After looking at the Kellogg's website I still wasn't sure their Protein Shakes were safe, so I emailed them. A couple days later here is their response!
Thank you for contacting us to request information about our products that do not contain gluten.
Yes, our Special K20TM Protein Water Mixes and Shakes would be considered as gluten free. They do not have any gluten containing ingredients in them at all.
Kellogg is aware that many consumers need special dietary foods, especially those with celiac disease. Unfortunately, at this time, we do not offer any bars, cookies or crackers formulated to be gluten free.
In addition, we are continuing to explore the possibility of offering other products that are formulated to be gluten free. You may also wish to try some of the other products listed below:
Kellogg's Rice Krispies Gluten Free Cereal
Kellogg's Fruit Flavored snacks
To determine if a product will fit into your specific dietary preferences, please visit www.kelloggs.com. Please let us know if we can assist you further by calling.
I'm always amazed when a big company takes time to actually response to customer emails and tweets.
I know they market their shakes to be weight loss aides, but they can be useful for getting good protein and fiber.
With the confidence that they were safe I went out today and bought some Strawberry flavored protein shakes. And I have to say it was pretty tasty! It did fill me up for longer that 20 minutes (my current hunger rate) and had a bunch of good stuff in it for me and the twins. I can see continuing to drink them once the babies arrive to keep my calories, protein, and fiber up while nursing.
So in case you where wondering: YES Kellogg's Special K Protein Shakes are Gluten Free!