The Skinny on the Diet Soda Study

A new study published this week in the journal Obesity got a lot of press this week for linking diet soda to weight loss.

But what’s the real story on diet soda? Does it cause more weight loss than drinking water will?

First, about the study: it was funded by the American Beverage Association, a trade association with backers such as Coca-Cola and Pepsi.

Just over 300 people were randomized into 1 of 2 weight loss groups: those who were allowed to drink diet soda and those who only could drink water. Both groups received intensive weight loss counseling, were encouraged to exercise more, and had to log their foods.

At the end of the 12 week study period, the diet soda drinkers had lost an average of 13 pounds, while the water drinkers had lost only 9 pounds. The diet soda drinkers also reported significantly less feelings of hunger than those in the water group.

A lot of healthcare professionals and researchers have weighed in on this study, questioning limitations such as:

  • Calories weren’t tracked in the study – so if you have a sweet tooth and were in the diet soda group, you could satisfy your craving with a zero calorie sweet-tasting product. But if you were in the water group with a sweet tooth, you likely just ate more food.
  • Correlation isn’t causation – this study showed a correlation between diet soda and weight loss, not a causal link. There’s nothing in diet soda that pushed the pounds off, it’s just that that behavior was linked in this case to more weight loss.
  • The study was only 12 weeks in length – almost anyone can follow almost any diet plan for a short period of time. But what about the impact of long term weight loss? Incorporating diet soda and being able to KEEP the weight off would be more impressive.
  • People in the water group could only drink 24 oz water per day – the part of your brain that controls your hunger, also controls your thirst. Only being able to drink 3 cups of water a day means the water drinker groupies probably turned to food when faced with thirst, instead of more water.

This new study’s results contradict other recent studies that have showed a negative impact on health from diet soda:

Bottom line: one small, short term study with some questionable beverage guidelines that may indicate a 4 pound weight loss difference compared to water drinkers certainly does not prove that diet soda is a weight loss panacea.