Diet beverages and other non-caloric, artificially sweetened foods and drinks may not be the healthy choice to manage weight that they appear, according to a Purdue University expert's review of recent scientific studies.
"Public health officials are rightfully concerned about the consequences of consuming sugar-sweetened beverages, such as soft drinks, but these warnings may need to be expanded to advocate limiting the intake of all sweeteners, including no-calorie sweeteners and so-called diet soft drinks," said Susan E. Swithers, a professor of psychological sciences and a behavioral neuroscientist. "Although it seems like common sense that diet sodas would not be problematic, that doesn't appear to be the case. Findings from a variety of studies show that routine consumption of diet sodas, even one per day, can be connected to higher likelihood of heart disease, stroke, diabetes, metabolic syndrome and high blood pressure, in addition to contributing to weight gain."
Swithers, who studies ingestive behavior and body weight -specifically the roles that artificial sweeteners and other food substitutes play in weight management and eating - reviewed and evaluated the most recent research on whether consuming high-intensity sweeteners, despite their zero or low calories, may result in overeating, weight gain or other health problems. Her findings were published by Cell Press on Wednesday (July 10) in an opinion article in Trends in Endocrinology & Metabolism.
The concerns for these chemical sweeteners emerged across studies that varied widely in design, methodology and population demographics, and they applied to sweeteners, such as aspartame, sucralose and saccharin. About 30 percent of adults and 15 percent of children in the United States consume artificial sweeteners.
"The concern that these non-caloric sweeteners might not be healthy is a message that many people do not want to hear, especially as the prevalence of artificial sweeteners increases in other products," Swithers said. "There is a lot of pressure from the public health sector to find solutions to counter the rise of obesity and chronic disease, and there is a lot of money and business at stake for the food industry as it develops and promotes these products. Beverages are becoming political issues as government leaders and politicians seek regulation and taxing to limit their availability and consumption, but most of these measures exclude diet soft drinks because they are perceived as healthy. When it comes to making policy decisions, it's more important than ever that the science is considered and that the public understands what the science says in order to help them make the best health decisions."
Swithers, who also is a member of Purdue's Ingestive Behavior Research Center, looked at a variety of studies, including the San Antonio Heart Study that reported an increase in body weight gain for adults and adolescents who consumed artificially sweetened beverages over beverages regularly sweetened. Data from a number of studies, including the Nurses' Health Study and the Health Professionals Follow-up Study also reported greater risk of type 2 diabetes, high blood pressure, heart disease and metabolic syndrome, which is related to diabetes and cardiovascular problems, for consumers of artificially sweetened beverages. Some data indicated that those who consumed artificially sweetened beverages had double the risk of metabolic syndrome compared to non-consumers.
Research also shows that non-caloric or reduced-calorie food and beverages interfere with a body's learned responses. The assumption is that fewer calories means less weight gain. Research, including studies from Swithers and colleagues, shows that frequent consumption of high-intensity sweeteners may have the opposite effect by confusing the body's natural ability to manage calories based on tasting something sweet. Swithers' research is funded by the National Institutes of Health, and she is continuing to study these effects.
Expanding studies from animal models to humans is one of the challenges for Swithers and other researchers trying to answer questions about how diet drinks affect humans. The studies that show specific mechanisms and metabolic causes are from animal models. In human studies, researchers can only see correlations and not identify specific causes. Swithers said it also is challenging to do well-designed studies in humans because of how ubiquitous sweeteners have become in the mainstream diet.
"For example, what are the biological mechanisms and behavioral factors that influence this connection between diet soda and diabetes?" Swithers said. "Some of the connection could be related to how people behave by saying to themselves, 'I'm having a diet soda, so this cheeseburger is OK.' But the animal work indicates that health problems can occur even without this kind of thinking. Since we don't fully understand the mechanisms, we don't really know how to reverse the consequences, and that will continue to be a problem as our population ages and the rates of chronic diseases like type 2 diabetes continue to increase."