Drink Diet Soda, Gain More Weight?

I know the concept seems counterintuitive: drink more diet soda, gain more weight. However, there has been a media buzz revolving research studies which indicate just that. These artificially sweetened, zero-calorie beverages are marketed as a way to consume less liquid calories, resulting in an energy deficit and thus weight loss. The FDA recognizes stevia, aspartame (Equal), sucralose (Splenda), and other no-calorie sweeteners as safe for the general population to consume.

In addition, food products containing artificial sweeteners has been on the rise over the past 20 years. Know what else has been on the rise? America’s rates of obesity. Are the two linked? I’m not so sure.

Source: Yang Q. Gain weight by “going diet?” Artificial sweeteners and the neurobiology of sugar cravings. Yale J Biol Med. 2010 June; 83(2): 101–108.

Now I’ll be completely honest here, I’m not afraid to admit I absolutely love an ice-cold glass of (fountain) Diet Coke/Pepsi every now and then (or perhaps more often than I care to admit). I’ve also had a few of my peers ask me about this diet soda-weight gain dilemma as well. So I thought it made perfect sense for a food blogger, such as myself, to delve into the sticky and sugary research to find the “truth” behind these claims.

However, when I began my literature search, the articles that supported this claim were only rat studies and human observational studies. For the most part, most large health organizations do not feel that these research studies are strong enough evidence to support the conclusion that diet soda can lead to weight gain.

The Rat Studies

In a 2008 article by Swithers and Davidson, 27 rats were randomly assigned to three diet treatment groups for 5 weeks. A control group, a group that consumed yogurt sweetened with glucose for half of the days, and a group that consumed yogurt whose sweetness alternated between glucose and saccharin for half of the days. Therefore, these two groups of mice were consuming the same number of calories, but with differing amounts of prolonged sweetness. Results found that rats gained significantly more weight and gained significantly more fat mass when they received the artificially sweetened yogurt.

There were a few more studies very similar to this one conducted by the same researchers on rats with different artificially flavored colas, puddings, etc…all revealing similar results.

So what did these studies tell us? They indicate that sweetness was associated with weight gain in rats, even when the “sweetness” was coming from a no-calorie sweetener.

These results are very intriguing because they support the link between artificial sweeteners and weight gain. But I have two problems with this study. One is that the test subjects are rats. It is difficult to compare a rat’s food intake to a human’s because, let’s face it, us humans tend to have more complicated reasons for what and how much we eat. Number two, the sample size is extremely small with only 8-10 rats per experimental group, which doesn’t tell us a whole lot.

The Human Observational Studies

An observational study of over 5,000 participants in San Antonio, Texas followed subjects for 7-8 years. Results found that, not only was artificially sweetened beverages associated with weight gain, but that the more people consumed the more weight they gained (shown in the graphs below).

How Much Is Too Much?

The upper limits of how much non nutritive sweeteners are deemed “safe” for the general population is surprisingly very high.

In a 2009 article from the American Journal of Clinical Nutrition, authors reported common zero-calorie sweeteners and their Acceptable Daily Intakes (ADI), presented in the chart below.  What do these numbers actually mean in terms of real food?

For aspartame, consumers would need to drink upwards of 18-19 cans of diet soda per day in order to reach the ADI, 8-9 sweetener packets for saccharin, and 6 cans of diet soda for sucralose.

Maybe We’re Just Looking for an Excuse?…

This same article looked at dozens of studies relating to the topic of artificial sweeteners, and the authors concluded that there wasn’t enough substantial evidence to link nonnutritive sweeteners with increased appetite and weight gain.

In addition, The Academy of Nutrition and Dietetics released a position paper this year which encourages the use of zero-calorie sweeteners as an aid in weight loss along with a reduced calorie, healthy diet. The Academy also made the conclusion that artificially sweetened beverages are not associated with poor appetite control or weight gain. The paper does state, however, that some of the research may be limited and more research may be needed. I’d have to agree with that. I would like to see many double-blind, randomized control studies which directly proposes an intervention on humans as opposed to just retrospective, observational, and animal studies.

That being said, after looking into some of the literature I still find it hard to completely associate diet sodas with weight gain. Even though the obesity epidemic is on the rise, artificial sweeteners can not be to blame when there are (literally hundreds of) other contributing factors as to why people are gaining more weight. For example, individuals may be choosing more higher calorie, higher-fat foods in conjunction with their diet sodas. For example, have you ever been in line at McDonald’s and seen someone order a Big Mac and a Diet Coke? I highly doubt it’s the Diet Coke adding inches to their waist line…

So in my opinion, if you feel the need to crack open a fizzy can of diet soda…at least it’s better than drinking regular soda which has an extra 140 calories per can. That’s a plus, right? And anyways, I’m more worried about artificial sweeteners being associated with a higher risk of cancer…but that story’s for another blog post some other time.


4 thoughts on “Drink Diet Soda, Gain More Weight?

  1. Good post! I think that artificial sweeteners do not cause weight gain, or at least are not to blame for America’s obesity epidemic. While our consumption of artificial sweeteners has increased in the past 50+ years, so has our consumption of protein, carbs, and fats. We’re just eating more of everything! Increased calories = more energy stored as adipose tissue.

  2. Hi Mary! This is a great article. What are your thoughts on what the artificial sweeteners do to the body overall? The chemicals in sweeteners, although approved by the FDA, can’t be healthy for the human body. I have no training in this area whatsoever, my knowledge of it comes from what I read, but I have read that aspartame is pretty much a poison. My whole lifestyle (and therefore, my blog) is based on avoiding chemicals in the diet, when possible. I

    • Hit enter somehow…anyway, I’d love to hear your thoughts on chemicals in the diet, and what you think about how so much of what we eat is actually food-like product, not real food.

      • Hi Jill! Thank you. Yes, I completely agree with you that aspartame as well as many other artificial sweeteners can be detrimental to overall health. While this post was focused mainly on weight gain, there is a vast amount of evidence in the literature linking consumption of aspartame with cancer incidence/risk. If you are interested in this area, there are literally hundreds of studies you can read up on! Good luck with blogging and let me know if you have any other nutrition-related questions.

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