Is Diet Coke Bad For You?

Diet coke may be the best option if you’re counting calories but is it actually doing more harm than good?
Updated 19 January 2022
Is Diet Coke Bad For You?

Diet Coke is bad for you.


When consumed in excess, Diet Coke can indeed be bad for your health, leading to issues such as:

  • Kidney problems
  • Obesity
  • Rotting teeth
  • Migraines and headaches
  • Irritability
  • Heart disease
  • Hypertension

However, drinking Diet Coke in moderation (one or two cups a day) is safe for most people. 

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Sections on this page
  1. Health Risks of Diet Coke
  2. How Bad Are Diet Coke Ingredients?
  3. Is Diet Coke Healthy?

Many people make the switch from regular Coca-Cola to Diet Coke because of the lower calorie count. A standard 12oz Coca-Cola contains 140 calories, while Diet Coke has zero—making it a popular soda of choice for those trying to lose weight. But is Diet Coke bad for you? Regardless of the calories, it’s still soda and may not be as healthy as you think. 

Health Risks of Diet Coke

Diet soda, such as Diet Coke, has been linked to various health issues, including:

  • Kidney problems
  • Obesity
  • Cell damage
  • Rotting teeth
  • Migraines and headaches
  • Irritability
  • Heart disease
  • Metabolic issues
  • Hypertension

Some studies have shown that even one can of diet soda each day leads to metabolic issues, and two sodas a day can lead to a decline in kidney function. 

Canned Drinks Come With Health Risks 

Soda cans contain endocrine disruptor bisphenol A (BPA), a chemical that has been linked to both obesity and reproductive issues.

However, for most people, one or two cans of Diet Coke may not lead to serious health issues, but everyone is different. Diet Coke may have more serious, long-term effects depending on your current health, eating habits, and other factors. 

Contrary to popular belief, there is not enough credible evidence to suggest that Diet Coke causes cancer of any kind.

How Bad Are Diet Coke Ingredients?

To determine whether or not Diet Coke is bad for you or not, we need to look at the ingredients:

  • Carbonated water
  • Aspartame
  • Caramel color
  • Phosphoric acid
  • Natural flavors
  • Potassium benzoate
  • Citric acid
  • Caffeine

Is Diet Coke bad for you? Check the ingredients.

If we look at the ingredients separately, we can start to understand whether or not Diet Coke is bad for you. The ingredients that we don’t need to worry about as there’s no evidence that they’re harmful to health include:

  • Carbonated water
  • Caramel color
  • Natural flavors

The ones we want to look further into are:

  • Aspartame
  • Phosphoric acid
  • Potassium benzoate
  • Caffeine
  • Citric acid
  • Aspartame


Although the U.S. Food and Drug Administration (FDA) states that aspartame is safe to use as a sweetener, there are some guidelines to follow when consuming it, specifically the acceptable daily intake (ADI):

  • FDA acceptable daily intake: 22.7 mg per pound of body weight (50 mg per kilogram of body weight)
  • European Food Safety Authority (EFSA) acceptable daily intake: 18.14 mg per pound of body weight (40 mg per kilogram of body weight)

In a single 12oz can of Diet Coke, there is 180mg of aspartame. This means a 150lb person would need to consume almost 19 cans of coke per day to reach the daily limit.

What’s more, it’s been found that aspartame only becomes toxic when you consume 1,814.4 mg per pound of body weight (4,000mg per kilo) in a single day. That’s equivalent to around 1,511 cans of Diet Coke in a single day

It’s safe to say that with regular consumption of Diet Coke, aspartame isn’t anything to worry about in terms of your health. However, in high consumption, it can cause:

  • Migraines
  • Headaches
  • Irritability

Aspartame is Harmful to Those With Phenylketonuria

Aspartame is harmful to those who suffer from phenylketonuria (PKU), a disorder that causes phenylalanine to build up in the body. Those suffering from PKU should avoid aspartame altogether.

Another side effect of drinking Diet Coke is weight gain, thanks to aspartame. Studies have shown that artificial sweeteners, such as aspartame, can cause your body to produce less of the hormone that inhibits your appetite. This means, when you drink Diet Coke, you may tend to eat more than you normally would.

Phosphoric Acid

Studies show that excessive amounts of phosphorus (including phosphoric acid) can:

  • Increase your risk of osteoporosis and heart disease
  • Impair your ability to use iron, zinc, magnesium, and other minerals
  • Lead to bone loss (by decreasing the amount of calcium in your body)

The recommended amount of phosphorus you need every day is 700 mg (for most people). Once you hit around 4,000mg of phosphorus in a single day, you’re putting your health at risk. 

A can of Diet Coke contains 32 mg of phosphorus. While that may seem like you can drink plenty of Diet Coke each day before you even come close to 4,000 mg, that’s not all you need to think about. Diet Coke isn’t the only food/drink that contains phosphorus. Phosphorus is also found in high-protein foods, such as:

  • Eggs
  • Chicken
  • Fish
  • Meat
  • Beans

For many, you’re already getting the recommended daily amount in the food that you eat. Drinking Diet Coke on top of a regular diet can push your phosphorus levels too high.

Potassium Benzoate

Potassium benzoate is the preservative used in Diet Coke to lengthen its shelf life. Although it is safe when consumed in small amounts, there are some health concerns:

  • May cause hives or other allergic reactions. 
  • May put young children at higher risk of attention deficit hyperactivity disorder (ADHD)
  • Severe DNA damage

The maximum ADI of potassium benzoate defined by the World Health Organization (WHO) and EFSA is 2.3mg per pound of body weight (5 mg per kg of body weight). This equates to around 10 cups of diet soda each day. 

If you usually eat a lot of processed foods, you should further limit your intake of Diet Coke, so you don’t surpass the recommended daily intake of this preservative.


Caffeine generally isn’t harmful to your health, but too much of it can be. The FDA states that 400mg a day is safe for most adults, lowering the number for pregnant women and adolescents. 

Caffeine levels are only toxic if you consume 10 grams of caffeine within a few hours (more than 200 cans of Diet Coke). Note that too much caffeine cause:

  • Insomnia
  • Restlessness
  • Headaches
  • Dizziness
  • Increase in heart rate
  • Anxiety
  • Dehydration
  • Dependency 

Compared to a regular cup of coffee, which contains around 140 mg of caffeine, a can of Diet Coke (46 mg of caffeine) isn’t anything to worry about.

Citric Acid

Although citric acid is considered safe and found in many natural foods (e.g., oranges), it causes Diet Coke to be highly acidic, which can lead to teeth erosion.

Is Diet Coke Healthy?

There really is no nutritional value to Diet Coke, Coke Zero Sugar, or regular Coca-Cola, for that matter. Sodas should be considered a tasty treat that you drink on occasion. It should certainly not be consumed as an alternative to water or consumed more than once or twice a day.

Contents Diet Coke Regular Coke Coke Zero Sugar
Calories 0 140 0
Fat 0g 0g 0g
Sodium 40mg 45mg 40g
Total Carbohydrates 0g 39g 0g
Sugars 0 39g 0g
Protein 0g 0g 0g
Caffeine 46mg 34mg 34mg
Potassium 0g 0g 60mg


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