamin D

no

no

no

no

Vitamin E

no

yes

yes

no

Vitamin K

no

no

yes

no

Thiamine

highly

no

?

> 100°C

Riboflavin

slightly

no

in solution

no

Niacin

yes

no

no

no

Biotin

somewhat

?

?

no

Pantothenic Acid

quite stable

?

?

yes

Folate

yes

?

when dry

at high temp

Vitamin B-6

yes

?

yes

?

Vitamin B-12

yes

?

yes

no

Vitamin C

very unstable

yes

yes

yes

(table, continued)

Nutritional Element

Is substance susceptible to losses
under given condition?

Acid
Solution

Alkali
Solution

Other

Vitamin A

?

?

--

Vitamin D

?

?

--

Vitamin E

?

?

contact with iron or copper

Vitamin K

strong acids

yes

--

Thiamine

no

yes

--

Riboflavin

no

yes

long cooking in large volume of water

Niacin

no

no

--

Biotin

strong acids

yes

oxidizing substances

Pantothenic Acid

yes

yes

--

Folate

heat-labile

?

storage

Vitamin B-6

no

yes

--

Vitamin B-12

strong acids

yes

contact with iron or copper

Vitamin C

?

yes

--

Significance of losses depends on a given food's context in the overall diet. Of course, not all vitamin losses have detrimental consequences, since some vitamins are widely available (such as pantothenic acid). The vitamins in which some deficiencies are occasionally observed are: A, D, E, thiamine, riboflavin, niacin, folate, and B-12. Of those, only thiamine, niacin, and folate would be destroyed significantly by excessive exposure to heat and/or water. It also appears from the above that many other factors than heat can destroy vitamins. Recommendations to preserve vitamins include: utilizing foods when fresh; using steaming in preference to boiling; and avoiding overly long cooking times.

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(Comparison of Vitamin Levels in Raw vs. Cooked Foods)

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SEE TABLE OF CONTENTS FOR: PART 1 PART 2 PART 3

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

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