What is the 72 Hour Sardine Challenge?

Have you heard of the 72 Hour Sardine Challenge? If you are struggling with High blood glucose and can’t get into Ketosis, this might be for you! Get all the sardine fast details here!

I was inspired to do the challenge when I saw Dr. Annette Boz’s youtube video where she went over the results from her clients who did it.

On the Sardine Challenge you will eat sardines for 72 hours. The 72 hour clock starts with your first can and ends with your last can.

I’ve got lots of info here as well as ways to make it easier and a section on how to ease yourself into sardines if you are still thinking No Way! So keep reading!

Get your free  Sardine Challenge Cheat Sheet pdf! It has everything you need including the sauce recipe everyone keeps asking me for!


sardine challenge poster


Guidelines for 72 Hour Sardine Challenge

  • Nothing but sardines. Apparently herring and mackerel are close enough as well!
  • No limit on number of cans, eat more sardines if you are hungry
  • No other foods but water, black coffee and tea
  • When hungry eat sardines
  • Sardines can be packed in water or olive oil. You can choose to drain or not drain. You can drain and add your own oil.
  • Do not use sardines packed in seed oils or soya oils!
  • The sardines in tomato sauce or mustard are ok, just check the ingredients for sugar. Or add your own zero carb condiments to make it more pleasing to you.
  • Smoked or kippered sardines are fine too but they do have higher sodium if that is a concern to you.
  • You can eat them hot or cold or room temperature.

Cute Sardine Plate with cans of sardines

What is the Goal of the Sardine Challenge?

  • The goal is to boost ketones and lower blood glucose and apparently it works really well for those that are insulin resistant.
  • If you have a way to test those things that’s great but if you don’t it’s not a reason to not do it.  You can get Keto Mojo here if you are in the US
  • Some are calling it a sardine fast and hoping for autophagy.
  • Dr. Boz seems to infer that autophagy can occur. I don’t know if that is true or not. So if that is your main goal I would do a traditional water fast instead.
  • What you CAN get though is an amazing GKI which will put you in the healing and therapeutic ketosis zone and it seems to carry over a couple days after the challenge is over.
  • You will also get a flood of omega 3’s into your body which is very anti-inflammatory.
  • People are saying it absolutely killed their cravings for carbs!

Sardine Challenge Resources:

GKI Levels of Ketosis

  • Greater than 9:  Not in Ketosis 
  • 6-9 Low level Ketosis
  • 3-6 Moderate Ketosis
  • 1-3 High Nutritional Ketosis
  • Less than 1:  High Therapeutic Ketosis

Breaded Sardines on white plate with lemon

How to Ease Your Way Into Sardines

Ok, I get it! Not everyone out there is ready to embrace eating canned sardines. Out of the can. For 3 days! I get it!

Here are some tips that just might help you to learn to enjoy sardines! 

I hope some of those tips help to expand your palate! I can’t tell you how many people have told me they were afraid to try sardines but once they did, they became hooked! That could be you!






109 thoughts on “What is the 72 Hour Sardine Challenge?”

  1. How often would you do this 3 day sardine fast? Monthly, twice monthly, less often? I’m finishing day 1 and really liking it!

  2. other than the sardine burps it’s been easier than I thought. I’m in the end of day two. Can I have coke zero while on this diet?

    1. Haha no diet soda for me while on this, though I will drink the zevia. Just feels wrong to chug the diet coke hahaha

  3. I’m starting today.
    I have osteo arthritis and am doing this to see if it helps inflammation and stiffness.
    I love your sauce. I just made it for lunch day one. Really makes a difference. I added Herbmare sea salt. I’m used to doing 4-5 day fasts quarterly for autophagy. I’m happy to have found this to see if it’s similar but you get to eat something! I think I can do this more regularly. Thanks for the tip about mineral salts!

    1. I found that doing this helped me a lot with my bone on bone knee! Afterwards I became more conscious of adding more seafood in general to my diet and it’s definitely helping! Good luck!

  4. I just completed this challenge. I am so disappointed in it. I ate 10 cans total in 72 hours and I have diarrhea, bloating and seem to have put on 3 lbs!!!

    1. Wow I would not eat canned sardines if I were you. Sounds like you have a pretty severe intolerance there. Hope you feel better soon!

  5. I’ve been eating OMAD (one meal a day) for a couple of years now and I’m just not hungry after that meal. It wasn’t always that way, believe me as I did the SAD with 3 meals and a couple of snacks, but my body has adjusted. So thankfully an oily fish like the sardine is very filling. I eat 2 (or rarely 3) – 3oz tins of sardines in that meal and I’m stuffed. Also thankfully, I love sardines. My dad loved them and I started eating them when I was a little girl. He also loved liver – but that one didn’t stick! I’ve lost 150 lbs BTW, not from eating just sardines, but they definitely contributed to my success. And as others have mentioned, sardine challenge is a great reset.

  6. I have just started the sardine fast thank you for posting your video and recipe im hoping to reset my satiety signals x

    1. Many people underestimate how important that aspect is! The sardine challenge does an excellent job of resetting those signals.

  7. Hi Dr. Boz,
    thank you for inspiring me to take the challenge. Way easier than anticipated. How often can one follow this 3 days sardines fast safely? Thank you!

    1. Hi, I’m not Dr. Boz but to answer your question I think it’s safe to do whenever you feel the need for a metabolic reset! Also some people simply add sardines into their week more often to keep the benefits going!

    2. Greetings!!!! I’m on the 2nd day of the sardine challenge, and I just about wanted to throw up, so I decided to add lemon juice and onions to my sardines, as well as lemon pepper, and air fry them a little bit. Is adding the lemon juice and onions going to affect the overall results of my challenge since we are only supposed to eat sardines and nothing else? I’m curious because once I added those to the sardines, I had no problem scarfing them down because the taste was a whole lot more pleasant. Thank you in advance for your response, and best wishes!!!

      1. This is exactly why I made the sardine sauce (did you download my cheat sheet!?). It helps make them taste super good! I would skip the onions due to the high carbs in those but lemon juice and mustard are great on sardines.

        1. Thank you so much for such a speedy response! Yes, I did download your cheat sheet, so I will do better tomorrow! I didn’t realize onions were high in carbs. 🤦🏻‍♀️🤦🏻‍♀️🤦🏻‍♀️ I had mustard and lemon juice on the ones I ate yesterday, but the taste still was not to my satisfaction, hence the reason I decided to add onions because I thought they were a good source of antioxidants, but now I know better! Thanks again for your response, and best wishes!

          1. It’s right in the blog post in 2 places! Just scroll down until you see the words ‘Download Sardine Cheat sheet’, it’s close to the top!

    1. I’ve presented this as per Dr. Boz and she says to eat the sardines. But you don’t need her permission or mine to eat some canned salmon if that helps you get through this.

      1. this is the 1st time in months my blood sugar was less than 100 when I woke up. I am at the end of day 2! I have been keto since 2017. I have been on a 2 year stall. My weight was down this morning!

  8. I’m on day 2 and all I am craving is something fresh, a peach, a tomatoe, heck even lettuce. Are you allowed anything other than sardines? Not sure I want to eat anymore. Maybe I’ll just fast until 9 am tomorrow. But if I don’t eat the last can at 9 am, did I still complete the challenge? Thanks.

      1. Thanks. I made it! Lost 3 pounds. Not sure about my blood levels as I don’t test for that. But totally helped with bloating and maybe even some general aches and pains. My husband and I are going to try and do this once a month, just to power some Omega 3s. Keep up the great work everyone!

  9. I really really dislike Wild Planet Sardines. They smell bad and taste very fishy to me. Not pleasant. But I have a ton of them that I got at a huge discount. I decided to buy a waffle maker. I made my first ever waffle this morning. Sardine waffles are a game changer for me. I love that they stay soft. I don’t like crispy waffles. I smeared mine with lots of ghee and topped with my homemade zero carb sweet chili sauce. It’s almost scary that I can call these waffles delicious. My only change to the recipe was to add 1/2 teaspoon of baking powder. I can now continue to eat my sardine stash. It’s very strange how different brands are so different tasting. I did find a couple brands I like. Brunswick fillets are my favorite so far. Unfortunately for the stray cats they aren’t getting any more of my Wild Planet Sardines. Thanks so much for this recipe.

    1. Haha, the stray cats, lol! But I agree, it’s good to try different brands! I had no idea that they could all taste so different as well as different textures and sizes. There’s a sardine for everybody out there!

  10. Hi – I am just in my 2nd day of the sardine challenge. I see that I could sauté the sardines in butter. Does that mean I could also just eat a small bit of butter alongside my sardines? I didn’t cook them but still feel a bit hungry – but not enough to eat a whole other can.
    I’m adding a little dijon mustard to them, which makes them tastier.
    Thanks for your great info – so far I’ve felt good. I’m an intermittent faster so have still been able to fast for part of this challenge.

    1. I don’t see anything wrong with adding butter, but I’m not the Sardine police! Some people are very strict about how this goes!

  11. I just did a 7 day Sardine Challenge. That’s right!! I’ve been eating LCHF for years but, after losing 43 pounds, I plateaued for about 8 months. So I did the Sardine Challenge to jump start my metabolism.
    I fasted for 24 hours each day and only ate one can of sardines per day. I found that I was usually not hungry but if I was hungry, it was usually late at night, 8-9 hours after I’d eaten my can of sardines. I drank only water or black coffee during the 7 days.

    So tomorrow is my last day of sardines and I’m wondering if there are any instructions about how to “break” the Challenge. Dr. Boz has alluded to the possibility of following the 3-day challenge with a 72 hour water fast. However, I’m not inclined to want to spend more time fasting after 7 + days of doing 24 hour fasts every day. That said, I don’t want to just jump into eating other meats or dairy or whatever if doing that could cause me problems, especially gastrointestinal problems. (I have had no GI problems during the 7 days.)
    Any suggestions??

    Leslie Ann

    1. I understand your concern completely! It’s probably not advisable to go from eating 1 can sardines a day to a full steak dinner! I would break the fast very gently. Maybe some bone broth when you are ready to break the fast and then some broth with cut up meat as your second meal, that should be easy to digest. Just add things slowly!

      1. Thanks for your response. I had forgotten about bone broth and that was a GREAT idea. I had been thinking about scrambling 2 or 3 eggs because I thought those were the least difficult for my body to process. But the bone broth is really the best way to break the “fast!”
        In fact, because I have been eating such a limited amount of food for 7-8 days, after drinking some bone broth today after eating my last can of sardines, I could actually fast for a day- or drink only bone broth for a day and then introduce eggs. That might give my the body the rest it needs and a chance to reset. By the way, I lost 5 pounds in this past week! I guess my body has reset ITS metabolism and maybe, if I continue to eat correctly, I’ll continue to lose that remaining excess fat!

        Thank you so much for you wonderful advice!

        Leslie Ann

      2. Simone Goudreaux

        Thanks for all the information and advice you post. Are lemon juice, garlic, and vitamin C permitted during the sardines challenge? I have a puree of these and it makes any sardine can taste much better. I would like to add that after a long fasting, kefir may be one of the best foods to restore the gut flora. Thanks!

        1. I think that any zero sugar condiment that makes the sardine challenge doable to you is ok! It’s better than not doing it.

  12. The pink part of the linked pdf titled, “72 Hour Sardine Challenge Guide” says,
    <9 Not in Ketosis
    6-9 Low Level Ketosis
    3-6 Moderate Ketosis
    1-2 High Nutritional Ketosis
    <1 High Therapeutic Ketosis"

    Shouldn't the "9” ?? Otherwise this set of relations doesn’t make sense.
    Thanks for clarifying.

    1. Hmmm, I guess because of the brackets, it didn’t come through in my question. To restate, “shouldn’t the LESS THAN 9 be GREATER THAN 9 ??”

        1. hi, I can’t figure out how to post my own comment. I was looking to confirm that butter is actually ok to consume on sardine fast. If so, how much should I limit it to? Thanks!!!

          1. Yes if your sardines are water packed I would recommend butter as an added fat. I don’t know what your limit would be. For myself I would probably try 1 tbsp per can of sardines.

  13. is this advisable for some one who needs to gain weight?
    plus can i add eggs with the fish.?
    i lost to much weight fasting for long fasts to get off insulin, which i did but landed up with unwanted bonus of weight loss.

    1. You didn’t mention what your goal in eating only sardines was? For most people it’s a metabolic boost that lowers blood glucose, raises ketones and sets them on a path to loose weight. If that’s not your goal then not sure how to answer your question. There are easier ways to gain weight than eating sardines.

      1. sorry no it was not on a sardien fast. it was a water only fast. now how does this sardien fast work in the body when you are eating all the time consuming nutrients. which means that your stomach do mot rest at all. so is it only because its a non sugar and carbohydrates diet that will only benefit diabetes people. they may get more insulin sencertive. that would do it for me as i still have to employ hacks like vinegar and exersise everytime i eat carbs.

      2. Sorry I did not find this until today – grocery day was yesterday :(
        I bought the wrong kind of sardines – packed in soy oil
        Can I drain and add olive oil, or even eat without any oil?
        Sorry if it’s been asked and answered

        1. Definitely drain as much of that seed oil off as possible. You do want some fat as this is a ketogenic metabolic boost, so add some olive oil or butter.

  14. Paula Pfarr Jackson

    I have been living a ketogenic lifestyle for 5 years. (Occasionally lazy keto or “vacation days”to have a treat; in maintenance mode. My sister and I did the three day sardine challenge & we loved it 😊 We had fun with it, sharing with family & friends who think we are nuts & some said it was unhealthy and Hugh sodium (We ignored the negative) and giggled a lot.
    We had fun making & videos;
    Day 1, Day 2 & day 3
    pictures & videos
    We tried the sardines salad recipe & used cracked pepper & chili sauce. We were both hungry on day 3. So we ate an extra can. I added a lil coconut & curry on the last day 😏
    All was good. My sister forgot to weigh herself but felt so much lighter. I dropped 4 pounds. Wr did get a little bit tired once in a while but nothing bad. I couldn’t figure out why I have less energy but maybe it’s because I wasn’t consuming much.
    We will do it again. Thanks for all the ideas.
    I did have one question I was wondering, are we allowed to make that carnivore bread chips to eat with her sardines?
    I can’t wait to explore new recipes.

  15. I know it says sardines, but you’ve talked about other single food fasts. How would canned small oysters compare? I love those, and they also come in all of the options listed for sardines. No bones though🤷‍♀️

    1. I am most familiar with egg fasts, where you eat eggs and fat. Other people do bacon only. I’m sure you can choose whatever nutritionally dense food you like! My only issue with oysters is that in my area they only come canned in seed oils. But if you can get them fresh or canned in water or olive oil then why not!?

  16. I ate sardines for the first time in my life last month after finding out the benefits of them and found that I like them very much. They remind me of tuna a bit. However, I have gout and read information that those with gout shouldn’t eat them. But if sardines help reduce inflammation, which is basically what causes a gout attack, sardine intake should help with that, correct? What are your thoughts? Thank you!

    1. Hi, I am not a doctor but I do believe that the sardines help to reduce inflammation. Even the Mayo Clinic says the following: Some types of seafood — such as anchovies, shellfish, sardines and tuna — are higher in purines than are other types. But the overall health benefits of eating fish may outweigh the risks for people with gout. Moderate portions of fish can be part of a gout diet
      Lastly I would watch Dr. Ken Berry’s video on gout, he explains what things are the worst things for gout: https://www.youtube.com/watch?v=95mhn0ry2LY
      I hope that helps you with your decision!

      1. My husband had severe gout, but started taking 5mg of Boron before bed and the gout is GONE! Thank You, JESUS!

        1. Hello Ketowoman,

          I have been doing the keto lifestyle since 2018 and love it. I am now on my second day of the sardine fast, I do not feel hungry nor craving for carbs but I am feeling tired with brain fog. I am taking in a zero carb, zero sugar electrolyte mix, thinking I am probably low in electrolytes. Any suggestions? I am in my early 60’s and still employed but am concerned with feeling this way while I am at work. I may have to just do two days instead of the three. Bummed out I really want to finish the last day. Any suggestions or know of a video where Dr. Boz covers this concern? I was not able to find it. Thank you for all you do in giving to this community!

  17. I made it through the 3-day challenge but did not feel well at all the last day. I woke up the last morning feeling very sweaty and shaky. My blood sugar tested at 46. I immediately ate a can of sardines and it went up to 51. After each can, the highest I could get my glucose to go was 54, so I felt pretty crummy all day long. I had to break the fast and drink some coconut water to elevate my glucose. Only then did I feel better. I had sardines, water, and black coffee only, so not sure what went wrong.

    1. You followed the fast the way it was recommended so no you did nothing ‘wrong’. Are you on medications? I’m not a doctor but those numbers are very low. You didn’t mention what your BG normally is or if you are T2D. I would not do it again until you check in with your doctor and get your lab work done!

  18. I’ve done the sardine fast several times. Since Dr. Boz doesn’t consider the fast starting until you eat your first can of sardines, my fasts are about 48 hours. I’ve noticed that it is healing my scar tissue. I believe my hair is regaining its color but it is hard to tell for sure. It might also be helping reverse my need of reading glasses, getting older. I highly recommend anyone that can handle sardines to try it.

  19. Does one have to be concerned about the potential for constipation on this fast? Why can’t one have a bit of parsley or plain chopped iceberg/romaine with the sardines? Will those few green really destroy the point of the fast?

    1. I think everyone is different and any big change in diet can cause either constipation or loose stools. For myself I noticed no difference in that department and it is only 3 days. As far as adding other things I followed the challenge the way that Dr. Boz recommended so if you wish to have parsley or lettuce that is your call.

    1. No minimum. If you ate no sardines for 3 days then you have done a 72 hour water fast, which Dr. Boz also recommends for her patients!

    1. They are definitely not the first choice but it’s a place to start if it’s your first time!

  20. Just finished my first 3 day sardine fast and it was so much easier than I thought it would be (day one was definitely the hardest day for me…but 4 cans got me thru! Seasons from Costco). Interested in trying other brands.
    Will do this often! Saving money, time, effort and exploding w energy❤️.
    Thank you for showing us the way!!

    1. I definitely like that it is so budget friendly! Congrats on the 3 days, I will do another one this week!

  21. Hi there!
    Thank you for your wonderful article. Because of your enthusiasm I am going to try a mono-diet. I’ve been doing carnivore for 2 years. But the year after that I have been struggling, and growing bigger and bigger. I was wondering if a sardine fast, an egg fast or even an (animal) fat fast would still work for seasoned carnivores? Or are they just for people who need to jumpstart their ketones production?
    Thank you very much!

    1. I 100% think these and especially the sardine fast or the egg fast will be great for seasoned carnivores as well! Not all of us are in tune to our satiety signals yet and boy, a mono food challenge for even 3 days will help you reset. If you are REALLY ACTUALLY hungry you will have no issues eating another can of sardines or another egg.

    1. Sure I don’t see why not. Just don’t go longer than that as you won’t be able to eat enough sardines in one sitting to get enough protein, but 3 days won’t hurt!

  22. Started my 3-day sardine fast on Saturday. It’s easy as can be, for me. I’m thinking of doing this every weekend until I see some budging of the belt line. It’s great — you don’t even have to think of cooking on the weekend, freeing up so much more time for fun stuff. I went shopping on Amazon for packs of sardines and love the Wild Planet, which I’ve already had a subscription to; I bought a new brand called Skin & Bone, which I like 5% better than Wild Planet; and tomorrow I should be receiving a VERY impressive gourmet version of sardines and mackerel, the Nuri brand. Can’t wait to see why this brand is SO much more expensive than everything else.

    When I started my fast, I’d eaten a ginormous salad the night before, and now that I’ve finished my Day 3 eating, I feel so much better. The salad bloat has gone away. I’ve felt light and energized on this three-day fast. Glad I did it.

    1. wow, I love your enthusiasm for this! I feel the same way as you about it! Thanks for taking the time to make my day!

  23. Hi,
    Tdy is my first day on Sardine challenge. I got through bfast, lunch i needed more flavour so had the tomato sardines.
    dinner was the best based on your suggestion: refrigerated with salt n white pepper added.
    May try breaded tmrw with pork cracking crumbs.
    thx for your suggestions as i would be eating ice cream now and broken the fast.

  24. I am on day three of the sardine challenge. I haven’t really found it eating just sardines because I like them but I do not feel well at all. I have the same nausea that I get when I do an extended fast. I thought I just needed electrolytes and it helps for a little but the nausea keeps coming back.

    1. That sounds a little like keto flu, so keep up the electrolytes. Some people feel better even just putting a piece of rock salt under their tongue.

  25. Would it mess up the results from the 3 day fast to fry the sardines? Did you just include the fried recipe because it’s delicious or as something to try during the fast? I don’t want to eat nothing but sardines for 3 days and then discover that I did the fast wrong!

  26. Hi. I decided to do the Sardine 72 hr challenge last month after watching your video on YT. I did it again last week and my husband joined me. Finished the challenge this morning with a total of 1.5lb down for me and 4lb down for husband. I am at my goal weight but he needs to lose 20lb. We did the biggest spring cleaning ever over the weekend, energy through the roof. Thanks for inspiring me. We’ll be doing this every month from now on. BTW Wild Planet is our favorite brand.

    1. Oh! I will look for that brand, I’m currently on a road trip in the US and we can’t get many of the brands in Canada.

  27. Although I’m a little apprehensive, I might be able to ease into eating sardines using some of your suggestions. Thanks for a quality blog.

  28. I just tried my first CAN of sardines this evening. I had ONE sardine about 35 years ago on a cracker. I had no desire to ever try again. Now that I’m older and looking for nutrition-packed foods, and having watched your video a month ago, I finally challenged myself to at least open the can. I smelled it….not too bad. I decided to make a teriyaki sauce (no sugar), maybe 2 tablespoons-worth, and plopped the sardines in olive oil in the bowl; tossed. OMGoodness! Tastes like a sushi roll innards. Delicious. I’m totally up for the challenge now!

  29. Are there any recommended preliminaries to starting this or do i just eat as many cans ofsardines asiwant for 72 hours? I assumewaTER ISTHEONLY OTHER THING OTHERTHAN SAUCE?
    GUIDO Passenante

    1. Eat to your hunger and packed in olive oil is fine as well! Grab the free cheat sheet for yourself, all the info is on there! Good luck!

  30. I have no idea how to check keystone levels but I check BGL once in a while.
    I am going to start this fast for a week.

    1. You can check blood ketones the same way as glucose if you have a dual monitor such as Keto Mojo. Not everyone needs to do that, I’m just a data geek so I like to test!

    2. Hi Frank,
      My favorite way to test ketones is urinalysis strips called Ketostix. They are inexpensive and most pharmacies carry them.

      1. They are good in the beginning of your journey but once you are fat adapted they no longer indicate much of anything! The reason for that is they indicate excess ketones in your urine and not how much is circulating in your system. I’ve even heard where people have quit because the sticks tell them they are not in ketosis so they think it’s not working. Blood ketones are the most accurate way to test.

  31. I’ve discovered sardines are delicious topped with tamari, pickled ginger and wasabi- basically sushi in a can!

  32. A friend directed me to Dr. Boz on YouTube. I was planning to start a fast to get into ketosis. I’d never thought of getting into ketosis before the fast! I’m on day two. I had 4 cans of oil-packed (drained) and one water-packed yesterday but was concerned about the low calories so I had six cans today. I think I’m turning into a sardine! I went from .1 ketones yesterday morning to .8 this afternoon. In the past it would take at least a week to get near a 1.0 ketone measurement. I’ll slide straight into a fast after my last sardine dinner tomorrow. I feel great! King Oscar is my least favorite- too bland for me. Wild Planet in Extra Virgin Olive Oil had the most flavor.

  33. I am on day three of the Sardine challenge. I have been eating three cans a day. After rinsing them they are not as bad as I thought. I used the dressing that Anita made it kills any fishy taste, which is what turns me off from fish. Since starting the challenge, I have tried them with hot sauce Mmmm and Hoisin sauce Mmmm. Thanks Anita

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