What if Diet Soda Wasn't Diet?

Ideas are cheap, actually pulling off the experiments is the difficult part. Sometimes these experiments aren't even possible to do at the present time. I'm probably not the only one who has a running list of experiment ideas in a text document, many of which will never see the light of day. I'm going to start something new around here by posting about research/experiment ideas that I think would be interesting and informative, but which I have absolutely no time to carry out right now (however, if you're up for collaborating definitely shoot me an email!). I'm naturally curious, so it would give me great pleasure to see SOMEONE figure out the answers to these observations or actually carry out experiments. Hell, someone might have even already done the experiments (if so, please send me a link in the comments!). Use these posts for inspiration or even just to get a feel for how I think about science, especially if you're keen on being my grad student or postdoc in the future. Point is that ideas are cheap but my mind keeps grinding. So without further delay here's where it goes sometimes...

Since my undergraduate days I've had a thing for "diet" drinks. Soda, fruit juice, etc...I always go for the "light" version. First it was the deliciously aspartame-filled Diet Coke (I definitely don't have phenylketonuria) and I've since transitioned into deliciously sucralose-filled products. Supposedly, drinking diet products can help you shed weight (see here but also here). Diet soda et al. have no calories because they contain artificial sweeteners that can't be metabolized by your body. I've always believed this, I could be completely wrong but this seems right. Relevant to this story, it does seem as though drinking diet soda can actually make you gain weight and can increase the incidence of type II diabetes (Hmmmm...)

Here's the thing. Your body is also teeming with microbes, especially in your digestive tract, billions of them. Some of these can even aid digestion by breaking down products. If there is one thing I know that microbes are good at, it's adapting to use novel resources. Unexploited potential energy sources are just another niche that microbes can thrive in. I don't see why microbes can't break down, or easily evolve to break down, aspartame, sucralose, and Truvia.

So here's a couple of potential experiments. I'd like to take some gnotobiotic mice, as gut flora may influence their weight. In the lab I'd adapt a suite of common gut microbes to growing on one of the artificial sweeteners. Then I'd transplant these bacteria back into the gnotobiotic mice in one group, and "ancestral" bacteria that can't break down the sweetener into another group. Next I'd feed different groups of mice a diet supplemented with one of the three sweeteners (as well as a regular control diet). The null hypothesis in this case would be that there will be no different in weight gain attributable to evolved vs. un-evolved microbes. A second experiment is really just a converse of the first. Basically I'd feed mice with "normal" gut flora a diet supplemented with one of the three sweeteners or the control diet with none. Then I'd measure if the ability of gut microbes to digest the artificial sweeteners changes over time.  Null hypothesis here is that there would be no change in the microbe's abilities to break down artificial sweeteners over time.

So that's the outline. Thoughts? Has this been done? If someone does this will the artificial sweetener industry put a hit out on them?

UPDATE: Thanks for the input folks! Definitely understand now that there is much less artificial sweetener in diet soda than regular. Maybe not the best example, but, doesn't change the thought experiment. I know people who replace regular sugar with sucralose or Truvia in coffee and baking. They use the exact same amounts so, plus or minus differences in the molecular formulas, there's roughly the same potential mass going in.