5 Scary Reasons You Should Stop Drinking Diet Sodas

Written by Tim Skwiat

Diet Soda is Bad

Most of us know that drinking regular soda—which fall under the umbrella of sugar-sweetened beverages (SSB)—is bad news for our health and waistlines. After all, they’re increasingly and notoriously associated with a laundry list of negative health outcomes. These include being overweight, obesity, type 2 diabetes, metabolic syndrome (MetS), neurodegenerative conditions, cardiovascular disease, stroke, dental cavities, and more.1 Pretty much, you name it, and you can find a connection to regular consumption of these sugary beverages.

Naturally, this has led many people to reach for diet sodas, which contain non-caloric, high-intensity artificial sweeteners. And they do so often at the urging of researchers, healthcare practitioners, and authoritative health organizations. On the surface, this seems rational and potentially beneficial. Especially for reducing caloric intake, promoting weight management, and improving metabolic health. However, striking evidence is accumulating that opposes the regular consumption of artificial sweeteners.

For instance, Susan E. Swithers, a professor of psychological sciences and a behavioral neuroscientist at my alma mater Purdue University, says, “Although it seems like common sense that diet sodas would not be problematic, that doesn’t appear to be the case. Findings from a variety of studies show that routine consumption of diet sodas—even one per day—can be connected to higher likelihood of heart disease, stroke, diabetes, metabolic syndrome, and high blood pressure, in addition to contributing to weight gain.”2

5 Reasons Diet Soda is Bad For You

Glycemic Control, Metabolic Function, and Gut Health

With zero calories and no sugar, there shouldn’t be any concern about diet sodas when it comes to carbohydrate management and metabolic health, right? Wrong. Multiple studies have shown that consuming artificially sweetened sodas is associated with an increased risk of type 2 diabetes and metabolic syndrome (MetS).3,4

If you’re not familiar with MetS, it’s the health-ravaging combination of high blood pressure, high blood sugar, excess belly fat, and unhealthy blood lipids/fats (e.g., high triglycerides, low “good” HDL cholesterol). It’s collectively tied to an increase in seemingly all non-communicable chronic diseases. (This includes cardiovascular disease, stroke, diabetes, certain cancers, neurodegenerative diseases, and more.)

It’s worth noting that one study found the daily consumption of diet soda was associated with a 36% greater risk of MetS. It was also associated with a 67% increased risk of developing type 2 diabetes.5 As far as MetS, daily diet soda consumption was associated with significantly greater risk for abdominal obesity and high fasting blood sugar. In other words, more belly fat and impaired glycemic control—no bueno!

It’s important to point out that studies like these show associations (not causation). Some studies have suggested that confounding factors (e.g., health status, diet quality, body mass index) may explain the association.6 There’s also “the chicken or the egg” argument. That is, some folks who drink diet sodas may be doing so to lose weight, which would confound the results of an observational study.

Having said that, there are plausible explanations for the association. For instance, some speculation suggests consuming artificially sweetened beverages stimulates the appetite for sweetness and more energy-dense foods at subsequent meals.7 Additionally, some people overcompensate for the calories they “saved” by drinking diet sodas by overconsuming other foods or beverages.5 This type of compensation falls under the umbrella of what’s known as “hedonic eating.” This is our drive to eat for pleasure rather than for hunger.

More recently, Israeli researchers found that artificial sweeteners negatively alter the balance of gut bacteria (i.e., gut dysbiosis), leading to glucose intolerance and impaired metabolic function.8 What’s more, previous research has shown artificial sweeteners (such as sucralose) may adversely affect glucose metabolism and increase insulin resistance. These are effects that may be especially pronounced in overweight and obese folks.9

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Cardiovascular Disease and Stroke

In a recent study published in the American Heart Association journal Stroke, researchers examined whether sugar- or artificially sweetened beverage consumption was associated with the risks for stroke or dementia. They found that drinking diet soda daily resulted in a threefold increased risk for dementia (including Alzheimer’s disease) and stroke compared to folks who don’t drink diet soda.17

Although this study has grabbed headlines, it’s certainly not the first to shine the spotlight on this potential link. For example, results from the Northern Manhattan Study found diet soda consumption was associated with an increased risk of stroke and heart attack.18 A study based on data from the Nurses’ Health Study and the Health Professionals Follow-Up Study found regular consumption of diet sodas was associated with a significantly higher risk of stroke.19 In a separate report from the Nurses’ Health Study, researchers found diet soda consumption was associated with an increased risk of coronary heart disease (CHD).20

In a study with nearly 60,000 women participants in the Women’s Health Initiative Observational Study, researchers from the University of Iowa found that compared with women who never or rarely drank diet sodas, women who consumed two or more per day were 30% more likely to have a cardiovascular event (such as CHD, heart failure, heart attack, or stroke). And, they were 50% more likely to die from heart disease.21 In a recent systematic review, researchers from Canada found consumption of artificial sweeteners was associated with higher incidence of high blood pressure and cardiovascular events.15

Considering that at least 20% of Americans drink at least one diet soda every day, these findings are momentous.22 On top of that, consider that type 2 diabetes and MetS, which seem to be closely tied to diet soda consumption, are also major risk factors for heart disease and stroke.

Weight Gain and Obesity

When it comes to weight management and diet sodas, you can probably already see the writing on the wall. We already talked about the potential link between artificially sweetened beverages and an increased risk for abdominal obesity. And we mentioned it’s not uncommon for folks to overeat—whether consciously or unknowingly—when they consume diet sodas.

Along these lines, recent research suggests diet soda drinkers seem to develop somewhat of a resistance to sweet tastes. In other words, they experience less of a reward response for a given amount of sweetness. This lends some insight into the link between diet soda consumption and obesity.10 But there’s more.

In the San Antonio Heart Study, researchers looked at weight change among over 3,600 men and women across a 7 – 8-year period. They found that risk of weight gain and obesity were significantly greater in those who regularly drank diet sodas compared to those who did not.11

Additional observational studies have corroborated these findings. And, several review studies have documented the potential link between diet soda consumption and weight gain.12–14 In a recent systematic review, researchers concluded that consumption of artificial sweeteners is associated with weight gain, increased waist circumference, and higher likelihood of obesity.15

While there are multiple explanations for this connection, it’s fair to point out that the results of these studies are inconsistent. And in these studies, there’s the possibility of “reverse causality,” or “the chicken or the egg” theory again. So, while all this associative research is intriguing, there’s no contending that randomized trials provide the most compelling (and causal) evidence.

Along those lines, in a recent study published in The American Journal of Clinical Nutrition, researchers from Iran compared the effects of replacing diet sodas with water during a weight-loss trial. After 24 weeks of following a reduced-calorie diet, all the women in the study lost weight. Interestingly, however, women who drank only water lost 16% more weight. They also experienced greater improvements in insulin sensitivity and glycemic control compared to women who drank diet soda.16 Even more interesting, the diet soda group only consumed one artificially sweetened beverage per day five days out of the week. That’s a relatively small amount.

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Dementia, Cognitive Dysfunction, Behavior, and Mood

We’ve already touched on the association between diet soda and dementia, including Alzheimer’s.17 Type 2 diabetes is also a known risk factor for dementia.23 In fact, many refer to Alzheimer’s disease as “type 3 diabetes” due to its overlap with type 2 diabetes, including insulin resistance in the brain.24 As we previously outlined, there’s compelling evidence suggesting the artificially sweeteners found in diet sodas can induce insulin resistance and impair glucose tolerance.

In a study published in the journal Drug and Chemical Toxicology, researchers found that long-term consumption of aspartame significantly reduced glutathione concentrations in the brain.25 Glutathione is an important component of the brain’s antioxidant defense system. The researchers also found aspartame ingestion led to an imbalance in the antioxidant/pro-oxidant status in the brain, which is the definition of oxidative stress. Unsurprisingly, given its role in preventing oxidative stress, reduced glutathione concentrations are associated with Alzheimer’s disease and numerous other neurodegenerative conditions.26

In a study published in the journal Redox Biology, researchers once again connected aspartame to altered neural function and neurodegeneration. In this study, researchers from India found long-term consumption of aspartame, a sugar substitute consumed by roughly 200 million people worldwide, significantly increased oxidative stress (e.g., reduced glutathione, increased free radicals) in the brains of rats leading to distorted brain function and to the death of brain cells.27

While many of the studies on artificial sweeteners have been conducted on animals, there is some emerging human evidence as well. For instance, in a study published in the journal Research in Nursing & Health, researchers assessed the short-term effects of aspartame on neurobehavioral effects. Subjects consuming a moderate amount of aspartame for 8 days were more irritable in mood, exhibited more depression, and performed worse on spatial orientation tests.28

In another study, researchers from the National Cancer Institute evaluated the connection between soft drink consumption and the risk of depression among a sample of over 260,000 participants in the NIH-AARP Diet and Health Study. They found frequent consumption of diet sodas significantly increased the risk for depression among older adults.29

One possible explanation is that artificial sweeteners such as aspartame has neurological effects. These may lead to imbalanced levels of key neurotransmitters, including dopamine and serotonin. This is interesting because it may also tie into issues like headaches and insomnia that some people experience when consuming diet sodas and other artificially sweetened products.30


Part of the reason the artificial sweetener aspartame is thought to increase the risk of neurologic deficits and cancer is because of its conversion to methanol and formaldehyde.30 Briefly, aspartame is made up of three ingredients: methanol, aspartic acid, and phenylalanine. When stored near or above room temperature, methanol is metabolized into formaldehyde, which is a known human carcinogen.

In a study published in The American Journal of Clinical Nutrition, researchers examining data from the Nurses’ Health Study and Health Professionals Follow-Up Study found an alarming statistic. Men and women drinking one or more diet sodas per day had a 42% greater risk of leukemia compared to those who consumed none.31

Listen, I’ll be the first to admit that the majority of the evidence highlighted here demonstrates associations (not necessarily cause-effect relationships). A fact I’ve made it a point to reiterate multiple times. However, it seems fair to speculate that diet soda consumption (via artificial sweeteners, hedonic eating, or another mechanism) is at least a “probable suspect” for various negative health outcomes including:

  • Type 2 Diabetes
  • Metabolic Syndrome
  • Gut Dysbiosis
  • Weight Management
  • Cardiovascular Disease
  • Stroke
  • Dementia
  • Cognitive Dysfunction
  • Mitochondrial Dysfunction
  • Behavior and Mood Disorders
  • Certain Types of Cancer

“’Are diet sodas worse for you than regular sugar-sweetened sodas?’ I think that’s the wrong question,” says Susan E. Swithers. The real question: “What good are [diet] sodas for you in the first place?”

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  • sugar and salt
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  • Pereira MA. Sugar-sweetened and artificially-sweetened beverages in relation to obesity risk. Adv Nutr Int Rev J. 2014;5(6):797-808. doi:10.3945/an.114.007062.
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  • Madjd A, Taylor MA, Delavari A, Malekzadeh R, Macdonald IA, Farshchi HR. Effects on weight loss in adults of replacing diet beverages with water during a hypoenergetic diet: A randomized, 24-wk clinical trial. Am J Clin Nutr. November 2015. doi:10.3945/ajcn.115.109397.
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  • sugar addiction
  • Clifford K Conner

    I have been a heavy drinker of diet beverages for over 13 years, and I have noticed most recently lapses in memory and Parkinson’s like symptoms. It very well could be a correlation between the tremendously large amount of diet beverage I drink and these symptoms. I would like more info on this if possible. Many people have warned me about the volume of diet coke that I drink as being unhealthy, but this article seems to have hit home more so than anything I have read or heard. Thanks for the insightful article.

    • Cristina

      Greetings, Clifford. Thank you so much for taking the time to review this article. Everyone here takes pride on what we do and it is through feedback like yours full of affirmations and encouragement that we renew our commitment to always trying our best.

      It is such a compliment to Coach Tim that this article hit home for you, and it resonated enough for you to take a deeper look into your current diet, more specifically your diet cola habit.

      Since we are not medical doctors, or privy to your health history, it would be ill advised to say for sure whether these concerns can be attributed to your choice of beverages, but it certainly does raise awareness of this could potentially be contributing to your symptoms. I would recommend discussing with your regular physician at your next visit, and be sure to be completely honest with your habits, as well as any other habits/factors no matter how insignificant they may seem.

      With that being said, I would be more than happy to offer additional information, and make recommendations to help you kick the habit. One article that Coach Tim also wrote that lends itself to this discussion can be found here:

      Ditch Diet Sodas

      I am looking forward to continuing this discussion with you, Clifford.

  • Guest

    I am not a doctor so I can’t contribute any truly scientific knowledge to this article. However, I have some personal observations to make. I drink Coke Zero occasionally because it quenches my thirst better than water or tea or coffee or whatever. So it has artificial sweetener in it. So what? What’s the difference if I drink a Coke Zero with artificial sweetener or drink a glass of ice tea with one packet of Splenda in it? I have heard the argument that the dark color of the drink is bad for you, it contains some sort of substance that makes it dark that is bad for you,you would be less harmed if you drank a drink with no caramel coloring in it. Well, I don’t LIKE the taste of those sodas. Also, if that is true, that the caramel coloring Coke Zero has in it is dangerous, you would certainly want to give up any grilled meats or veggies, because that burnt substance would be just as bad for you as a Coke Zero. Because the “experts” apparently can’t state a real reason why Coke Zero is bad for me, they try to say that artificial sweeteners make you crave other sweets. That is absolutely untrue. I have what amounts to one packet of artificial sweetener a day, whether in tea or Coke Zero, and I don’t crave other sweets, nor do I eat them. If you waved candy or cake in front of my nose I would push it away because with the exception of Coke Zero, I don’t like sweet foods. Until scientists can come up with some better “reasons” than that, at least stop with the BS reasons.

    • Cristina

      Hi Guest. Thank you for taking the time to share your feedback, and allow us to hear about your personal experiences and nutrition habits.

      Before I begin, I would also like to mention that I am also not a doctor, however I still highly recommend that folks consume water as their primary source of hydration above any/all other liquids.

      With regards to your inquiry about the difference between consuming a Coke Zero or consuming a glass of iced tea with Splenda, the main difference I see is that Coke Zero is sweetened with a blend of aspartame and acesulfame potassium (Ace K), while Splenda is a brand name, no calorie, artificial sweetener which is made from sucralose. Both of which are potentially harmful for you in their own right. More on this in a moment.

      In terms of the dangers of the artificial caramel coloring, this is not the same as the natural charring of foods that occurs during grilling or cooking. The caramel color used in sodas, more specifically Coke Zero, is shown on nutrition labels as 4-Mel (4-methylimidazole), and is considered worse for your than light-colored sodas. This artificial coloring is classified as potentially carcinogenic to humans by the International Agency for Research on Cancer.

      While you may not experience any of the side effects of consuming diet sodas, or have any cause for concern, I would like to share the following article with you so you may understand the potential dangers of these various artificial sweeteners.

      Side Effect of Artificial Sweeteners</a

      Please visit us again soon, as we look forward to your contributions.