I’m getting a fizzy discomfort in my stomach about the potential negative health effects of diet soft drinks.  That’s right – those seemingly harmless, artifically sweetened knock-offs that become the drinks of choice for many people fighting the battle of the bulge.  Afterall, aren’t diet drinks a healthier alternative than regular sodas that are loaded with calories from high fructose corn syrup?  The answer to this is a resounding “probably."  But it turns-out that they may not be risk free.

Enter the epidemiologists, whose elegant analyses can tease-out relationships that help launch new lines of investigation about cause and effect, and for whom we have much to thank in contemporary medicine.  They are the sleuths who first showed us that cigarette smoking causes lung cancer, high cholesterol poses a risk for heart disease, and maternal folate deficiency leads to birth defects.

Three independent epidemiologic studies have recently found an association between the consumption of diet drinks and heightened risk for the development of obesity and the metabolic syndrome, conditions that are often a precursor to cardiovascular diseases such as heart attack and stroke.

Each of these studies was a longitudinal study of a population cohort – meaning that the investigators collected a lot of information about participants at the outset and over a period of years, while oberving the relationships that emerged between certain  exposures (like to nutritional components including diet sodas) and subsequent health outcomes (like obesity and/or the metabolic syndrome.) 

Collectively, these three studies include analysis of about 17,000 participants including those in the Framingham Study of residents from Framingham, Massachusettes; the Multi-Ethnic Study of Atherosclerosis (MESA) following adults from 6 major cities across the US; and the San Antonio Heart Study, which followed adults in San Antonio for over 10 years.

In the Framingham study, both regular and diet soft drinks appeared to pose similar metabolic hazards for the development of metabolic syndrome, which flies in the face of conventional wisdom implicating high fructose corn syrup and insulin resistance as the sole mechanism leading to weight gain, high blood pressure, high triglycerides, and low HDL. 

But wait, you say.  What about other variables that haven’t been taken into consideration?  Perhaps people who drink diet sodas are doing so to compensate for poorer dietary choices.  Not according to their food diaries – in fact, they tended to make better choices (eat more whole grains, vegetables and consume less fat) than those who drink sweetened soft drinks. 

Well, what if they had more baseline obesity and that’s why they were drinking diet sodas?  Not so – researchers controlled for levels of obesity and the occurrence of metabolic syndrome at the outset.  And the team in San Antonio found the equivalent of an epidemiologist’s “smoking gun” when they uncovered a classic dose-response relationship between diet drinks and obesity, meaning that a linear relationship was seen and those with higher exposure to diet drinks had a greater likelihood for obesity.

What could possibly serve as a biologic explanation for these findings?  Does the caramel content of both regular and diet drinks result in more advanced glycation end products, leading to insulin resistance and inflammation? Do artificial sweeteners, which are several hundreds or thousands times sweeter than sugar, lead to taste distortion and increased appetite for intensely sweet, high caloric foods?  Aspartame in rodents damages a portion of the brain involved in leptin signaling that reduces food intake. 

A recent study by neurobiologists at Purdue showed tha rats, who guage a food’s caloric content by relying on its sweetness and viscosity, lost the ability to self-regulate consumption and overate when chronically exposed to artificially sweetened drinks.

Years of watching medical debates evolve while research findings ebb and flow tells me that it’ll be a decade or more before this gets settled.  Meanwhile, we have lives to live and decisions to make.  I gave-up diet sodas about a year ago and drink more water, unsweetened tea, and skim milk.  I don’t miss the fizzy drinks or my contribution to our enormous pile of plastic and alumnium packaging, to boot!

 Jan  

1.  Dhingra R, Sullivan L, et al.  Soft drink consumption and risk of developing cardiometabolic risk  factors and the metaboic syndrome in middle-aged adults in the community.  Circulation 116:480-488,2007.
2. Fowler SP, Williams K, et al.  Fueling the obesity epidemic?  Artificially sweetened beverage use and long-term weight gain.  Obesity 16:1894-1900, 2008.
3. Nettleton JA, Lutsey PL, et al. Diet soda intake and risk of incident metabolic syndrome and type 2 diabetes in the multi-ethnic study of atherosclerosis.  Diabetes Care 32:688-694, 2009.
4. Swithers Susan E, Davidson Terry L.  A role for sweet taste: calorie predictive relations in energy regulation in rats.  Behavioral Neuroscience 122:161-173, 2008.