Half-truth: Microwave cooking Kills Nutrients

There are claims and counter-claims that cooking vegetables in a microwave oven zaps all the nutrients and renders vegetables worthless. Does microwave oven really kill nutrients?

What causes loss of nutrients during cooking?
There are three key factors that contribute to the loss of nutrients during cooking of vegetables whether over open fire, by hot plate, gas cooker or microwave oven.

If these critical factors are well controlled, losses are minimised and the cooked vegetables deliver high levels of nutrients.
Long cooking periods using slow methods leads to high losses while fast, short cooking periods are less detrimental to nutrients. Therefore, very fast cooking methods such as microwaving and pressure cooking are offer an advantage of minimal loss of nutrients.

On the other hand, slow cooking methods such as open fire, hot plate and gas cooker that involve long periods of cooking lead to high losses of nutrients.

During the cooking, water soluble nutrients (mostly vitamins, minerals and other health promoting compounds) migrate from the food into water and eventually get lost through evaporation. High amounts of water provide a sea into which nutrients can get lost. That is why boiling and similar cooking methods that use a lot of water lead to high losses of nutrients.

High cooking temperatures destroy nutrients. Most beneficial minerals and Vitamins such as Vitamin C are heat sensitive. They easily get lost at very high heat (temperatures). Combination high heat and long periods of cooking cause very high losses of nutrients and therefore are never recommended for cooking vegetables.

Why microwaving causes minimal loss of nutrients in vegetables
Microwave heats the food by rotating water molecules at very high speed (approximately 2450 times per second) causing them to collide and rub against each other. This leads to friction which generates heat. Therefore microwave cook foods very fast.

It is also advisable not to add any water to vegetables during microwave cooking. If water has to be added, it should be very little. Combination of fast heating and water-free cooking is the reason for minimal loss of nutrients in a microwave oven. A research carried out in Cornell University, USA, one the world’s respected University for Food Science and Nutrition found out that spinach cooked in a microwave retained nearly all its vitamin B-complex but lost about 77% when cooked on a stove in presence of water.
Other study comparing microwave cooking and conventional cooking reported that broccoli cooked in a microwave in presence of water lost 97% of compounds called flavanoids.

Similarly, preparing different vegetables by conventional cooking methods (boiling) but in water results to equivalent or higher losses of nutrients.

This shows that the actual cause of nutrients is the presence of water and length of cooking and not the microwave oven.

Tips on cooking vegetables in a microwave oven to reduce loss of vitamins and minerals.

  1. After cleaning, rinse the vegetables in cold water, this leaves them with sufficient water.
  2. To make it completely water-free cooking, dry the vegetables with a kitchen towel.
  3. Place the vegetables in a covered, microwave-safe container.
  4. Do not add water (some times it is recommended to add 1 to 2 tablespoonfuls of water-this depends with the type of vegetables).
  5. Heat at the recommended power as indicated on the packaging instruction.
  6. For the vegetables bought in the open market, cook for three to four minutes or until vegetables are tender. This requires trial and error. Do not overcook.

Bottom line: Microwave cooking causes some loss of nutrients, but when compared to conventional cooking such as boiling and steaming, microwave cooked vegetables retain higher level of nutrients due to rapid heating and use of little or no water.

You might also like:

Joshua Arimi simplifies complex scientific facts on food to user friendly, understandable and applicable information. You can view his blog at www.arimifoods.com