How does Cooking Affect Nutrition in Food

We all are aware that fruits and vegetables should be an important part of our diet. Most of us try to consume as much as possible. Yet we don’t see positive results, we don’t seem to be really getting all the nutrients from the food. This may be because of many reasons – the food is not fresh, and hence has lost most of the nutrients; we lack knowledge about how a particular vegetable should be cooked, so that we can absorb most of the nutrients;  Should the vegetable be eaten raw or cooked? Most of the time, we lose a lot of vitamins during the process of preparing, storing and cooking food.

Know your vitamins

First of all it is necessary to know our vitamins. For instance, we all know that tomatoes, red capsicums, spinach are rich in vitamin C. So we cook them and eat them, thinking we have had a very nutritious diet. But the truth is that vitamin C is water soluble and when we cook it, it leaches out into the water, and if you don’t drink the water or use it in a soup, you didn’t really get vitamin C from the food you ate. So its best to eat them raw or steamed.

But wait a minute, there is something called Lycopene in tomatoes, that is not available all that much in raw tomatoes. Lycopene increases as the tomatoes are cooked more and more. Also, when eaten with oil or fat, it increases lycopene absorption by the body.

Spinach has quite a good amount of calcium. But it also has oxalic acid which can interfere with the absorption of calcium by the body. Since spinach offers a lot nutritionally, you cannot stop eating spinach. The answer is to eat yogurt to get calcium and spinach to get all the other nutrients like vitamin C, Iron and vitamin A.

The secret here is to know your vitamins and minerals, and how to cook them.

Water-Soluble and Fat-Soluble Vitamins

There are water soluble vitamins and fat soluble vitamins. We can avoid specific types of vitamin loss, by cooking them right. Vitamins A, E, D and K are fat soluble vitamins, therefore the food has to contain some fat, to be a good source of one of these vitamins, and to get the most from them. In general, fat soluble vitamins are fairly well retained while preparing food, largely because they don’t dissolve in water. Fat-soluble vitamins are stored in the liver and fatty tissues. They are used by the body as required and eliminated more slowly than water-soluble vitamins. So an overdose of these vitamins could lead to toxic results.

Water-soluble vitamins cannot be stored in the body and as such have to be replenished every day. The water soluble vitamins are the B vitamins, vitamin C and folates. These vitamins are also easily excreted by the kidneys. Water soluble vitamins readily dissolve into the water used in cooking. This is one reason why you should cook with just enough water or use the liquid from cooking to make soups. Heat is another problem for many water soluble vitamins.

Vitamin C loss on cooking in vegetables
Percentage vitamin C lost during exposure to 140 degree F (from

Vitamin C is a water-soluble and temperature-sensitive vitamin, so gets easily degraded during cooking. High temperatures and long cooking times have been found to cause particularly severe losses of vitamin C. Thiamine (B1) and pantothenic acid are all highly sensitive to damage by heat.

Heat Stable Vitamins

Vitamin D is said to be stable in heat, and slightly sensitive to light. Freezing foods high in vitamin D content does not reduce their vitamin D content and vitamin D content stays high even when foods are cooked.

Vitamin B12 is stable to heat but is sensitive to light and oxygen.

Fat-soluble nutrients such as vitamins A, E and K are more stable and fare better when you cook them. So do carotenoids like beta-carotene, alpha-carotene, lycopene, and lutein, and antioxidants found in leafy greens, carrots, winter squash, sweet potato.

Vitamin K is sensitive to light, alkaline conditions, and air, but is not destroyed by cooking heat

Vitamin E is relatively resistant to heat and insoluble in water, but when you heat the oil at very high temperatures for frying, there can be a loss of vitamin E.

Vitamin A is a fat-soluble vitamin. It is not easily destroyed by heat but is readily oxidized. You must, therefore, protect it from oxidation. In the absence of air, vitamin A is unaltered at moderate temperatures.

A study on the ‘Effect of different cooking methods on the content of vitamins and true retention in selected vegetables’, concluded that, “Cooking may cause changes to the contents of vitamins and it depends on the type of vegetables and the method of cooking methods. Therefore, further research is needed to optimize cooking procedures to enhance retention of vitamins”.

Tips to Cut Down nutrient Loss while Preparing and Storing Food

Following these tips will help cut down the nutrient losses from foods while preparing and storing food.

  • Use fresh fruits and vegetables, as soon as possible after purchase, as nutrients get destroyed with the passage of time.
  • Avoid soaking vegetables in water for long periods of time.
  • Keep the skin intact whenever possible, as in some vegetables and fruits the nutrients are often just below the skin.
  • Do not wash the vegetable after cutting it and try to cut it into larger pieces as there is less loss of nutrition.
  • Vitamin C also evaporates into air, hence keep juices covered tightly in the fridge.
  • Riboflavin is destroyed by exposure to light, hence keep food with riboflavin, covered and in the fridge as soon as possible.
  • Serve cooked vegetables immediately, as it starts losing nutrition after 24 hours in the fridge.

Cooking Vegetables

  • Where cooking vegetables rich in vitamin C and B vitamins is concerned, it is best to steam the vegetables than to boil them. As the vegetables do not come into direct contact with water, more vitamins are retained.
  • Don’t cook for long and avoid high temperatures.
  • To avoid stickiness in food like pastas, adding some oil is a better alternative than to rinse them, as some vitamins will also be washed off.
  • The key is to cook vegetables gently, with the least amount of water. This will help protect the water-soluble vitamins. If boiling in water, then use the cooking water in soups or gravies.
  • Blanching the vegetables will also help preserve the color and nutrients in the food we eat.
  • Dry cooking methods such as grilling, roasting and stir-frying retain a greater amount of nutrients than boiling.

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