Can you drink diet soda while fasting?

Written by Aly Owen

Medically reviewed by Josie Porter, RD

No matter how long or for whatever reasons you’re trying intermittent fasting, there’s one golden rule to follow during your fasting windows: don’t eat anything. 

But that one rule can be confusing when it comes to what you drink. You want to keep your body in a fasted state — which means no carbs, protein, or fat — but you also need to stay hydrated. 

So, what breaks a fast? 

Beyond water, zero-calorie drinks like tea or black coffee are still on the table. (Feel free to exhale a sigh of relief here for those of us whose survival is reliant on those morning cups of joe.) 

While there are other zero-calorie drinks out there, we’re often asked about one in particular: “Can you drink diet soda while fasting?”

We won’t keep you on the edge of your seat: the short answer is yes (hallelujah!). However, there are some conditions to keep in mind. Our experts break down what you should know about drinking diet soda while fasting and what else you can drink so you — and your fridge — can be prepared for a safe, effective fasting experience. 

If you’re still working out the basics of intermittent fasting, you can also check out our guide on intermittent fasting for beginners. Plus, our Simple quiz can help you figure out which intermittent fasting schedule might work best for you if you’re just starting out.

So, does diet soda break a fast? 

Does diet soda break intermittent fasting? 

On a surface level, diet, zero, and no-sugar sodas all lack calories, which means technically, they’re all fair game for your fasting window. So if you’re craving that cool, crisp carbonation, go ahead and pop that top. Live out your blissful summer soda commercial fantasy. 

But if you’re wondering specifically, “Can I drink diet soda while fasting?” the answer may depend on your reasons for fasting in the first place. 

Science is still working out the impact diet soda can have on health — and we’ll dig into those potential side effects and risks shortly — but it’s worth keeping in mind that diet soda is ultra-processed, and these types of foods and drinks have been linked to poor health outcomes like metabolic diseases and inflammation.[1] 

So, especially if you’re fasting to improve your gut health or reach your happy weight, we recommend avoiding large quantities of diet soda. 

Like anything you eat or drink, diet soda isn’t fundamentally “good” or “bad” for you; some things are just more nutrient-dense or health-promoting than others. So whatever your fasting goals, moderation is your best drinking buddy. A can or two per day is a good rule of thumb. 

Whether you’re a fasting newbie or a pro, figuring out what and how much to eat and drink along the way can be tricky. We’re here to help make it simple. To start working out the best approach for your unique body, preferences, and lifestyle, take our Simple quiz. 

Alternatives to diet soda while fasting

We get it: fasting can be boring. Even if you’re used to it, your tastebuds can get tired of biding their time until your next meal. 

During intermittent fasting, diet soda isn’t the only drink that can help you through the monotony of your fasting window. If you’re at the stage where the thought of having regular old H2O is feeling more like H2-NO, there are other beverages that could start a party in your mouth (even if, admittedly, that party is less all-out-rager and more mid-afternoon office birthday). 

For some caffeine, carbonation, or flavor kicks without breaking your fast, try sipping on things like: 

• naturally-flavored sparkling water
• green and herbal teas 
• black coffee
• Gatorade Zero or Powerade Zero 

If you’re an apple cider vinegar fan, you can also dilute a few tablespoons in water. 

Health side effects and risks of diet soda

Now that you know the short answer to “Can you drink diet soda while intermittent fasting?” let’s dive into the longer answer about how intermittent fasting diet soda drinking may impact your body. 

The thing that makes diet soda “diet” — meaning calorie-free and sugar-free — is artificial sweeteners. These sweeteners are typically laboratory-made sugar replacements that give diet soda that sweet and acidic cola taste without any actual sugar. 

While these sweeteners are safe in moderation, more research is needed to figure out their long-term impact on overall health. Scientists also agree we need more insight into whether they’re processed differently than natural sugars and in exactly what quantities or under what circumstances they may be detrimental. 

Based on what we know so far, here are some possible side effects and risks of drinking diet soda. As always, everybody is unique, so your body’s response to diet soda may be different than your friend’s, roommate’s, or partner’s.

Glycemic impact

One of the biggest concerns with artificial sweeteners is that in some specific cases — like adults who have type 2 diabetes, prediabetes, or obesity — they may be associated with increased insulin resistance and obesity (though the jury’s still out about the sweeteners specifically in diet soda).[2,3,4] 

However, studies on adults without these conditions have found that regular consumption of artificial sweeteners doesn’t affect glucose levels, glucose tolerance, glucose metabolism, or insulin sensitivity.[5,6,7] 

It’s difficult to extrapolate these findings to all types of sweeteners, though, so even though the sweeteners used in diet soda are fairly consistent and there have been some larger studies in this area, more long-term, inclusive research is needed.

Sweet preferences

It’s rumored that artificial sweeteners increase sweet cravings, but most of these findings are from animal studies. A more recent review suggests these sweeteners aren’t associated with changes in sweet preferences or motivation to eat.[8] 

Gut health

Some emerging evidence suggests some artificial sweeteners could impact the composition of your gut microbiota (in other words, all the bacteria and other stuff that live inside your gut).[9,10] These changes could, in turn, affect how your body metabolizes sugar and other nutrients. However, more evidence is needed to confirm these findings. 

Sleep quality and duration

In addition to artificial sweeteners, some diet sodas also contain caffeine. They may not pack the same hyper-jittery punch as coffee or strong green tea, but they can add up enough to mess with your sleep. Avoiding diet soda (and all sources of caffeine) for at least six hours before bed will help you sleep better and longer.[11] 

Heart health 

One recent prospective study found a potential association between higher artificial sweetener consumption and increased risk of cardiovascular disease.[12] Again, more supporting evidence is needed before we can say for sure that diet soda may impact heart health in certain conditions.

In addition to these specific potential health impacts, one thing to keep in mind is that diet sodas are ultra-processed. Consistently consuming large quantities of ultra-processed food has been linked to a variety of chronic illnesses, decreased brain health, and changes in eating behaviors.[13,14,15] 

Before you hit the panic button and rue every time you thought you were making a health-promoting choice by picking diet over full-calorie soda, don’t worry: it would likely take a lot of daily diet soda to put yourself at serious risk. Stick to the moderation mantra, and you’ll be fit to slay another day.

What can you drink while intermittent fasting?

One of the most common intermittent fasting mistakes we see is not staying hydrated. Drinking enough water (or mineral / sparkling water) is crucial for a safe, effective fast, so if you’re not a big water fan, try jazzing it up with some mint or slices of fresh fruit. We love a bit of lemon or orange, but things like cucumber and lime work just as well. You can also mix in a spoonful or two of apple cider vinegar — though we recommend not combining that with other flavors or drinking it straight up (ick). 

Beyond diet soda, there are lots of other non-water drinks that can help keep any pesky hunger pangs at bay. Tea (without milk, sugar, cream, or sweeteners) and coffee (without milk, sugar, cream, syrups, or sweeteners) are a particularly good support squad to call in. 

Sadly, Long Island iced teas are off the menu (as well as all alcohol, full-sugar soda, and other sugary drinks like fruit juice), but there are literally hundreds of other fun teas to explore. 

And, of course, spilling “tea” is always a good way to pass the time without breaking your fast … as long as you don’t head for some cathartic comfort cookies straight after!

Looking for more of a deep dive into what you can drink while fasting? Our full guide has you covered. If you’re feeling meal-planning motivated, we also have one about what to eat during intermittent fasting. 

Written by Aly Owen

Medically reviewed by Josie Porter, RD