Does Diet Coke Make You Fat?

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Today we’re talking soda and weight gain.

Specifically, does Diet Coke make you fat?

The answer is no.

Anything with zero calories cannot make you gain weight. It’s that simple.

I could leave this article right there, because that’s the top and bottom of it, but I won’t. I’ll give you some science today.

Because there’s a lot of confusion on this topic across the internet, so in this article I want to give you some research and definitive answers. The next time someone tells you you’re going to gain weight from a glass of soda, you’ll be fully equipped to shut them down.

does Diet Coke make you fat

Check out this e-mail from website subscriber Katie:

“Hey Russ!

So I’ve lost 25lbs, which makes me really happy, but I have a question for you:

I always have a glass of Diet Coke with my lunch, and my colleagues (one in particular!) tell me it’s going to ruin my results.

I’ve still been losing weight, so I don’t follow what she means, but she’s telling me I need to only drink water.

Could you answer this for me?”

I certainly can.

Now, we all have someone at work who likes to go instructing other people what they should and shouldn’t do, particularly with food, so this is quite common.

We used to have a lad called Hunter at my first gym who would do this every day. Ironically, he was vegan. So we called him Gatherer.


Anyway, overconfidence doesn’t make them right…

what happens after you drink diet coke

Does Diet Coke Make You Fat?

I’m sure you’ve seen the popular infographic above.

It keeps coming back every so often on social media, and it’s utter bulls**t.

When we look at the actual research, we get to the bottom of the matter really quickly!

This graphic, complete with bulging can of Diet Coke (HA!) makes a number of scary claims, some of which are true, and some of which are very incorrect.

The one which jumps out immediately is the claim that:

“Can switch on fat storage mode.”


Apparently, this is because aspartame will trigger insulin release, and tell your body to begin storing fat like a motherf**ker, because artificial sweeteners “trick” the body into thinking it has just processed sugar.

Flat out not true.

Aspartame does not cause an insulin spike. (1, 2, 3, 4)

The only thing which will make you store excess body fat, is eating too many calories. And this contains zero calories.

I’ve said this many times; there is no “tricking” the human body. (5, 6)

There is no ‘one weird abs exercise for a flatter stomach’. There are no ‘3 foods you should eat for a slimmer waist’. And there is no ‘magic pill’.


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


We’re talking about dopamine production here.

By this logic, we should also stop exercising and eating food every day, because they also have a similar effect.

This is sensationalism at its best.

Further still, there’s no clinical evidence to support claims that caffeine stimulates the part of the human brain involved in reward. (7)

But the use of words like “potentially deadly” is enough to strike fear into the hearts of most people without checking. Common sense must be applied here…

Anything can be deadly when consumed in crazy amounts; water… fruit… pizza… hell, I licked a battery when I was a kid. I’m still here.

But if I’d went through them like ice lollies, we might have a problem.

At the levels found in a normal can of Diet Coke, you’ need 19 cans per day to exceed the daily limit for aspartame consumption. (8)

… and if you’re drinking 19 cans of Diet Coke per day, my friend, you’ve got bigger problems than whether it’ll make you gain weight.

“The FDA’s recommended daily intake for aspartame is 50mg per kg body weight. For a 70kg person, that’s 3500mg. A can of Diet Coke contains 185mg, so that’s 19 cans.

In terms of a toxic (i.e. potentially deadly) dose, we’d be taking over 1000 cans in a day.

Still worried?”

Fitness Reloaded
does diet coke cause weight gain
“Don’t drink this much per day…”

What About Studies Linking Diet Coke To Weight Gain?

Here’s the thing…

There are no studies showing Diet Coke leads to obesity.

What there are, however, is studies linking diet soda to obesity. Notice I said linking, not causing. Meaning, studies showing an association between drinking diet soda and negative health effects like diabetes, etc.

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. Which makes perfect sense!

When the target market for a drink is overweight people, the majority of people who drink it will be (you guessed it!) overweight people. It’s more likely that obesity was the cause of their reason to start drinking diet soda, instead of regular soda, in a bid to be healthier.

Correlation does not equal causation.

So what’s the real problem here?

It’s this:

does Diet Coke make you fat

A 2009 study published in the Journal of Endourology confirmed that diet carbonated drinks are not harmful to overall body composition. Nor will they slow down the metabolism. (9, 10)

A fascinating 2009 study from the University of Texas found compared the effects of diet soda consumption versus other calorie free drinks. Total calories were controlled, and there was no difference in weight loss! (11)

That, right there, is conclusive proof that Diet Coke won’t make you fat.

But there’s another issue we must address…

Because the majority of weight related issues arising from Diet Coke are caused by our incorrect assumption that it’s “healthy”.

Make no mistake, it’s not healthy.

By that, I mean it’s not something which is designed to improve your results in the gym.

Many of us mistakenly believe that opting for a “healthy” Diet Coke gives us a free pass to eat whatever the f**k we want, without repercussions. (12)

Don’t be a d**k.

Aside from the obvious dental issues of drinking fizzy drinks, you needn’t worry about your Diet Coke ruining your weight loss progress at all.

In fact, if you enjoy it as part of your lunch (like Katie), 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)

Make sense?


I’ll leave you with a couple of my favorite science-based Diet Coke infogaphics, created by the great folks at CompoundChem and Food For Fitness.

The next time someone tries to use a poorly constructed meme to scare you into buying their latest detox diet bulls**t, now you have something to fire straight back at them.

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

If you’ve enjoyed my article “Does Diet Coke Make You Fat?”, jump on my email list at the bottom of the article for more training tips. And if you don’t have my workout app yet, give yourself a slap.

Russ Howe PTI


  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)

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