Clever chemists have attempted to circumvent those problems by formulating artificial sweeteners, which promise pleasure without peril. More than 15 per cent of Americans consume artificial sweeteners in thousands of products, according to the Yale Journal of Biology and Medicine.
But the use of artificial sweeteners seems to coincide with a climb in obesity rates, notes Susan Swithers, a behavioral neuroscientist at Purdue University in Indiana, who studies how experience with foods affects food intake.
Watch: Does sugar by any other name still taste as sweet?
Artificial sweeteners might "break a basic type of learned relationship between sweet tastes and the arrival of calories and sugars in the digestive system," Swithers says. "People who routinely use artificial sweeteners show responses that are dramatically different from those who do not."
People who ingest simple table sugar get a boost of glucose in their blood, which flips a switch of satiety that curbs the appetite. The brain learns this, and the satiety signals start to show up even before the sugar is absorbed.
Noncaloric sweeteners, however, appear to mislead us into what scientists term a "metabolic derangement," which prevents satiety signals from developing. "More food has to be eaten to feel as satisfied," Swithers says, "even when real sugar is eaten."
When our unconscious calorie switch becomes confused by noncaloric sweeteners, we must rely on conscious effort, such as reading food labels, to curb our intake.
"But we know people have a difficult time with that," Swithers says. "Noncaloric sweeteners can also produce cognitive distortions, like making people overeat because they think what they're doing is healthy."
Indeed, several large-scale studies correlate the use of artificial sweeteners with weight gain. A University of Texas study found that people who consumed two or more diet sodas per day over a period of almost 10 years had waist circumference increases five times greater than those who followed a different beverage path - a group that included people who drank sugar-sweetened sodas, although regular soda use was relatively infrequent.
But James O. Hill, director of the University of Colorado's Anschutz Health and Wellness Center, takes issue with the methodology of that study. "The links sometimes found between low-calorie sweeteners (LCS) and obesity in epidemiology may be explained by the fact that it is those with obesity who are more likely to choose LCS," Hill wrote in an e-mail: "Epidemiological studies cannot determine cause and effect."
With funding from the American Beverage Association, a trade group for makers of soft drinks, Hill spearheaded a study of 308 overweight and obese diet-drink consumers who were placed in a behavioral weight-loss program.Half of those were told to change their behavior and switch to water. Those who drank diet beverages lost an average of 13 pounds in 12 weeks, compared with the nine pounds lost by those who drank only water.
"LCSs seem to be doing exactly what they were designed to do," Hill wrote in an editorial in the American Journal of Clinical Nutrition: "helping reduce total energy intake while providing the sweet taste we value."
Swithers is highly critical of Hill's study. One of several issues that she has with the research: Hill's water-drinking group was allowed to continue using artificial sweeteners in foods. "That study is unfortunately so fundamentally flawed that it's impossible to draw any conclusions from it other than that people can lose weight over the course of three months, which we already know," she said.
On another front of uneasiness with artificial sweeteners, a recent study published in the journal Nature found that three synthetic sweeteners - saccharin (Sweet'n Low), sucralose (Splenda) and aspartame (Equal) - upset the balance of intestinal flora, causing glucose intolerance in mice and in some humans tested.
"Studies in rodents cannot necessarily be extrapolated to humans," Hill says. "Also, virtually everything affects the intestinal flora."
Nevertheless, some people attempt to sidestep potential problems with artificial sweeteners by turning to natural alternatives, but even those can cause trouble. For example, sugar alcohols, which are sweet, low-calorie chemicals naturally found in fruits, can produce bloating or laxative effects if used in large doses.
"It doesn't really matter whether things are 'natural' or fully synthesized in the lab," Swithers says, "they will be problematic. Foods and beverages that are sweetened, regardless of the type of sweetener, should be thought of as occasional treats, not as things that are consumed on a daily basis, much less at every meal."
"No one actually needs to eat sweeteners of any kind," says Swithers, who avoids consuming artificial sweeteners and closely monitors her sugar intake. "They can be pleasant, but given the current environment of overweight, obesity and all of the attendant chronic diseases, it's hard to argue that any benefits outweigh the risks over the long term."
"I believe it is unreasonable to think we can wean ourselves away from sweets," says Hill, who, according to a disclaimer published with his paper, has received consulting fees from Coca-Cola. "I believe that those recommending against use of these products are basing their recommendations on emotion more than science."
