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Is coke zero safe? (Or any Aspartame sweetened drinks)

Coke Zero, Diet Coke and other diet sodas use artificial sweeteners, to give them that sweet taste, with no sugar. But with so much speculation in the media, is it right to say Coke Zero is safe?

I’m certain you’ve heard someone say

“It’s worse than full-fat coke, it will give you cancer”

Or something along those lines. There are lots of rumours about various negative health effects. Rumoured health issues include cancer, diabetes, dementia, kidney disease and high blood sugar.

It’s easy to see why most assume Coke Zero sugar is bad for you.

So in this article, I’m going to explain why Coke Zero sugar or Coke with aspartame isn’t bad for you. And why you’d be far better off having it instead of the full-sugar version.

What is aspartame?

Aspartame is a substance, which is 200x sweeter than sugar. (1) Other yet soda’s sometimes use sweeteners such as Acesulfame potassium. But for this article I’m focusing on Aspartame.

Like sugar, a gram of aspartame contains 4 calories. (2)

But because it’s 200x sweeter than sugar, a lot less is is used, in making Coke Zero and other diet sodas.

The reason it’s used, is that you cut a lot of calories, whilst keeping the same sweet taste. You also benefit from not causing as much damage to your teeth.

It’s used in an array of food and substances, such as:

  • Fizzy drinks
  • Sugar-free gum
  • Sugar-free sweets
  • Chewy supplements
  • Mouthwash
  • Medicines
  • Protein powders
When people ask "is coke zero safe", they ask because they are scared of aspartame.

A 330ml can of Coca-cola has 35g of sugar, which is 5g over the UK recommended limit. (3)

A can of Diet Coke has 125mg of aspartame, which is 280 times less of the sugar in Coca-Cola. This means there are technically 0.03125 calories in Diet Coke. (4)

If you drink a can of most sugar sweetened beverages, you’d drink 140 calories. If you drink 2 a day, that’s 280 calories. Let’s say in a year, you’d swap those 2 cans of Coke for Diet Coke, you’d save 99,680 calories per year.

There are 3500 calories in a pound of fat. Thus, if you drank 2 Diet Coke’s, instead of 2 full sugar Coke’s, you’d save 99,680 calories a year, which is 28.5lbs of fat. (5)

What happens you drink Coke Zero?

When you drink Coke Zero or any other diet sod, which is artificially sweetened, the sweetener is broke down, in the body.

The 3 constituents of aspartame are (6):

  • Aspartic acid
  • Phenylalanine
  • Methanol

Fear not, these substances aren’t the evil toxic devil you may think they are….

Aspartic acid and phenylalanine are amino acid proteins you’d find in foods such as beef and eggs. As for methanol, though it sounds scary it’s often food in foods such as tomatoes and onions.

A glass of tomato juice contains, up to 6 times the amount of methanol of a can of Diet Coke. A glass of milk contains 6x more phenylalanine and 13x more aspartic acid than a Diet Coke. (7)

Thus if Coke Zero sugar was bad for you, you could argue tomatoes and milk are bad for you.

For example, a glass of non-fat milk provides about 6 times more phenylalanine and 13 times more aspartic acid, and a glass of tomato juice provides about 6 times more methanol than does an equivalent volume of beverage sweetened 100% with aspartame

(Virani, et al, 2004)
When people wonder "is coke zero safe" it's because of Aspartame. When its broken down, it's broken into normal food constituents.

And I don’t know about you, but I don’t know anyone or any media headlines, claiming milk and tomatoes to be toxic.

I know the names of various food additives sound scary, but that doesn’t mean they are dangerous. These chemicals also occur in “natural” foods too. Most people don’t question the chemicals in modern life-saving medicine either.

What about all the claims, which say aspartame is dangerous?

Let’s look at the claims, by various bodies, then analyse what the evidence is actually showing.

The media

The media make outrageous headlines to make you click on their site or read their papers. Journalists who lack the education in these fields will cherry-pick a study to cause “outrage”.

Then the next day, there’s a headline claiming Coke Zero sugar is bad for you and worse than smoking.

The media gets its fuel from shock, outrage and misinterpretation. Meet anything you see in the media with skepticism. I’m not saying they’re always wrong, but you need to be vigilant. It’s best to check their sources.


Cancer seems to be the biggest rumour when it comes to aspartame. Yet, these rumours are often misconstrued.

Cancer Research UK and US National Cancer Institute state sweeteners don’t cause cancer.

99.99% of us consume artificial sweeteners, whether we know it or not. This is because they’re used in medicines and toothpastes.

If there was any truth to them causing cancer, the western world would be in great danger. Sweeteners have been around for many years. If there was any truth to these claims, trust me, we would know by now. As far as I’m aware nobody has yet died, from sweetener poisoning.

So if anyone asks if Coke Zero sugar is bad for you, question if toothpaste is bad for you.

Despite some rather unscientific assumptions, there is no evidence that aspartame is carcinogenic.

(Weihrauch & Diehl, 2004)

The only times, aspartame has shown to cause cancer, is in rat studies. As for humans there is no increased risk.


  1. We are not rats – We metabolise things at different rates
  2. They gave the rats 4000 cans worth of sweetener per day (8)

“most of the studies have limitations such as effects shown only in animals not in human, small sample size, high doses, statistically non-significant or borderline significant, etc.”

(Tandel, 2011)


One study suggested there’s a link between dementia and sweeteners. Which, yes it did show a correlation. But correlation does not equate to causation.

In the studied, they hypothesised, due to the people being ill, they were drinking sugar-free drinks to mitigate their illness. (9)

Many people in this study were choosing these drinks to improve their health. Thus this created a correlation, between those who are ill and those who drink these drinks. The paper mentioned this (9)

For instance, people that wear shoes in bed are more likely to wake up hungover. Do shoes make you drunk? No. But if you were drunk the night before, you’re more likely to fall asleep without removing your shoes. Same with people drinking diet soda, such as Coke Zero sugar…

“previous studies linking artificially-sweetened beverage consumption to negative health consequences have been questioned based on concerns regarding residual confounding and reverse causality, whereby sicker individuals consume diet beverages as a means of negating a further deterioration in health”

(Pase et al, 2017)

Safe daily dosage

All foods and substances can be toxic. It’s all on a spectrum. It’s not a case of certain foods are poisonous and others are safe. All foods can be safe and poisonous. The danger is in the dosage.

Even water can be toxic if drank to excess. (10) A lot of people who claim Coke Zero isn’t safe don’t realise this.

They measure aspartame safety using the “Acceptable daily intake” (ADI).

The ADI for aspartame is 40-50mg per kg. (11)

For a 50kg woman, that means she can consume 2000-2500mg of aspartame per day

For an 80kg man, that means he can consume 3200-4000mg of aspartame per day.

The companies approve those numbers:

The average diet drink contains 50-125mg of aspartame. So if we do a bit of maths, we can work out how many cans of drink you can consume, without any

The average diet drink contains 50-125mg of aspartame.

So if we do a bit of maths, we can work out how many cans of drink you can drink, without any adverse health effects.

A 50kg woman should look to limit her intake to under 16 cans to 50 cans a day.

An 80kg man, should look to limit his intake to under 25 to 80 cans a day.

A person drinking the amount of Coke, for any adverse effects to happen is unrealistic. (12) Nobody is ever going to overdo it on the sweetener.

A similar situation was observed for aspartame. In this way, the EDI for soft drinks was 1.1 mg kg(-1) day(-1), representing only 2.9% of the ADI.

(Lino, et al, 2008)

Finally, I must mention. They add a safety factor of 100 on the ADI. After calculating the ADI, they multiply that number by 100. Thus, for aspartame to have an effect you might actually need to consume 80,000 cans per day if you’re an 80kg man.

They add a 100x factor, to account for people who may see adverse effects, drinking a lower amount. This means for most people, they’d be OK drinking 5000 cans a day. (13)

You’d definitely drown, or end up shelling out a fortune before that ever happens. This is another reason, you can’t assume Coke Zero is not safe.

Effects on weight

There’s a lot of people who believe diet drinks cause weight gain, meaning Coke Zero can’t be safe.

First of all, they these drinks have no calories (or 1 or 2 calories) and over-consuming calories are the only way to gain weight.

But, there could be other factors, which come into play…

One is what I call the ‘McDonald’s effect’. Don’t get me wrong I love McDonald’s and always order a Coke Zero with no ice. But, it’s thought a lot of people might think Diet Coke or Coke Zero will negate things, thus overeat.

This is how someone smarter than me, would phrase it:

“It is plausible that the effects of NNS on weight loss might be greater when people are actively trying to lose weight in a formal behavior change program compared to when NNS are simply used as a dietary substitute for regular sugar. For example, some people (e.g., those not intentionally focused on losing weight) might cognitively compensate for the absence of energy in the NNS beverages by intentionally consuming more solid food which would mitigate weight loss.”

(Peters et al, 2016)

There’s another theory that drinking lots of diet drinks make you crave more sweet foods. It’s not something I’ve noticed with my clients or I’ve seen backed by any real scientific evidence. But if you do crave more sweet foods, you could try limiting your Coke Zero to see if that makes a difference.

People also say, they only notice overweight people drinking Coke Zero or Diet Coke. First off that’s quite rude. Also, have they never thought that there’s a chance, they’re trying to lose weight? So there’s a possibility they are making better choices.

To make a change you have to start somewhere, those people drinking Coke Zero may have lost a lot of weight already. It’s not good to make judgments on someone over a 5-second observation, you don’t know their full story.

“It is possible that results from observational studies are due to reverse causality whereby overweight individuals may choose to consume NNS beverages to reduce their risk of weight gain”

(Peters et al, 2016)

Evidence of weight loss

Finally, let’s get into some science.

One study showed people, who often drank diet drinks lost more weight than those who drank water.

There’s nothing more nauseating than people who say “I only drink water” when you drink your Coca-Cola Zero. Good for you, nobody cares.


Anyway, I’m not saying you must replace your water intake with Coke Zero. But I’m saying if weight loss is the goal, a few cans here and there might actually help you stick with your goal.

This study had 303 people, who either drank diet drinks or water only for a whole year. This was for a weight-loss treatment programme. The diet drink group kept off a greater amount of weight than the water group. (14)

 “NNS beverages were superior for weight loss and weight maintenance in a population consisting of regular users of NNS beverages who either maintained or discontinued consumption of these beverages and consumed water during a structured weight loss program. These results suggest that NNS beverages can be an effective tool for weight loss and maintenance within the context of a weight management program.”

(Peters et al, 2016)

Peters has a theory on why diet drinks might work better than water. It’s because you’re allowing yourself something sweet, without calories. So you are less likely to eat sweet things with sugar, which does have calories and would lead to weight gain. After helping people lose weight and losing a lot of weight myself, I agree. From my own experience, it definitely made losing a lot of weight easier and I may have struggled without it.

“It is possible that, in the water group, limiting access to sweetness in beverages may have promoted a desire to seek sweetness from other aspects of the diet, perhaps to achieve some “reward homeostasis”, thereby leading them to consume more sweet foods resulting in greater energy intake and less weight loss”

(Peters et al, 2016)

Another study showed similar results. The women who consumed aspartame in this study lost more weight and kept more weight off. (15)

“Among women assigned to the aspartame-treatment group, aspartame intake was positively correlated with percentage weight loss during active weight loss (r = 0.32, P < 0.01). During maintenance and follow-up, participants in the aspartame group experienced a 2.6% (2.6 kg) and 4.6% (4.6 kg) regain of initial body weight after 71 and 175 wk, respectively, whereas those in the no-aspartame group gained an average of 5.4% (5.4 kg) and 9.4% (9.4 kg), respectively. The aspartame group lost significantly more weight overall (P = 0.028) and regained significantly less weight during maintenance and follow-up (P = 0.046) than did the no-aspartame group.”

(Blackburn et al, 1997)

One more study for good measures. This one showed, replacing calorific drinks, with calorie-free drinks, elicited weight loss. (16)

Replacement of caloric beverages with noncaloric beverages as a weight-loss strategy resulted in average weight losses of 2% to 2.5%. This strategy could have public health significance and is a simple, straightforward message.

(Tate et al, 2012)

This study shows you are better off drinking Coke Zero than “full fat Coke”. Another reason to not assume Coke Zero isn’t safe.

Is Coke Zero safe during pregnancy?

Another common question I hear is; Is Coke Zero safe for pregnancy?

According to the current data, we have today, it is. The only caveat being, you don’t drink more than the ADI. (17)

“It is recommended that they be consumed in moderation and that pregnant women adhere to the ADI levels outlined by regulatory directives.”

Pope et al, 2014

Even if aspartame was harmful, which it’s not. When eaten or drunk by pregnant women, it does not cross the placenta. So it wouldn’t go to the baby’s system anyway. (17)

So, if you like a Coke Zero, or a sweetener in your tea or coffee, please enjoy.

Aspartame sensitivity

Some people claim sweeteners give them headaches or makes their skin itch. My mum is one of those people. The data suggests it may be a placebo effect.

The placebo effect is very real. People can start to act tipsy after drinking non-alcoholic beers.

What’s interesting with my mum, is that when she drinks what she thinks are full-sugar drinks, she’s fine. What she doesn’t realise is, most of them also contain sweeteners. This so the companies can avoid the UK sugar tax. (18)

Here’s a study to back this. When people drank placebo diet drinks, they felt adverse effects. (19)

These results indicate that aspartame and its conversion products are no more likely than placebo to cause urticaria and/or angioedema reactions in subjects with a history consistent with hypersensitivity to aspartame.

(Geha et al, 1993)

The bottom line is this, you’re most likely fine. Yet if you’re adamant it makes you itch, then avoid it. But on the whole, this is no reason, to assume Coke Zero is not safe.


Despite the itchiness, there is a certain subset of people who must avoid aspartame at all costs. These are people with a very rare genetic called phenylketonuria. (20)

If you have this disorder you’d already know and would be avoiding aspartame as you should anyway.

With this disorder, people are unable to break down phenylalanine. This is due to not having the enzyme phenylalanine-hydroxylase. This means that if they eat or drink aspartame, phenylalanine would fester in their system. This would lead to issues such as seizures. (21)

It’s not only Coke Zero they have to avoid. They’d also have limited foods which also have phenylalanine, such as milk and various meats and fish. (22)


Though, not as good as water, aspartame is better for your teeth than sugar. Or fructose corn syrup, which is used in the States.

When you eat sugar, some of it will stay on your teeth. Sugar is not an issue with your teeth. Yet, there is this certain bacteria, which feeds on the sugar.

When the bacteria feed on the sugar, it excretes acid. It’s this acid, which causes damage to the teeth.

It causes enamels and tiny holes, which left untreated can lead to serious teeth decay. (23)

Sweeteners don’t have this issue.

Yet, the carbonation from Coke Zero can still cause issues with your teeth, from the phosphoric acid. But, unlike regular sugar drinks, it’s not a double whammy of tooth abuse. (24)

I recommend you your diet drink through a straw, this helps the drink avoid some contact with your teeth.

Final thoughts

Aspartame is one of the most studied substances on the planet.

We are not rats and you’re not going to drink over 20 cans a day. You’d be more likely to suffer from water toxicity first.

There is evidence that drinks like Coca Cola Zero might be more effective than water alone in helping aid weight loss.

The majority of people are either overweight and obese. Telling someone to stop doing something, which is helpful, is very disempowering.
In the UK we eat and drink too much sugar.

Though sugar itself is not bad, it’s not filling and it’s easy to over-eat on calories, leading to weight gain. Especially in liquid form.
A couple of cans of Coke Zero sugar is safe for most people.

Is Coke Zero better than water? No. We all could drink more water, no doubt about that.

But, I don’t want people to stop doing something, which might be very helpful. This isn’t me telling you, you must drink Coke Zero sugar.

But if someone says Coke Zero sugar is not safe, they’re wrong. Same logic applies to sugar free energy drinks.

So, is Coke Zero safe? I would say yes.

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