Can Diet Coke Make You Fat?

Soda. Coke. Pop.

Whatever you call your carbonated beverage (it’s SODA, by the way! Ha!), you’re probably already aware of how terrible it is for you.

Other than rotting your teeth, sugary beverages like soda are a huge reason there are so many overweight people in this country.

It seems like not a day goes by before a story like this comes out:

ept_sports_nba_experts-686956474-1256580685The NBA’s Caron Butler (pictured, right) of the Washington Wizards was so addicted Mountain Dew that when he gave it up this summer, losing 11 lbs in the process, he went through actual withdrawals:

To try and give this up was crazy for me! I was going through withdrawals. I was in the bed sweating.

My wife would turn over in the bed and ask “Are you OK?” Honestly, those first two weeks without The Dew [were] the roughest two weeks of my life. I’m talking headaches, sweats and everything. Before that I drank at least six 12-ounce Mountain Dews a day.

I know if you Google “soda weight loss,” you’ll find 2 million hits on how terrible these beverages are for you…so I won’t get into it.

Instead, I wanted to take a look at the effect of DIET soda on weight loss. I know there are conflicting reports on whether or not this stuff can actually make you fat. Hopefully you already know that what you drink is a small part of whether or not you’ll lose weight.

It also comes down to how you eat, which I believe can account for 80-90% of the reason you succeed, or the reason you stay overweight.

For that reason, we actually built a free resource that really digs into the psychology behind your weight loss – we created our 10-Level Nerd Fitness Diet strategy guide, which you can get for free when you sign up in the box below. Pick your starting level, follow the instructions, and level up when you’re ready!

I wanted to quickly dig into all of these things here.

I have done a more extensive article with significantly more research on diet soda, but this article today should get you started!

My Initial Thoughts Before Research

Diet soda has zero calories (generally) and zero actual sugar, which means it can’t directly make you gain weight, right?

A normal 20 oz. Coke, on the other hand, has 240 calories and 68 grams of sugar (holy ****), which definitely causes weight gain.

Now, if diet soda doesn’t have calories, it can’t contribute to the calorie equation (calories consumed vs. calories burned), which means diet soda alone can’t make you bigger.

However, is Diet Coke responsible for insulin spikes and increased appetite, which would indirectly cause weight gain?

Everybody also seems to think that “Diet Coke has aspartame and thus gives you cancer.”

Why is that such an expected reaction to Diet Coke, and is there any truth to it? 

So I put on my nerd researcher cap and wanted to see what I could track down.

Sources I Don’t Trust

If you look up “diet coke weight gain,” you’ll find all kinds of articles that say Diet Coke is the devil.

Note: I do not think the Lucifer the Prince of Darkness comes in liquid form in a can, but I haven’t proved that yet.


Unfortunately, many of the articles that tell you that Diet Coke will make you fat often cite no sources, are written by people who are trying to sell their own supplements, and use pseudo-science to scare you.

On the flip side – other sites say that Diet Coke is perfectly fine for you, as it has no calories and therefore no ill effect.

As hopefully you’ve learned, not everything on the internet is true (shocking), and when it comes to fitness and diet our bodies are so complex that things are very rarely so black and white.

Sources I  Do Trust

After reading some of the crazy extremist websites, I tried to track down some actual studies (and not hearsay) that could prove or disprove the effects of diet drinks. 

I came across this study from the San Antonio Heart Study, where the amount of diet soda consumed directly correlated (I’ll explain why this specific word is important in a second) with an increased chance of weight gain:

“On average, for each diet soft drink our participants drank per day, they were 65 percent more likely to become overweight during the next seven to eight years, and 41 percent more likely to become obese,” said Sharon Fowler, M.P.H., faculty associate in the division of clinical epidemiology in the Health Science Center’s department of medicine.”

Now, because diet studies always take place with people of various levels of health, wealth, genetics, and social standing, along with thousands of other variables that take place, I’m hesitant to place the blame squarely on Diet Coke.

Correlation does NOT prove causation, as you hopefully already know from this article. 

Maybe the people who drink Diet Coke generally don’t take into consideration what constitutes a healthy diet, while people who don’t drink it generally could be more knowledgeable about their diets and thus eat better?

Maybe the heavy DC drinkers work stressful jobs (and ‘need’ the caffeine to stay alert), and the stress along with poor diet choices (from working late) is causing their weight gain?

Maybe people Diet Coke and use that as an excuse to then eat really really unhealthy food otherwise (and thus gain weight).

As that study above points out, and the study in THIS article points out – Diet Coke isn’t the cause, but is correlated with being overweight – the strong correlation between the two has me definitely leaning towards “Diet Coke can be part of the reason you are fat, but certainly not the whole reason” camp.

That comes down to the food you’re consuming.

If you eat healthy food in moderate portions and also drink diet soda, you’re still going to be SIGNIFICANTLY healthier than somebody who eats unhealthy food in large portions but doesn’t drink any soda.

Your nutrition is everything!

Next: although it’s become common practice for people to believe that Diet Coke/Aspartame can cause cancer, this has proven to be unfounded and should be classified under “Old Wive’s tale.”

So, Diet Coke is not causing cancer, though if you find it hard to not worry about this despite the evidence – no problem, don’t drink it!

My Thoughts On Diet Soda

My big problem with Diet Coke is that I don’t like the taste compared to a regular soda, but that’s personal preference.

Give me an ice cold Coke with real sugar (not high fructose corn syrup), and it’s heaven in a bottle. I’d rather drink one of those once a month than drink a case of 12 diet sodas every day.

But that’s beside the point.

In a previous article “Is a calorie a calorie, we agree that consuming fewer calories is the first step in a process to losing weight. That means that consuming a Diet Coke compared to drinking a regular Coke means you are consuming significantly fewer calories per day.

We focus on quantity of calories and then move into quality of calories in our 10-Level Nerd Fitness Diet. If you’re trying to kick a soda addiction or slowly change your diet and you’re overwhelmed with trying to change too much, I got you covered.

Download the strategy guide free, pick your level, and start changing today.

I’d say Diet Coke is absolutely the lesser of two evils when compared to regular Coke if you’re trying to lose weight.

By the way, here are our thoughts on Caffeine – when consumed in moderation, and from a source like black coffee or black/green tea – caffeine can be a powerful aid in productivity (and life satisfaction if you’re a coffee aficionado!)

I believe in those instances, one should get to the source code of why that much caffeine is required!

My Recommendation

I recommend that you cut back on soda/sugary drinks as much as possible, and if that means switching to Diet Soda for the time being, great.  

If you think water is too boring, consider sparkling water with a lime wedge squeezed into it!

If you need caffeine, go with black coffee or unsweet iced tea. I didn’t drink coffee until a few years back, but now I make pour-over, freshly ground coffee in the morning, or make my own cold brew in the fridge!

If you’re committing to removing diet soda from your diet: Slowly transition your diet, and start to cut back on the amount of diet soda you consume every day. Just like with slowly adjusting your diet soda consumption, you too can slowly transition your diet, level by level, so that you never jump too far that it gets overwhelming.

Download our Nerd Fitness Diet Strategy Guide, pick the level you want to start with, and start to level up your diet (and your weight loss) today!

Now It’s Your Turn

I want to leave you with one final caveat:

If you decide that drinking a Diet Coke occasionally makes you happy, and makes life worth living.

Go for it.

Personally, I might not drink soda, but I will certainly enjoy an adult beverage even though it’s unhealthy, and not feel bad about it!

I’d love to hear some actual stories from you about how soda and diet soda has affected your weight loss and health.

If you’ve given up regular soda and switched to diet and lost a lot of weight I want to know!

If you’re struggling to lose weight but you can’t kick your Diet Coke habit, I want to hear about it too!

I’ve mostly given up soda completely, with the occasional Coca Cola (with real sugar) once in a blue moon. No diet soda for me personally – I get my caffeine from black coffee and black tea.



photo credit: C. Vizzone Monochrome Diet Coke , jacreative Project 50 #43 Refreshing

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