Thursday, February 5, 2009

What's in kale? Glucosinolates

(Photo: 2008 Farmers' Market purchase of irises, kale, lamb's quarters, and spinach.
Yes, spring is coming!)


One reader asked a good question. Is there a difference in indole-3-carbinole content of brassica vegetables when comparing light-colored ones like light green cabbage to dark-colored ones like dark green kale?

Most likely yes, however, I like to think of the 3-V's of good eating as "variety, variety, variety". :-) Researchers have hardly begun to really examine all the molecules in our foods that are first there for the plants natural defenses against insects, herbavores, viruses, and other plant pathogens and secondarily, also help promote our good health when eating them. So, what I am saying is don't get stuck eliminating one entire food based on its content of just one molecule. A general rule of thumb is that darker is better, but that thinking would incorrectly minimize the many benefits of consuming garlic, onions, leeks, and cauliflower, just for starters.

Indole-3-carbinole (i.e., I3C - the molecule I discussed in a previous blog post) in kale and other brassica vegetables is a metabolite made in these vegetables from a large group of ~120 parent compounds called glucosinolates. Thus, to just think about the content of I3C in vegetables is potentially missing a big part of the picture. I3C may be getting a lot of attention right now, but it may only be a small part of the 1,000 piece jigsaw puzzle.

The Linus Pauling Institute website has a great chart showing the overall analysis of total glucosinolate content of several brassica vegetables (you can see this list is not complete).

Glucosinolate Content of Selected Cruciferous Vegetables (90)
Food (raw) Serving
Total Glucosinolates
(mg/g of food)
Garden cress ½ cup (25 g)
3.9
Mustard greens ½ cup, chopped (28 g)
2.8
Brussels sprouts ½ cup (44 g)
2.4
Horseradish 1 tablespoon (15 g)
1.6
Kale 1 cup, chopped (67 g)
1.0
Watercress 1 cup, chopped (34 g)
0.9
Turnip ½ cup, cubes (65 g)
0.9
Cabbage, savoy ½ cup, chopped (45 g)
0.8
Cabbage, red ½ cup, chopped (45 g)
0.6
Broccoli ½ cup, chopped (44 g)
0.6
Kohlrabi ½ cup, chopped (67 g)
0.5
Bok choi (pak choi) ½ cup, chopped (35 g)
0.5
Cauliflower ½ cup, chopped (50 g)
0.4


The optimal intake of of glucosinolates is simply not known. Although I3C is now available as a dietary supplement, I do not recommend its use in that form until much more is understood about its "solo" action, which is in essence as a drug. There have been a few studies actually showing increased cancer development in animals who were given isolated I3C and then implanted with cancer cells. These few studies are difficult to interpret into "real world" recommendations. However, consuming whole foods within whole meals is and has been "real world" for a long time and is a far safer way to get multiple essential nutrients plus health promoting phytochemicals that are acting from within the entire "real world" matrix of consumption, digestion, absorption, and metabolism. Aim for 1 serving of kale or a different brassica vegetable each day.

In future posts, I will discuss food preparation techniques and the various effects of boiling versus steaming, etc, on the bio-availability of these components of kale and other brassica vegetables. So, stay tuned and keep checking back (or subscribe to a "feed" for this blog - easy instructions on the right side of my blog)!

Thanks for the great question, Buttercup!

Where kale is more than decoration on my plate,
Diana Dyer, MS, RD

3 comments:

Buttercup said...

So Brussels Sprouts are high in the good stuff! You just convinced me to try growing them again this year. I find them more accessible on a day-to-day basis than kale, though I like kale.

Diana Dyer said...

My husband had to teach me to like Brussels sprouts, a dislike left over from childhood. Now I love, love, love them, especially oven-roasted with a little olive oil. They are also superb just poached with a tiny bit of milk added to water, which completely dissipates any bitter flavor. They are so much fun to grow and harvest!

Kateri said...

The bunch of lambs quarters made me smile. My garden in michigan had no lambs quarters, so one time when I was home on my parents farm I took a cup of soil to throw around in my garden hoping to get lambs quarters to grow. It worked. I know have them. I have always liked them better than spinach.