will diet soda break my fast?

Will Diet Soda Break My Fast?

Intermittent fasting has grown in popularity over the past few years, and many people are jumping on the intermittent fasting train. For those of you who are familiar with intermittent fasting, you understand the importance of monitoring what you drink while fasting to ensure you do not “break” your fast. For those of you who are new to intermittent fasting, I will give a brief overview. Intermittent fasting is a period or time restriction away from food. This also includes exclusion from drinks that contain calories. You essentially are required to consume ZERO calories while fasted, in order to remain in a fasted state. So obviously the best zero calorie drink you can have while fasted is water.

But the question is, can you consume diet soda while fasting, because it also contains zero calories?

I often get asked about acceptable drinks while fasting, and the most popular drink people want to know about is diet soda. You may be a soda drinker, and it can be very challenging for some of you to not consume soda during the day. Or you were one who used to drink coffee with cream/sugar, and now that you started intermittent fasting you want to find an acceptable caffeine source to consume while fasting. Especially if you hate black coffee. So in this article I will be discussing the implications to drinking soda while fasting, and whether or not diet soda truly breaks a fast.

Diet soda Nutriton Label

will diet soda break my fast

First let’s take a look at the nutrition label on a diet soda. You can see it contains 0 calories, 0 fat, 0 carbs, and 0 protein. The only thing it contains on the nutrition label is a very small amount of sodium, which is fine to consume while fasted. So based of the nutrition label, it would appear that diet soda is an acceptable drink while fasting. But, let’s take a look at the ingredient list. It is carbonated water, some coloring, and artificial sweeteners.

The issue that arises from consuming diet soda while fasting, is whether or not these artificial flavors can disrupt/break your fast. There has been some discussion whether or not artificial sweeteners have any affect on intermittent fasting, and there is not a clear consensus. Some people believe artificial sweeteners are not healthy/natural to the human body so in a “health/evolutionary” standpoint they say you should not consume artificial sweeteners while fasted. Whereas, others say artificial sweeteners do not break your fast, and therefore they are okay to consume while fasting.

Do artificial sweeteners break your fast?

The ONLY problem with diet soda and intermittent fasting is the artificial sweeteners. If it wasn’t for the artificial sweeteners I would say 100% “Yes, you can consume diet soda while fasted”, but the artificial sweeteners make it a little trickier to answer. Let’s look at the current research to determine whether or not artificial sweeteners from diet soda will break your fast.

Research studies looking at the effects of artificial sweeteners while fasting:

The problem with the artificial sweeteners is the sweetness that your tongue receptors receive when you consume diet soda. In an animal research study, it showed that just the sensation of  “sweetness” on the tongue can trick the body into believing that it has just been fed. Meaning, the tongue receptors sent a signal to the brain, which indicated that food was just consumed. So if this research holds true in humans, then all the neurological benefits of intermittent fasting would be broken, because cellular autophagy would stop when this brain signal is received. The research on animals, also showed that there was a small insulin response from the sensation of sweetness on the tongue. Even though, there was absolutely zero calories/zero carbs consumed. I found this very interesting. Even though there was absolutely 0 calories & 0 carbs, there was still a small insulin response just from the sweet taste of the artificial sweeteners.

Let’s look at a human study. There was another research study that examined the insulin response on humans, where they ingested 200 ml of diet soda (with aspartame and acesulfame potassium). Fasted blood glucose levels were tested before and after the consumption of the diet soda. This research study found that diet soda did not increase blood glucose levels. So this study shows that the insulin response seen in animals may not hold true when examined in humans.

Both of these research studies hold contradicting views. The study on animals showed that artificial sweeteners caused a slight insulin response when consumed, and another animal study showed that just the taste of sweetness can trick the brain into believing it is fed. Whereas, the human study showed there was no increase in blood glucose levels after consuming diet soda.

So will diet soda break my fast?

Technically, yes. But there is conflicting research on the true effects artificial sweeteners can have on the brain. Whether or not the artificial sweeteners on your tongue can trick your brain into believing you are now fed is still debatable. The fact that diet soda contains 0 calories, 0 carbs, 0 fats, 0 proteins still makes it a better choice than coffee with cream. In a study, it showed that there was no glucose response when subjects consumed diet soda while they were fasted. This study is very promising for those who still want to drink diet soda while fasting.

I believe it also depends on the reason you are doing intermittent fasting. If you are intermittent fasting for the weight loss, calorie restriction, and diet flexibility aspect, then I feel more comfortable saying diet soda is acceptable for you to drink while fasted. Whereas, if you are intermittent fasting for the neurological (brain) benefits, cellular autophagy, and longevity reasons then I would say try to restrict yourself from consuming diet soda while fasting.

TheMuscleMaster’s Final Say:

will diet soda break my fast

Whether or not diet soda will truly break your fast is not a clear cut answer. It depends on how strict you want to be with intermittent fasting. If you want to follow intermittent fasting to an absolute “Tee” then you really should only be consuming WATER. Although, the majority of people who intermittent fast will atleast drink black coffee, black tea, or diet soda/energy drinks while they fast. It makes your fasting window much more bearable to atleast sip on something palatable.

I believe intermittent fasting should be followed with flexibility, and without stressing on what you can/cannot consume while fasting. That defeats the purpose of fasting. So if you really need to have diet soda while you fast, then have diet soda. If diet soda enables you to stick with intermittent fasting then I say go for it.

Intermittent fasting with diet soda is still healthier than not fasting at all. So whether you need diet soda for the caffeine (because you hate black coffee ) or because you need something to drink other than water, then I would say drink diet soda in moderation. Try to avoid it while fasting if you can, but it will not completely hinder your results from intermittent fasting. If you want to know all of the acceptable drinks for intermittent fasting, check out our ultimate guide.


  1. Thank you, I started IF two weeks ago and like the results so far, However, I don’t drink coffee and drink Diet Pepsi for my caffeine bump. I drink water in the morning then 10:00 or 10:30 I get my diet soda, it made me wonder if it would affect my fast . The diet soda does seem to curb my appetite.

    1. Author

      Hey Kevin, the artificial sweeteners in diet soda technically break your fast. However, if drinking diet soda allows you to stick with IF then I say go for it. You are still getting the gut rest and fat loss benefits.

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