With millions of Americans following low-carb, low-sugar diets, artificial sweeteners are more popular than ever. But new research suggests that these sugar substitutes may actually promote overeating in the long term.
How fake sugar may fake out your body. I'm Bob Hirshon and this is Science Update.
If you think chugging down diet sodas saves you calories, think again. According to Purdue University psychologist Susie Swithers, you might overcompensate for those calories later.
She explains that the body learns to feel full by associating certain tastes, like sweetness, with calorie intake.
Our interest was in figuring out what happens if you mess up that relationship: what happens if you make it so that a sweet taste sometimes tells you you're going to get calories and sometimes tells you you’re not going to get calories?
To find out, she and psychologist Terry Davidson experimented with rats. They found that rats who were occasionally given artificially sweetened drinks were more likely to pig out on a chocolate snack later on. Rats that consistently drank naturally sweetened liquids were more restrained.
This hasn't been tested in people, and Swithers isn't recommending a sugary diet. But she says that people who consume artificial sweeteners may have to pay more attention to determine when their stomachs are full.
So they may have to read the label, they may have to control their portion size, they may just need to be a little bit more vigilant about what other calories they are getting in their diet.
I'm Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
Much of what we take for granted today–including plentiful food, effective medicines, and labor-saving machines–has made life longer and more comfortable than our ancient ancestors could ever have dreamed. Our bodies, however, still haven’t adjusted to the changes. We're still designed to stay lean and trim with active exercise and a hunter-gatherer diet, so we get soft and fat when we eat cupcakes and watch TV all day. Our flesh, bones, and blood may be fairly new, but the design is still a classic.
And when you introduce something like an artificial sweetener to your old-fashioned body, it gets confused. At least that's what's implied by Swithers and Davidson's study. It makes sense: Over the course of human history, just about anything that tasted sweet–from fruit to honey to sugar cane–had calories. After you ate them, your body used the sugars for energy. So our ancient bodies have learned a simple rule: sweet = calories. Since it takes up to a half hour or so to actually feel full from a meal, your body can use the sweetness of a food to roughly gauge how much you need to eat later on in the day. It's a kind of shorthand that makes it easier for you to regulate what you eat.
But throw a few diet colas into your system, and the rule breaks down. The diet colas taste sweet, so your body assumes they have calories. But a little while later, your stomach and your brain aren't reporting any new calorie intake. In fact, they're saying, "Hey, where are the calories? We're hungry!" Then you eat a banana, which is sweet AND has calories. So it seems like you're back to normal. But then you have a sugar-free fudge bar and the body gets confused again.
Eventually, your body (or rather, your brain) assumes that the old "sweet = calorie" rule just doesn't work anymore, so it throws it away. So now every time you eat a sweet snack, whether it has calories or not, you're hungrier later on. That's what happened to the rats in Swithers and Davidson's experiment. If hunger regulation works the same way in people (and there's no reason to think it doesn't), then people who use artificial sweeteners may tend to eat more than they otherwise would.
Fortunately, humans, unlike rats, have powers of reasoning. They can make more conscious decisions about what to eat and when to stop. And as life for our species gets more and more comfortable–and less and less natural–we'll have to rely more on our wits and judgment to keep us from overeating.
Now try and answer these questions:
- What was the major finding of Swithers and Davidson's experiment?
- How were the two groups of rats fed differently? Be specific. Why is that important?
- If a group of rats were fed an artificially sweetened treat every day, and then injected with a sugar solution immediately after the treat, what do you think would happen? Would their eating habits change later on? Why or why not?
- Can you think of other modern human eating habits that might work against the design of our bodies? Explain your answers.
Stone Age Diet, an article from the Nutrition Reporter website, compares the modern human diet to that of our ancient ancestors.
The British Nutrition Foundation offers lots of interesting information about food and nutrition aimed at the public.
This article from TeensHealth, Digestive System, gives students the opportunity to learn more about the different parts of the digestive system and how they work together.