Diet Sodas
I do occasionally but I don't like them much so not often.
They cannot stretch your pouch, although it seems to be a pretty popular misconception.
There are two openings to your pouch, one at the top and one at the bottom. LIquids, including soda, doesn't stay in your pouch more than a minute or two. Even while it's in there, the gas from the carbonation cannot build up and stretch the pouch because there are two openings from which the gas can escape.
If you want to do an experiment, open a bottle of soda, put a balloon on the top, and then snip a small hole in the top of the balloon. Then give the bottle a gentle shake. If you do the same experiment without snipping the top of the balloon, that balloon would fill up with gas from the carbonation in the soda. That's what would happen if you didn't have two openings in your pouch. But since you do have two openings, nothing will happen because the gas can get out.
Kelly
Please note: I AM NOT A DOCTOR. If you want medical advice, talk to your doctor. Whatever I post, there is probably some surgeon or other health care provider somewhere that disagrees with me. If you want to know what your surgeon thinks, then ask him or her. Check out my blog.
No, the sleeve has a pyloric valve at the bottom, where the small intestine connects. It's just like a "normal" stomach. I don't see how soda would be any more likely to stretch out a sleeve than it would a non-WLS stomach, but it does not have two openings like a RNY pouch does, just one.
Kelly
Please note: I AM NOT A DOCTOR. If you want medical advice, talk to your doctor. Whatever I post, there is probably some surgeon or other health care provider somewhere that disagrees with me. If you want to know what your surgeon thinks, then ask him or her. Check out my blog.
I have one more days than not (at 6 years out).
As Kelly explained, it is physically impossible for enough pressure to build up in your pouch to stretch it. That is an urban myth perpetuated by surgeons and nutritionists who use it as a scare tactic to get patients to give it up. It isn't a very healthy choice of beverage (nothing but chemicals, may trigger urge to eat for some people, may contribute to problems with calcium, etc.), but it angers me that doctors lie to try to manipulate patients rather than telling patients the truth and allowing them to make their own decision.
Lora
14 years out; 190 pounds lost, 165 pound loss maintained
You don't drown by falling in the water. You drown by staying there.
I'll admit, I'm still hooked on my Diet Coke. I gave it up for about 6 months after my surgery, but I still drink one or two cans a day now. I know it's not healthy, but I mixed it with ice so it's a little watered down (less fizzy), and I can only sip and burp, sip and burp. :) It doesn't stretch the pouch, but I should really be drinking more water instead.
I gave up Diet Coke for 4 1/2 years and started drinking it again a few months ago. I have no problems drinking it when I feel like it and love it on a hot day. They do not stretch your pouch, mine is still small and tight.
Martha 
High 250/Consult Weight 245/Surgery 205/Now 109
Height 5'4.5" BMI 18.4
In maintenance since June 2009
I gave up my go-to diet soda until a few weeks ago (I'm 6 months out). I drink a bunch of it each day, along with other fluids. I find that I can get much more fluid in me if it is in the form of diet soda, than say, water (even if flavored with Mio, etc.) No stretching here, and no significant weight-loss slowing either.
HW: 274 | SW: 232 | CW: 137 | Goal: 145 (ticker includes a 42 pound loss pre-op) | Height: 5'4"
M1: -24 (205) | M2: -14 (191) | M3: -11 (180) | M4: -7 (173) | M5: -7 (166) | M6: -8 (158) | M7: -11 (147) | M8: -2 (145) | M9: -3 (142) | M10: -2 (140) | M11: -4 (136) | M12: -2 (134) | M13: -0 (134) | M14: -3 (131) | M15: +4 (135) | M16: +2 (137)
