A reader wrote to say, “I just read a story in the news that said research published by the ADA shows diet soda can make you obese. Should I stop drinking diet soda?”
I saw that report, too, and at first it’s hard to know what to think. But before you start to empty your fridge, here’s some background to that report.
Diatribes against diet soda have been all the rage for the last few years. It has been linked with an increased risk of weight gain and of getting diabetes.
Now, drinking diet soda has been associated with increasing abdominal girth, (the type that often coincides with metabolic syndrome and type 2 diabetes).
The results of the San Antonio Longitudinal Study of Aging, which was presented at the June meeting of the American Diabetes Association, linked diet soda consumption with increasing waistlines.
The study followed 474 participants aged 65 to 74 over an average of 9 years and looked at their change in waist circumference over time in comparison to their diet soda consumption.
Soda drinkers had a 70% greater increase in waist girth than abstainers. Those drinking the most diet sodas had the greatest gains in girth. Those drinking 2 or more diet sodas a day had 5 times the increase in waist circumference as their non-imbibing peers. The results were controlled for initial waist circumference, diabetes status, leisure-time physical activity level, neighborhood of residence, age and smoking status at each measurement period, as well as sex, ethnicity and years of education.
The study expands the findings of a previous study by the same authors in 2008 where consuming more than 21 diet sodas a week was associated with almost double the risk of becoming overweight.
Does this prove you should raid your refrigerator and throw out all the cans and bottles of diet soda you have stocked? That every can of soda is another pound on the scale?
Not necessarily.
Let’s begin with some basics about these studies. They are epidemiological or observational studies. No intervention happens during the study period; people meeting certain criteria are simply watched over a period of time to see what happens.
The gold standard for research is the double-blind, controlled intervention study. An example using soda would be that 200 people with diabetes of the same age, sex, weight and diabetes control would be divided into two even groups. One group would be asked to drink two cans of diet soda a day, and the other group would drink water disguised to look and taste like diet soda. The two groups would be given the same food in a quantity calculated to meet their caloric needs. At the end of a specified time period, both groups would be weighed to see if there was any change. Neither the researchers nor the participants would know which group drank the real diet soda. It is hard and costly to do this type of study, so a lot of research is done observationally first.
In the San Antonio study, many things could account for the results.
It could be that all the people who drink diet soda have something else in common that is the real cause of their weight gain and increased abdominal girth.
It could be that people who drink diet sodas feel they are reducing their calorie consumption in this area, so they can eat more of other things they like .
It could also be that the sweet taste of the sodas devoid of calories stimulates the appetite in some way, causing people who drink diet sodas to eat more.
Right now we just don’t know.
Nobody is recommending diet soda as a nutritional powerhouse. Essentially it is a soup of chemicals with not much to recommend it nutritionally. The reason it is suggested for people with diabetes is because the more healthful alternatives–water, water with a splash of juice, milk, even coffee and tea–don’t always appeal to people.
If you decide to drink diet soda, do so in moderation and be careful of calories coming from other sources. And, if it’s a choice between regular soda and diet soda for people with diabetes, the diet soda still wins, at least until we have some conclusive proof that it is dangerous.
