Might be part of the reason diet soda drinkers gain more weight.

It's hard to understand the Nature article -- they use a lot of big words -- but the gist is this: "Preliminary findings indicate artificial sweeteners can impair glucose metabolism, a warning sign for type 2 diabetes, by changing the composition and function of the microbes in our guts."

Read more:

https://sciencenews.org/article/artificial-sweeteners-may-tip-scales-toward-metabolic-problems

That article has a fascinating picture of the microbes -- they look like filaments:

From that article:

“This is the home run experiment,” says immunologist Cathryn Nagler of the University of Chicago. “It’s telling you that it is some change in the bacterial community that is detrimental.”

...

“We have to respect the power of the microbiota,” she says, “We need to step back and see what we are doing.”

This finding just made it onto Reddit too:

http://reddit.com/r/science/comments/2gom1b/preliminary_findings_indicate_artificial/

another in the chain......

The chain of stories saying not to drink things with artificial sweeteners?

yup

I'm beginning to believe that all sweet things are bad for us. 

Berries are good for us!

Not all berries! Some berries are poisonous!

Also, make sure you're eating real berries, not processed berry product:

http://cracked.com/article_19433_the-6-most-horrifying-lies-food-industry-feeding-you_p2.html

Just a few thoughts: 1. The majority of the data was done on rats with three various sweeteners - saccharine, aspartame, and sucralose. 2. Tying it to humans, there was an observational portion looking at food questionnaires and relationship of artificial sweeteners and metabolic syndrome. Thus, no proof of causation. 3. There was then a portion looking at 7 people who don't usually ingest artificial sweeteners. They report that 4 out of the 7 people developed worse glucose tolerance (with saccharine). I can't seem to find the actual data of glucose tolerance, all I see is a small graph in the paper and not the numbers to really depict this - maybe I am blind. All in all I would be cautious of viewing this in such a negative light and resort to drinking regular soda (or adding sugar to food instead of artificial sweeteners). This data is so preliminary it is really only useful for  hypothesis generation.

Well hold up, people: here is a thoughtful response to the study:

http://www.slate.com/articles/health_and_science/medical_examiner/2014/09/artificial_sweeteners_and_obesity_did_america_get_fat_by_drinking_diet_soda.html

Thanks for this link HB. Clearly still an area of hot debate. 

Re-reading this article it is clear to me that there's still so much we don't know.

"Perhaps diet soda doesn’t make us fat (at least at first), but only messes with our metabolism."