Some people think raw foods are more nutritious than cooked ones. However, some foods are less nutritious raw because they contain substances that destroy or disarm other nutrients.
For example, raw dried beans contain enzyme inhibitors that interfere with the work of enzymes that enable your body to digest protein. Heating disarms the enzyme inhibitor. Some, foods (such as meat, poultry, and eggs) are positively dangerous when consumed raw (or undercooked).
There’s no denying that some nutrients are lost when foods are cooked. Simple strategies such as steaming food rather than boiling, or broiling rather than frying, can significantly reduce the loss of nutrients when you’re cooking food.
Virtually all minerals are unaffected by heat. Cooked or raw, food has the same amount of calcium, phosphorus, magnesium, iron, zinc, iodine, selenium, copper, manganese, chromium, and sodium. The single exception to this rule is potassium, which — although not affected by heat or air — escapes from foods into the cooking liquid.
With the exception of vitamin K and the B vitamin niacin, which are very stable in food, many vitamins are sensitive and are easily destroyed when exposed to heat, air, water, or fats (cooking oils). The following table shows which nutrients are sensitive to these influences.
| Nutrient | Heat | Air | Water | Fat |
|---|---|---|---|---|
| Vitamin A | X | X | ||
| Vitamin D | X | |||
| Vitamin E | X | X | X | |
| Vitamin C | X | X | X | |
| Thiamin | X | X | ||
| Riboflavin | X | |||
| Vitamin B6 | X | X | X | |
| Folate | X | X | ||
| Vitamin B12 | X | X | ||
| Biotin | X | |||
| Pantothenic acid | X | |||
| Potassium | X |
To avoid specific types of vitamin loss, keep the following tips in mind:
Vitamins A, E, and D: To reduce the loss of fat-soluble vitamins A and E, cook with very little oil. For example, bake or broil vitamin A–rich liver oil-free instead of frying. Ditto for vitamin D–rich fish.
B vitamins: Strategies that conserve protein in meat and poultry during cooking also work to conserve the B vitamins that leak out into cooking liquid or drippings: Use the cooking liquid in soup or sauce.
Do not shorten cooking times or use lower temperatures to lessen the loss of heat-sensitive vitamin B12 from meat, fish, or poultry. These foods and their drippings must be thoroughly cooked to ensure that they’re safe to eat.
Do not rinse grains (rice) before cooking unless the package advises you to do so (some rice does need to be rinsed). Washing rice once may take away as much as 25 percent of the thiamin (vitamin B1). Toast or bake cakes and breads only until the crust is light brown to preserve heat-sensitive Bs.
Vitamin C: To reduce the loss of water-soluble, oxygen-sensitive vitamin C, cook fruits and vegetables in the least possible amount of water. For example, when you cook 1 cup of cabbage in 4 cups of water, the leaves lose as much as 90 percent of their vitamin C. Reverse the ratio — one cup water to 4 cups cabbage — and you hold on to more than 50 percent of the vitamin C.
Serve cooked vegetables quickly: After 24 hours in the fridge, vegetables lose one-fourth of their vitamin C; after two days, nearly half.
Root vegetables (carrots, potatoes, sweet potatoes) baked or boiled whole, in their skins, retain about 65 percent of their vitamin C.