Zero Calories

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  • Is there any reason it is not advised to intake 0 calories on a fasting day?

    Russell Cox

    The fewer calories, the better.
    The whole fasting lite thing is merely a concession to sustainability. The thinking being that if you don’t feel that you are being restricted too much on fast days the likelier you are to continue with the diet.

    I do zero calories on 2 consecutive fast days. The way my body works it is more manageable to limit myself to water than to restrict myself to small meals or minimal calories.

    It’s working well for me for 4 weeks. I’m not weighing but I’ve gone down 3 jeans sizes. I simply tell myself firmly after my last meal that a fast begins the following day and do it.

    I get some feelings of hunger around lunch time but if I get busy it passes and the rest of the fast days are pretty easy. I am even able to cook and bake for my family on fast days without succumbing or feeling resentful.

    This program is — after decades of being increasingly overweight since childhood — a godsend for me! And I think I’ve always known fasting was what made my out of control appetites manageable but so often it was health professionals that told me I was doing damage to myself and I had to do the conventional programs that simply DID NOT work for me. The confirmation that my particular body NEEDS a break from eating and a chance for my metabolism to catch up is beyond a blessing!

    I did this today, after reading your post. I have a bit of a headache, but the hunger does go away after mid-morning. I may try doing zero cal once a week at least.

    It gets easier the more zero calorie fast days you do. The headaches tend to diminish. I suspect that the liver starts to get damn efficient at ketosis, converting fats into glucose and ketones. Originally when I first started zero calorie fasting Id get the headaches and I couldn’t do much exercising. Now the headaches are either not there or very mild at worst, and I can ride my bike with ease. Albeit not as hard or as long as I can when my glycogen levels a 100% topped up.

    I do 0 calories on Mondays and Thursdays, 600 calories on Tuesdays. it’s not as difficult as I thought it would be.

    One oddity I’ve noticed is my dog fasts along with me. I fill up his bowl at dinner but if I don’t eat he won’t eat either. I end up throwing it out the next morning. He’s been a fussy eater since I’ve had him but didn’t know he’d go for 5:2.


    Hi, On fasting days females caloric intake is 500 and males 600.That’s what the site says. I can handle that. The other five days intake is based on your BMI.
    Eat smart. I keep a journal. Helps me to track.


    I’ve been doing zero calories twice a week since last July. It gets easier and easier and I’m feeling great. My energy levels were a bit off for the first few months on the fast days, but nowadays it feels my body has fully adjusted. No hormonal imbalances any more, no cravings, no discomfort to mention. I feel happier, prettier and smarter, whatever the reasons for this may be 🙂

    Good luck to everyone regardless of the no of calories consumed when fasting! 🙂


    Been reading up on the true fasting concept. You slowly adapt your cells to cope better with a lack of carbohydrates. You become Keto adapted and are able to convert stored fats a lot better. If you are regularly fasting there is almost a Darwinian survival of the fittest concept happening. Cells that are better able to convert fats into ketones for energy will survive better. During autophagy (the body’s controlled killing off of cells, happening all the time) cells will be preferentially replaced with new cells that can better cope with fasting rather than relying on constant glucose hits. Ive been doing zero cals since the beginning of November. After a few weeks the headaches go away and it gets easier. In fact I cant even eat anything with a lot of sugar in it anymore. Every now and then I’ll eat a treat and I pay the price and get a headache from a sugar overload.

    Hi folks,

    I did my first ever 0 cal fast day. I found that when I went to the gym the following day (after my usual low carb/high fat breakfast) I found myself lacking energy and I felt a bit ill for the remainder of that day. – Anyone else found this or did I do something wrong?

    I’m to do another 0 cal fast day tomorrow (Friday 2nd March) so perhaps it will all be easier this time.

    Looking forward to your opinions and thoughts


    I did this today, after reading your post. But the hunger does go away after mid-morning. I found myself lacking energy and I felt a bit ill for the remainder of that day

    I started two weeks ago with a four day fast, and have been doing zero calories (sort of) every other day, and when I can squeak in an extra fast day, I do. I didn’t weigh myself initially so I don’t know what I lost the first week, but I’ve lost 7 pounds this second week. Like other posters, I’ve noticed that my body seems to have adapted to fasting. I feel good and energetic now on fasting days, where at first I felt a little queasy and unwell. The reason I said I “sort of” do zero calories is that I do have black coffee in the morning (which technically has a few cals) and allow myself tea, sparkling water, or bone broth if necessary. I had a cup of bone broth twice in the early days with some salt added when I started to feel light-headed, and figured it was because I was flushing so much salt. I don’t know what’s going on in my cells, but I do feel healthier and my skin looks great.

    There are quite a few people on these forums that always do zero calorie FDs. From what I’ve read, it does have some additional health benefits over very low calorie days. I’ve tried it a couple of times. It wasn’t too difficult but I found it kind of boring without some sort of meal to look forward to. It would probably be better on busier days when I was out and about.

    Just be sure to drink enough liquids so you don’t get dehydrated.

    My zero calorie days are getting purer all the time. For a while I used fruit teas and/or sugar-free mints or gum. I used to dink a lot of diet cola while fasting. Lately I’ve only been drinking black coffee, straight tea, water and club soda. I’ve slowly come to dislike the sweetness of things like gum and diet cola at least while fasting.

    Headaches have been rare for me. The only issues I used to deal with a lot were feeling too light headed about 20 to 22 hours into a fast and having trouble sleeping the second night. Oh and I used to briefly get the runs after breaking a fast. Those problems have mostly gone away, although I can still notice it when my blood sugar dips around 20 hours into a fast. I think bigbooty is right, the body adjusts to the fasting.

    Hi There

    I actually read in Fungs book that it is harder for people to fast with trying to stay under 500, because once people start eating, sometimes it is hard to stop. I am not sure how others feel but I think this is true for me. I would much rather just not eat then try to calorie count or deal with limiting my food.

    I am on day two of zero or near zero calorie diet. I have tried 500 calories before. I am finding no calories at all easier. Also I’m taking fibre supplements during fast days. Hope it will workout.

    Wow, I really salute all of you doing zero calorie fast days! I’m starting 5:2 officially on Monday, starting with the “new” 800 calorie limit. As time goes on, I hope to gradually cut down, if necessary. We’ll see!

    Sheryljoyce53, I’m impressed by the people that can make it through a day just eating 500 to 800 calories. Once I start eating I’m done. I have only two states, fasting or feeding!

    Dykask, I hear you. I think I’ll be ok though if I focus on protein and no sugar, which the 800 calories really forces you to do anyway. I just bought Dr. Mosley’s latest book, his Clever Gut Cookbook. 5:2 is talked about in many places, along with some really great tips. Monday, here I come!

    Sheryljoyce53 people do often turn to protein. Personally I’m trying to keep my protein lower so that isn’t an option for me. Besides the diet I’m using is working very well for building lean body mass which is my primary goal. I think the improved hormone balances from fasting helps with that.

    below 1000 kcal daily is to dangeorus for health, no food and no drink state weakens your body. Your body needs energy … You should at least drink a lot of water and you don’t do such days like this one so often

    Update! I’ve been one meal a day (OMAD) (no snacks) for 6 months and now introducing a 2 day fast once a week. Never felt better and losing belly fat. No side effects at all. Wooohoo!

    I loose 4kg’s in a month by doing exercises/cardio in a gym and by maintaining diet woohoo that is great feeling.

    daniela, are you a Faster? If so, how many calories do you eat on a Fast Day? Less than 1000 calories is the norm for a Fast Day you know. If you are not a Faster, what are you doing on this Forum?

    @daniela. Have to agree with Fasting_me. Why is less than 1000 calories dangerous? What science do you base that on? I used to regularly water only fast for 60+ hours, Ive now backed that off to 36 hours once per week as Im in maintenance mode. I find it a little bit odd that that youre advocating not to fast on a fasting website? Seems strange.

    In fact looking at the biggest loser studies 1000 a day is the worst way to fast.

    Restricted calories (including carbs) still causes Insulin to rise. We store fat not burn it in the presence of Insulin.

    We need insulin to drop so our fat cells start to cover the deficit by releasing fat to use as ketones.

    As I understand it, we use glucose in the blood first for energy, then stored glycogen. If Insulin is present the body cuts the metabolic rate instead of burning fat (starvation mode) and another consequence is the hunger hormone. So the key is to reduce insulin so that the hormones that burn fat into ketones are released. The body burns protein last of all, it’s not easy for the body to use protein and to start with it burns gubbins protein such as remains of dead cells, excess skin before it uses muscle.

    The brain appears to prefer ketones as fuel.

    So a water fast of 3 days or more takes you to fat burn, (about half a pound a day of fat).

    The order of burn appears to be:

    Blood sugar
    Fat stores (And body fat is saturated fat!)
    Gubbins protein

    To move from burning glycogen to fat when the body isn’t used to it can be very uncomfortable for some. For me it takes 3 days to burn all my glycogen and switch to fat burn. Initially it took nearly 2 weeks before ketones showed up. I speed it up by doing cardio on days 1 and 2. At the point I burn fat hunger disappears completely as no insulin and minimum hunger hormone.

    After day 3 I burn fat and no hunger. Day 2 is my worst day so I never do two day fasts. A lot of discomfort for little benefit.

    From day 4 I also work out with weights, on my last 7 day fast I added 2lbs of muscle and lost 3 lbs of fat. Net loss 1 lb but my body shape is so different.

    On the August challenge there will be a 10 day fast challenge.

    I find in order to make life easy on a water fast then for two days before I start WFD I eat LCHF (below TDEE).

    Each one of us is different and can be so at different stages of this WOL, so we have to monitor ourselves and learn to biohack to get the results we want. What works for me with only 15 lbs to lose might not work for someone with 80lbs or it may be overkill.

    So do that which works.

    Hope that explains my thinking


    Just a very brief observation there seem to be elements to fasting that are very important

    1. The number of calories eaten before insulin is triggered for most that 800 cals in a window for others 500 is too much, for me it’s about 200 cals

    2. The time frame we eat, for some OMAD (window of an hour) is ideal others go to 8 hrs. Over 8 hrs and generally the body is in full insulin state for the whole 24 hrs. Others like me it takes a couple of days to start burning fat, as we are so resistant. For me it’s as a result of former life choices.

    3. The composition of the diet, for some LC is ideal for others only full on keto will help

    That’s my thinking, so biohack we can work out our own strategy.

    I don’t think one size fits all.


    Mari, anytime you eat carbs or protein insulin is released. Animal studies show that there is very little difference in fat loss with a less than 10 hour window with time restricted eating with an equal # of calories.

    I’ve found that my body has become keto adapted as I’ve done more water fasting. I measure ketones daily and have seen a more rapid response over time. When I do a “fasting mimicking diet” for 6 days I eat < 600 calories of fats and low glycemic carbs and I get into ketosis but much milder than for a water fast. I can go as high as 7.1 mmol during a 5 day water fast but on fasting mimicking it’s typically only 1.3 mmol.

    Of course I burn a lot more fat on a water fast.

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