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Diet Soda Will Kill Us All!

Not really. But it won't help anyone much, either.

Kevork Djansezian/Getty Images

Welcome to Threats, an intermittent assessment of everyday risks.

Of the various instances of alarm over artificial sweeteners in the 126 years since saccharine was first mass produced, the most memorable was probably the one that triggered the diet cola panic of 1977.

The crisis began in early March. A lab in Canada had shown that saccharin caused bladder cancer in rats, and the Food and Drug Administration announced that the artificial sweetener—then the only one for sale in the U.S.—would soon be taken off the market. Though the rat study was not yet published, and despite the fact that the crystalline compound had been in steady use since 1886, the FDA declared saccharin a menace. Shares in sugar companies abruptly jumped in value.

Many consumers, though were fretting not about cancer but at the prospect of being denied sugar-free soda. There were soon demands for the decision to be repealed. The American Dental Association warned Congress that the country's teeth would slide into decay; the Pharmaceutical Manufacturers Association said that pills made without saccharin would be too bitter for America's children; doctors theorized that a move away from diet products might produce another 25,000 cases of cardiovascular disease per year. By early summer, the FDA had received 40,000 letters. Lawmakers got many tens of thousands more.

A few days after the agency's announcement, a nine-year-old diabetic named Mike Schindler told the Associated Press that he'd had it up to here with regulators in Washington. "I'd like to punch the daylights out of them," he said. To appease young Mike, and to prevent a diet-soda famine, Congress suspended the FDA's decision and demanded that more research be conducted. Which meant that scientists would have to continue wrestling with the same century-old set of questions: Do artificial sweeteners make us sick or keep us well? Are they dangerous adulterants or inexpensive ways to keep us lean and fit?

Thirty-six years later, they’re still wrestling with the subject, although the specific question has changed. Back in 1977, the panic focused on carcinogens. Research eventually disproved the Canadian study: Scientists no longer say that saccharin causes bladder cancer. Rates of the disease turned out to be no higher among diabetics, who use artificial sweeteners more often; nor did they appear to have risen after World War 2, when sugar rationing made saccharin ubiquitous. The danger posed to rats seems to be a product of their physiology: rat urine reacts with saccharin in a different way from ours.

Rather than going away, however, the cancer worries merely migrated. Half a dozen sweeteners have come to market since the 1970s, and one of these—aspartame—has been accused of causing cancers of the brain and breast. Those claims have been debunked as well. Though the latest round of additives are still relatively new—more evidence may come to light in 10 or 20 years—the fear of getting carcinoma from a Diet Coke now seems somewhat diminished.

Unfortunately for diet soda lovers, though, a new and more au courant concern has attached itself to artificial sweeteners. Today’s public health officials worry more about obesity than cancer, so instead of counting tumors they look at whether diet soda really makes us thin. And, once again, artificial sweeteners are under the microscope.

What researchers have found this time has been surprising: Drinking diet soda doesn't seem to lead to losing weight; in fact, there are signs it does the opposite. The data to support this bolder, more disturbing claim—that fake sugar can be fattening— come from several long-term studies, conducted on many thousands of participants starting in the 1970s and 1980s. Researchers have uncovered in these groups a correlation between the consumption of artificially-sweetened beverages and the incidence of weight gain. The effect even appears to be dose-dependent, which is to say that people who drink more diet soda put on more pounds from one year to the next. Rodents also seem to put on weight when they're given certain sugar substitutes.

If low-calorie sweeteners are fattening, then we could be on the verge of a spiraling disaster. The bigger we get (and the greater our incidence of diabetes), the more of these sweeteners we'll consume. That in turn will make us bigger, and more interested in diet products, and bigger still forevermore. But scientists have not yet proved that sugar substitutes make us fat. It's possible that people who are gaining weight start drinking Diet Coke to compensate, rather than the other way around. Moreover, the link between artificial sweeteners and obesity doesn't appear to hold up when seen in the light of other long-term trends. Between 1999 and 2008, obesity rates in the U.S. finally leveled off as the use of artificial sweeteners doubled among children and went up by 29 percent among adults. (Meanwhile, the average intake of added sugar—the real, caloric kind—dropped by almost one-fourth.)

It’s not yet clear how diet soda would cause us to pack on the pounds, if it does. It could be that artificial sweeteners serve to train our flavor preferences, meaning that the additives dull our taste for healthy foods and prime our mouths for sugar. (Animal studies show that a sweet tooth can be induced, even in the womb.) If sweet taste is addictive in this way, then artificial flavors might worsen our dependence. 

Another theory holds that artificial sweeteners fool our bodies from within. Sugar substitutes may lock onto receptors in the gut—receptors that have only lately been discovered—and gum up the body's metabolic mechanisms. That way the additives could produce a hormone spike affecting hunger and digestion, even though they offer few if any calories of their own. On the other hand, human studies suggest that our bellies can distinguish between real sugar and the sweeteners, at least when taken on their own, without an accompanying meal. Glucose and fructose tend to sit inside the stomach; they interact with gut receptors and slow the rate at which it empties. Sucralose, saccharin and aspartame don't have the same effect, which suggests that they're inert. (This explains why cocktails made with artificially-sweetened mixers are more intoxicating: The alcohol is absorbed more quickly.)

In any case, when humans try out artificial sweeteners in real experiments, in which subjects are split in groups ahead of time and assigned at random to drink diet soda or avoid it, they don't seem to gain weight, but neither do they have much success at losing it. In many cases, a switch to diet soda leads to greater caloric intake from other sources, so the net effect is nil. Short-term studies find that children in particular are prone to this effect.  

And so, we’re back once again to a fake sugar stalemate. It figures. As far back as 1907, the first FDA commissioner, Harvey Wiley, warned President Theodore Roosevelt that saccharin ought to be excluded from the nation's processed foods. (He'd found signs that the additive was toxic, and declared it a swindler's substitute for sugar.) But Roosevelt had been taking saccharin on a doctor's orders, as a way to stave off corpulence. His response to Wiley was as pugnacious as Mike Schindler's: "Anybody who says saccharin is injurious to health is an idiot," he announced, and then appointed a panel of experts to reassess—that is, rebuke—the FDA's position.

All the same, the contrast between the earlier anxiety about saccharine and the current concerns is telling. Back then we thought that artificial sweeteners might be so different from real sugar that they're poisonous. Now we like to say that sugar is the toxin, and we worry that artificial sweeteners are, in fact, too similar to sugar. This flip-flop should come as no surprise. For all the dueling studies, our attitudes toward confectionery flavors have more to do with who we are than what we know (since we don't that much at all). For centuries sugar was a status symbol, a fancy import eaten only by the rich. Then the product spread and cheapened, and its fame turned into notoriety.

Today we call sucrose a scourge of the poor, like crack cocaine, and imply that people in the ghetto overdose like rats. For now the rich and educated drink diet soda, figuring it helps more than it hurts, but artificial sweeteners may soon fall victim to another shift in sensibility. If that happens, it probably won't be on account of new or better science. As far as we can tell right now, it doesn't really matter whether you drink diet soda or not. The risks are insignificant—and so are the benefits.