Does cooking kill the nutrients in food? Specifically broccoli? If so, how much cooking and at what temperature? And, isn't microwaving the worst way to cook it? Doesn’t microwaving kill all the nutrients? And what about storing broccoli in the refrigerator?
These are all questions I get all the time from clients and patients. And, when I tell them the answer found in most studies, it is as if they don’t want to hear the answer and just want to go on believing in myths.
So, what is the answer?
Researchers at both the Warwick Medical School and the Department of Chemistry at the University of Warwick investigated these very questions and published their results this week in the journal Food and Chemical Toxicology. The researchers bought broccoli, brussels sprouts, cauliflower and green cabbage from a local grocery stores and took them to the lab within 30 minutes of purchasing them. They then investigated the effects of cooking by several methods; boiling, steaming, microwaving and stir-frying, to test the effects on the loss of glucosinolates, which are cancer protective substances.
Steaming for 0-20 minutes, microwaving for 0-3 minutes, and stir-frying for 0-5 minutes resulted in no significant loss of the glucosinolates. Even microwaving produced no significant nutrient loss.
In regard to storage, storing the vegetables at either room temperature or in a refrigerator for seven days also had no significant effect on the nutrients.
However, when the vegetables were boiled for 30 minutes, there was significant loss of glucosinolates content: 77% on the broccoli, 58% in the brussels sprouts, 75% in cauliflower and 65% in the cabbage. But, almost all of the loss of the glucosinolates (approximately 90%) were found in the cooking water. So, you can avoid the loss of these nutrients by either drinking the cooking water or adding it to soups.
More importantly, keep in mind, that these reductions were found in the vegetables only after boiling them in water for 30 minutes!
Hopefully, no one, with the exception of our British researchers, is boiling broccoli for 30 minutes.
We don’t need a study to tell us that boiling broccoli for 30 minutes, has a negative effect.
So, bottom line, do not worry about conservatively cooking (low heats for a short period) your vegetables and food.