Do Diet Sodas Make You Fat?


A recent study out of the University of Texas Health Science Center may have left a few people scratching their heads in puzzlement.  It showed that people who drink diet sodas were more likely to become overweight than those who didn’t.  And the more diet sodas you drink, the fatter you’re likely to be.

How does that work?  Actually, it’s a good example of correlation, not causality.  The study was conducted by examining questionnaires and medical records of over 1,000 people.  It showed that the heavier folks tended to be the ones who drank the most diet soda.   That doesn’t prove that diet soda causes the weight gain; it just shows that when you see one (diet sodas), you likely see the other (higher weights).

This is an important distinction because research correlations are frequently but mistakenly assumed to be proof of cause and effect.  For example, one of the bigger arguments today in ‘weight’ circles is whether health problems like high blood pressure and diabetes are unavoidable consequences of obesity.  Said another way, there are people who are classified as obese according to the charts, yet they live healthy lifestyles and show it in terms of all health parameters except their weight.

Which is what the argument centers on.  If these healthy folks are also fat, then can weight be accurately considered an independent indicator of health?  It can, according to those who incorrectly cite correlational studies as the proof.  But when you look at healthy fat folks, you see there’s something else in play that correlational studies can’t account for – there has to be another causal factor.

Anyway, back to the diet sodas.

My personal take on this is that this correlation suggests something I’ve long noticed about the eating habits of many people who struggle with their weight.  They suck!  That is, they don’t eat well – they skip meals, they try to keep calories to a minimum, they’re constantly worrying about eating too much.  So when hunger attacks, what do they turn to?

Something calorie free that will hopefully turn their hunger down a notch.  Things like black coffee and diet soda seem to do that fairly well…for a while.  But then the hunger wins; good intentions for eating lightly go out the window in the face of extreme hunger.  Even if someone can manage to keep calorie intake low, they toy with reducing their metabolic rate, which then makes it even easier to gain weight.

The last thing any of us who have struggled with weight needs is another food fear.  I strongly doubt that there’s anything inherently wrong with diet sodas that cause people to gain weight.  Instead, I think it’s how we use the sodas that’s the problem.

5 responses to “Do Diet Sodas Make You Fat?”

  1. Lori says:

    Marsha – thanks for posting on this. I have read several articles now about this and was wondering myself how drinking diet sodas could lead to being overweight.

    I think you hit the nail on the head with your idea that overweight people tend to look for calorie free anything when they are hungry. I know that I have had that conversation with myself.

  2. Mermaid on the Rocks says:

    re: Diet Pop

    It is usual, almost routine, to see fat & obese people washing down their meals with diet pop. BAD IDEA!

    The pop, with its strong taste & carbonation, seems to numb – temporarily – the taste buds. (It can be a useful thing – like tea, coffee or water – to have on the counter to sip, when you are preparing food). For a little while, it seems to kill hunger, just like coffee.

    It is the LAST THING you need when you are eating, as you certainly want to taste your food, as your taste buds can then register when you have had enough of something.

    Steak is probably the classic example: there comes a moment when the steak simply chews like cardboard, with no taste at all. Your taste buds are satiated: they don’t want any more of that. Time to stop eating it – IF you are paying attention.

    Difficult to notice that, however, if you are swilling down your food with pop.

  3. Marsha says:

    Thanks for your thoughts, Mermaid on the Rocks. I’ll agree with you that diet sodas are abused by a large portion of weight-struggling folks. We don’t serve them at meals at Green Mountain for that very reason — they can get in the way of mindful eating if you’re accustomed to using them to kill hunger (which they really don’t do — they can just send it ‘underground’ and when the hunger pops back up, it can be vicious!). That’s a good reason to be judicious in our use of diet sodas — not because we think diet sodas themselves cause weight gain, but because how we use any foodstuff can affect our eating habits and subsequently our weight status. If we use diet sodas as just another beverage, then I would suspect there’s no correlation with weight. Personally, when I drink soda — which isn’t that often — I choose the real sugar variety. That tastes better to me.

  4. Tage says:

    Some suggest that diet soda makes you hungrier. As you consume more sweet things that have no calories, your body is expecting calories, and this dramatically increases your hunger for sweets.

  5. marsha says:

    Yes, I’ve heard that but reserve judgment until there’s some hard science to that point. I’d rather make my own decisions about what makes me feel satisfied. I would agree that diet sodas generally don’t do that because I usually don’t eat (or drink) much when I’m not hungry (anymore — at one point, wasn’t so good at that). Bottom line for me and what i encourage for anyone is to tune in and really find out for yourself satisfies you, what makes you feel well, and what doesn’t. We’re all different, and science is only beginning to get a clue about how much.

    Thanks for your comment!

About the Author

Marsha Hudnall, MS, RDN, CD

If you’re looking for an embodiment of dedication disguised as obsession, look no further. Marsha is a registered dietitian who has spent the last four decades working to help women give up dieting rules and understand how to truly take care of themselves. Her mission in life is to help women learn to enjoy eating and living well, without worries about their weight. She encourages women to embrace their love of food, which you might call being a foodie. If so, it’s appropriate because being a foodie means you pay attention when you eat. That’s a recipe made in heaven for eating well. Marsha is the President and Co-Owner of Green Mountain at Fox Run.

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