Sweet Debate
Do artificial sweeteners contribute to rather than combat obesity?
By Trout Lowen
Drink diet soda. Switch to low-fat or no-fat products. Cut down on or eliminate sugar. People who are overweight, have diabetes, or have metabolic syndrome hear advice like this all the time. But is it the right advice?
Some say it isn't. Results from several large-scale population studies suggest that regular consumption of artificial sweeteners such as aspartame and sucralose, particularly in diet soda, may actually contribute to rather than combat weight gain and type 2 diabetes.
No study so far has identified a direct causal link between artificial sweeteners and weight gain or diabetes, and proving one is difficult because there are so many confounding factors. But the positive association raises interesting questions: Do artificial sweeteners, most of which are hundreds of times sweeter than sugar, increase our desire for more and sweeter foods? Do diet soda drinkers overestimate the number of calories they're saving and then eat more? Do artificial sweeteners somehow disrupt or alter the body's processes in ways we don't yet understand? Or are those who are prone to weight gain or who have a family history of diabetes more likely than others to consume diet soda?
Of Mice and Man
In late June, epidemiologists and nutritional immunologists from the University of Texas Health Science Center at San Antonio presented the results of two new studies at the annual meeting of the American Diabetes Association (ADA). One study found that artificially sweetened soft drink consumption was associated with increased waist circumference in elderly people. The second found aspartame raised glucose levels in diabetes-prone mice.
The human study tracked diet soda consumption and waist measurement in 474 participants in the San Antonio Longitudinal Study of Aging at enrollment and at three follow-up exams over 10 years. As a group, participants who consumed artificially sweetened soft drinks saw a 178 percent greater increase in waist circumference compared with those who did not, and those who consumed two or more beverages containing artificial sweeteners per day saw a 500 percent (or almost three times greater) increase. "That's quite a statistically significant trend," says Sharon P. Fowler, M.P.H., co-author of the study.
That study reinforced the results of Fowler and colleagues' earlier analysis of San Antonio Heart Study data published in Epidemiology in 2008 that looked at the relationship between consumption of beverages containing artificial sweeteners and weight gain. That analysis showed that subjects who were 25 to 64 years old at baseline who consumed more than 21 artificially sweetened beverages per week almost doubled their risk for obesity over the next seven to eight years, compared with nonconsumers, and that their adjusted body mass indices increased 47 percent more than those of nonusers.
Both of the San Antonio studies support the findings of an earlier analysis of data from the Baltimore Longitudinal Study of Aging presented at the annual meeting of the Endocrine Society in 2009. That analysis found artificial sweetener consumers were younger and heavier, and had a higher body mass index than nonconsumers, although the number of calories and the amount of fat, carbohydrates, and protein consumed was the same in both groups. Three other studies published in Circulation and Obesityin 2007 and 2008 also showed an association between consumption of artificially sweetened soda and the development of obesity and metabolic syndrome.
In the mouse study presented at the ADA meeting, 40 diabetes-prone mice were divided into two groups. Both were fed a high-fat diet. Half of the mice were also fed high doses of aspartame. After three months, the mice that were given aspartame weighed the same or slightly less than the control mice, had better lipid and triglyceride levels, and their nonesterified fatty acids were much lower, Fowler says. But their fasting glucose values were 37 percent higher. In addition, 69 percent of the mice fed aspartame became hyperglycemic compared with 31 percent of the control group.
Other Explanations
But could artificial sweeteners be changing human chemistry? Some researchers think they may increase consumers' desire for ever-sweeter tastes. As a group, artificial sweeteners are much sweeter than sugar—saccharine is 300 times sweeter than sugar, aspartame 180 times sweeter, and sucralose 600 times sweeter. Some experiments have shown that sweet taste, whether it's derived from sugar or artificial sweeteners, increases appetite. One study found drinking aspartame-sweetened water increased appetite in normal-weight adult males, but swallowing an aspartame capsule did not. In another study, aspartame, saccharine, and acesulfame potassium were all associated with an increased motivation to eat more.
Other research suggests that artificial sweeteners do not provide the same food reward that natural sweeteners do, and that may contribute to increased appetite and, as a result, weight gain. There are also other variants on theories about behavior that may explain the study results. People may overestimate the calorie-saving benefits of artificially sweetened foods and eat more as a result. Study subjects may over-report their consumption of artificially sweetened soda when they are really drinking sugar-sweetened soda. Those mostly likely to drink diet soda may already have difficulty maintaining weight or have a family history of obesity or diabetes.
What about Sugar?
Although there is concern that artificial sweeteners may contribute to obesity and the diseases associated with it, there's clear evidence that sugar, particularly as it's consumed in sweetened beverages, is a major contributor to weight gain and the development of metabolic syndrome and type 2 diabetes. A recent meta-analysis of studies involving nearly 20,000 people in four countries published in Diabetes Care in 2010 found sugar consumption was associated with development of both metabolic syndrome and type 2 diabetes. In a lecture made popular on YouTube, Robert H. Lustig, M.D., professor of pediatrics in the division of endocrinology at the University of California, makes the case that sugar consumption is the main cause of obesity and diabetes and that it ought to be considered a toxin. Yet multiple studies have shown consumption of sugar-sweetened beverages including soft drinks, fruit drinks, ice teas, and energy and vitamin water drinks is rising in the United States and around the world. Sugar-sweetened beverages are now the primary source of added sugars in this country.
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