Is Diet Coke Bad For You? A Registered Dietitian Answers

Is Diet Coke Bad For You? A Registered Dietitian Answers

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Diet Coke is one of the most popular sodas, and consumers are often curious about whether it’s a better option than regular Coke due to the lack of sugar. Most people don’t consider Diet Coke to be healthy, but many wonder if it’s actually bad for you.

Does Diet Coke contain ingredients proven in medical studies to be bad for you? Is it a healthier or less healthy option than regular Coke? How does it compare to other soda brands? And can too much of it negatively affect the brain?

In this article we’ll answer all of these questions and more as we analyze the ingredients in Diet Coke based on medical studies to give our take on whether or not it’s bad for you.

We’ll share some surprising research on how Diet Coke may affect the brain, compare its nutrition to regular Coke, and give our healthy soda recommendation.

Does Diet Coke Contain Harmful Ingredients?

Diet Coke ingredients

The ingredients in Diet Coke are shown above. The majority of them have questionable health effects according to clinical studies.

Aspartame is an artificial sweetener, and is what causes Diet Coke to taste sweet while containing no sugar.

A medical review published in the Nutrients journal documented some potential safety concerns about the substance. The breakdown of aspartame by the body results in formaldehyde which “may damage DNA,” and one liter of diet soda results in around 60 milligrams (mg) of formaldehyde, which is 400 times the acceptable daily intake (ADI) level.

Potassium benzoate is a synthetic preservative which has been shown in a clinical trial to be clastogenic (DNA-damaging), mutagenic (potential for genetic mutation) and cytotoxic (toxic to living cells).

Citric acid is a flavor enhancer and preservative typically derived from a fungus, which is clinically shown to cause whole-body inflammatory reactions in some individuals, as we documented in our is Coke Zero healthy article (Coke Zero also contains this ingredient).

Natural flavors is a broad category descriptor that fails to identify the specific flavoring agents used. There are documented toxicity concerns with some flavoring ingredients.

Phosphoric acid is a flavor enhancer associated with hypocalcemia (low blood calcium levels) in a medical review. Women who consumed one or more soda drinks with phosphoric acid were 28% more likely to have low blood calcium levels, which can lead to osteoporosis if not treated.

Healthiness is subjective, but overall we consider Diet Coke to be bad for you given the number of questionable additive ingredients that are associated with negative health outcomes in clinical research.

But can it also be harmful to the brain? We'll feature an interesting animated video that investigates this question in the next section.

Is Diet Soda Bad for the Body and Brain?

An interesting, animated video published by Science Insider examined whether diet soda intake could be harmful to the body and brain. The video is only three minutes long:

Is Regular Coke Healthier?

Coke ingredients

The ingredients in regular Coke are shown above.

Both products contain phosphoric acid and natural flavors which we recommend avoiding. The key difference is that Coke is sweetened with high fructose corn syrup, which we consider to be an even worse option than aspartame or cane sugar.

High fructose corn syrup has been extensively studied in medical trials, and is one of the processed food ingredients that's most highly associated with obesity. A Cleveland Clinic review found that high fructose corn syrup “promotes obesity more than regular sugar.”

A meta-study published in the PLOS One journal found that high fructose corn syrup can induce metabolic dysregulation.

Even though the beverage contains more questionable additives like a preservative and citric acid, we consider Diet Coke a healthier option than regular Coke just because of the research that suggests that high fructose corn syrup should be avoided. Diet Coke is also zero-calorie, which may make it a better option for overweight and obese individuals, given that regular Coke contains 140 calories and 39 grams (g) of added sugar in a 12 ounce can.

Our Healthy Soda Pick

Olipop is our healthy soda pick.  

This natural soda uses no flavoring additives or refined sugar, and is instead flavored with nutritionally-rich botanical ingredients like mandarin juice (which is clinically shown to be a potent antioxidant), nopal cactus and calendula flower.

The cans have only 2 to 5 g of added sugar from natural sources like cassava root syrup and apple juice.

Stay up-to-date on our research reviews


We consider Diet Coke to be bad for you, although we would recommend it over regular Coke which is sweetened with high fructose corn syrup.

Avoiding soda altogether and replacing its intake with water, tea or coffee is probably your best bet from a health perspective, but for consumers who want soda we consider a brand called Llama Mama to be the healthiest option currently on the market.

Not only does Diet Coke contain an artificial sweetener with questionable health effects called aspartame, but it also contains a synthetic preservative, a flavor enhancer that’s often derived from fungus, and another flavor enhancer that’s associated with low blood calcium levels.

In the future if enough customers (and researchers like us) voice concern, we hope that Coca-Cola will update the Diet Coke formulation to a healthier set of ingredients.