Jun 26, 2012

Do artificial sweeteners lead to weight gain?

The personal genomics firm 23andMe recently released the results of a user survey indicating that the consumption of diet soda is very highly correlated with high body mass index (BMI).  You can read this surprising result here.
people who drink diet soda five or more times a day have an average BMI nearly 5 units higher than those who never drink diet soda. 
Of course, this could be because people who are obese are more likely to choose diet soda.  However, it fits very well with something I have suspected for some time now, that consumption of artificial sweeteners leads to weight gain.

A 23andMe survey revealed that consumption of diet soda is correlated with BMI.  (The cartoon is also from their site.)

Although I know of no data in support of this hypothesis, I will explain two reasons why I think it likely.

Taste.  Consumption of sweet foods leads to a preference for sweet foods.  This was directly addressed in a study by Sartor et al. (Appetite 2011), who found that "overweight/obese individuals are more implicitly attracted to sweet" and "one month of soft drink supplementation changed sweet taste perception of normal-weight subjects."  My own preferences affect my thinking on this.  While I truly enjoy the sweetness of a ripe peach, fresh sweet corn or dark chocolate, I find many popular foods (including soda and iced cupcakes) to be too sweet and truly unpleasant.  The idea here is that when someone consumes artificial sweeteners they get used to sweet flavors and come to enjoy sweeter tastes, which ultimately leads to the consumption of more calories.  For more on taste, including possible links to obesity, see the Outlook on taste in this week's Nature, especially a summary of research  on taste and obesity

Homeostasis. This is a similar idea, but involves unconscious processes.  The gut is filled with sweet taste receptors (Dyer et al. Biochem Soc Trans. 2005). Although I don't know what they are doing there, it seems likely that information from these receptors is used to regulate appetite, or metabolism, or both.  If your gut is constantly full of sweet flavors, then they will be ignored.  The sugars released from real food will not make you feel satisfied, or will be improperly dealt with in some other way.  The body's homeostatic mechanisms are complex and I don't claim to understand them, but I do suspect that artificial sweeteners disrupt the natural response to food and contribute to craving and binge eating.