Dear Dr. Blonz, In our house, broccoli is a go-to vegetable due to its availability and relative low cost. I prepare the stems as well as the florets, cutting the stems in diagonal disks so they can get tender when steamed. I am guessing there is less nutritional value in the stems than in the darker florets. How significant is that difference? I.K. Gilroy, CA
Dear I.K.: Broccoli is a member of the crucifer family. Other members of this healthful group include cauliflower, Brussels sprouts, kale, bok choi, turnips, rutabagas and cabbage. All of these contain a number of healthful phytochemicals, but broccoli is high in vitamins A and C and is also a source of vitamin K and dietary fiber.
It also contains sulforaphane, which has been reported to have cancer-fighting properties. Young broccoli sprouts and seedlings are the richest source of the sulforaphane, but the florets are next best. The fibrous stems contain less of the nutrients and phytochemicals, but are a great source of dietary fiber. Your method of preparation allows you to have it all. An item of interest regarding broccoli is that there is an enzyme in the broccoli that helps the sulforaphane form. When the cells are ruptured, such as during cutting, mashing or chewing, the enzyme goes to work, but it can be inactivated by heat. This means uncooked or quickly cooked broccoli will offer more sulforaphane than broccoli that has been overcooked.
Dear Dr. Blonz, I read your column every week and also love all the advice that you give on your website. I read the column about the cooking methods and destruction of vitamins, especially the water-based vitamins. My question is this: I love mixing all kinds of vegetables and making mixed veggie soup. The vitamins of the vegetables that have been ruined -- are they in the broth of the soup, or they are completely gone? Does any percentage of them stay in the broth? Though I love raw vegetables, my digestive system cannot handle the raw fiber, but if I cook them and eat the soup as well, then I am OK. So I hope that I do get some nutrients. Thank you very much. A.S. Oakland, CA
Dear A.S.: There can be losses when there is destruction by heat. In such cases there will less of the heat-labile nutrients once a key temperature has been exceeded for a period of time. (As with the broccoli answer above, longer times equal greater destruction.) There can also be nutrient losses through dilution if the nutrients are water-soluble and the portion that ends up in the cooking water is not a part of the meal. Minerals tend to be heat-stable, but depending on the form they are in and how the food is prepared, some can be lost with the cooking water as well.
It is difficult to come up with specific percentages that remain, but if you eat a healthful, varied diet, I don’t recommend you be overly concerned about these losses. There are usually other foods that provide these nutrients, and oftentimes these other foods represent the primary sources. For example, cooking vegetables may destroy their vitamin C, but it is fruits, not vegetables, that tend to be the major source in most diets. Your vegetables and soup combination sounds wonderful, so don’t sweat the small stuff.
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