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Not-So-Sweet Side Effects of Artificial Sweeteners


This is SCIENCE FRIDAY. I'm Ira Flatow. Diet drinks seem like the healthier way to have your soda and keep down those calories. But Susan Swithers, of Purdue University, says that these artificial sweeteners may change your brain's sweetness pleasure centers and cause, quote, "metabolic derangements." Her views appear in the opinion paper, in the journal "Trends in Endocrinology and Metabolism."

Susan Swithers is professor of psychological science at Purdue, and author of the opinion paper published in the journal "Trends in Endocrinology and Metabolism." And she joins us. Welcome to SCIENCE FRIDAY.

SUSAN SWITHERS: Thanks for having me.

FLATOW: Could you explain what you mean by metabolic derangements?

SWITHERS: So the goal of using the term metabolic derangements is to try to shift some of the focus about the effects of diet sodas from weight - overweight and obesity - to some of the other sorts of health consequences that we know are really important, like type 2 diabetes, cardiovascular disease and stroke. And all of those kind of metabolic derangements have been implicated in people who drink diet sodas.

FLATOW: I have to read to you the American Beverage Association - I'm sure you're getting a lot of pushback...


FLATOW: ...on this. So let me just read what - we got a statement from them today. It says...

This is an opinion piece, not a scientific study. Low-calorie sweeteners are some of the most studied and reviewed ingredients in the food supply today. They're safe and an effective tool in weight loss and weight management, according to decades of scientific research and regulatory agencies around the globe.

How do you react to that?

SWITHERS: So I have a couple of reactions. So the first is the use of the term opinion. This is a scientific journal that routinely publishes articles that they call opinion papers, including mine. These are papers that are solicited from scientific experts, and they undergo a rigorous peer-review process to make sure that what is actually stated in the papers is supported by the scientific literature. So this isn't my personal opinion. This is my expert scientific opinion, based on reviewing the past five years, the most recent relevant research on this topic.

And my second response is that the job of the American Beverage Association is to sell beverages; and the job of scientists, like me, is to understand what the consequences of people consuming those beverages are.

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 you think about a world where 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.

FLATOW: Does that make you want to have more of the sweet taste and drink more and more - and then maybe go to the carbs- because it's not getting what it thought it was getting?

SWITHERS: Well, we don't necessarily think that it's making people want more sweetener but instead, what it's 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 tastes 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.

FLATOW: So how - tell us about the connection between other risks, like heart disease and stroke, then.

SWITHERS: Well, there's - it's a little bit more difficult to know exactly what's going on, but one 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 but also in satiety, 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.

FLATOW: We always talk about, you know, something in moderation is OK. Would you agree, then, that artificial sweeteners in moderation are OK? Or should we eliminate them?

SWITHERS: That's one of those questions that's really tough to answer, partly because it depends on how you define moderation. For most of these big studies, the risks were highly apparent even in people who only consumed one diet soda a day - which doesn't actually seem like very much. And in some of the studies, the biggest risk that was observed was between people who never consumed any sort of artificial sweetener, and those who consumed even fewer than three a week. So right now, we don't have the science that tells us whether or not there are levels of consumption of these products that actually won't produce these outcomes.

FLATOW: Could we have that science? Could we do those studies?

SWITHERS: We could, but I want to point out that many of these studies are studies that took 15, 20, 25 years before the risks started showing up. So these are not - you know, this is not, you have a few drinks this week and next week, you're diagnosed with diabetes. These are long-term studies. But we certainly could try to get closer to the answer of exactly how much sweetener needs to be consumed before you run into these risks. But I think a better strategy is probably for people to be much more mindful of how much sweetener they're consuming overall.

So I want to make it clear that in the study, what we found was not only were diet sodas drink - drinking associated with these risks, but regular sodas are associated with similar risks. So the message is not that we have to be paying attention to how much artificial sweetener we're consuming, but probably that we need to be paying a lot more attention to how much sweetener we are consuming overall, both in drinks and in the rest of our diet.

FLATOW: All right, some interesting stuff to think about. Thank you very much, Dr. Swithers, for taking time to be with us today.

SWITHERS: Thank you.

FLATOW: Susan Swithers is professor of psychological science at Purdue University, and author of the paper published in the journal "Trends in Endocrinology and Metabolism." Transcript provided by NPR, Copyright NPR.