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.













