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Does diet soda cause weight loss… or weight gain?


By Julie Hughes

October 5, 2009




        As obesity rates escalate rapidly in the United States, many people are looking for a quick fix to this epidemic.  For this reason, more and more people are reaching for a diet soda instead of a regular soda as their soft drink of choice.  Since the mid-1990s, sales of regular soda have declined while sales of diet soda have risen consistently ("A new front in the cola wars").  But is drinking diet soda really an effective weight loss strategy?  More and more people are arguing that it is not.  In fact, some adamantly claim that drinking diet soda could actually cause weight gain.  In this essay, I examine some web-based theories regarding diet soda and weight loss and gain.  I then attempt to compare these theories to the actual scientific research that has been conducted. 

How do you lose weight?

        First, it is important to understand exactly how weight loss occurs in the body.  Alexander and Stare (1967) declared that weight loss only occurs when more caloric output is greater than caloric input.  Therefore, the idea of weight loss is conceptually simple: you just have to burn more energy than you take in.  The most efficient approach is to simultaneously limit your food intake while increasing your physical activity.  In reality, weight loss can be challenging for a variety of reasons.  There is no magic solution to the problem of obesity, despite the plethora of weight loss gimmicks and medications advertised today.  The question is: are people who drink diet soda in an attempt to cut calories making weight loss easier or more difficult for themselves?

Web-based sources

        If you do a Google search for diet soda you will see more links to websites claiming that diet soda is ‘bad for you’ than ‘good for you.’  You may have to look a little harder, but there are a few unscientific websites that note the potential benefits of drinking diet soda.  One reason why more articles emphasize potential dangers of diet soda could be to capture the audience’s attention.  Most people already assume a drink labeled ‘diet’ is healthy and helps you lose weight; they don’t need a website to tell them this.  However, if this notion that diet soda may be not only unhelpful but actually detrimental emerges, people will want to hear about it.  Such a counter-intuitive claim is interesting and grabs our attention.  However, should you jump to the conclusion that diet soda is harmful just because more popular websites claim it is?  Not without researching the topic further.  These internet sources vary in reliability and should not be blindly accepted. 

Possible reasons why drinking diet soda will help you LOSE weight, found on the web 

        If you’re going to drink regular soda anyway, switching to diet will undoubtedly reduce the number of calories you’re consuming ("Diet coke can help weight loss").  A can (12 fl oz) of Coca-Cola classic contains approximately 146 calories, while the same amount of Diet Coke contains only around 2 calories ("Coca-Cola soft drink nutrition information").  Since one pound of fat is stored in the body for every 3,500 excess calories, drinking a lot of regular soda could quickly add on unwanted pounds. 

        The same website claims that diet soda promotes weight loss because it contains caffeine ("Diet coke can help weight loss").  The site claims that caffeine increases energy, which would allow you to burn more calories.  It also states that caffeine can decrease appetite, which would limit the number of calories you consume.

        Another reason to drink diet soda if you’re trying to lose weight is that calories found in liquids impact weight gain even more than calories found in foods ("Fewer sugary drinks key to weight loss").  The rationale behind this statement is that the body can adjust its own food intake, but not its liquid intake.  So, if you eat an especially large lunch with lots of calories, you will feel fuller and not eat as much at dinner.  However, liquid calories do not register with the body in the same way.  You could consume a large, high-calorie regular soda at lunch and again at dinner without your body protesting.            

Possible reasons why drinking diet soda will make you GAIN weight, found on the web

        Most of the web arguments against drinking diet soda for weight loss center around the artificial sweeteners found in diet soda.  An article on by David L. Katz, MD, admitted that though the scientific evidence is not definite, Katz personally believes diet soda can cause weight gain ("Do diet drinks actually cause weight gain?").  Katz mentioned research which showed that artificial sweeteners weakened rats’ ability to assess how much they’ve eaten, leading them to overeat and gain weight.  He notes that the same process might be occurring in humans who drink diet soda.  Katz also pointed out that sweetness is slightly addictive, so tasting more of it could cause you to need more sugar to feel satisfied.  This might mean you would eat a larger piece of cake for dessert, negating the calories you had saved by drinking diet soda.   

        Aspartame, the artificial sweetener used in the original Diet Coke, is about 200 times sweeter than natural sugar, and Splenda, another artificial sweetener in some diet sodas, is about 600 times sweeter than natural sugar ("Sweeteners and you").  Some worry that the ultra-sweetness of these artificial sweeteners could cause those who consume them to crave more sweet things ("The truth about diet soda").  Typically, sweeter foods have more calories, so acting on that intensified craving for sugar could lead you to consume more calories than you would have before.

        Donovan Baldwin’s article on argues that diet soda sets off a “sugar trap” in your body ("Water, diet sodas, and weight loss").  This “sugar trap” is triggered when the body consumes an artificially sweetened drink or food.   The body expects to receive energy from the sweet-tasting substance, and it is disoriented when it does not.  Therefore, the body will not be “very happy” until it is actually given calories.  Donovan also cautions against the caffeine found in many diet sodas.  He says that caffeine (a diuretic) will dehydrate the body, slowing down metabolism.  In addition, that dehydration will cause you to feel thirsty, which the body easily interprets as hunger, so you eat more food.  Donovan is not a nutritional or medical expert, nor does he cite actual scientific research to back up his claims.  Therefore, his article must only be considered as his individual speculation.      

What does scientific research actually say about diet soda and weight loss/gain?

         Wolff and Dansinger (2008) examined existing research regarding soft drinks and weight gain.  They were trying to see if evidence of a causal relationship was actually present.  They identified a number of observational studies that showed an association between soft drink consumption and weight gain.  However, the absence of actual clinical trials led them to conclude that there may not be a true causal relationship.  Soft drink consumption and weight gain are certainly correlated, but we don’t know that soft drinks are causing the weight gain.  Any number of confounding factors could be involved.  

          Mattes and Popkin (2009) conducted a review of the available literature about non-nutritive sweeteners and their influence on human appetite and food consumption.  Non-nutritive sweeteners are those artificial sweeteners, like the ones used in diet sodas, which do not contain calories.  They found that some studies have shown adding a non-nutritive sweetener (NNS) can indeed foster hunger.  However, other studies showed that the presence of a NNS in an energy-yielding food or drink does not cause hunger.  Thus, the nature of the relationship between non-nutritive sweeteners in diet sodas and hunger is not conclusive. 

        Sweetman, Wardle, and Cooke (2008) studied how children’s “desire to drink” (DD) relates to drink consumption and preferences.  They determined that a greater DD was associated with increased soft drink consumption.  Their study suggested that the desire to drink is linked to a preference for the taste of sugary drinks, not just thirst or hunger.  This may give some merit to the idea that the taste of sweetness is slightly addictive.      

        McKiernan, Houchins, and Mattes (2008) investigated the true nature of thirst, hunger, drinking, and feeding.  Though we widely believe that thirst prompts us to drink and hunger prompts us to eat, this is not necessarily the case.  In fact, this study found that people do not correctly respond to thirst and/or hunger the majority of the time.  The researchers believe modern developments (such as bland high-calorie sports drinks or artificially sweet zero-calorie diet sodas) may be contributing to this disturbance of our natural associations between thirst and hunger.  Also, this study found that calories ingested in liquid are not accounted for by the body in a comparable way to calories in food.  This may support some of the claims made against diet soda on the web.

        Shimoda, Seki, and Aitani (2006) conducted an experiment to determine whether green coffee bean extract affected the deposition of fat in mice.  They found that the caffeine in the green coffee bean extract did actually reduce the amount of fat absorbed in the mice.  Thus, this study would support the use of caffeinated diet soda for weight loss.        


         So, can drinking diet soda cause you to gain weight?  The quick and technical answer is no, since only an excess of calories can actually cause weight gain.  However, drinking diet soda might make you more susceptible to gaining weight.  Specifically, the artificial sweetener found in diet sodas may induce diet-busting sugar cravings.  The scientific evidence is not conclusive, and more studies need to be done before any drastic assumptions can be made regarding diet soda and weight gain. 

        Thus, I think it is perfectly okay to drink a diet soda every now and then.  Just understand that diet soda isn’t a magic liquid that will melt the pounds away.  Be conscious of your other food and drink consumptions as well, and you will be able to see results.   



Literature Cited

Alexander, M. M., & Stare, F. J. (1967).  Overweight, Obesity and Weight Control.  California   Medicine, 106(6), 437-443. 

Mattes, R. D., & Popkin, B. M. (2009).  Non-nutritive sweetener consumption in humans:         Effects on appetite and food intake and their putative mechanisms.  American Journal of   Clinical Nutrition, 89(1), 1-14.

McKiernan, F., Houchins, J. A., & Mattes, R. D. (2008).  Relationships between human thirst,        hunger, drinking, and feeding.  Physiology and Behavior, 94(5), 700-708. 

Shimoda, H., Seki, E., & Aitani, M. (2006).  Inhibitory effect of green coffee bean extract on fat        accumulation and body weight gain in mice.  BMC Complementary and Alternative Medicine, 6(9).

Sweetman, C., Wardle, J., & Cooke, L. (2008).  Soft drinks and ‘desire to drink’ in preschoolers.      The International Journal of Behavioral Nutrition and Physical Activity, 5(60).

Wolff, E., & Dansinger, M. L. (2008).  Soft drinks and weight gain: How strong is the link?  The   Medscape Journal of Medicine, 10(8), 189.




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