April 03 2019

The Definitive Guide To What Breaks a Fast

By Mark Sisson
57 Comments

One of the most common questions I get is “Does [x] break a fast?”

What they’re really inquiring about is: “Does this interfere with, negate, or nullify the benefits of fasting?”

These benefits include:

Ketosis: Fasting is the quickest way to get into ketosis, an metabolic state characterized by increasing fat burning, fat adaptation, and—in some people—improved cognitive function.

Fat Loss: When you’re fasting, you’re not eating, and not eating is the best way to force your body to burn the fat it already possesses. Fasting also means no additional calories are coming in, and many people find that fasting is a great way to control their calorie intake.

Autophagy: Autophagy, or “self-eating,” is the process by which our cells prune damaged components, maintain proper function, and keep aging at bay. Fasting triggers autophagy. Breaking the fast will stop autophagy.

Let’s go through the most popular queries one by one and figure out how each one affects an intermittent fast. (For questions about what supplements break a fast, check out my post, “What Breaks a Fast: Supplements Edition.”)

Common Drinks

Coffee

Depends on who you ask. Some say the fact that coffee triggers a metabolic response means it breaks the fast. I say that coffee increases fat mobilization and burning, independently triggers autophagy (something we’re looking for when we fast), and makes it easier to stave off hunger. For my full treatment, check out this post on coffee and fasting.

I’m going to say “no.”

Tea

Tea contains no calories, improves metabolic health, and can aid fat burning. All signs point to it being great during a fast. Of course, if you had a tablespoon of sugar and a half cup of milk, you’re breaking the fast. But tea itself is a great addition.

I’m going to say “no.”

Yerba Mate

Yerba mate is essentially non-caloric, like tea or black coffee. It also has beneficial effects on glucose tolerance, which is a big plus.

I’m going to say “no.”

Bone Broth

I covered this in full a few months ago. Go read that post. In short, a bit is probably okay. Just keep in mind that the more gelatinous your broth is, the more collagen protein it will contain and the greater its potential to inhibit autophagy. This isn’t established in humans yet (see the collagen section below), but it’s worth considering. A nice salty broth has gotten many a faster through a tough fast, especially if they’re still learning the ropes and need some electrolytes.

I’m going to say “technically yes” but “realistically no.”

Lemon Water

A tablespoon of fresh squeezed lemon juice has a couple calories and a decent amount of potassium. Combined with salt, lemon water is actually a nice way to hydrate during a fast without breaking it.

I’m going to say “no.”

Diet Soda

Diet soda may mess with your gut. It’s linked to weight issues, though not conclusively and certainly not in a causative manner; it’s just as likely that the relationship can be explained by overweight and unhealthy people using diet sodas in a bid to lose weight. I don’t like them myself, and I’ve witnessed people fail to ever kick the sweet tooth as long as they drank diet sodas. But many people find they do improve dietary adherence and do improve fasting tolerance. If that’s the case, they are very pro-fasting.

I’m going to say “no.”

Juice

A juice fast isn’t really a fast. You’re consuming fewer calories than you might eating normal food, but you’re still consuming a good number of calories—most of them carbohydrate, no less.

I’m going to say “yes” unless you’re specifically engaging in “juice fasting,” in which case it’s still not fasting despite what you call it.

Common Drink Additions/Condiments

Cream (Unsweetened)

Technically, as a source of calories, cream breaks a fast. But it doesn’t provoke an insulin response when consumed in isolation, it doesn’t impact ketosis, and many people find it makes sticking to the fast easier.

I’m going to say “technically yes, but realistically no—just keep it to a couple teaspoons or less.”

Almond Milk

It depends on the almond milk. A full cup of the standard sugar-free almond milk has just 36 calories, about a gram of carbs, 2 grams of fat, and a gram of protein. That’s almost nothing. You could probably get away with a quarter or third cup and have minimal impact on your fast, but why not just drink some water or coffee?

I’m going to say “technically yes,” but you can get away with a little bit.

Butter

Like cream, butter doesn’t provoke an insulin response in isolation. It’s more calorically dense than cream, though, so watch how much you eat.

I’m going to say “technically yes, but realistically no as long as you’re not using more than a teaspoon.”

MCT Oil/Coconut Oil

MCT oil is pure fat and thus calorically dense, but it has three benefits going for it. First, it doesn’t provoke an insulin response in isolation. Two, it increases energy expenditure. Three, it converts directly to ketones. People new to fasting can often speed up the fat adaptation process by incorporating a little MCT oil. Coconut oil is the main source of MCT oil, so it’ll have similar effects, though not as pronounced.

I’m going to say “technically yes, but realistically no—and it may even enhance your fasting experience when consumed in moderation.”

Cinnamon

I don’t advise eating cinnamon alone, dry, and isolated. It’s a terrible and potentially deadly idea. But in some coffee or tea during a fast? Sure. It can even improve insulin sensitivity.

I’m going to say “no.”

Salt

Salt does not break a fast. Actually, adding a pinch or two of salt to your water during a fast can increase your tolerance of the fasting process and improve hydration status.

I’m going to say “no.”

Non-caloric Sweeteners—First Natural, Then Artificial

Stevia

Stevia contains no calories and has no effect on insulin secretion (if anything, it increases insulin sensitivity). However, it’s often used to sweeten foods that do contain calories, so be mindful of how you’re using it.

I’m going to say “no.”

Monk Fruit

For a good overview of monk fruit, read this. Suffice it to say, monk fruit is similar to stevia in that it’s a non-caloric, naturally-occurring sweetener with unique health effects. It will not break your fast.

I’m going to say “no.”

Swerve

Swerve is a sweetener that blends erythritol (a sugar alcohol) and oligosaccharides (a prebiotic fiber that tastes kinda sweet) with natural flavors. Erythritol has no effect on insulin or blood glucose (you just pee it out mostly). I couldn’t find any studies on oligosaccharides during a fast, but as humans cannot by definition digest them, they shouldn’t affect the course of a fast.

I’m going to say “no.”

Xylitol

See the gum section above. Stick to reasonable amounts.

I’m going to say “no.”

Sucralose (a.k.a. Splenda)

Sucralose does not provoke an insulin response or increase blood glucose—great news for fasters who want to use it—but it does seem to impair whole body insulin sensitivity. That’s bad for everyone.

I’m going to say “no,” but there are other downsides.

Aspartame

Those same studies on monk fruit and stevia also tested aspartame, finding similar results. Aspartame does not provoke an insulin or glucose response. I’m no fan of the stuff, but I don’t see any evidence that it will break a fast.

I’m going to say “no.”

Supplementary Powders, Oils, Etc.

CBD Oil

Assuming you’re doing the kind of hemp oil that comes in droppers and not the kind that you pour from a culinary oil bottle, the caloric content can’t possibly impact your fast. There are no studies examining the metabolic effects of CBD in the fasted state, but I don’t see any reason why it would impact ketosis, autophagy, or fat-burning—and without psychoactive THC involved, you won’t be getting the munchies.

I’m going to say “no.”

Protein Powder

Protein powder provokes an insulin response, which opposes autophagy, which means you’re breaking your fast. Plus, protein powder contains calories.

I’m going to say “yes.”

Collagen

If you’re strict and technical, then yes, collagen breaks a fast. There’s evidence that glycine—the most prominent amino acid in collagen—can inhibit autophagy, but it was a convoluted animal study where inhibiting autophagy with large doses of glycine after brain injury actually improved outcomes. It probably doesn’t apply to someone adding a scoop of collagen to their coffee. Besides, even if it slightly reduces autophagy, a little collagen won’t negatively impact ketosis, fat-burning, or energy intake.

I’m going to say “technically yes,” but “realistically no.” Avoid if your main focus is autophagy, though.

Branch Chain Amino Acids (BCAAs)

BCAAs trigger an insulin response and thus stop autophagy and the fast. That said, many proponents of fasted training recommend using BCAAs before a workout to help preserve muscle and improve the post-workout anabolic response.

I’m going to say “yes.”

Apple Cider Vinegar

Apple cider vinegar is made by double fermenting the sugars present in apple juice. First, yeast convert the sugars to alcohol. Next, the alcohol converts to acetic acid. The result is a liquid that’s virtually calorie-free. Studies showing that consuming vinegar lowers the blood glucose response to a subsequent meal aren’t really relevant if you’re fasting, but they don’t hurt.

I’m going to say “no.”

Electrolyte Powder/Tabs

Electrolyte powders/tabs used to come festooned with sucrose, making them decidedly anti-fasting. These days, most of them are sweetened with stevia or some other natural non-caloric sweetener. Even the ones that have a little bit of sugar (1-2 g) are probably okay to consume without much negative effect. Best of all, electrolytes can really help you tolerate a fast.

I’m going to say “no.”

Breath-Freshening Items

Gum

If we’re talking sugar-rich gum, the answer is yes. Those definitely break a fast. If we’re talking xylitol gum, the answer is more mixed. In healthy individuals, 30 grams of pure xylitol triggers a small but significant rise in glucose and insulin. That might sound scary to a prospective IFer, but most people aren’t chewing gum made with 30 grams of xylitol. The average piece of xylitol gum barely weighs a gram.

I’m going to say “no,” unless you’re chewing gum made with real sugar or you’re throwing back 30 pieces of xylitol gum in a sitting.

Toothpaste

I always consume my toothpaste (around a tablespoon of the good stuff per brushing) and I’ve never had it knock me out of ketosis, autophagy, or in any way shape or form break my fast. I’m kidding. I don’t consume my toothpaste, but brushing your teeth doesn’t break a fast.

I’m going to say “no.” Don’t eat it though.

Mouthwash

Pretty much the same as toothpaste. Look for a brand that doesn’t contain sugar or one of the artificial sweeteners above that trips insulin. As the instructions (and common sense) suggest, don’t drink it.

That’s it, folks. If you have additional questions about what does or doesn’t break a fast, leave them down below. Thanks for reading, and I hope you found the post helpful. Forward it on if you did.

References:

Hansson P, Holven KB, Øyri LKL, et al. Meals with Similar Fat Content from Different Dairy Products Induce Different Postprandial Triglyceride Responses in Healthy Adults: A Randomized Controlled Cross-Over Trial. J Nutr. 2019;149(3):422-431.

Anton SD, Martin CK, Han H, et al. Effects of stevia, aspartame, and sucrose on food intake, satiety, and postprandial glucose and insulin levels. Appetite. 2010;55(1):37-43.

Ili? V, Vukmirovi? S, Stilinovi? N, ?apo I, Arsenovi? M, Milijaševi? B. Insight into anti-diabetic effect of low dose of stevioside. Biomed Pharmacother. 2017;90:216-221.

Noda K, Nakayama K, Oku T. Serum glucose and insulin levels and erythritol balance after oral administration of erythritol in healthy subjects. Eur J Clin Nutr. 1994;48(4):286-92.

Müller-hess R, Geser CA, Bonjour JP, Jéquier E, Felber JP. Effects of oral xylitol administration on carbohydrate and lipid metabolism in normal subjects. Infusionsther Klin Ernahr. 1975;2(4):247-52.

If you'd like to add an avatar to all of your comments click here!

57 thoughts on “The Definitive Guide To What Breaks a Fast”

Leave a Reply

Your email address will not be published. Required fields are marked *

  1. I find this topic pretty strange. Intuitively, it feels like people who are trying to fast AND put all or some of the things listed above into their bodies are missing a bit of the point. I’m all for living awesome and using science to inform our choices…and my gut is telling me that actually putting something besides water in it breaks a fast. I did a 3 day water only fast a month or so ago, and it felt very different from a fast interrupted by coffee.
    This is coming from someone who “fasts” for 14-18 hours every day and drinks coffee every morning, so I don’t mean to be holier than thou at all.

    1. I want to avoid a no coffee headache and in order to also avoid a
      stomach ache with said coffee I add a little cream which takes care of that.
      So I was hoping a little wasnt going to break my fast.

      1. Yep. Same here. Pry my coffee with heavy cream from my cold, dead, fasting hands.

  2. What about homo 3% milk?

    I do IF and have black tea with milk (as the civilized people do) in the AM.

    How much milk can I have until I create an insulin response?

    1. I’m not sure about your question, but I can tell you that not having black tea in the morning doesn’t necessarily have anything to do with how civilized one is. Sure, I’m an American, but I’m also an IFer. Coffee is fine on my empty stomach. Tea makes my empty stomach SUPER queasy, particularly black tea. Even with cream or milk. Therefore I save it for afternoon tea time. 😉

    2. Well, c’me on, Ash! Milk has carbohydrate and protein, both of which cause an insulin response. Insulin release breaks the fast. Read the article again.
      Why not use a couple of teaspoons of heavy cream instead of taking a chance with milk?

  3. Does your body remain in a fasted state if you have a significant calorie deficit beyond any calories you consume? As an example, yesterday I burned over 2,000 calories from exercise, and I consumed around 1,000 calories with a total of less than 10 carbs (spinach). Note that the 2,000 calorie burn (~2 hours running + ~2 hours biking) is in addition to my basal metabolic rate (1,800 calories). I find that exercise is ok when fasted, but that I struggle and am considerably slower if I burn more than about 1,000 calories a day (10+ miles running) after I have used up all my glycogen. My body still feels like it is in a fast even if I consume food, but I would appreciate your guidance. Thanks!

    1. negative energy balance is not the same as fasting. Burning more calories in a day than you consume does not provoke autophagy or necessarily put you into ketosis. This is what I’ve gathered from reading sites such as this. I am not, nor do I pretend to be, an expert.

    1. I have this question, too – a drop about the size of a dime in my case.

    2. He didn’t mention sources of pure sugar because it should be self-evident.

      1. That isn’t self-evident. Raw honey consist of mainly fructose, and fructose doesn’t raise insulin. Too much fructoseof would cause fatty liver, though, but a half teaspoon a day might have health benefits. (It’s prebiotic, contains a wide spectrum of vitamins and minerals and polyphenols that reduces oxidative stress). Also a study shows that fasting blood sugar actually decreased in a group receiving 70 g og honey, compared to a group receiving 70 g of white sugar. (Rasad H, Dashtabi A, Khansari M mfl. The effect of honey consumption compared with sucrose on blood pressure and fasting blood glucose in healthy young subjects. Global Journal of Medicine Researches and Studies 2014; 1: 117)

        I think this is a good question.

        1. Thanks for this info, Anne. it’s helpful.

          A “definitive” guide has no “self evident.” It’s meant to be complete, for the layperson. A definitive guide wouldn’t assume you’d read 30 other posts. Like many readers here, I’m counting on Mark to do this research so I don’t have to.

          I would simply like to know just how much of a healthy sweetener like raw honey breaks a fast. Does a little honey reduce the benefits a bit — or does a molecule of honey negate ketosis entirely?

          He jokes about a tbsp of sugar and half a cup of milk, but gives no info on the real effects / amounts, nor does he mention honey.

          Thus, the question, which Mark asked for.

          1. Hi Franka, my remark was ment for Jason. I think your question was good, and I’ve been wondering about the same myself. 🙂

            Honey is sugar, but nature seems to have given it some form of “x-factor” we might not quite understand yet.

            Br Anne S

  4. I’m shocked about the BCAA. I used to fast and take BCAA’s (yes, to continue dynamic exercise). I used to find it extremely difficult to fast compared to now when I fast without taking them. Does that mean that the insulin response made fastic more difficult?

  5. Thank you very much for this info!! I am a butter-coffee-for-breakfast drinker, and I always worry about the ingredients breaking a fast. Could you please comment on coconut milk (in the can)? I love putting that in my coffee/breakfast.
    Thanks.

  6. Does prebiotic(resistant starch) fiber break a fast? Acacia senegal or potato starch? Thanks!

  7. What about the consumption of medicines? For example, vitamins, cough syrup or painkillers? Even if they are calorie-free, what effect- if any-would their medicinal properties have on the fasting process?

    1. Sue, thanks for your question. I’ll be doing a follow-up post on supplements and medications while fasting. Thanks — M

      1. Fasting aside, I’d love some info about which supplements should be taken on an empty stomach vs not. It’s surprisingly hard to find that information online.

    2. I echo this question but regarding medications like Synthroid for hypothyroidism.

  8. Great input Mark as someone 3days into a 7day water fast with electrolytes of course whats your view on longer fasts.

  9. Okay it’s almost creepy the way Sisson answers my questions before I even ask them! I was wondering about this yesterday and then this post popped up in my inbox.

    How does he do that…? 😉

  10. I like fasting. It’s just simpler, haha.

    With that said, the easiest fast is including your sleep in the equation. I’m not super hungry in the morning anyway so no big deal. Coffee with cream (I just don’t like black coffee that much and heaven knows I’ve tried enough hipster varieties) in the morning is less about “food” and more about ritual. I imagine the appetite suppression that comes with it doesn’t hurt either.

    Sounds like coffee with cream isn’t going to be a big deal in terms of the general benefits. Which is good. I could do without it but that chunk of the morning (brewing + drinking) is often my only me time in any given day. I could do other things but you know what? I don’t have to force that one. I just like it.

    Just knowing cream doesn’t spike an insulin response (why would it) is nice info. Thanks for the article.

    1. I’ve always said MEH to the claims that the heavy cream I have in my morning coffee breaks my fast. I have reactive hypoglycemia (which has been just about cured by strict keto). I figure if I’M able to make it to noon with no sugar crash then the impact on insulin is truly minimal, because, oh boy, does my pancreas seem to love to pump out the insulin every stinkin’ chance it gets!

  11. What about a small snack of paleo sausages, smoked or dried? So meat and fat (beef,pork or lamb), and some spices. Maybe 100g worth.

  12. When I first went Paleo my buddy joked that I only ate tree bark. A couple years later I started snacking on straight cinnamon sticks, and thanks to my improved cognition I remembered those Paleo jeers from my buddy years before. When it hit me, I lol’d.

  13. Great post! What about alcohol? Specifically, a shot or 2 of liquor. I would assume beer and wine would break a fast, but what about whiskey or tequila?

  14. This isn’t relevant to this post, but wanted to say thanks to Mark for the “dairy alternatives” post a few weeks ago. I am dairy intolerant and loathe the taste of almond milk. I had never thought about hemp milk until Mark mentioned it, and I love it! The flavor and texture are very similar to milk, and it feels very soothing to my tummy. I also can’t eat eggs, so I was stumped about a good liquid for a late-morning smoothie. Great recommemdation!

  15. Great article, but I have few ingredients on mind you didn’t mention – cacao powder, essential amino acids (alone or together with semi essential amino acids). What about combination of for example mct and collagen? or it’s just dose (calories) that matter in this case? Thanks

  16. Lived you piece on things that do or don’t break a fast! My question is can I still get into autophagy if my glucose and ketone rmonitoring go very low and very high respectively when I fast more than 36 hours? I’ve done two 3 day and one 4 day fast( a challenge from my son) over the last 18 months and with each one my monitored values were scary. How long must my body fast and still get autophagy?

    1. I work out nearly every morning in a fasted state.

      I eat at 6-8pm the night before, wake up at 4:30am to train folks until 9-10am, and then I do my own workout.

      That’s 13-16 hours usually, and I do that 1-3 time per week.

      I have found I can do heavy weightlifting, long cardio workouts, and intense exercise of any sort without any issue. In fact, I feel lighter on my feet and more energetic.

      Today for example, I am going on 19 hours on a fast which started at 8pm the night before, and did a super tough workout this morning at 9am.

      I feel great.

  17. Does creatine considered as BCAA? Sorry dumb question. i usually take 5gram creatine with 15 gram hydrolyzed collagen peptide as my pre workout mix.

  18. Just completed a one week water fast. I’m already underweight, so this was tough. Not due to hunger, but due to my very low energy levels and low blood pressure. Working up the energy to get out of bed (or my car) was not terribly fun. Here’s hoping it did something.

    Anywho, wanted to share these articles about the problems with artificial sweeteners. Are we all in agreement that they aren’t good for our microbiomes?

    https://www.scientificamerican.com/article/artificial-sweeteners-may-change-our-gut-bacteria-in-dangerous-ways/

    https://www.eurekalert.org/pub_releases/2016-11/mgh-amp112216.php

    https://www.nature.com/articles/nature13793

  19. There’s so much conflicting information out there, thanks for providing this! I intermittent fast daily and was wondering about the bone broth. Will definitely use it if needed to reach my eating window.
    Any suggestions for occasional GERD? Chia Seeds?

  20. I am actually really curious about prescription medications. As someone who takes an anti-anxiety drug first thing in the morning how much is the medicine interfering with the fasting.
    I have been unable to find anything online. I can certainly experiment with pushing the medicine back.

    Thoughts?

  21. Hi Mark, I was wondering if hot cocoa made with unsweetened cocoa powder would break a fast? I make a spiced one with ginger powder, cinnamon, cayenne and vanilla extract using organic raw cocoa powder and boiling water.

  22. Salt, coffee, and some fat lets me continue working out through an extended fast that goes beyond two days. I mostly fast for the anabolic boost and to maintain set weight, avoiding the midlife drift into obesity. So I recently also started throwing in a couple tsp of beef gelatin powder when blending coffee and discovered that the gelatin seems to help a lot with keeping the fats homogenized.

  23. This post was perfect timing for me. I had just promoted intermittent fasting to my new followers and this perfect follow up appeared two days later. Thanks. Also for myself there is great new information. I wouldn’t have guessed the answers for Apple Cider Vinegar, nor Coconut Oil. Both items I use, but was avoiding when fast.

  24. “I consume a tablespoon of good toothpaste per brushing.” Ha, ha, ha, ha….. at first I was reading it, like, what?!? That was so great! Informative article-thank you for your hard work!

  25. This is great – looks like I can continue to consume loads of food while I “fast”. No more going hungry!

  26. Hey Mark

    Have you looked into the impacts of creatine monohydrate? Can you add any color there?

  27. What about oils like peppermint oil? Sometimes I like to flavour my water and coffee with one or two drops. Does this trigger an insulin response similar to artificial sweeteners and therefore break the fast if my main goal is autophagy?

    Thanks

  28. Instant coffee in coconut milk is good. I tried that the other day and now I want to try it with cocoa / cacao powder.

  29. “Does 4 lbs of cream break a fast?”
    Mark Sisson: Technically yes, but I’m going to say no.

    “Does 12 jars of coconut oil and a whole churn of fresh butter break a fast?”
    Mark Sisson: Technically yes, but I’m going to say no.

    “Does a steak dinner break a fast?”
    Mark Sisson: Technically yes, but I’m going to say no.

    “Does a deep fried mars bar break a fast?”
    Mark Sisson: Technically yes, but I’m going to say no.

    “Does eating the candy from a 250 pack of mini m&m’s window break a fast?”
    Mark Sisson: Technically yes, but I’m going to say no.

  30. Hey the “Mouthwash” section advises to “look for a brand that doesn’t contain sugar or one of the artificial sweeteners above that trips insulin”,

    but the *only* artifical sweetener mentioned above that affects insulin is xylitol — is that right?

  31. I want to find out where the claim that “MCT oil boosts calorie expenditure” came from, I’ve been hearing it all over the internet but I couldn’t find a source that is both scientific and supportive.

    would you help me with citation to what you wrote on MCT oil in that section? I’m really intrigued by it, because it doesn’t make a lot of sense, but hey, I’m not a doctor.

  32. Supplements – do they break a fast? I take probiotic, magnesium, potassium, oil of evening primrose, multi vitamin, vitamin D, chondroitin and glucosamine for rheumatoid arthritis. I also take ginseng for fatigue. Most days I take them when I break my fast but some days I’ll take them a couple of hours before.