Many vitamins such as Vitamin C, are destroyed by heat and their benefits are lost. This means that cooking fruits, vegetables and meats will progressively mean that the level of such vulnerable vitamins in the food dishes will decline.
However, surprisingly eating raw foods does not necessarily mean that all the potential vitamins in the fruits and vegetables will be available.
Studies have shown that people who ate a raw food diet had below average levels of plasma lycopene which is a bright red carotene and phytochemical found in tomatoes, red bell peppers, watermelons.
Cooking breaks up the thick cell walls of many plants, so that the nutrients inside can be utilised. Many cells in raw food remain intact and pass through the digestive system without releasing their vitamin bounties for absorption.
Foods rich in fiber may pass through the gut partially undigested.
Other studies have shown that cooking changes the chemical structure of lycopene so that it is more available to be ingested from food.
When the 'linear' lycopene molecules in tomatoes are heated with fat during cooking the molecules are changed to a bent form that is more easily transported into the bloodstream and tissue in the body.
Cooking can enhance the availability of other vitamins as well. To cook or not to cook - that is the question and which cooking method retains the most vitamins.
► Water soluble vitamins are more susceptible to cooking and canning processes.
► Canned carrots and peas lose about 90% of their natural Vitamin C.
► Frozen dark cherries have been shown to lose 50% of anthocyanins (an antioxidant associated with their red color) after six months.
► Cooking removes about 70% of the vitamin C in fresh spinach and general loses for other foods range from 15-55% depending on the methods and how long the food is cooked.
► Fat-soluble compounds like vitamins A, D, E and K and the carotenoids generally are retained better when cooked than the water soluble ones.
► A research study reached the following conclusions:
► Cooking in the Microwave and in Pressure Cookers retained the most Vitamin C.
► The results from a research study conducted in 2007 found the following for retention of Vitamin C:
► Food is cooked quickly with no added water than can wash nutrients out of food.
► Reheated cooked foods generally lose no nutrients when reheated. You are less likely to overcook foods.
► Cooking times are relatively short
► Very little added water is used.
► Boiling is generally considered the second worst method for cooking vegetables because the items tend to be cooked for a long time and are often over cooked. Frying is the worst
► Many vitamins and other nutrients are dissolved into the water and are poured down the sink when the cooked vegetables are drained.
► Nutrient loss varies a lot depending on cooking tines, the type of vegetable, whether or not the item is peeled and how finely it is chopped before being cooked.
► Use little water
► Place food in water only when it's at full boil and cook for minimum time.
► Cover the pot, to speed up the cooking
► Re-use the cooking water soups and gravies
► Don't peel vegetables. Peeled potatoes lose about 25% of Vitamin C when boiled, but hardly any when not peeled.
► Don't over-cook. The longer the cooking time and the higher the temperature, the more vitamins are lost.
► The lower the temperature the less quickly vitamins are destroyed
► Standard frying at very high temperatures causes the loss of most vitamins as the temperatures are far in excess of the boiling point of water.
► Frying is the worst method for cooking most vegetables.
► Very quick and very light stir-frying is better, but expect loss of many vitamins.