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Do diet soft drinks lead to obesity?

Thursday, January 15, 2009 Posted by Travis Saunders

Are diet soft drinks bad for you? I received this question from Perry Romanowski after it came up on his blog, Just Your Average Joggler (which I highly recommend) and I thought it would make an excellent topic for today. More specifically, I would like to discuss the relationship between diet soft drinks and obesity.

At first, I did not expect there to be any relationship between diet soft-drinks and obesity - if they contain no calories, they can't possibly contribute to a positive energy balance, right? (e.g. energy in > energy out). Early studies of calorie-free sweeteners like aspartame seem to support that position. For example, a review article from 1991 suggests that "aspartame-sweetened foods or drinks is [sic] associated with either no change or a reduction
in food intake
". However, more recent studies suggest that the issue is not quite so simple.

An article published last summer by Sharon Fowler in the journal Obesity suggests that individuals who consume diet soft drinks are at dramatically increased risk of overweight and obesity than those who do not consume diet soft drinks. For example, over an 8-year period, individuals who consumed just 3 diet soft drinks a week were 40% more likely to be overweight or obese than those who consumed none. The risk of overweight and obesity continued to increase dramatically with increased diet soft drink intake, and was independent of other factors like exercise, smoking, and socioeconomic status.

The Fowler study doesn't prove that diet soft drinks cause obesity (people who drink more diet soft drinks may also have other behaviors that put them at increased risk for weight gain), but they are still pretty surprising. While diet soft drinks may themselves be free of calories, recent evidence suggests that they may increase caloric intake at future meals. For example, when rats are given access to unlimited amounts of food, those who are used to consuming calorie-free drinks eat dramatically more than those who are used to consuming drinks flavoured with sucrose. It may be that calorie-free drinks impair the body's ability to anticipate the caloric content of a given meal, eventually resulting in increased caloric intake and weight gain. Others have suggested that calorie-free sweeteners like aspartame may also increase appetite at future meals.

So, while it is not yet completely clear if diet soft drinks cause obesity, there are some good reasons to limit their intake. Plain water is always a great choice, and if you find that too boring, consider adding a few slices of lemon or cucumber to add some fresh flavour (an idea I had never heard of until I came across it on the Thought for Food blog). And as always, a little physical activity is always a good decision :)

Thanks again to Perry Romanowski for the interesting question.


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7 Response to "Do diet soft drinks lead to obesity?"

  1. Perry Said,

    Thanks for the answer. I think the idea that diet drinks screw up your body's sugar/calorie sense is an interesting one. No doubt more research needs to be done.

    Now I wonder, based on what you found, what would be a better strategy?

    1. Drinking diet sodas
    2. Drinking regular sodas

    Of course, drinking water or tea or seltzer would be better, but if you are going to drink sodas, which is better? (Assume equal amounts of soda are consumed in each strategy).

    True, option 2 would result in more calories from the soda but maybe less calories from eating.

    Should I switch back to regular soda?

    Posted on January 15, 2009 at 12:41 PM

  2. Travis Saunders, MSc Said,

    Great question Perry. Here is another article on the work of Sharon Fowler, which I mentioned in today's blog:

    In it, she says that people who drank diet soda are at a higher risk of obesity than those who drink regular soda. It doesn't prove causation, but it's a pretty interesting finding. My personal suggestion is to try to keep your consumption of either to a minimum.

    Since you have a few hundred days of joggling left to go, I'm sure you'll be fine either way :)

    Posted on January 15, 2009 at 4:29 PM

  3. Darya Pino Said,

    This reminds me of a post I just saw on a diet blog touting the benefits of different low-calorie frozen foods. I would bet you the people who eat those foods are more likely to be overweight too, similar to diet soda drinkers.

    Fat people eat diet foods, thin people eat real food.

    Posted on January 15, 2009 at 7:13 PM

  4. Darya Pino Said,

    One more note: sodas and Twinkies aren't real food either.

    Posted on January 15, 2009 at 7:14 PM

  5. Travis Saunders, MSc Said,

    Darya - agreed on all counts!

    Posted on January 16, 2009 at 10:30 AM

  6. Perry Said,

    I heard an interview with someone on NPR who had written a book that summed up his diet advice in like 8 words.

    Eat real food, mostly plants. Not too much

    Unfortunately, this is easier said than done.

    Posted on January 18, 2009 at 6:32 PM

  7. Travis Saunders, MSc Said,

    I have read the book myself - In Defense of Food. It's an excellent read.

    Posted on January 20, 2009 at 10:51 AM


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We are PhD students in the School of Kinesiology and Health Studies at Queen's University in Kingston, Ontario. Our research focuses on the relationships between obesity, physical activity, and health risk. This blog is our attempt to consider the many "cures" for obesity that we read about on a daily basis. Enjoy.


The opinions expressed here belong only to Peter and Travis and do not reflect the views of any organization. Any medical discussion on this page is intended to be of a general nature only. This page is not designed to give specific medical advice. If you have a medical problem you should consult your own physician for advice specific to your own situation.

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