On NPR's Science Friday yesterday, Ira Flatow interviewed Susan Swithers, Professor, Behavioral Neuroscience, Purdue University, (PhD from Duke), and author of an "opinion paper" published in the journal Trends in Endocrinology and Metabolism with the following thesis: artificial sweeteners may change your brain's sweetness pleasure centers and cause "metabolic derangements." (The abstract of the paper, entitled "Artificial sweeteners produce the counterintuitive effect of inducing metabolic derangements" is here and the full text is here.)
Here are excerpts from the NPR interview, the full text of which and the audio as well are at the link in the first line of this post:
FLATOW: I'm very interested in what goes on in the brain, and reading your opinion paper and from scientific studies we have done in the past on this, it seems like your brain and your body sort of get confused about what's happening when they taste artificial sweeteners.
SWITHERS: Exactly. That's what we think is the big problem. So if we think about a world there are no artificial sweeteners, when we taste something sweet, it's often a sugar, and that means when the sweet taste hits our mouth, our bodies, our brains, based on this experience can learn to anticipate that calories and sugar are going to show up. And as a result, we'll start to produce changes, physiological changes, like the release of hormones and the activation of our metabolism so that we can deal with the arrival of those calories in that sugar. And we think that's kind of a learning process, and that helps us not only regulate how much we eat but also to keep our blood sugar in a more healthy range.
And now if you introduce an artificial sweetener, what you do is you get this very strong sweet taste in your mouth, but you don't get the consequences that normally ought to show up. No calories show up. No sugar shows up. And so your body will then adjust to that new reality by saying wait a minute, I've tasted something sweet. I have no idea what's going to happen. I'm not going to release those hormones, or I'm not going to release as many of those hormones. And that's what we really think the confusion comes from.
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[W]hat [the confusion is] doing is making it so that when people taste something sweet that does deliver sugar and calories, they don't have as strong an ability to deal with that. So they drink a regular soda or they eat a piece of fruit, anything that taste sweet and does provide the sugar and calories, and their bodies can't anticipate that those are going to show up. And if these physiological processes normally help us regulate things like food intake, then that's where you run into the problem. We eat a chocolate cake. We don't know what's going to happen. And so we end up with these negative outcomes.
* * *
[O]ne of the things that might be happening is that some of these same hormones that are released in response to sugar that help us regulate food intake are also implicated in helping regulate not only blood sugar but having cardio-protective effects. And one of the things we tried to do in this paper was to sort of use converging approaches, so looking not only at large epidemiological studies in people but use more basic research where we can get more directly at mechanisms.
And those studies, for example, have suggested that there's a hormone named GLP-1 that is thought to play a role not only in helping regulate blood sugar [ed.: think diabetes] but also in satiety [ed.: think obesity] and also to have cardio-protective effects. So if it turns out that these artificial sweeteners blunt the release of a hormone like GLP-1, then over the long term we're going to be losing out on those sort of protective effects.
The entire entire interview (which is very short) is well worth reading (or hearing).
Professor Swithers has done earlier work that indicates a link between artificial sweeteners and weight-gain.