What Breaks a Fast? [How to Figure Out + Specific Examples]

What breaks a fast

The most common question I see from people new to fasting is, “Does _____ break a fast?”

Here’s the trouble:

It’s not a simple yes or no answer, because every situation is different.  

Today I’ll walk you through some general guidelines that can help you decide for yourself if something will “break” your fast.

Then we’ll go through several specific examples — things that people ask about a lot.

Let’s get started. 

2 Ways to Figure Out What Breaks a Fast (For You)

Leaving the most strict definition of fasting aside, it mainly comes down to two things:

  1. Your fasting goals
  2. What’s in your food / drink / etc (and what does it do)

(This applies to both short-term “intermittent” fasting and multi-day “extended” fasting.)

What are your fasting goals?

First of all, what are you hoping to accomplish by fasting?

Fasting goals

There are many possibilities. Here are several common examples:

  • Lower your body fat
  • Lower your blood sugar
  • Lower your insulin
  • Improve / cure diabetes (type 2)
  • Boost your ketone levels
  • Improve your mental focus
  • Control hunger
  • Lower your blood pressure
  • Rest your bowels
  • Feel better
  • Live longer
  • Boost autophagy
  • “Reset” your immune system

Fasting (intermittent or extended) can give you a ton of health benefits, so the list goes on and on. And your goals may be different from anyone else’s.  

Here’s the bottom line: 

To decide whether something will break your fast, you need to know why you’re fasting.  

Examples – Using Your Fasting Goals 

Here’s what this might look like in real life.

If you’re pre-diabetic and your main goal is to have lower blood sugar, try to avoid anything that raises blood sugar while fasting.  

If your primary goal is to lower your body fat, avoid anything that promotes fat storage (like sugar / carbs). 

And so on.  

Sometimes you can use objective measurements to see if you’re hitting your goals.  

For example, I like to check my blood sugar once or twice a day during prolonged fasts (with a cheap $20 glucose meter). It’s a little messy because I have to prick my finger, but it’s worth tracking if your main goal is to have lower blood sugar.

If your goal is to boost ketones, you can measure those as well.  

I mostly use urine test strips because they’re cheap and quick. If you want a more specific result, you can get a breath ketone meter, or a fingerstick device (like a glucose meter). 

It’s probably worth it if boosting ketones is your main goal.   

Other goals are more subjective, like controlling your hunger or feeling better.  

In those cases, you’ll need to use trial and error to see what works for you, and what doesn’t.  Keeping a daily record of how you feel in a little notebook (or an app) can be helpful.

For more “specialized” goals–like boosting autophagy, or resetting” the immune system (both related to extended fasting of about 3 days or more)nobody knows how much you can eat or drink during a fast and still accomplish these goals. It just hasn’t been studied enough in humans.

Basically, if you’re going for stuff like that, you should be as strict as you can tolerate (i.e. just water, +/- salt), to give yourself the best chance of success.   

Make sense? 

That’s how you can use your goals to decide if something “breaks” your fast.  

In the next section, I’ll show you another important step to use when deciding if something breaks a fast. 

What‘s in your food / drink / etc (and what does it do)?

To decide if you should eat or drink something while fasting, you need to have an idea of what’s in it.  

How many grams of carbohydrates, protein, or fat does it have in each serving? How many calories? 

If you don’t know (I often don’t), you can check the nutrition info on the label, or look it up online.   

Let’s look at how this “stuff” in your food can affect your body (and your goals).

Carbs – Avoid (Almost) Like the Plague While Fasting

Sugar and other carbs raise your blood sugar, so you wouldn’t want to eat any carbs while fasting if your goal is to lower blood sugar (like if you have type 2 diabetes, or prediabetes).

Carbs also raise insulin (a hormone that promotes fat storage), so they’re no good if you’re trying to reduce body fat or lower your insulin level.  

If you’re not familiar with insulin, this little cartoon video covers the basics:

Little known fact:

High insulin is actually one of the first signs of developing diabetes (even before you get high blood sugar).

Anything that raises insulin will also lower your ketone levels (and you need ketones to feel energetic and focused while you fast).

Here’s the bottom line:

Sugar / carbs basically do the opposite of everything we want while fasting. So you should avoid them as much as possible.  

eating carbs while fasting

Exception: Tiny amounts of carbs (like 1 or 2 grams in a serving of bouillon, for example) probably won’t raise your blood sugar or insulin enough to matter. But don’t overdo it.  

Protein Is “Okay”, But Not “Ideal” For Fasting 

Protein doesn’t raise blood sugar or insulin very much, so it’s not as problematic as carbs if you’re trying to lower blood sugar, improve diabetes, or boost ketones.  

For example, the first time I did an extended fast (5 days long), I decided to eat about 200 calories worth of protein per day (as tuna or protein powder) to help preserve muscle mass.  

(I’ve since realized that’s not necessary, and a better way to preserve muscle while fasting is to exercise.)  

Even while consuming that much protein (maybe 40-50 grams per day), my blood sugar was still very low (50-70 mg/dL range), my ketones were very high (dark purple urine strips), and I lost several pounds.   

However, protein does send a signal to your body that food is abundant, so you won’t be in a fully “fasted state” if you consume more than a tiny amount of protein.

Why does this matter?

If your body thinks that food is abundant, you’ll be less likely to activate some of the “special” benefits from fasting (like resetting the immune system, or autophagy, among others).  

Here’s the bottom line:

You can eat some protein while you fast and still get a variety of health benefits.   

But since you’re not in a completely “fasted state”, you’ll limit some of the health benefits you could get from fasting (especially those that come after multiple days).

eating protein while fasting

Fat Is (Mostly) Fine When You Fast

Of the three macronutrients (carbs, protein, and fat), fat is the least likely to interfere with fasting.

That’s because dietary fat doesn’t significantly raise your blood sugar or insulin levels. It also doesn’t signal “abundance” to your body as much as protein does.

In addition, eating fat boosts your ketone levels (unlike carbs and protein, which do the opposite), because ketones are made from fat. 

So if you need something to tide you over during a fast, fat is probably your best choice.

For example, when I feel low on energy during a fast, sometimes I drink a splash of MCT oil to boost my ketone levels.

Other people like using coconut oil, or some butter in their coffee. 

Here’s the bottom line:

You can eat some fat and still experience just about all the health benefits of fasting.

eating fat while fasting

There are a couple caveats:

First, keep in mind that the more dietary fat you consume while fasting, the less of your own body fat you’ll burn. 

That’s simply because your body uses the fat you eat first, before tapping into your own stored fat.

Second, even dietary fat may limit some health benefits (like autophagy) at least a little bit, because it still shows your body that food energy is coming in.

Speaking of food energy… 

Do Calories Matter?

Calories simply represent the amount of energy in your food.

So when you’re fasting, you want to keep calories pretty low (or extremely low).

The more calories you consume, the further away from actual fasting you will be, and the less likely you’ll be to gain significant health benefits. 

I generally try to stay under about 200 calories per day (sometimes way under) while fasting, including any and all supplements (like broth, bouillon, MCT oil, and so on). 

That small amount of food energy doesn’t seem to have much impact on my blood sugar, ketones, or the amount of weight I lose, so it works for me. 

You can see if the same thing is true for you by running a few “experiments”.

Wait, There’s One More Thing

Even if a food (or supplement) is low in carbs, protein, and total calories, it may not be ideal for fasting.

For example, artificial sweeteners have no calories and no carbs, but they can still raise your insulin (indirectly), and seem to promote weight gain as well. 

They also stimulate cravings for some people.

Bottom line?

Even if something has zero calories, it may have other effects that can prevent you from reaching your fasting goals. 

Does ____ Break my Fast? [Specific Examples] 

what breaks a fast specific examples

Now that we’ve gone over some basic guidelines, you can probably figure most of this out for yourself.

But just in case it’s helpful, let’s go through some examples that people often ask about.

Lemon Water / Lemon Juice

Lemon water (water with a splash of lemon) has barely any carbs or calories (and no protein or fat), so it’s generally fine to drink modest amounts when you’re fasting.

Lemon juice, on the other hand, is much higher in sugar, and should be avoided.

For more info, read my full article: Does Lemon Water Break a Fast?

Apple Cider Vinegar

Apple cider vinegar is a popular supplement that–like regular vinegar–seems to have a variety of health benefits.

It has barely any calories, and may help control your appetite during a fast.

If you’re not trying to do an ultra-strict fast (to stimulate autophagy, for example), apple cider vinegar is a great supplement to use.

A reasonable dose would be 1 or 2 teaspoons per day, diluted in some water (to prevent the acid from damaging your teeth).

Full article: Does Apple Cider Vinegar Break a Fast?

Artificial Sweeteners

We’re mainly talking about aspartame and sucralose (aka Splenda), since those are by far the most popular artificial sweeteners.

Here’s the bottom line:

You may be able to get away with using artificial sweeteners while you fast (I’ve done it before), but they’re not good for your health in the long run.

Artificial sweeteners can raise insulin (at least indirectly), and appear to cause weight gain over time.

They also stimulate cravings for some people, which makes it more difficult to fast. 

Do your best to avoid artificial sweeteners while you’re fasting, if possible. 

(Ideally, see if you can avoid them when you’re not fasting, as well.)

Related articles:

“Natural” Sweeteners

Stevia is a popular “natural” sweetener (derived from a plant), and can be okay to use in moderation when you fast. 

It doesn’t seem to have the same harmful effects on insulin and weight gain that artificial sweeteners do.

However, like artificial sweeteners, stevia sometimes stimulates hunger or cravings, which makes it more difficult to complete your fast. So be cautious.

Full article: Does Stevia Break a Fast?

Sugar alcohols (like sorbitol or xylitol) are another type of natural sweetener. More on these in the next section.

Chewing Gum

You should definitely avoid chewing sugary gum while you fast.

Sugar-free gum, on the other hand, is generally sweetened by a combination of sugar alcohols (like sorbitol, xylitol, or maltitol), and artificial sweeteners (like aspartame–see above).

Sugar alcohols are slightly modified sugar molecules that don’t get absorbed into your bloodstream as much as regular sugar. As a result, they don’t raise your blood sugar as much (though they can raise it a little bit).

Here’s the bottom line:

If you’re not trying to be extra-strict with your fasting, chewing a few pieces of sugar-free gum while you fast is reasonable. Just don’t overdo it!

Full article: Does Chewing Gum Break a Fast?

Black Coffee / Bulletproof Coffee / Coffee with Cream

A lot of people do well drinking black coffee (no added sugar) while they fast. It has no calories, no carbs, and they’re able to get their usual caffeine fix.

“Bulletproof” coffee (aka keto coffee) refers to coffee with butter and/or MCT oil mixed in. In other words, it’s coffee + fat.

Recall that dietary fat is a better choice to consume while fasting (compared with carbs or protein), but you don’t want to overdo it. The more fat you eat or drink, the less of your own body fat you’ll burn. 

The same thing applies to bulletproof coffee (coffee + fat), or coffee with cream (also mostly fat).

Related articles: 

Tea

By itself, tea doesn’t have any calories or carbs. 

So assuming you don’t add sugar, tea is basically fine while you’re fasting.

Be cautious of any pre-made tea–it usually has added sugar.

If you’re a caffeine fanatic, green tea and black tea are reasonable ways to get your caffeine while you fast (better than, say, diet soda).

When it comes to various herbal teas, including peppermint tea, these are also calorie-free, and basically fine for fasting (again, as long as you don’t add any sugar).

Alcohol 

Most alcoholic drinks (including beer, and usually wine) contain sugar, so they should be avoided while fasting.

(Some types of wine are supposed to be very low in sugar, but you can never know for sure, because wine-makers aren’t required to have a nutrition or contents label. Most of the time, wine probably has more sugar than people realize. So I don’t recommend that you drink it while fasting.)

Sugar-free alcoholic drinks (like spirits / hard liquor) are theoretically ok to use while fasting, but only in extreme moderation. 

Not only does alcohol itself have calories, your body will probably also be more sensitive to alcohol while you fast.

For most people, it’s probably better to avoid alcohol altogether when fasting.

Full article: Does Alcohol Break a Fast?

Vitamins

Some people like taking vitamins while they fast. I personally don’t bother anymore.

If it’s fine to go a few days without food, it’s probably also fine (for most people) to go a few days without vitamins.

(Obviously there are exceptions. Consider your own health circumstances.)

Will vitamins “break” your fast?

In the vast majority of cases, I would say no.

Unless you’re taking gummy vitamins (or some other brand with added sugar), vitamins probably won’t prevent you from reaching your goals.

So taking vitamins while you fast is typically fine.

What About Fish Oil?

Fish oil is not really a vitamin. It’s just another type of dietary fat.

It only has about 10 or 15 calories per capsule, which is not enough to matter for most people (assuming you don’t take a whole bunch!).

So unless you’re trying to avoid all calories, taking some fish oil while you fast is generally ok.

Bone Broth

There are various kinds of broth, and the amount of carbs, protein, and fat varies dramatically from one kind to another.

For example, I buy a brand of veggie broth from my local supermarket. It has 5 calories per cup, and basically zero carbs / protein (less than 1 gram of each). It’s also very high in salt (which is why I drink it–to keep my sodium up).

In contrast, bone broth usually has a lot of protein, and way more calories than my veggie broth. 

So before you start guzzling broth, take a look at the nutrition info and consider how it will impact your goals. How much protein, carbs, or calories do you want to be consuming?

Some people use bone broth as a sort of crutch, or “training wheels”, when they first start fasting, and that’s totally fine. Feel free to use bone broth (or anything else) if it makes fasting easier for you.

But just like actual training wheels, as you gain more confidence and experience, you can probably stop using bone broth while you fast.

Turmeric 

Turmeric is a seasoning and a health supplement, which may have some benefits for conditions like arthritis.

Fun fact: It’s also responsible for mustard’s brilliant shade of yellow.

Like most zero-calorie supplements, it’s typically fine to take turmeric while you fast.

As always, consider your goals. 

What about Medications and Fasting? 

With medications, it’s not really a question of whether they “break” your fast. Instead, the question is whether it’s safe and appropriate to keep using the medication while you fast. 

Some medications can affect your blood sugar, insulin, or blood pressure, and may need to be adjusted (or discontinued) while fasting–especially if you’re fasting for multiple days.

The most obvious example is insulin itself. Some diabetic patients inject insulin to help lower their blood sugar. If you stop eating, but still inject insulin, your blood sugar can go dangerously low.

Similarly, many people take medicine to lower their blood pressure. Since fasting also lowers blood pressure, taking blood pressure medicine while you fast is often overkill, and can cause symptoms like dizziness (from the drop in blood pressure).

Outside of those categories, most other medications can be continued as normal. 

But there are a lot of nuances and potential exceptions, so this is definitely a situation where it makes sense to consult with your doctor beforehand. 

Conclusion 

When it comes to what “breaks” your fast, it depends on your goals.

It also depends on what’s in your food (or drink, etc).

By looking at the nutrition data, together with your individual goals, you can usually figure out the answer.

If you’re doing an extended fast to stimulate autophagy, “reset” your immune system, or something similar, you may need to be extra strict.  

For most other fasting goals, you’ll have some wiggle room.

Everybody is different, so it can take some trial and error to see what works for you.

Keep in mind, it’s better to fast with a few supplements than not to fast at all. 

Your health will still improve, and you can always change things up later.

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Ben Tanner, PA-C

Ben Tanner, PA-C

Ben has been practicing as a physician assistant (PA, or PA-C, similar to a doctor) in emergency medicine, urgent care, and family practice since 2014. Since 2016, he has developed an avid interest in various forms of fasting, using it to improve his own health while helping friends, family, and patients do the same.

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