Wednesday, February 1, 2012

Cruciferous Mini Chemistry Lesson


I was at the doctor yesterday and got a question by text about whether green smoothies were unhealthy and I was completely perplexed why anyone would think that.  Sure you can make an unhealthy green smoothie by loading it up with fruit and eliminating the kale and adding a little spinach instead. However the person who asked this question is a fan of healthy green smoothies with kale so I knew something was up.  We texted back and forth for a while and I called her and we talked about it and got everything cleared up. Once I got home the email questions started flooding in and that was when I knew I had really needed to write this post for everyone who was confused but didn’t have anyone to ask about this. So much for my day off, darn it!  *ugh*

I make my green smoothies with kale for a number of reasons but the primary one is that kale is the most nutritious raw and I think works well in smoothies from a flavor perspective.  However kale (like all cruciferous veggies) is generally more nutritious when eaten raw which I will explain so that you understand the process and aren’t confused the next time someone writes something to the contrary. When I first heard about this controversy the first thing I thought of was the comment I wrote yesterday about being careful what you read in popular books, clearly the same thing goes for what you read on blogs.

All vegetables contain protective micronutrients and cruciferous veggies are no exception.  If you were to look at the cells of kale under a microscope you would see each one contained a number of separate items included myrosinase (enzyme) and glucosinolates (organic compound) inside a vacuole (membrane). Think of myrosinase and glucosinolates like chickpeas and tahini before they are combined into hummus. When kale leaves are intact (whole) the myrosinase is physically separated from the glucosinolates. (1)  However in order for the cruciferous veggies to form indoles and isothiocyanates the myrosinase and glucosinolates need to be combined. (1) They can be combined by blending, chopping or chewing. (2)  Obviously blending does a more complete job of breaking down the cell walls releasing the maximum amount of myrosinase so it can combine with the glucosinolates.  However it is also important to know that myrosinase is inactivated by heat (cooking) (3).  If you cook whole or roughly chopped kale you are getting significantly less of the indoles and isothiocyanates (ITCs) because of the reduction in myrosinase.  The human digestive tract does have some myrosinase activity but the absorption of the ITCs is substantially lower for cooked cruciferous veggies according to numerous studies. (4)  Glucosinolates are water-soluble so boiling is not a good way to prepare cruciferous veggies. (5)  Boiling (2), steaming (3) and microwaving (6) are thought to completely inactivate myrosinase making the cruciferous vegetables far less nutritious.

Why should we care about our absorption of ITCs?  ITCs are critical for optimal human health since they not only kill cancer cells (7) but they remove carcinogens in both the phase I and II processes. (4) Additionally ITCs are anti-inflammatory (8), induce cancer cell-cycle arrest (7) and have been shown to eradicate H. pylori (9) (a major cause of stomach cancer). A better question might be why wouldn’t you want to absorb as many ITCs as you possibly could?

Why do we need indoles?  In the acidic environment of the human stomach indole-3-carbinols (I3Cs) combine to form acid condensation products (10) which include:  dimer 3,3’-diindolmethane (DIM) and cyclic trimer (CT).  The biological activity of DIM and CT differ from I3C but I3C is typically credited for the effects.  Both these (DIM and CT) form to a lesser degree when myrosinase has been inactivated by cooking. (11)  I3Cs have been found to inhibit estrogen activity and thereby are thought to decrease estrogen-sensitive cancers (think breast and prostate). (12)  Additionally I3Cs also have anti-angiogenic (13) properties (stop the growth of blood vessels to cancerous tumors) and they induce cell death (14) (apoptosis).  I3Cs have been shown to eradicate precancerous cervical lesions in some women. (15)  I don’t know about you, but I say bring on the I3Cs and as many as possible which means more raw cruciferous vegetables please.

First, I apologize for all the endnotes but when something is put out without any backup I worry that no one will have any confidence in the information that is being provided. I will not be boring you with endnotes often going forward but I thought it was necessary in this post.

Here is the bottom line for me.  Consuming cruciferous vegetables is important for our health.  Based on the science I have read blending raw kale is not only healthy but is the healthiest way to consume your kale.  As with everything else I will continue to stay current on the latest science on this topic and if anything changes I will let you know. Until I see scientific research that tells me that raw pureed kale is unhealthy I will continue to enjoy green smoothies (made with copious amounts raw kale I might add) most days of the week.  Dan and I both had green smoothies for breakfast this morning if you are curious.  ;-)

Endnotes:

1.       Holst B, Williamson G.  A critical review of the bioavailability of glucosinolates and related compounds, Nat Prod Rep 2004; 21(3):425-447

2.       Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talay P. Chemoprotective glucosinolates and isothiocyanates of broccoli sprouts:  metabolism and excretion in humans.  Cancer Epidemol Biomarkers Prev 2001;10(5):501-508

3.       Conaway CC, Getahun SM, Liebes LL, et al.  Disposition of glucosinolates and sulphoraphane  humans after ingestion of steamed and fresh broccoli.  Nutr Cancer 2000;38(2):168-178

4.        Lampe JW, Peterson S.  Brassica, biotransformation and cancer risk: genetic polymorphisms alter the preventive effects of cruciferous vegetables. J Nutr 2002; 132(10):2991-2994

5.       McNaughton SA, Marks GC. Development of a food composition database for the estimation of dietary intakes of glucosinolates, the biologically active constituents of cruciferous vegetables. Br J Nutr 2003;90(3):687-697

6.       Rouzan G, Young SA, Duncan AJ. Hydrolysis of glucosinolates to isothiocyanates after ingestion of raw or microwaved cabbage by human volunteers. Cancer Epidemiol Biomarkers prev 2004;13(1):125-131

7.       Zhang Y.  Cancer-preventive isothiocyanates:  measurement of human exposure and mechanism of action.  Mutat Res 2004;555(1-2):173-190

8.       Heiss E, Herhaus C, Klimo K, Bartsch H, Gerhauser C.  Nuclear factor kappa B is a molecular target for sulforaphane-mediated anti-inflammatory mechanisms. J Biol Chem 2001;276(34):32008-32015

9.       Galan MV, Kishan AA, Silverman AL.  Oral broccoli sprouts for the treatment of Helicobacter pylori infection: a preliminary report. Dig Dis Sci 2004;49(7-8):1088-1090

10.   Hertzer HG, Senft AP. The micronutrient indole-3-carbinol:  implications for disease and chemoprevention.  Drug Metabol Drug Interract 2000;17(1-4):159-188

11.   Shapiro TA, Fahey JW, Wade KL, Stephenson KK, Talalay P.  Human metabolism and excretion of cancer chemopreventive glucosinolates and isothiocyanates of cruciferous vegetables.  Cancer Epidemiol Biomarkers Prev 1998;7(12):1091-1100

12.   Jordan VC, Gapstur S, Morrow M. Selective estrogen receptor modulation and reduction in risk of breast cancer, osteoporosis, and coronary heart disease. J Natl Cancer Inst 2001;93(19):1449-1457

13.   Chang X, Tou JC, Hong C, et al.  3,3’-diindolylmethane inhibits angiogenesis and the growth of transplantable human breast carcinoma in athymic mice.  Carcinogenesis 2005;26(4):771-778

14.   Chinni SR, Li Y, Upadhyay S, Koppolu PK, Sarkar FH.  Indole-3-carbinole (I3C) induced cell growth inhibition, G1 cell cycle arrest and apoptosis in prostate cancer cells. Oncogene 2001;20(23):2927-2936

15.   Stanley M, Chapter 17: Genital human papillomavirus infections-current and prospective therapies.  J Natl Cancer Inst Monogr 2003;31:117-124

How to Make a Healthy Green Smoothie:

Making a healthy green smoothie is easy and you all know what I am going to say based on what you see me prepare. First include a lot of raw kale in your smoothies.  Frozen banana added to the mix makes the smoothie creamy.   Including walnuts and flaxseeds for healthy fats assists your body to absorb the fat-soluble vitamins in the kale.  Cinnamon is also added to our green smoothies for additional antioxidants as well as flavor.  Vanilla is included because it smoothes out the sharpness of the greens allowing me to add much more of them to our smoothies.  You can also add frozen cherries and cocoa powder for flavor and antioxidants. That is how you make a delicious and healthy green smoothie.

Calories Burned Chewing:

This is just a side issue but I am mystified that anyone would believe chewing kale could result in 100 calories being burned.  *scratches head* It takes 1 mile, either running or walking to burn 100 calories and that is using the largest muscles in the human body.  Let’s think about that for a minute. If you walk a mile in 15 minutes you are using your legs and buttocks to generate movement and that burns 100 calories. The muscle mass of those muscles is what at least 100 times greater than your jaw muscles, and probably more? So that would imply that you would need to chew for at minimum of 1500 minutes (15 times 100) to burn 100 calories.  Since there are only 1440 minutes in a day I find it impossible to see how this math works.

Signing off:

I appreciate that so many of you wrote to ask me what I thought about green smoothies.  Your faith in my ability to cut through the controversy and give you the truth has really touched me.   I would prefer to give up my day off if it means that I can clarify things for you.  I wanted to include plenty of endnotes so that you could follow the science for yourself if you choose, or at least realize that this wasn’t just “my opinion on the matter” but rather there is hard science which backs up everything that I wrote.  Now I am going to try to enjoy the rest of my “day off”. 

If you ever see anything that confuses you in the future just ask me. If I don’t know the answer I will do my research and find out for all of us.

22 comments:

  1. Thank you SO MUCH for your insights on this. The "Green Smoothies are not good" take comes from Dr. T. Colin Campbell and others and so it had me very confused. Perhaps they should define a "green smoothie", maybe they are talking about something other than what I make (which is similar to yours).

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    1. Elizabeth,

      You are very welcome. I got so many email questions about this I knew I had to write it. I don't read Happy Herbivore (nor did I read her post on this) but I have to say I am completely shocked that Dr. Campbell would say that. I feel like it must have been taken out of context or based on how "green smoothies" were defined like you said. Everything that I have seen tells me that raw blended kale is the most nutritious way to eat kale. I know that some people don't find green smoothies to be filling and that could cause them to eat something in addition to the smoothie which could cause weight gain. But otherwise I can't even guess why a green smoothie made with a lot of kale and a little fruit would be unhealthy.

      Thanks for letting me know this helped,
      Ali

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  2. Thanks so much for your post on this. I was quite surprised and perplexed when I read Happy Herbivore's post. Burn 100 calories while chewing? I also scratched my head.

    Speaking of cruciferous vegetables, have you heard of DIM (diindolylmethane) supplements? If so, what's your opinion of them? http://www.dimfaq.com/site/toc.htm

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    1. Kaitlyn,

      Sometimes you read things and they just don't add up. Burning 100 calories chewing is one of those times.

      They make supplements for almost everything. IMO it is always better to get our nutrition from food. There is a lot that science doesn't know about how different phytochemicals interact. For all we know DIM may require a number of other phytochemicals in order to be absorbed and therefore the supplement isn't doing anything. Also supplements are most often a man-made version of the naturally occuring item and those tend to not be well absorbed. I guess you can tell I am not a big fan of supplements in general. Thanks for the question, I am sure you aren't the only one who was wondering about that.

      enjoy the rest of your evening,
      Ali

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    2. Thanks for the reply - I also meant to say thanks for so many wonderful posts throughout the month on January! They were all so very thorough. You could write a book! :-)

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    3. Thanks Kaitlyn,

      That is very sweet of you to say. :-) I am happy to hear that you enjoyed them.

      Ali

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  3. I know I've never commented before but I've been reading your blog for over a year at least now! Anyway, I watched as this whole controversy blew up yesterday over Twitter and Facebook, and just wanted to say THANK YOU for being a voice of reason here. It's so comforting to know that I'm not crazy! I'm very grateful for your thorough, level-headed, and fact-based approach.

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    1. Hello Hannah,

      I heard about the controversy blowing up on Twitter and Facebook and was in shock. Not being a fan of drama I wasn't certain what to make of it initially. When I starting getting emails asking me if they should throw out their blender I knew things were out of control. I study nutrition every day and I haven't seen any science that would indicate raw blending kale is in any way unhealthy.

      thanks so much for commenting and letting me know that you agree, it is comforting not to be alone on this,
      Ali

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  4. THANK YOU!!! This was such a relief to read. I'm 11 weeks pregnant, and even though I loved eating steamed vegetables before I got pregnant, now I can't stand them! The only way I've been able to get my greens in is by eating them in green smoothies (and I don't include a lot of fruit in my smoothies). I was a little confused because it usually takes me an hour or more to finish a green smoothie, and then I'm full for several hours afterward--definitely not something I just suck down in a few minutes and then feel hungry an hour later.

    But I'm sorry that you had to do this on your day off. :( Still, I'm incredibly appreciative of your thorough and scientifically-back response to the whole thing. Thanks again!

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    1. Sarah,

      You are very welcome. Raw blended kale is more nutritious than cooked from everything I have read on the subject. It takes me a while to drink a smoothie too and they keep me full for 4 or 5 hours. Also my hubby has forgotten to fast and had smoothies before blood tests and his blood glucose was 103 approximately 45 minutes after the smoothie which told me they weren't elevating his glucose since his fasting level is usually upper 70s or low 80s.

      Please don't be sorry, I would much rather have done this since I knew people were confused. I got over 20 emails asking me about it and could only imagine how many people wanted to know but didn't know who to ask. If you ever have another question please feel free to ask. I am happy to help anytime. Research is something that I enjoy, so if I don't know the answer I like the search for it.

      congratulations on your pregnancy,
      Ali

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  5. I'd like to add to the "thank you!" club! I won't pick on her, but I KNOW I can trust your endless research and knowledge. I've changed a lot of things since starting to read your blog, and will continue to do so ;-)

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    1. sgcorrie,

      You are very welcome! If you ever see anything and aren't sure what to believe please ask. I am happy to help any way that I can. Awwww, thank you so much! It is very nice to hear that I have helped. :-)

      enjoy the rest of your evening,
      Ali

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  6. Another "thank you" from me, too! I thought her whole post (and many of her others, actually) was total bollocks, so it's good to have it confirmed here. I prefer spinach in my smoothies to kale, partly for texture, but partly because I really don't like spinach by itself but love kale. Blending it is one of the only ways I can convince myself to eat spinach. :)

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    1. Brigid,

      Thanks! You know I love your honesty, right? :-)

      If you are going to cook your kale just be sure to cut it up finely (I usually shred it) so that the myrosinase can combine with the glucosinolates before the heat destroys the myrosinase and you should be fine.

      Have you ever tried shredding the spinach and then adding it to soup or salads? Also you could make salads with some spinach but also include other greens that you do like. I enjoy putting raw spinach in the bottom of my soup bowl and covering it with hot soup to wilt it. My favorite use of spinach is probably in savory oatmeal? Have you given that a try? Then there is the way they make spinach at Jaleo which is lightly wilted with garlic, golden raisins and green apple. I bet one of those might work for you. ;-)

      enjoy your weekend,
      Ali

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    2. I'm nothing if not honest! :)

      Salads are the only other way I like spinach, and it has to be the raw baby stuff. I don't like the slimy texture it gets when wilted or heated in any way (except if finely chopped in curries or ravioli). I like most other greens raw or wilted, though. Maybe the answer is to stop buying spinach and switch entirely to kale, chard, etc.

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    3. Brigid,

      You are definitely honest and I love that. :-)

      It does sound like maybe you need to stop buying spinach except for salad. I am not crazy about if it is cooked more than about 30 seconds myself so I understand. Sounds like the texture bothers you more than me though.

      talk with you later,
      Ali

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  7. Awesome post Ali!

    I love the citations - it's so refreshing and important on issues such as this.

    From everything that I have read, many of the fruits we do add to a green smoothies are nutritious power houses - blueberries, strawberries, cherries - I don't think anyone could overdo them at the rate of a cup of berries in a huge blender of greens and banana! I could never eat as much kale or fruit at a time if I just ate it raw. Blending allows one to maximize the nutrition.

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    1. Thanks Possum (N),

      After all the controversy I felt like I had to write this. I thought the references waere necessary this time, but don't expect to see those often since it takes a lot longer to write using them.

      I agree with you on the issue. When I make green smoothies I get more kale and more berries and both are good for you. I am guessing that the issue was too much fruit, not enough kale and that resulted in too many calories. Since most people are overweight in North America excess calories becomes a big issue. But that is only a guess since the original post didn't provide any "real information" to back up why green smoothies weren't healthy. I don't respond very well to "change because I told you to" without knowing why.

      hugs,
      Ali

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  8. THank you, you inspired me to make a smoothie (er. instead of dinner, haha). 2 kale leaves, 2 collard leaves, some almond milk, blueberries and a banana and two drops of stevia. It was delicious! I like your side bar traffic viewer...a lot of people view your blog! Wow!

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    1. Hi Steph,

      We have smoothies for dinner sometimes too, they are great when you don't feel like cooking. ;-) Great minds think a like. I love the sound of your smoothie BTW.

      The traffic viewer on my blog is the free version. Follow the link from my blog to install it on yours. Dan is always shocked by the traffic the blog gets, and I have to say I am a bit surprised too. It is interesting to see all the different locations of readers.

      talk with you later,
      Ali

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  9. Ali, thanks for the well-researched article. I am hypothyroid and have always read that I should avoid raw kale and spinach because of their "goitergenic" qualities. What are your thoughts on this? Thanks!

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    1. No Food Diet,

      Sorry for the delay in my response, life has been busy and I wanted to research my answer before I replied. Raw kale is part of the cruciferous family and as such does contain goitrogens which are inactivated by cooking. However I haven't seen anything that indicates raw spinach is an issue. Also I would suggest that you check with your doctor since everything that I read referred to "untreated" thyroid problems which I assumed isn't you. Other foods which are goitrogens and not in the cruciferous family which you should know about include: millet, peanuts, pine nuts, and soy beans. Additionally have you had your iodine level checked? If you live in the midwest this population has more trouble with iodine deficiency. Since iodine is required for the thyroid to create hormones that would be something I would look into if I were you.

      I hope that helped,
      Ali

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