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Do diet soda drinkers consume more calories? Questionable.

Diet Coke
Diet Coke

A paper by Sara N Bleich and others from the Johns Hopkins Bloomberg School of Public Health published late last week seems to indicate that overweight adults consuming diet sodas are also consuming more calories than normal weight adults. The paper, Diet-Beverage Consumption and Caloric Intake Among US Adults, Overall and by Body Weight was published online ahead of print in the American Journal of Public Health.

The popular press has covered this extensively, with this CBS News article being typical. They report that “overweight and obese adults who drank diet beverages took in more food calories on average than their counterparts who drank the sugary stuff.”

But this is not exactly what Bleich actually did, and the press reports are rather misleading. We obtained and read the original paper and explain it below.

This was a data mining study of a collection of data called the National Health and Nutrition Examination Survey (NHANES 1999-2010) which surveyed participants using daily diet questionnaires (24 hour recall) and weight and height were measured at a mobile examination center.

They divided the data from participants into 5 beverage groups:

  1. Sugar sweetened beverages,
  2. Diet beverages
  3. Alcohol
  4. 100% juice
  5. Milk

Overall, 61% of adults consumed sugar sweetened beverages and 15% consumed diet beverages on a typical day. The researchers found that overweight and obese adults were more likely to consume diet beverages than normal weight adults. This is not really surprising. If you are overweight, you probably are more likely to drink diet beverages.

They report that overweight diet soda drinkers consumed more calories in solid food than did overweight adults who drank sugar sweetened beverages. Healthy weight adults consumed 73 fewer calories if they drank diet beverages, but overweight and obese adults consumed 88 and 194 more calories per day.

They hypothesize that artificial sweeteners activate the brain’s reward centers, “thus altering the reward a person experiences from sweet tastes.” They suggest that the brain’s sweet sensors no longer “provide a reliable gauge of [calories].”

But you can interpret these findings more simply:

  • Overweight people eat more calories.

They really do not provide any reliable measurement that shows that those drinking diet sodas causes greater caloric intake. At best, they have found correlation, but certainly not causation. The experiment that someone really needs to do is to switch overweight people TO diet drinks and continue monitoring total caloric intake. And that has not been done.

This hypothesis that diet sodas somehow cause obesity comes up again every few months, and in every case, the workers seem to ignore all the work to the contrary in this field. Below we repeat our summary from last time when Swithers’ opinion piece appeared.

Earlier work

In a 2009 study by Chen, Appel and others, 810 adults were monitored for 18 months with careful recording of their beverage intake. Intake of sugar sweetened beverages was correlated with weight gain, and there was no significant weight gain from artificially sweetened beverages. Let’s repeat: in a randomized study, diet drinks did not cause weight gain.

And in a study published last year by Blackburn a group of 163 obese women in a weight loss program were randomly assigned to a group using aspartame or one abstaining from aspartame. Initially, both groups lost about 10% of their body weight. But during follow-up the aspartame group lost significantly more weight overall, and regained less weight. Again, aspartame was not shown to cause weight gain.

There are a number of other studies with similar conclusions. A 2009 study by Brown reviewed 18 studies of weight loss and gain in children with the express purpose of studying weight gain associated with aspartame, and decided that that there was “no strong evidence for causality regarding artificial sweetener use and metabolic health effects.”

A study in the European Journal of Clinical Nutrition compared satiety scores for milk, sugar sweetened beverages and artificially sweetened beverages. They found no evidence that artificially sweetened beverages increased appetite or energy intake. And a paper by Maersk and Belza found that “diet cola had effects similar to water.”

So, after reading through Bleich’s paper, we don’t agree with her conclusions. And there is quite a body of research that also disagrees.

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