Like a can of Diet Coke with your lunch? Then you’ll want to know this.


Written by Russ Howe PTI, and most recently updated 1 day ago.

8 min read

There seems to be a lot of confusion out there regarding whether diet soda drinks, like Diet Coke, can cause weight gain or not.

Check out this email from Kathryn:

“Hey Russ! I’ve lost 25lbs so far but there’s a guy at work who says I’m ruining my diet by having a Diet Coke at lunchtime. Is this true? I absolutely love my can (please don’t take it away lol),but I don’t want to ruin it. What’s the truth?”

I’ve got some good news and some bad news.

The good news is that Diet Coke does not cause weight gain, so you can enjoy your lunchtime can without fear. The bad news is that this won’t stop your colleague from lecturing you, because people be dicks.

Table of Contents

Why Diet Coke Does Not Cause Weight Gain


Yeah, your resident work expert is wrong on this one.

Diet Coke contains zero calories, therefore it has absolutely no impact on weight gain or weight loss.

Now, some people will claim that “the sweetener contained within Diet Coke (aspartame) will trick your body into thinking it’s had sugar and force it into fat storage mode” – this is also wrong; first because there’s no evidence to suggest this happens, and second because if something provides zero calories then there are zero calories to store.

So drink your lunctime Diet Coke without fear.

I personally don’t like it, but I do know that one of the biggest dieting mistakes we can make is to remove the small things which you really enjoy. (11, 12)

Are There Any Studies Which Show That Diet Coke Causes Weight Gain?

can Diet Coke cause weight gain?

There are none.

And I’d be pretty interested if there were, too, because this would be the first time in human history where the law of thermodynamics (calories in versus calories out) has been broken.

can diet coke make you store fat

This is where the water gets a little bit murkier.

So from the outset, it’s important to remember that correlation does not mean causation.

That statement will help you navigate through much of the bullshit out there, because when studies only show a link from one thing to another (as opposed to direct confirmation) it leaves the door open for the results to be twisted to suit an agenda.

For example, if you look at the yearly murder rates in New York City, you’ll notice that they spike at the exact same time ice cream sales are peaking. That’s correlation. It does not mean that ice cream is turning people into crazed monsters.

Well, maybe this kid!

So what is there in terms of solid research?

Well, a 2009 study published in the Journal of Endourology confirmed that diet soda drinks are not harmful to body composition. They will also not slow down your metabolism, as per a trial published in the American Journal of Clinical Nutrition in 2011, and a fascinating study from the University of Texas showed that diet soda drinks have the exact same impact on weight gain and weight loss as any other zero calorie beverage, which is none. (9, 10, 11)

The last study above is particularly interesting, because folks often claim that “it’s the other stuff in there” which causes weight gain, right? Well, if this was really true then it would have showed up in a study which compared diet soda against other zero calorie drinks, but that’s not the case.

Overall, the closest we can get to blaming Diet Coke (or any other diet soda) for weight gain is to say that it’s guilty by association.

For example, when we consider that the vast majority of diet soda drinkers are overweight, it’s easy to see why the general public might assume that the drinks are part of the problem, but it’s important to remember that the target market for diet soda is overweight people, many of whom began drinking it as a way of reducing their daily calorie intake. This would be like me saying five-finger training shoes make people become huge bellends, because everyone who wears them is a one. The shoes didn’t do anything, of course, other than make their target market huge bellends.


This infographic has been floating around on social media for quite some time.

It makes a simple can of Diet Coke look like 330ml of pure disaster.

Most of my readers know that I absolutely despise fearmongering bullshit like this, so I want to end this article by going through the silly claims made in this picture and debunking them one by one.

  • Claim 1: “Diet Coke switches your body into fat storage mode!”

This is dead wrong.

Back in the 1980s, people believed that sweeteners like aspartame could trick the body into believing it has just received sugar, leading to an insuling spike, which could trigger fat storage. Science has since shown us that this is complete nonsense, and the only thing which can trigger fat storage is a calorie surplus. (1, 2, 3, 4, 5, 6)

  • Claim 2: “The potentially deadly combination of caffeine and aspartame creates a short addictive high, similar to the way cocaine works!”

There’s no evidence to suggest that caffeine stimulates the brain’s reward center, but it wouldn’t even be a problem if it did. This part of the brain is stimulated by anything fun – which definitely includes cocaine, but also includes daily activities like eating food and performing exercise. (7)

Also, the term “potentially deadly” can be applied to literally anything. It’s all about the dose, and in order for combination to become deadly you’d need to consume more than 1000mg (/day) caffeine and 3800mg (/day) aspartame. There’s 48mg caffeine and 185mg aspartame in one 330ml can, so you’d need to drink more than 21 cans per day! (8)

  • Claim 3: “Routine consumption of diet sodas, even one per day, are connected to higher likelihood of heart disease, stroke, diabetes, metabolic syndrome, and high blood pressure.”

If a can of Diet Coke had this kind of power, I suspect Thanos would have dropped an infinity multi-pack from the clouds and saved himself the hassle of snapping his fingers.

There are no studies confirming any of the claims made above, but the reason they’ve used the term “connected to” is because it enables them to twist the facts to suit their narrative. As mentioned earlier, overweight and obese people make up a large percentage of the target market for diet soda companies, so most studies on diet soda use these type of individuals. It’s important to remember that the risk factors which those individuals are experiencing were not caused by diet soda, but by the unhealthy lifestyle they had followed for however many years beforehand.

  • Claim 4: “It will attack the enamel on your teeth!”

This one is true.

You’re an adult, and you probably already know that drinking soda is bad for the enamel on your teeth. (13)

In Summary: Don’t Be A Dick!

can Diet Coke make you fat

I don’t want to give you the impression that Diet Coke is good for you, or healthy, because it’s not.

I mean:

  • Diet Coke serves no nutritional purpose other than tasting nice.
  • Diet Coke will not improve your performance in the gym.
  • Diet Coke will not make you perform better in any sport.

That being said, there’s no need for your lunchtime can of Diet Coke to become a lunchtime can’t of Diet Coke, and there’s nothing wrong with consuming Diet Coke (or any other diet soda drink) as part of your healthy diet. Enjoy!


  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. Shenkin J. D., et al. Soft drink consumption and caries risk in children and adolescents. Gen Dent (2003).
  13. Koliaki C., et al. Defining the Optimal Dietary Approach for Safe, Effective and Sustainable Weight Loss in Overweight and Obese Adults. Healthcare (Basel) (2018).

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I’m Russ. I’ve been a personal trainer since 2002, and I own

My job is to simplify fitness for my readers.

I send out free fitness tips to over 100,000 men and women every week, all in the same no-nonsense style as the article you’ve just read, so if you enjoyed reading it be sure to jump on my email list below.

2 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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