The claim that: microwave oven kill nutrients is believed and even circulated to friends and loved ones warning them of the dangers of microwave oven.
Who is right? Which part of the story should we believe?
The root of all evil
A simple search of ‘microwave kills nutrients’ on the internet yields uncountable pages. All carrying the same uncorroborated idea that microwave kills 97% of nutrients in broccoli and other vegetables.
The article that is repeatedly quoted was published in 2003 in the Journal of Science of Food and Agriculture by researchers from Laboratory of phytochemistry, Department of Food Science in CEBAS-CSIC, Murcia, Spain.
These researchers studied the loss of phenolic compounds before and after cooking broccoli using pressure cooker, steaming and microwaving.
The authors reported that microwaving caused the highest reduction of flavanoids (97 %), boiling caused a reduction of 66 %, steaming led to 11 % reduction, while pressure-cooking resulted in the least reduction of 9 %.
Flavanoids is a class of phenolics and are not nutrients per se, but offer health promoting benefits. Some of the healthy benefits attributed to flavonoids include: anti-allergic, anti-cancer, antioxidant, anti-inflammatory and anti-viral
This figure, (97%), is often quoted by most articles that imply microwaving causes high losses of nutrients in vegetables and presumably other foods.
Sure, 97% loss is extremely detrimental and any cooking method that can cause such high losses is unsuitable for use. However, is it really true that microwave oven causes 97% loss of nutrients in vegetables?
Road less traveled.
To find out the real truth, I took the road less traveled; I obtained that article and studied it carefully. One thing that came out clearly in that study is that, the researchers did not evaluate all nutrients, therefore, the proposition that microwave kills all nutrients, is by itself far fetched, misleading and over interpretation of scientific data.
Food contains plethora of nutrients ranging from macronutrients which are: proteins, carbohydrates and fats and micronutrients which include; minerals and vitamins.
The flavanoids reported are actually not nutrients; they are bioactives, chemicals from plants that when consumed offer healthy promoting benefits.
This study has been misunderstood and misreported, triggering undue paranoia of microwave oven. The idea that microwave oven destroys 97% of nutrients is not what is presented in the article.
The truth is; microwave heating of foods does not destroy or affect antioxidants, vitamins, minerals or any other nutrients in our foods in a more severe way than conventional cooking methods.
The researchers dipped 150g (weight equal to 1/4 kg of meat divided by two) of broccoli in 150 milliliters (2/3 of a glass) of water and cooked them for 3 minutes by high pressure and 5 minutes by low pressure using pressure cooker.
A similar weight of broccoli was suspended over boiling water for 3.5 minutes during steaming. An equal amount of broccoli in exactly similar amount of water was microwaved at full power of 1000 W for 5 minutes. It is very important to know these exact cooking conditions because they directly affect the level of nutrients lost.
These conditions are arbitrary and do not represent universal cooking procedures. These cooking conditions were selected for experimental purposes only. It is therefore unjustified to simply classify them as ‘boiling’ and ‘microwaving’.
In actual kitchen practice, the microwave power, pressure-cooker pressure, cooking times and amounts of water will vary widely, affecting the amounts of flavonoids and nutrients differently.
The microwave used in this study is a 1000 W microwave oven, at full power, it is very powerful. The power of an average kitchen microwave is 800 W. In fact microwaved broccoli was cooked for longer period (5 minutes) in comparison to the steamed (3.5 minutes) and boiled samples (3 minutes for high pressure boiling).
In addition, the amount of water 2/3 of glass added to microwaved broccoli was too much. All microwaveable vegetables come with an instruction to use just a tablespoon or two of water.
Adding more water than this is detrimental to nutrients. Actually water-free cooking is preferred. That is why steaming is the best method to cook vegetables.
In steaming, the vegetables do not come into contact with water thus retain the highest amount of nutrients. Ideally, vegetables cooked in a microwave oven without any water retain extremely high levels of nutrients.
The Spanish authors reported that the abnormally high losses of flavanoids in the microwaved samples were contrary to those reported previously by colleagues from the same university and University of Glasgow, UK; all opponents of use of microwave oven pay no attention to this fact.
The researchers cited the high amount of water and length of cooking in their microwaved samples as the main cause.
Most flavanoids are water soluble and they may have evaporated with the water. Heating a 2/3 glass full of water in a 1000 W microwave at full power as done in the experiment can cause most of the water to evaporate taking away most of the water soluble and heat sensitive nutrients.
In conclusion, the researchers recommended short cooking periods with no contact between vegetables and water. Basically, steaming or water-free microwaving.
The vegetables cooked by steaming or water-free microwaving retain high amounts of phenolic compounds and other nutrients. To my surprise, this conclusion is ignored and never mentioned by proponents of the myth that microwave kills nutrients.
Why was this article taken very seriously?
The reason is very simple; the research reported the loss of nutrients in broccoli, a darling vegetable, thanks to its health promoting benefits. Broccoli contains multiple nutrients with potent anti-cancer properties such as diindolylmethane, selenium and indole-3-carbinol.
Over the last two decades, broccoli has been refused and eventually universally accepted. It was in 1990, and the then President George Bush made a daring proclamation: “I’m president of the United States and I’m not going to eat any more broccoli”
In 1992, a researcher at Johns Hopkins University, USA announced the discovery of a compound found in broccoli that not only prevented the development of tumors by 60 % in the studied group, it also reduced the size of tumors that did develop by 75 %.
Since then, scientists have unearthed one health benefit of broccoli after another especially the cancer fighting nutrients. Actually, broccoli is now one of the best-selling vegetables in the United States and Europe.
Broccoli belongs to same family of cruciferous with cabbage, kales and brussels sprout. Broccoli is an excellent source of the vitamins providing two times the daily requirement of vitamin C in one serving and has as much calcium as a glass of milk. It’s also a rich source of fiber, Vitamin A, K, and folic acid.
It’s also a good source of the minerals calcium, potassium, phosphorus, and magnesium, as well as vitamins B6 and E. To enjoy all these nutrients, broccoli has to be cooked properly. Improper cooking, especially boiling destroys all its healthy benefits and cancer fighting nutrients.
Are there other studies to show that microwave cooking does not kill nutrients in vegetables?
Yes, there are numerous studies from different countries by different researchers showing that microwave cooking is not any detrimental to nutrients than conventional cooking methods. Find all that in the second part of this article.