Promoting diet soft drinks as healthy alternatives to sugar-sweetened drinks may be “ill-advised” researchers told a conference in the US this past week. The American Diabetes Association’s 71st Scientific Sessions held in San Diego 24 to 28 June, learned how one study linked diet soft drink consumption to larger waistlines in older people and another study suggested heavy consumption of the artificial sweetener aspartame, commonly used in diet sodas and other foods, may help raise blood glucose, a high level of which increases diabetes risk.

In the first study, epidemiologists from the School of Medicine at the University of Texas Health Science Center San Antonio (UTHSCSA), looked at the link between diet soft drink consumption and long-term change in waistline circumference in 474 people taking part in the San Antonio Longitudinal Study of Aging (SALSA).

SALSA is a large population-based study of how elderly Mexican and European Americans gradually become more and more disabled. The principal investigator is Dr Helen P Hazuda, who has been leading the study for the last 20 years.

Hazuda, a professor and chief of the Division of Clinical Epidemiology in the School of Medicine at UT Health Science Center, told the conference that:

“Data from this and other prospective studies suggest that the promotion of diet sodas and artificial sweeteners as healthy alternatives may be ill-advised.”

“They may be free of calories but not of consequences,” she added.

The participants were aged between 65 and 74 years at the start of the study, when the first set of measurements were taken. After that, they underwent three further follow up exams, when further measurements were done. The exams took place on average every 3.6 years, for a total of 9.5 years.

The measurements included height, weight, waist circumference, and diet soft drink intake.

The researchers used statistical tools to compare average waistline of diet soft drink users versus non-users in all the follow-up periods. They adjusted the results to take account of any potential effects from waist size at the start of the study, gender, age, ethnicity, education, where they lived, level of physical activity, diabetes and smoking, and the length of follow-up.

Although on average the waistlines of the participants went up over the follow ups, those of the diet soft drinks users increased by an extra 70% compared to those who did not consume diet soft drinks.

And for “frequent users”, ie those who drank two or more diet soft drinks a day, their increase in average waist size was five times greater than for non-users.

The researchers commented that waist circumference is often used as a measure of visceral adiposity or fat around the belly area, which is known to be a major risk factor for diabetes, cancer, heart disease and other chronic conditions.

They said these findings suggest that “amidst the national drive to reduce consumption of sugar-sweetened drinks”, policies that promote the consumption of diet soft drinks “may have unintended deleterious effects”.

In the second study, senior author Dr Gabriel Fernandes, a professor of rheumatology and clinical immunology at UTHSCSA, and colleagues, examined the relationship between consumption of aspartame, a popular artificial sweetener, and fasting glucose and insulin levels in 40 mice that were bred to be susceptible to diabetes.

All 40 mice had the same diet (chow), which included a 10% corn oil supplement (to make it the equivalent of a high-fat diet), except that 20 of them were also given aspartame (the experimental group) while the other 20 were not (the control group).

After three months, the mice whose diets included aspartame started showing a pattern of higher levels of fasting blood glucose, and lower levels of insulin, which the researchers note is “consistent with early declines in pancreatic beta-cell function”. Beta cells make insulin, the hormone that reduces blood sugar after a meal: insufficient insulin is a feature of diabetes.

However, the difference in insulin levels between the two groups was not statistically significant, meaning we can’t be certain this difference was due to something more than chance.

Also, of the mice whose diet included aspartame, only 50% survived 6 months to reach 18 months of age (all the mice had started on the diets at 12 months of age), whereas in contrast, of the mice that did not have aspartame, 65% survived to 18 months, however this difference was not statistically significant.

Fernandes and colleagues also found that the livers of half the mice whose diet included aspartame showed “large perivascular lymphoid aggregate”, whereas the livers of the mice that were not fed aspartame showed similar growths, but none could be described as large.

This is interesting, because although you might expect to see more liver damage resulting from a high fat diet, these patterns are striking, noted the researchers, because the mice fed with aspartame had lower body weights and more favorable levels of blood fats than the controls.

Fernandes said in a statement:

“These results suggest that heavy aspartame exposure might potentially directly contribute to increased blood glucose levels, and thus contribute to the associations observed between diet soda consumption and the risk of diabetes in humans.”

Funds from the Institute for the Integration of Medicine and Science (IIMS) paid for these studies.

“Diet Soft Drink Consumption Is Associated with Increased Waist Circumference in the San Antonio Longitudinal Study of Aging.”
Sharon P Fowler, Ken Williams, Helen P Hazuda.
Abstract no: 0062-OR
Presented Sat 25 Jun 2011.

“Aspartame Consumption Is Associated with Elevated Fasting Glucose in Diabetes-Prone Mice.”
Sharon Parten Fowler, Ganesh V Halade, Gabriel Fernandes.
Abstract no: 0788-P
Presented Mon 27 June 2011.

American Diabetes Association

Additional source: University of Texas Health Science Center at San Antonio.

Written by: Catharine Paddock, PhD