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Is Diet Coke Bad? The Answer May Surprise You

Posted on Posted in Food Science

As a food scientist this is one of those questions that comes up, again and again. It rears it’s ugly head at parties, with work colleagues and extended family. There are multiple levels of answer depending on the situation. Here are the short, medium and long answers to the question, ‘Is diet coke bad for you?’

The short answer

Diet coke isn’t bad for you. But, water is always better.

The medium answer

Most likely you have read a blog post at some point saying aspartame causes cancer. The thing you should take into account is that ‘toxicity is in the dosage’. The sweetener aspartame is one of the most thoroughly tested food additives in history. It is used in very small quantities in diet coke. There are many review papers about aspartame consolidating its safety. It seems to be one of those urban legends that got way out of hand. However consumer pressure always wins, this is why we’re seeing the development of more stevia sweetened options by the soda giants.

The long answer is the most concerning

By this stage you may already be satisfied. However things start to get interesting, and sound very scary, when you look even deeper into aspartame. The following is an overview of complex processes.

The metabolites of aspartame are the reason why aspartame is surrounded by so much controversy. Metabolites just means the things aspartame is broken down into next after you eat it. And they may sound like enough reason to quit diet coke for life when you look at them in isolation.

The metabolites of aspartame sound like scary chemicals, when viewed in isolation

  • Aspartic acid, an amino acid which is also a neurotransmitter.
  • Phenylalanine, an amino acid which is toxic to people with a genetic disorder called Phenylketonuria. You might have you seen this label on diet coke and sugar free gum.
  • Methanol, this is a poisonous alcohol not to be confused with Ethanol from spirits, wine etc.

Ok, you may now be thinking how can this possibly be safe. Here’s a few numbers to help put things in perspective. This is the dosage aspect.

Aspartic acid from diet coke, a similar amount is found in 170g of milk or 84g of beef

The top 1% of the highest aspartame users in the world would consume the equal (pardon the pun) of 57 packets of sweetener or 10 cans of diet soda per day. This is about 2500mg per day. The average intake is closer to 2 diet soda cans per day, or 500mg per day. This more average amount of aspartame has a similar amount of aspartic acid and phenylalanine as found in 170g of milk or 84g of beef. And as much methanol as found in 230g of vegetable juice or 55g of gin.  We’re talking about less than 1 cup of milk, a palm size of steak and a double shot of gin. It turns out there are scary sounding compounds lurking in most everyday food items, but in minute quantities that don’t harm us.

Food additives go through a rigorous approval process

The other factor to consider is the rigorous approval process for food additives in the USA, and other counties. Animal and human models are used in scientific studies to figure out the safe levels in food. To give you a very rough idea, in these studies rats and mice may be fed up to 1000 x per day what would be consumed in an equivalent human diet. Once a safe level is determined, safety factors are added to account for interspecies differences. This is usually a factor of 10, which is quite big in toxicology terms. So roughly speaking, what is found to be safe is reduced by another 10 times as a precaution.

Better than a full sugar soda, but not better than water

Without a doubt, diet soda is a much better choice than a full sugar soda. Sugar (specifically the fructose part) acts like a chronic toxin. Our livers struggle to break down fructose, it’s one of the main reasons high sugar packaged foods are so unhealthy. However, artificially sweetened products may come with their own issues. Addiction to sweetness may be more than just our body’s response. It could be that the taste factors into our cravings.

In conclusion..

Having a diet coke occasionally might not be as bad for you as many scaremongers would lead you to believe. Just remember that nothing beats pure water in terms of a healthy beverage choice.


Extra for experts:

Authority Nutrition, Aspartame: Good or Bad?

Aspartame: a safety evaluation based on current use levels, regulations, and toxicological and epidemiological studies

New York Times, The Evidence Supports Artificial Sweeteners Over Sugar


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