Is Diet Coke bad for you?

by Benjamin S. Newell

A can of Diet Coke

Table of Contents


It's difficult to have a meaningful discussion among peers about the health effects of Diet Coke. There's a lot of misinformation out there regarding diet drinks that have led many people to believe Diet Coke is harmful to your health. While there are a few health risks associated with it, the vast majority of claims made by your friends are typically overblown. There's a lot of contradictory information on the Internet and on the news, and most of it is provided by people who don't know what they're talking about. Yahoo Answers, Bodybuilding Forums, Biking communities, Fox News, MSNBC and other entertainment networks are all guilty of sensationalizing the issue while providing false information and half truths. The claims coming from the corporations themselves are not trustworthy, either, because it's essentially legal for them to lie and mislead consumers as long as they use the correct wording. The purpose of this article is to give you a direct answer regarding the health effects of Diet Coke and whether or not it is a good and safe alternative to Coca-Cola classic. This article is aimed at people who are average consumers of Diet Coke and are unfamiliar with the controversies surrounding the product. I intend to cite sound science while keeping the tone relatively lighthearted and enjoyable to read. This is not a scientific paper, just a communication of evidence to convey a reasonable conclusion.

Fun Fact: The Coca Cola formula was invented in Columbus, Georgia in 1886 after pharmacist John Pemberton created a syrup to cure his morphine addiction. He called this syrup "Pemberton's French Wine Coca". This formula would later be altered when, for various reasons, Pemberton decided to turn it into a soft drink. Pemberton sold the patent and died shortly thereafter. He never got to witness Coca-Cola's success.

Nutritional Information

Nutritional Information of Diet Coke

This is the nutritional information for a standard 12 oz (355 ml) can of Diet Coke (as listed on the can):

Calories:   0
Total Fat:  0 g
Sodium:     40 mg
Total Carb: 0 g
Protein:    0 g

It's important to note that we trust these numbers given by Coca-Cola because we have a government organization, the United States Food and Drug Administration (USFDA), to review and confirm them.

If we examine Diet Coke's affect on our diet based strictly on the given nutritional information, we can clearly see that it does not affect it at all (negatively or positively). If you are on a low-carb diet, Diet Coke does not contain any sugar or other carbohydrates, so it is okay to drink. If you are on a low-fat diet, Diet Coke does not contain any fat, so it is okay to drink. I've never heard of anyone being on a low-protein diet, but if they were, it would be okay to drink. According to the National Institutes of Health, the Recommended Daily Value of sodium in a 2,000 calorie diet is 2,400 mg. As you can see, a can of Diet Coke contains 40 mg of sodium, which makes up about 1.6% of the Recommended Daily Value. [2] Based on the nutritional information alone, consumption of Diet Coke has no noticeable affect on diet whereas a can of Coca-Cola Classic has 140 calories with 39 grams of sugar (which certainly affects diet).


Ingredients in Diet Coke

So what's in Diet Coke that could be bad for you? Here is the total list of ingredients as printed on the Diet Coke can label that I am holding on February 10th, 2014:

Note: I'm aware that ingredients can differ from country to country. Since I reside in the United States, these are the ingredients I've based my research on.

Out of these few ingredients, which is it that causes all of the controversy? I'm sure that everyone reading this is already somewhat aware that the most controversial ingredient listed here is the artificial sweetener "aspartame". But there are other ingredients such as the caramel coloring and the food preservative "potasium benzoate" that people are concerned with as well. Let's go through each ingredient and see if there's any evidence to suggest that these are harmful to your health.

Disclaimer: Human physiology is a very complex field of study. I am not an expert in this area, so I simply refer to the experts. I respect and accept scientific consensus in areas of science that I do not fully understand or study.

Carbonated Water

Carbon dioxide dissolved in water. You don't hear many negative statements about this one, but one rumor I've heard is that the CO2 can weaken your bones. According to an article posted on Mayo Clinic's website by dieticians Jennifer K. Nelson, R.D., L.D. and Katherine Zeratsky, R.D., L.D. there is currently no evidence to suggest carbonated water is bad for your health. [3] The "weaken your bones" bit comes from incorrectly associating sweetened carbonated soda studies with carbonated water. Based on the lack of claims made against CO2 and the studies confirming it's safety, I would say this ingredient really needs no further evaluation. Carbonated water is harmless.

Caramel Color

Also known as "caramel E150d", this is what makes Diet Coke (and other coke products) brown. Unfortunately, a by-product of making this coloring is a chemical called 4-methylimidazole or 4-MEI. In 2007, the potential carcinogenicity of 4-MEI was evaluated in a National Toxicology Program (NTP). From this study, the NTP concluded that there was clear evidence of carcinogenic activity in the mice subjected to 4-MEI.[4] However, the FDA concluded that the levels of 4-MEI in the 2007 study far exceeded the current estimates of human exposure to 4-MEI and that there is no immediate or short-term danger presented by 4-MEI. According to the FDA, a human would have to consume 1,000 cans in a day to be at the equivalent levels found in the NTP study.[5] Disregarding the FDA's conclusion, in 2011, California added 4-MEI to its list of probable carcinogens and forced manufactures to have a warning label on products containing more than 29 micrograms of 4-MEI. [6] This forced Coca-Cola to announce in 2012 that they had their caramel coloring suppliers change their manufacturing process to meet California's standard, though, they emphasized they weren't doing it because of health risks and were only making the change to avoid California's warning label. [7] In 2013, the Center for Environmental Health claimed an independent study found little or no 4-MEI in 9 out of 10 Coke products. [8] To sum all of this up nicely, there was never enough evidence to suggest the amount of caramel coloring (really the 4-MEI) humans were consuming on a day to day bases was enough to cause cancer. Regardless of this fact, manufacturing processes were changed to reduce the 4-MEI and now there really is a negligible amount found in Coke products. There's no further reason to assume the trace amounts of 4-MEI in your Diet Coke is harmful to your health.


Aspartame has a really bad reputation with the majority of it being undeserved. The majority of friends and family I've spoken to believe it is a carcinogen and is much worse for you than high-fructose corn syrup. I can't blame them because I've heard similar horror stories and rumors. The fact is, there is no evidence to suggest it's bad for your health and/or causes cancer. It's been in use as a sweetener for more than 20 years and in many countries throughout the world. There were four studies conducted on animals in the 1970s and 1980s that were evaluated by regulatory bodies worldwide that concluded there was no evidence of genotoxic or carcinogenic effects with regards to aspartame. [10] It was approved by the FDA in 1981 after many tests on lab animals showed it did not cause cancer or have any adverse effects. The few studies that have come out since then that show a link between aspartame and cancer have all been debunked and disproven. Let's go through some of the main ones that have caused some controversy:

- A 1996 report associated an increase of brain tumors between 1975 to 1992, with the increased use of aspartame. This was essentially refuted when National Cancer Institue statistics showed that brain cancers began to rise in 1973, 8 years prior to aspartame being approved for consumption. Also, increase in brain cancer incidences occured mostly in the elderly, which was a group not known for their aspartame use. [12]

- A 2005 study published in the European Journal of Oncology by the European Ramazzini Foundation (ERF) found high incidences of cancer when they fed rats extremely large doses of aspartame. To reach equivalent levels in humans, one would have to drink upwards of 2,083 cans of diet coke a day. The European Food Safety Authority's review of this study concluded that the study's conclusions were flawed and were not actually supported by the data they provided. The EFSA concluded that the incidences of cancer in this study were unrelated to aspartame. [10] [13] The FDA agreed with the EFSA's conclusion stating "FDA reviewed the study data made available to them by ERF and finds that it does not support ERF's conclusion that aspartame is a carcinogen." [14]

Furthermore, there have been numerous studies conducted on animals and humans that have actually proven the safety of aspartame. One of the biggest being a long-term study published in Cancer Epidemiology Biomarkers and Prevention in 2006 by the National Cancer Institute; this study involved more than 500,000 people and found no increased risk of cancer among heavy users of aspartame. [12] There is simply no scientific evidence linking regular use of aspartame to cancer, but a laundry list of research that confirms its safety. Aspartame is now one of the most thoroughly tested and studied ingredients with over 200 scientific studies conducted over 30 years to confirm its safety.


Caffeine is very well known and researched stimulant. Coca-Cola's website says Diet Coke contains about 32 mg of caffeine per 12oz can. According to the National Institutes of Health, 200 - 300 mg of caffeine per day is considered average use and shouldn't have a negative affect on your health. [16] Caffeine (in beverages) is considered relatively harmless by most people's standards, but it is not without its risks. Power users can develop a condition known as caffeinism, which is essentially a caffeine dependency that can lead to a variety of negative health conditions including anxiety and sleep deprivation among others. [30] This is not really a concern for Diet Coke drinkers as it takes roughly 9 Diet Coke cans worth of caffeine per day to reach a conservative "average" use. It would take around 35 cans of Diet Coke per day to reach levels associated with cafeinism.

Phosphoric Acid

According to Coca-Cola, phosphoric acid adds tartness to the soda. The main element, phosphorous, has been the target of several health based controversies. To start, there is 56 mg of phosphorous per 12 oz can of soda, which contains about the same amount of phosphorous as a glass of Orange Juice. Many other common foods such as chicken, ham, peanuts, milk, cheese, and bread contain much higher levels, up to ten times the amount, than what's contained in Diet Coke. [17] With that said, it has been proven that acids, in this case phosphoric acid, can weaken tooth enamel and cause dental erosion. [18] [19] It's important to note that Diet Coke is less acidic than regular Coke, so it will not erode your teeth as much. [20]

Citric Acid

Citric acid is the acid that is found in citrus fruits such as oranges, lemons, and limes. It adds tartness to the soda and helps give it that bite that we all know and love. As with phosphoric acid, citric acid can cause dental erosion by weakening the enamel. [19] It's important to note that Diet Coke is less acidic than regular Coke, so it will not erode your teeth as much. [20]

Potassium Benzoate (Preservative)

According to the US FDA, potassium benzoate "may be added to beverages to inhibit the growth of bacteria, yeasts, and molds". [31] Basically, the purpose of it is to help Coke retain its shelf life. It is approved for consumption in almost every country including in the U.S., Canada, and the majority of countries in European Union. One of the issues with Potassium Benzoate is that when mixed with ascorbic acide (Vitamin C) and/or erythorbic acid (also known as d-ascorbic acid), a by-product chemical can be formed called benzene. Well, we already know that there are trace amounts of sodium in Diet Coke, so it would be wise to look into benzene. The US Environmental Protection Agency (EPA) has set the maximum contaminant level (MCL) for benzene in our drinking water at 5 parts per billion (5 ppb). When benzene levels in our tap water exceed these levels, water suppliers must notify consumers within 30 days. The US EPA sums up the health risks for benzene by stating that people who consume benzene in excess of the MCL for many years "could experience anemia or a decrease in blood platelets, and may have an increased risk of getting cancer". [32] So benzene sounds like it could have some pretty serious negative health effects on people who consume too much of it; the main consequence being cancer. This is serious. Well, how much of it is in Diet Coke? In 2006, the FDA conducted a survey on over 100 soft drinks to determine the levels of benzene in each beverage. Benzene in Diet Coke came in at less than 1 ppb, which shows that it is safe to consume as it falls quite a under the maximum contaminant level (5 ppb) set by the EPA. [33] Benzene is mainly a concern in soft drinks that are fruity and use potassium benzoate a preservative, as the two react to form higher levels of benzene.


Aspartame is made up of a few amino acids, one being phenylalanine and the other being aspartic acid. Studies conducted on aspartame apply to phenylalanine. Coca-Cola is required by law to list this under a warning label. [11]

Common claims made against Diet Coke

Aspartame eats holes in your cellular membranes

It's important to remember that allegations against aspartame have been made for around 40 years. There have been hundreds of studies conducted in over 200 countries proving that aspartame is safe for consumption. So when we come accross a claim such as this, we have to be skeptical. We can't just read a chain letter claiming aspartame was created by Satan and eats holes in your cellular membranes and just believe it without seeing proof. This is a very serious accusation and could have dire consequences. To me, this is the first thing that gives away that it might not be true. When a claim this grand is made against a product that has been proven safe repeatedly and by numerous independent sources, the burden of proof lies in the claimants hands. Meaning, if aspartame really does eat holes in your cellular membranes then whoever made that claim needs to provide some scientific research to back it up. Another important thing to remember is that aspartame is safe for consumption up to a certain amount per day. The FDA sets the Acceptable Daily Intake (ADI) for aspartame at 50 milligrams per kilogram of body weight per day (50 mg/kg bw/day). Give yourself a minute to read over what that means. Seriously, go back and reread it. Diet Coke has 131 mg of aspartame per can. I weigh 180 lbs, which is the equivalent to 82 kilogrames. So according to the FDA's ADI, I can consume 4100 mg of aspartame per day and still be at a safe consumption levels. This means I can drink 31 cans of Diet Coke per day and remain at safe levels of consumption. So when studies come out involving mice consuming aspartame levels equivalent to 3,000 cans of Diet Coke per day, the negative effects are mostly irrelevent. The truth is, almost any product consumed in massive quantities like this would have detrimental effects. So it's not enough to simply say, "when you consume large and unrealistic levels of aspartame, you will develop brain tumors", because when you consume large and unrealistic levels of water, you die. This is called water intoxication and it really doesn't concern us in our day to day life.

Diet Coke causes weight gain

This is one of the more recent arguments against Diet Coke that I've heard, though, studies researching it have been around a long time. Alot of people misinterpret this claim as being that the actual ingredients in Diet Coke cause you to gain weight. What the claims actually make is that consuming Diet Coke will make you hungrier, ultimately causing you to overeat. To me, this isn't the greatest argument against Diet Coke or aspartame. It's an argument against lack of will power and poor snack choices. If this claim were true, it could easily be augmented by more will power, saying no to food even if you're hungry, or choosing a healthier snack choice while still enjoying your Diet Coke. It's really that simple. But the fact is, there is no conclusive evidence that Diet Coke will make you hungrier and/or overeat. A review of published data published in 1994 in Physiology & Behavior concluded that the conclusions of then-current published works does not support the idea that consumption of artificial sweetners increases caloric intake. [25] A more recent study published in 2010 concluded similarly stating that,

"When consuming stevia and aspartame preloads, participants did not compensate by eating more at either their lunch or dinner meal and reported similar levels of satiety compared to when they consumed the higher calorie sucrose preload." [22]

Meaning Diet Coke (aspartame) did not cause them to eat more than they normally would have. If it were true, the fact that I may want to eat more at dinner time isn't a strong enough reason to make me stop drinking Diet Coke, as I could simply use will power to not eat as much or simply eat more broccoli.

Your body reacts the same to aspartame as it does to sugar

This assertion that your body treats aspartame the same as sugar seems to be a reasonable conclusion on the surface. Because Aspartame tastes pretty similar to sugar on our tounges, it's easy to preemptively assume the rest of our body's physiological response would be similar as well. I read an article in regarding weight-loss strategies where a Dr. Cederquiest claimed

"Studies show that artificial sugar stimulates the same hormonal and metabolic responses of real sugar ... As you eat fake sweetener, receptors in your brain and gut anticipate getting calories from sugar; in response, your body releases the fat-storage hormone insulin." [26]

This is a pretty bold claim and one that readers of Shape would probably take seriously considering it's coming straight from a doctor. The good news about this claim is that it can be verified or refuted pretty easily because we can actually measure the levels of hormones in the body after consuming beverages. There is no need to guess what our body's physiological and metabolic response would be, when we can actually measure it. According to a placebo-controlled, double-blind study published in the British Journal of Nutrition in 2011, the consumption of artificial sweeteners had vastly different levels of secretion of gut hormones (GLP-1, PYY, and ghrelin) compared to sugar. Sugar stimulated GLP-1 and PYY secretion and reduced ghrelin, whereas artifical sweetener had absolutely no effect on any these hormones whatsoever. The study concluded that the

"data demonstrate(s) that the secretion of GLP-1, PYY and ghrelin depends on more than the detection of (1) sweetness or (2) the structural analogy to glucose." [21]

This is in direct contradiction to Dr. Cederquist's claims that artificial sugar stimulates the same hormonal and metabolic response as sugar. With that said, the chemical composition of artificial sweeteners is different for each one, and each one may have a different metabolic responses, so further research would need to focus on a specific sweetener to be accurate. Furthermore, other studies have concluded the same non-effects of artificial sweeteners on other gut hormones as well (including plasma CCK, GIP, and insulin). [24]


The majority of negative health effects that are typically associated with Diet Coke are either false or inconclusive. These false associations get so much attention that they can drown out the real negative impact of the drink. The problem with diet drinks is not aspartame or the food coloring or carbonated water, but the citric and phosphoric acids that can rot your teeth. Many other drinks such as regular Coke, Orange Juice, and Gatorade all contain potentially teeth rotting acids as well. But if you're trying to decide between a regular Coke and Diet Coke, the Diet drink is much better for you because it is less caloric and does not contain high fructose corn syrup, which has been correlated with negative health effects such as obesity, insulin resistance, and diabetes. [27] [28] [29] Diet Coke can be important for people who are on calorie strict diets because a can of regular Coke is about 140 calories, which can easily set you over your limit if you're not careful. The ideal drink is obviously water but drinking a Diet Coke with a meal can be very enjoyable. So if you want to drink a Diet Coke, drink it and don't feel bad about it or buy into all of the negative hype surrounding it. I've provided sources for the majority of claims in this article, so feel free to read directly from the source if you do not trust my summary.

In ultimate summary, Diet Coke isn't that bad for you and certainly isn't as bad as some would have you believe. There are a few things to watch out for when consuming Diet Coke, such as the phosphoric and citric acid that can rot your teeth, but overall it is the healthier choice when compared to Coca-Cola classic.


  23., Physiological mechanisms mediating aspartame-induced satiety.