Are Diet Sodas Really That Bad?

Today I’m reviewing one of the topics that interest me the most: Diet Coke. I’m one of the weirdos who actually likes the taste of Diet Coke better than regular Coke. I think it’s because Diet was usually what we had in my house growing up. And also because it doesn’t leave my teeth feeling all grimy like regular Coke. I gave up Diet Coke all together from about 2012-2015 after hearing about how terrible it was, even compared to sugary drinks. However, lately I’ve been skeptical of most health claims and decided it probably wasn’t a big deal. Out of my own curiosity and because of requests from other readers, today I’m giving artificial sweeteners the full review.

  1. The Claim

Regular soda is bad for you, but diet soda is even worse. It makes you gain even more weight and causes cancer. It’s a neurotoxin and is basically the same as drinking formaldehyde.

  1. Results from Initial Search

I trolled the internet for hours just to see what I would find. The internet was pretty split, just as it is for most controversial health claims. A few of the sites making diet drinks out to be the devil were:,, Dr. Axe,, and MD

These sites made claims that diet drinks trick your taste buds into craving sweeter foods and overcompensating for the calories not provided in the drink. Some state diet drinks trigger insulin and glucose intolerance leading to type 2 diabetes, weight gain, heart disease, and other symptoms of metabolic syndrome.

Other health problems they considered to be associated with diet drinks included: kidney damage, tooth erosion, compromised lungs, migraines, depression, anxiety, short term memory loss, multiple sclerosis, fibromyalgia, hearing loss, fatigue, brain tumors, epilepsy, chronic fatigue syndrome, birth defects, Alzheimer’s, ADHD, Parkinson’s, gut dysbiosis, DNA damage causing breast cancer, liver cancer, lymphoma, and leukemia, urinary and bladder cancer, depression, and lower bone density.

Some sites, such as WebMD,, and were more cautious with their claims. They generally agreed that drinking diet soda didn’t help people lose weight and that it only caused cancer when given to lab animals in amounts that greatly exceed the acceptable daily intake (ADI). However, they supported the notion that people probably give themselves permission to eat other unhealthy foods to compensate for the diet soda. They also agreed that diet soda increases a person’s risk for diabetes. These sites were careful to say that just because conditions like diabetes and weight gain were associated with drinking diet soda, diet soda was not necessarily the cause. Perhaps people who know they are at risk for metabolic syndrome choose to drink diet soda more often than the general population.

Finally, several sites claim diet soda probably doesn’t cause any health problems if limited to 1-2 cans per day, with the exception of tooth decay. However, tooth decay is caused by the acidity of the drink, not the artificial sweetener.  These sites include: Mayo Clinic,, and (American Cancer Society).  They say there is no evidence to suggest diet soda causes weight gain, spikes insulin levels, or inhibits fat loss. Evidence for overcompensation is mixed and metabolic syndrome associations are confounded by other dietary behaviors. The American Cancer Society fights the formaldehyde claim by explaining that the amounts are not harmful. Methanol from fruit juice breaks down into 10 times more formaldehyde than aspartame. They also state that the FDA sets a max daily safe amount of each artificial sweetener (acceptable daily intake) which is set to many times less than the smallest amount that could cause concerns in lab animals. An average size person would need to drink 19 cans of diet soda per day to reach levels that might be dangerous. The exception to this is people with Phenylketonuria (PKU). This is a rare genetic disorder where people can’t break down phenylalanine found in many foods. These people should avoid diet soda.

  1. Follow-Up Questions

Once again, I’ve found that I need to narrow my focus. How should I do this? I decided to focus on the middle group from the list above. This is the group that regards diet soda with caution. They don’t claim it causes every health problem known to man, but they are concerned that it may paradoxically contribute more to weight gain than weight loss. They also believe diet soda may contribute to metabolic syndrome, especially type 2 diabetes. This seems like the area with the most debate and valid health concerns.

There may be evidence to link artificial sweeteners to other health risks, but these will have to be explored more in depth at another time. My peer reviewed research below was narrowed to focus mainly on artificial sweeteners and weight gain/metabolic syndrome. You will notice that some of the experimental designs I reviewed looked at other health effects along with weight gain and metabolic syndrome markers.

  1. Reader Comments

None yet. Please leave me questions and/or articles you’ve found on topics you’d like me to explore!

  1. Primary Source Review

The first group of studies is in chronological order and generally concludes that artificial sweeteners are safe and may help with weight loss. The second group is also in chronological order and generally concludes that artificial sweeteners may be harmful and do not help with weight loss.

Group 1

  • Effect of drinking soda sweetened with aspartame or high-fructose corn syrup on food intake and body weight. (1990)
    • Healthy, normal-weight people were divided into groups that were given either aspartame sweetened soda or soda with high fructose corn syrup. They were allowed to eat their regular diets. A control group that was not given soda was also included.
    • Results: The group that got diet soda ate fewer calories than the control group during the 3-week study. The males that drank diet soda lost weight, but not the females. All members of the group that drank regular soda gained weight. Both the diet and regular soda groups ate less sugar in other forms than the control group without affecting intake of other nutrients. Researchers concluded that diet soda reduces sugar intake and may help control calorie intake and body weight.
  • Effects of consumption of caloric vs noncaloric sweet drinks on indices of hunger and food consumption in normal adults. (1991)
    • 20 healthy subjects consumed water, aspartame, saccharin or sucrose (sugar) sweetened drinks 3 hours after breakfast.  The subjects recorded how hungry they felt 15 and 45 minutes after their drink. Researchers also measured how much they ate at lunch.
    • Hunger reports were highest for the people who drank water and lowest for the people that drank sugar. There were no differences in how much people ate at lunch.
    • Results: artificial sweeteners do not increase hunger or food intake.
  • The effect of aspartame as part of a multidisciplinary weight-control program on short- and long-term control of body weight. (1997)
    • 163 obese women were divided into an aspartame group and a non-aspartame group during a 19 week weight loss program, a 1 year maintenance program, and a 2 year follow up period.
    • During the weight loss program, both groups lost about 10% of initial body weight.
    • After the 1 year maintenance, the aspartame group regained 2.6% of the weight and the non-aspartame group regained 5.4% of the weight.
    • After the 2 year follow up, the aspartame group regained 4.6% of the weight and the non-aspartame group regained 9.4% of the weight.
    • Researchers suggest including aspartame in a long term weight loss program may help with maintenance.
  • Nonnutritive sweetener consumption in humans: effects on appetite and food intake and their putative mechanisms. (2009)
    • Literature review conclusions: People who consume artificial sweeteners generally do not compensate by eating more. The addition of artificial sugar poses no benefit for weight loss or reduced weight gain without purposeful calorie restriction. Consuming artificial sweeteners probably does not contribute to weight gain or obesity.
  • Low-calorie sweeteners and body weight and composition: a meta-analysis of randomized controlled trials and prospective cohort studies. (2014)
    • 15 randomized control trials (RCT) and 9 prospective cohort studies (PCS) that looked at the relationship between low-calorie sweeteners and body weight were reviewed.
    • The randomized control trials associated low calorie sweeteners with reduced body weight, BMI, fat mass, and waist circumference.
    • The prospective cohort studies found that low calorie sweeteners were not associated with body weight or fat mass, but were associated with higher BMI.
    • RCTs provide more reliable evidence than PCSs. Therefore, researchers suggest substituting artificially sweetened beverages for regular calorie versions may result in moderate weight loss and be useful on a maintenance plan.
  • Substitution of sugar-sweetened beverages with other beverage alternatives: a review of long-term health outcomes. (2015)
    • 6 cohort studies and 4 RCTs with acceptable to high quality ratings through 2013 were analyzed.
    • All studies associated substituting sugar sweetened beverages with other types of beverages (did not specify) with lower weight gain.

Group 2

  • Effects of artificial sweeteners on body weight, food and drink intake. (2010)
    • Mice were divided into 2 groups: control and artificial sweetener. The mice who were fed artificial sweeteners were given the acceptable daily intake which can be compared to reasonable human consumption. All mice were allowed to eat as much regular chow as they wanted.
    • Results: consumption of artificial sweeteners resulted in significantly increased body weight even though food intake was the same for all groups.
  • Cytotoxic effect of aspartame (diet sweet) on the histological and genetic structures of female albino rats and their offspring. (2012)
    • Rats were divided into control groups and experimental groups. Experimental groups were fed the acceptable daily intake of aspartame.
    • Every 2 weeks, measurements were taken. Researchers found that the experimental groups had decreased body weight, high histological lesions, increases in chromosomal aberration and DNA fragmentation compared to controls.
  • Saccharin and aspartame, compared with sucrose, induce greater weight gain in adult Wistar rats, at similar total caloric intake levels. (2013)
    • Rats were divided into 3 groups and fed either: yogurt with sucrose (sugar), yogurt with saccharin, or yogurt with aspartame. Amounts of sweetener were a reasonable amount that could compare to levels of human consumption. Physical activity was restrained
    • Conclusion: After 12 weeks, there was no difference in caloric intake among groups. The groups fed artificial sweeteners gained more weight than the group fed sugar. Researchers think this is due to either retention in fluid or decreased physical activity.
  • Effects of a nonnutritive sweetener on body adiposity and energy metabolism in mice with diet-induced obesity. (2014)
    • Obese mice were divided into 3 groups: sugar, artificial sweetener, and water. Amounts were consistent with what might be consumed by a human. After 4 weeks, measurements were taken.
    • Results: The mice that drank sugar had increased weight, body fat and hyperglycemia compared to the others. The group that drank artificial sugar had increased body fat, hyperinsulinemia, leptin levels and triglycerides compared to controls.
  • Impact of aspartame and saccharin on the rat liver: Biochemical, molecular, and histological approach. (2015)
    • Rats were divided into 5 groups: control, acceptable daily dose aspartame, acceptable daily dose saccharin, 4 times daily dose aspartame and 4 times daily dose saccharin
    • After 8 weeks, rats given artificial sweeteners had significantly reduced weight. However, they also had increased risk of liver cancer due to decreased suppression of a tumor gene, lower antioxidant levels, and “histological changes reflecting the hepatoxic effect of aspartame and saccharin”.
  • Metabolic and feeding behavior alterations provoked by prenatal exposure to aspartame. (2015)
    • I did not have access to the full article
    • Results: When female animals consume artificial sweetener during pregnancy, their offspring are more likely to have negative outcomes in adulthood including: higher consumption of sweet foods, increased blood glucose, LDL and triglycerides. The effects were more pronounced in males than females.
  • Artificial sweeteners are not the answer to childhood obesity (2015)
    • I did not have access to the full article
    • Artificial sweeteners are associated with increased risk of the same chronic diseases as sugar consumption. Researchers are not sure exactly why, but make several suggestions:
      • Diminished release of hormones involved in blood glucose regulation
      • Altered gut microbiota which also may impair glucose regulation
      • Exposure to hyper-sweet foods may increase preference for sweetness
  • Low-calorie sweetener use and energy balance: Results from experimental studies in animals, and large-scale prospective studies in humans. (2016)
    • This is a review of animal and human studies.
    • Researchers state that both animal and human studies find that low calorie sweeteners are associated with weight and fat gain, obesity, cardiometabolic risk, and even total mortality even when other lifestyle factors are controlled for.
  • Aspartame intake is associated with greater glucose intolerance in individuals with obesity. (2016)
    • Cross-sectional survey, nationally representative sample. 2856 adults tested. Results are based on what people in the study reported that they ate or drank within the last 24 hours.
    • Discussion: aspartame is associated with obesity-related deteriorations in glucose tolerance and fasting glucose. Consumption of aspartame may be associated with greater diabetes risk in people who are obese. Aspartame was related to impairments in glucose tolerance for overweight people, but not lean people. However, very few lean people reported consuming aspartame.
    • Conclusion: aspartame may be associated with greater glucose intolerance, particularly for those with obesity.
    • The authors don’t think people with diabetes purposefully chose diet sodas because they only included people who were not already diagnosed with diabetes.
  • Effects of long-term administration of aspartame on biochemical indices, lipid profile and redox status of cellular system of male rats. (2016)
    • Rats were divided into 4 groups and given either: water, 15 mg/kg aspartame, 35 mg/kg or 70 mg/kg daily for 9 weeks.
    • Results: the groups receiving 15, 35 and 70 mg/kg aspartame had “increased lipid peroxidation products in the kidney, liver and brain”. The 35 and 70 mg/kg groups had increased levels of total cholesterol, triglycerides, and LDL as well as other health problems.
  1. What We Know and Don’t Know

Looking at these studies, we can see a few trends. First of all, diet soda seems to be pretty bad for rodents. Not a single study using mice or rats found the artificial sweetener to be harmless. The studies I reviewed all gave the rodents small amounts of sweetener that could reasonably be consumed in an equivalent ratio by humans. So, if mice and rats have fat gain, higher LDL and triglycerides, glucose intolerance, liver cancer, and chromosomal problems at low levels of consumption, are humans at risk too? Maybe. All of these rodent studies have been done fairly recently (many published in 2015 and 2016) and have not been repeated on humans. I’d be willing to bet this is because humans are harder to control and have much longer life spans. 3 weeks in mouse time is probably something like 3 decades in human.

The studies involving humans were mostly done in the 90’s. They looked at large groups of people and collectively determined mild weight benefits for people drinking diet sodas compared to regular sodas. They didn’t usually measure the same other kinds of health outcomes as the rodent studies. We don’t really know how artificial sweeteners affect us at a metabolic level over long periods of time because there are so many confounding variables.  There is some consistency when it comes to people who are already overweight or diabetic. These people seem to experience more glucose intolerance related to artificial sweeteners than healthy people at lower body weights.

During my research I didn’t come across any overt conflicts of interest. However, some may exist on either side of the fence.

  1. Conclusions and Applications

I was actually quite surprised at the end of this one. I had initially thought the research would show artificial sweeteners to be harmless at reasonable doses. I figured the rodent studies would reflect very high levels of sweetener being force fed until poor health outcomes were reached. I was wrong about this. Mice and rats had some pretty alarming health outcomes at fairly low doses after just a few weeks. As the dose increased, health decreased. The human studies, even the RCTs, were broad and outdated. They relied on measurements such as BMI which have little to do with actual health. Their outcomes showed very modest weight reductions and didn’t delve deeply into other components of metabolic syndrome.

In my review, I mainly focused on weight, diabetes, and metabolic markers. I didn’t get into the other issues such as cancer and neurotoxicity. Admittedly, I think arguments claiming diet soda causes these problems are fairly weak, but I might be surprised to see what I find here as well.

My personal conclusion is that diet sodas are probably just as bad for a person’s health as regular sodas, possibly in different ways. However, neither diet nor regular soda is going to kill you if consumed occasionally. Both diet and regular soda can be treated like dessert. Eat sparingly. I’d rather have ice cream for dessert anyway. As for beverages, Topo Chico for the win!

I would love to hear some opinions on this!

Author: Tara

Skeptical health and fitness enthusiast (and also speech-language pathologist)

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