Two weeks ago I wrote a post about the mistake we make when we think of some medicine or food as generally “good for you” or “bad for you” as opposed to having specific benefits and harms. I started with an anecdote in which a friend asked me whether diet sodas or regular sodas were better for you.
Susan Dopart, a terrific dietitian who I’ve known for over a decade, emailed me to bend my thinking about diet sodas and about non-nutritive sweeteners (i.e. artificial sweeteners) in general. With her permission, I thought I’d share her thoughts with you.
She shared with me an article reviewing studies that link the use of artificial sweeteners with various adverse health outcomes, like obesity and insulin resistance. The studies were all observational, that is, not randomized. For example, one study showed that people who drink more diet sodas tend to weigh more than people who drink fewer diet sodas. That’s exactly the kind of study that makes me want to pour lemon juice on my paper cuts. The media misunderstands this kind of study and reports that diet sodas cause obesity. But an equally likely possibility is that people who have stronger cravings for sweets will be overweight (by eating actual sweets) and will also drink more diet sodas (because they’re sweet). It’s like noticing that my lawn wilts on the same days that the beaches are crowded and blaming the crowds for my wilting lawn. But both are caused by a third phenomenon – hot days.
So, fancying myself the Defender of Science Against Confusing Nonsense, I emailed Susan that the studies were completely unconvincing and that artificial sweeteners haven’t been proven to have any adverse health effects. Susan agreed that there is no solid science on the subject, but said that in the absence of good science the best guide we have is our professional experience. She certainly has lots of experience, and she believes that sweeteners, whether natural or artificial, increase cravings for more sweets. In her experience patients who have stopped drinking any kind of soda have noticed their cravings for sweets decrease.
That’s a potentially important lesson, and someone should test it rigorously. In the meantime, I appreciate Susan sharing her expertise with us.
There is a mechanism that could explain how sweets cause increased cravings for sweets. It’s a theory by psychologist Seth Roberts that weight gain is mediated by a learned association between tasty foods and calorie content. This hasn’t been tested in a good study (yet) but I found his paper intriguing and easy to read. (I have no idea what Susan Dopart thinks about it.)
What Makes Food Fattening? A Pavlovian Theory of Weight Control by Seth Roberts
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