Microwave ovens decrease nutritional content of food?

Dear Alice,

My family uses microwave ovens a lot, and I was wondering if cooking foods such as broccoli in a microwave can really diminish the antioxidants in the food. I came across a web site that said there was a study published in a science journal that showed that broccoli lost 97 percent of its antioxidants after being cooked in a microwave. I'm not sure whether to believe this or not. Could you help me out?

Needing Antioxidants

Dear Needing Antioxidants, 

Microwave ovens may be a common and convenient fixture in many kitchens. No matter how you slice it, the act of cooking fruits and vegetables can affect some of their nutrients. In many cases, certain minerals, vitamins, and antioxidants can’t withstand the heat. The good news, however, is that microwave cooking generally doesn’t reduce the nutrients in food than other cooking methods such as baking, boiling, or sautéing. Additionally, there are many ways you can reduce the amount of nutrients lost when cooking. 

The study you mentioned noted that the broccoli was immersed in a large amount of water when it was cooked. Using a large amount of water when cooking could be the reason for such a high proportion of the antioxidants being destroyed, as the nutrients likely leaked out into the water while being cooked. Other studies have shown that when broccoli was cooked in the microwave with no water, the degree of antioxidant loss was much lower. Thus, the key ingredients for preserving antioxidants and other nutrients seem to be a shorter exposure time to heat while using as little water as possible. In that case, microwave cooking can be better than other methods of cooking, as it cooks food quickly and therefore reduces the time the food is heated. Other tips to keep the nutrients intact during cooking include: 

  • Leave vegetables in big pieces so less surface area, and therefore less nutrients, are exposed. 
  • Cover your container to hold in heat and steam, which will reduce the cooking time. 
  • If possible, avoid peeling the vegetable, as many nutrients are in the peel itself or just below its surface. 
  • Use a timer to make sure you don't overcook your vegetables; take them out when they are crisp and tender. 

If you’re really concerned about getting enough antioxidants, you can also stick to choosing fruits and vegetables that you can eat raw, such as carrots, tomatoes, or cucumbers, or simply eating more of them in a variety of preparations (microwaved, raw, boiled, steamed, sautéed, etc.). Not only is variety the spice of life, but it's also the best way to make sure you get all the antioxidants you need. Bon appétit! 

Last updated May 14, 2021
Originally published Jun 06, 2008

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