Saturday, March 7, 2009
How should I eat my kale, raw or cooked?
How should I eat kale (and other brassicas)? Which way is best, raw or cooked? Is there any advantage or reason to eat it one way versus the other? As with all questions, there is rarely only one right answer. Life consists mostly of shades of grey, and the answer to this question is the same (only maybe it is shades of green and purple).
Several months ago, I signed up to receive all research articles published each week about Brassica vegetables in peer-reviewed journals. I have to say that I am rather surprised (pleasantly so) to see that 5-10 articles are published nearly every single week, thus I have accumulated a little stockpile of interesting articles to summarize on this blog that are relevant to eating these health-promoting greens. With 5-10 articles being published weekly, I don't think I'll run out of information to share!
In spite of my backlogged articles, I am choosing to summarize one I saw today, because it gets right to the heart of responding to the very practical question I posed at the top of this post. Raw versus cooked. That is an appropriate beginning. In subsequent posts, I'll explore what is known about the effects of different types of cooking on these vegetables, but for today, let's start at the very beginning.
Steam cooking significantly improves in vitro bile acid binding of collard greens, kale, mustard greens, broccoli, green bell pepper, and cabbage.
Nutr Res. 2008 Jun;28(6):351-7., Kahlon TS, Chiu MC, Chapman MH.
This study compared the vegetables listed above (which includes several Brassica vegetables) when raw versus when lightly steamed for their ability to bind to bile acids in a simulated human situation. Using a pharmaceutical drug to bind the bile acids after they are secreted by our gall bladder into our digestive tract is a strategy that has been used to lower serum cholesterol levels, reducing risk of heart disease.
Thus this study evaluated the effects of these various vegetables' ability to bind bile acids when prepared under different conditions (raw versus steamed) compared to the drug often used (cholestyramine). This study is of importance because bile acid binding potential has been related to lowering the risk of heart disease and that of some cancer. If we know which foods are able to lead to similar favorable outcomes as medications, a practical and easily achievable alternative strategy to the use of costly medications with potential side effects could be recommended.
Compared to the drug to cholestyramine, the bile acid binding was: for the collard greens, kale, and mustard greens, 13%; broccoli, 10%; Brussels sprouts and spinach, 8%; green bell pepper, 7%; and cabbage, 5%. Steam cooking significantly improved the bile acid binding of all the vegetables tested except the spinach and Brussels sprouts when compared with previously observed bile acid binding values by the same authors for these vegetables when raw.
Thus, while not as powerful as a drug (food rarely is when only looking at one isolated food or molecule within food versus a total diet and lifestyle), it is clear that including steam-cooked collard greens, kale, mustard greens (these three being the highest of those tested), broccoli, green bell pepper, and cabbage in our daily diet as health-promoting vegetables should be emphasized. These green/leafy vegetables, when consumed regularly after steam cooking, would lower the risk of cardiovascular disease. In addition, increased binding of bile acids in our digestive tract may also be associated with reduced risk of various cancers, thus recommending consumption of lightly steamed Brassica greens and other vegetables is certainly recommended for optimizing overall health.
I will continue to look for articles or information that can help answer the practical questions such as 'raw versus cooked'. At this point, my bottom line is still variety, variety, variety for both types of foods eaten and how they are prepared. Some methods may clearly be "out" (i.e., I remember a study a couple of years ago that microwaved broccoli in 2 cups of water ?? and found a dramatic reduction in nutrients, not an unexpected result with such a poor cooking technique, but of course that study got lots of press), however, my guess is that more ways will be in than out.
Enjoy your kale and other Brassica vegetables both raw and also lightly steamed. I always use a steamer basket, and I always save the small amount of water I used for steaming, putting it in the freezer to use for future vegetable stock. Hopefully, the majority of healthful nutrients that may have been leached out during the cooking process will still be unchanged and available when consumed at some point in the future.
Where kale is more than decoration on my plate!
Diana Dyer, MS, RD