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Can Diet Coke make you gain weight? Will it ruin your diet? Let’s put the memes aside, and look at what the science says on this topic.

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Can drinking Diet Coke make you gain weight?

Depending who you ask, you’ll typically hear two different answers to this question..

“Expert 1” will say something like:

“No. Diet Coke contains zero calories, therefore it won’t lead to weight gain.”

Meanwhile, “Expert 2” will say:

“Yes. Diet Coke tricks your brain into believing it’s had sugar, spiking insulin levels and putting the body into fat storage mode.”

Which “expert” is correct?

… and with such vastly different answers, is it any wonder the general public feels a bit lost?

So let’s get stuck into this one…

“You’ll Never Lose Weight If You Drink Diet Coke!”

can Diet Coke make you fat

Check out this email from subscriber Katheryn:

“Hey Russ! So, I’ve lost 25lbs and I feel great! But a workmate keeps telling me my lunchtime glass of Diet Coke is ruining all of my results…? Is it?

I look forward to my Diet Coke break every day, please don’t take it away LOL!”

We all have a workmate who likes to poke fun at our food choices and act all superior – even if you’re seeing results.

At the first gym I worked, we had an annoying lad who did this every day. “You’re eating the wrong stuff”… “You’re drinking the wrong stuff”… He’d go round the gym with a very closed mind, lecturing anyone who’d listen.

And some of these super polite people were in amazing shape, but he didn’t care, he knew better than everyone.

Funnily enough his name was Hunter and he was vegan, so we called him Gatherer.


Anyway, being annoying doesn’t make ’em correct…

What About STUDIES That Show Diet Soda Causes Weight Gain?

There are none.

That’s right.

There are no studies that show diet soda causes weight gain.

There are studies out there which show an association, but none that show proof. Remember, correlation does not equal causation.

For example, murder rates in New York City escalate at the same time of year ice cream sales are at their highest. Does this mean strawberry sundaes are turning people into f**king monsters?

Of course not.

Well, maybe this kid:

There are plenty of studies showing an association between drinking diet soda and negative health effects like diabetes, etc – but the diet soda was not the cause of the obesity. What this really tells us is that the majority of diet soda drinkers are overweight people.

And that makes perfect sense.

After all, the target market for diet soda is overweight people. So the majority of diet soda drinkers are overweight people. It’s more likely that obesity was the reason they started drinking diet soda (instead of regular soda) in a bid to be healthier.

But let’s get stuck into some research…

A 2009 study published in the Journal of Endourology confirmed that diet soda drinks are not harmful to overall body composition. (9)

Nor will they slow down the metabolism, according to a trial published in the American Journal of Clinical Nutrition. (10)

And finally, a study from the University of Texas ends the weight gain debate once and for all…

In this trial, researchers compared the effects of diet soda consumption versus other zero calorie drinks.

This is a fascinating research paper because folks who claim diet soda causes weight gain often gloss over the fact it contains zero calories, and instead claim “it’s the other stuff in there” which makes you put on weight.

If that’s true, this trial would show it to be the case.

Except it doesn’t. Because the researchers confirmed that when total calories were controlled, there was no difference in weight loss results. (11)

So don’t stress about your lunchtime Diet Coke.

Of course, don’t fall into THIS trap:

does Diet Coke make you gain weight

We all know one of these people, right?

They order Diet Coke with their Big Mac and Super-Sized Fries that are the size of actual human legs, and then complain when they don’t lose any f**king weight!

See, I must point out that the majority of weight related issues arising from Diet Coke are caused by our incorrect assumption that it’s “healthy”.

Make no mistake, Diet Coke is not healthy.

By that, I mean it’s not something which is designed to make you a better athlete. But you knew that, right?

You’d think it’s common sense… but lots of people mistakenly believe opting for a “healthy” diet soda gives us a free pass to eat whatever the f**k we want without repercussions. We humans are a strange bunch, and we do this with many foods we deem healthy, as was shown in a 2004 study from researchers at Purdue University, West Lafayette. (12)

Anyway, now you’ve seen some science, here’s my advice:

If you do enjoy a fizzy drink with your lunch, and it helps you stick to your diet, by all means go for it. In fact, it would make more sense to keep it in there as this leads to greater diet sustainability, which is a huge factor in building your best body. (13, 14)

Just don’t be a d**k.

Make sense?


Now let’s look at one of the biggest causes of misinformation on this topic… social f**king media.

You’ve Probably Seen This Meme Before…

diet coke weight gain

If this is true, drinking a can of Diet Coke is going to do all of these things:

  • Trick your body into thinking it’s just had sugar
  • Switch on fat storage mode, causing you to gain weight
  • Attack the enamel on your teeth
  • Trigger the same part of the brain as cocaine and get you addicted
  • Make you crave junk food

Well this sounds like 330ml of pure disaster, right?!

If there’s one thing social media is good for, it’s scaring people.

But some of the claims made in this meme are 100% true, and some are 100% false. Let’s run through them and see which is which…

does diet soda ruin your diet

“Drinking Diet Coke can switch your body into FAT STORAGE mode.”

This is the one most of us are worried about, so let’s answer it first:

No it can’t.

The belief here is that aspartame will trigger insulin release, telling the body to store fat like a motherf**ker, because artificial sweeteners (like aspartame) supposedly “trick the body” into believing it’s just had sugar.

Of course, they’ve overlooked one crucial fact – that’s not how any of this works.

I’ve said this many times; there is no “tricking” the human body.

30 years ago we may have believed this, but nowadays it’s well-documented that aspartame does not cause an insulin spike. (1, 2, 3, 4, 5, 6)

Also, the only thing which will make you store excess body fat is eating too many calories, and seeing as this contains zero calories, that’s not happening.

does diet coke cause weight gain

“The potentially deadly combination of caffeine and aspartame creates a short addictive high, similar in the way cocaine works.”

This is also false.

There’s no evidence to support claims of caffeine stimulating the part of the human brain involved in reward. (7)

But even if it did, that’s not necessarily a bad thing. I mean, food and exercise do. Should we cut those out?

And just how “deadly” is this combination of caffeine and aspartame they speak of?

Turns out, not very…

But using phrases like “potentially deadly” is enough to strike fear into the hearts of most people without fact checking, and that’s what they want, because that means more shares. So it’s important to remember that anything can be deemed deadly when the dose is high enough. This dose makes the poison.

Too much water can kill you… Too much fruit can kill you… Heck, the rock band Queen once sang “Too Much LOVE Will Kill You”… they were probably correct.

This is important to know, because you’d need to drink a whopping 19 cans of Diet Coke per day to exceed the recommended daily limit for aspartame consumption… and if you are, then you’ve got bigger problems than weight gain, my friend. (8)

(Like an empty wallet, or a bloat-fart that’s gonna see you fly around the room like an untied balloon.)

And that’s not even the amount we’d need to make it deadly.

If we wanted to do that, we’d have to go A LOT higher!

“The FDA recommended limit for aspartame is 50mg per kg body weight per day.

For a 70kg person, that’s 3500mg of aspartame. A can of Diet Coke contains 185mg, so that’s 19 cans. In terms of a toxic dose (i.e. potentially deadly), we’d need over 1000 cans in a day.”

Fitness Reloaded
does diet coke cause weight gain
Don’t drink THIS MUCH, obviously.

“It will attack the enamel on your teeth.”


I know… I know… when I said some of the claims made in the meme were 100% true, you were probably expecting it to be one of the bigger revelations relating to fat storage.

But no, THIS is the one that’s true. (13)

If you want to keep your teeth nice and shiny, you shouldn’t drink lots of fizzy drinks.

New Era. New Meme.

Social media can be a b**ch.

So the next time a friend tries to scare the living daylights out of you on your lunch break by sharing that out of date graphic, here’s a couple of more scientifically accurate ones to send back to them.

These were created by the lovely folks at CompoundChem and Food For Fitness.

can diet coke make you gain weight
is diet coke bad for you

If you enjoyed the article, hop on my free e-mail list at the end of today’s article for more nutrition, supplement and workout tips.


  1. Smeets P. A. M., et al. Functional magnetic resonance imaging of human hypothalamic responses to sweet taste and calories. Am J Clin Nutr. (2005)
  2. Møller S. E., et al. Effect of aspartame and protein, administered in phenylalanine-equivalent doses, on plasma neutral amino acids, aspartate, insulin and glucose in man. Pharmacol Toxicol. (1991)
  3. Wolf-Novak L.C., et al. Aspartame ingestion with and without carbohydrate in phenylketonuric and normal subjects: effect on plasma concentrations of amino acids, glucose, and insulin. Metabolism. (1990)
  4. Horwitz D. L., et al. Response to single dose of aspartame or saccharin by NIDDM patients. Diabetes Care. (1988)
  6. Howell S., et al. “Calories in, calories out” and macronutrient intake: the hope, hype, and science of calories. Am J Physiol Endocrinol Metab. (2017)
  7. Nehlig A., et al. SPECT assessment of brain activation induced by caffeine: no effect on areas involved in dependence. Dialogues Clin Neurosci. (2010)
  8. Andrew G., et al. Sweet-taste receptors, low-energy sweeteners, glucose absorption and insulin release. Br J Nutr. (2010)
  9. Passman C. M., et al. Effect of soda consumption on urinary stone risk parameters. J Endourol. (2009)
  10. Maersk M., et al. Sucrose-sweetened beverages increase fat storage in the liver, muscle, and visceral fat depot: a 6-mo randomized intervention study. Am J Clin Nutr. (2011)
  11. Nettleton J. A., et al. Diet soda intake and risk of incident metabolic syndrome and type 2 diabetes in the Multi-Ethnic Study of Atherosclerosis (MESA). Diabetes Care. (2009)
  12. Davidson T. L., et al. A Pavlovian approach to the problem of obesity. Int J Obes Relat Metab Disord. (2004)
  13. Shenkin J. D., et al. Soft drink consumption and caries risk in children and adolescents. Gen Dent. (2003)
  14. Koliaki C., et al. Defining the Optimal Dietary Approach for Safe, Effective and Sustainable Weight Loss in Overweight and Obese Adults. Healthcare (Basel). (2018)

Responses to “Can Diet Coke Make You Fat?”

  1. Bennie avatar

    My workmate used to tell me my Diet Coke at lunch would ruin my gym progress haha 22lbs gone so far, and I definitely couldn’t have stuck to it so easily if I’d tried to remove my Diet Coke.

  2. Reggie avatar

    Always appreciate your no BS style Russ. Great read.

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