Not all Americans guzzle sugary drinks by the barrel. In 2008 around a quarter of weight-conscious American adults and more than 12 percent of children said they regularly drank artificially sweetened, or “diet,” sodas instead.
On the weight-loss front, that's undeniably good news. “The evidence is now clear from randomized trials that artificial sweeteners can help reduce weight if they replace standard sugar-sweetened beverages,” Walter Willett, chair of the Department of Nutrition at the Harvard School of Public Health, said in an email interview.
Nevertheless, artificial sweeteners are relatively new products, so the effects of consuming large amounts of them for decades isn't fully understood, prompting scientists to advise using them in moderation. Artificial sweeteners “are not the ideal long-term solution,” said Willett, but they can “be useful in helping some people withdraw from products that are seriously harmful to their health.”
The Food and Drug Administration (FDA) has approved for human consumption five so-called artificial sweeteners that consist of manmade molecules: saccharin, aspartame, acesulfame potassium, sucralose and neotame. A sixth approved non-caloric sweetener, rebaudioside A, is a natural extract from the stevia plant.
The FDA banned a seventh sweetener, cyclamate (Sucaryl), in 1969 based on studies suggesting it caused bladder cancer in rats. Worried about a surge in sales of diet soda sweetened with much cheaper artificial sweeteners, the sugar industry was one of the loudest groups sounding the alarm about potential health dangers from cyclamate.
“If anyone can undersell you nine cents out of 10, you'd better find some brickbat you can throw at him,” remarked John Hickson, vice president of the sugar-industry-affiliated International Sugar Research Foundation.
A subsequent study 20 years later found that monkeys fed massive amounts of cyclamate remained cancer-free, raising serious doubts about the applicability of the rat findings to humans and other primates. “With cyclamate we made a mistake,” said Robert Scheuplein, an FDA scientist who headed the agency's toxicology office in the early 1990s.
Cyclamate remains banned in the United States, but it is sold in Canada — as SugarTwin — and throughout Europe. Research has produced no clear evidence that any approved artificial sweetener is associated with human cancers, says the National Cancer Institute.
Aspartame comes under fire from food-additive opponents in part because, in storage and during digestion, it breaks down into methanol (wood alcohol) and then formaldehyde, best known as an embalming chemical. Toxicologists point out, however, that most fruits and vegetables break down into the same chemicals and that the body makes use of them without allowing toxins to accumulate.
Plenty of questions remain about artificial sweeteners' effects on the body, however. The San Antonio Heart Study, for example, which followed 3,682 adults for eight years, found that those who consistently used artificially sweeteners weighed more. Such results leave some scientists wondering whether the sweet taste of noncaloric sweeteners might stimulate the appetite more than sugar.
In search of answers, researchers use brain imaging to discover how humans respond to calorie-laden and no-calorie sweet tastes and observe rats that are fed both sugar and artificial sweeteners.
A typical diet — which includes both calorie-rich and no-calorie sweets — may confuse the brain, said Susan Swithers, a professor of behavioral neuroscience at Purdue University in West Lafayette, Ind. “The brain normally uses a learned relationship between sweet taste and the delivery of calories” to regulate eating by switching off hunger pangs after consuming sugar. But when one eats both no-calorie and calorie-rich sweeteners, the appetite-suppression mechanism may go haywire and lead to overeating, she hypothesized.
Another recent study, however, found no link between artificial sweeteners and appetite, said its lead author, Bjørn Richelsen, a professor of endocrinology and metabolism at Denmark's Aarhus University.
In a test of how hungry people were after drinking water, milk, Coke or Diet Coke, “we found if you're drinking soft drinks without calories it behaves [on the appetite] exactly like drinking water,” Richelsen said.
— Marcia Clemmitt