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Diet Sodas Do Cause Obesity Study Finds

Tim Boyer's picture
diet soda cause of obesity

Are you still not convinced that drinking diet sodas can be as bad as drinking a regular soda? A new study found that drinking diet sodas is a direct cause of obesity in at least one special subset of Americans.


When it comes to obesity, health experts share the opinion that one of the biggest causes of weight gain is the fact that many of us are essentially drinking ourselves fat by downing too many sugary drinks. This should come as no surprise due to many of us sip soda like human hummingbirds from a sugar-laden feeder.

But what is surprising to many is that diet drinks that have replaced calorie-heavy syrup with zero-calorie sweeteners, may really be as bad as drinking a regular sugar-filled soda. In fact, past news reports tell us that scientists have discovered that diet sodas are altering the type of bacteria that live in our gut and as a result are affecting how food is digested and metabolized in the body.

This discovery is backed by a study in which mice who had never been fed artificial sweeteners before, were fed large amounts of a variety of different sweetener types such as aspartame, sucralose and saccharine. What the scientists discovered was that the artificial sweeteners were not only feeding the mice, but also feeding―and selecting for―the type of bacteria that lived in the guts of the mice. What they saw was a change in the normal population of good bacteria called “Clostridiales” to a potentially harmful type of bacteria called “Bacteroides,” which are bacteria that have been associated with obesity in humans.

While the debate and research continues as to whether and how much of a role the bacteria in our gut play toward obesity, a new study published in the Journal of the American Geriatrics Society supports the growing belief among health experts that an increasing diet soda intake trend is directly linked to greater belly fat obesity in senior citizens. This is especially dire news for the aging as increased belly fat contributes to metabolic syndrome and cardiovascular disease.

The uniqueness if this finding is that previously published research on the effects of artificially flavored beverages on health has focused on the young and the middle-aged.

According to a press release from the journal’s publisher:

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"Our study seeks to fill the age gap by exploring the adverse health effects of diet soda intake in individuals 65 years of age and older," explains lead author Sharon Fowler, MPH, from the University of Texas Health Science Center at San Antonio. "The burden of metabolic syndrome and cardiovascular disease, along with healthcare costs, is great in the ever-increasing senior population."

The study consisted of 749 Mexican- and European-Americans ages 65 and older whose diet soda intake, waist circumference, height, and weight were measured at the beginning of an earlier (San Antonio Longitudinal Study of Aging (SALSA)) study and followed up on three occasions in 2000-01, 2001-03, and 2003-04, for a total of 9.4 follow-up years. By the time of the 3rd follow-up, there were 375 remaining surviving participants.

What the follow-up data showed was that the increase in waist circumference among diet soda drinkers per follow-up interval, was almost triple that among non-users―0.83 inches versus 0.30 inches respectively. After factoring in potential confounders that could affect the data, the researchers determined that this translated into a waist size increase of 3.16 inches for diet soda drinkers versus a 0.80 inch waist size increase for non-diet soda drinkers after the 9.4 year long follow-up period.

"The SALSA study shows that increasing diet soda intake was associated with escalating abdominal obesity, which may increase cardio-metabolic risk in older adults," Fowler concludes.

The results of the study led the authors to recommend that older individuals who drink diet soda daily―particularly those at high cardio-metabolic risk―should try to curb their consumption of artificially sweetened drinks such as diet sodas and diet sweet tea beverages in spite of their zero-calorie claims of being a diet drink.

For more about why you should avoid diet sodas, here is an informative health risk warning about artificial sweeteners.

Reference: “Diet Soda Intake Is Associated with Long-Term Increases in Waist Circumference in a Biethnic Cohort of Older Adults: The San Antonio Longitudinal Study of Aging” Journal of the American Geriatrics Society, March 17, 2015; Sharon P.G. Fowler, Ken Williams and Helen P. Hazuda.



As obesity rates are at an all-time high, finding ways to reduce calories safely is a top health priority, and diet beverages are a great option. There are sever major issues with this study and their proposed implication: 1) They did not control for food intake - it’s impossible to identify if it is the diet beverages consumed or other components of the diet leading to a modest (~1 inch) increase in waistline over 10 years. Are people drinking diet beverages because they are already overweight and looking to lose weight? Are the people drinking diet beverages doing so to offset high calorie food choices? 2) It’s an observational study so it can’t prove causation. Randomized controlled clinical trials can, such as the CHOICE study, which showed that diet beverages can reduce calorie intake and lead to greater weight loss than people drinking water. 3) There is no reasonable mechanism to explain how having a reduced calorie beverage could lead to weight gain. Overall, diet beverages can provide a low-calorie alternative treat to satisfy your sweet tooth, and help in weight management.
You will of course continue to try to sell your products no matter the cost to public health. Pointing out that the study is observational isn't helpful. If there is an association between obesity and diet beverages why not avoid them all together? Randomized controlled studies take years. There is too much evidence showing artificial sweeteners are not recognized by the body. Phosphates in sodas are a health hazard. I wish the food industry had integrity.