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    Alternate day fasting works exactly as it sounds.

    • Eat one day.
    • Fast the next.
    • Alternate through the week. 

    Alternate day fasting (ADF) is also known as the 4:3 diet, because it goes on a 4:3 fast / eat rhythm week by week, like this:

    Just like other intermittent fasting methods, you can tailor ADF fasting to suit your needs. This personalization will make a big difference to the alternate day fasting results you’ll get! 

    Let’s look at how to do alternate day fasting like a pro. 

    Key takeaways

    • ADF is eating one day, fasting the next, on repeat.
    • You can follow a modified fast (500/600 calories) or a strict fast (0 calories).
    • ADF can improve your health and help you lose weight.
    • ADF is SIMPLE, easy to follow, and can be tailored to suit your life.

    What is alternate day fasting?

    As we’ve seen, alternate day fasting is:

    • fasting every other day, and 
    • eating as you typically would on the days between.

    It’s a SIMPLE way of creating a caloric deficit, as you’re eating only half as often as you usually would. 

    It’ll also improve your health: There are several benefits to intermittent fasting, alternate day style that are well supported by research. More on that later, but for now get the general idea:

    ADF fasting is eating then fasting, flip-flopping each day. 

    How to do alternate day fasting

    An ADF fasting schedule roughly works out to around 36 fasting hours and 12 eating hours, on repeat. It looks something like this:

    Monday: Eat 8 AM-8 PM

    Tuesday: Fast 

    Wednesday: Eat 8 AM-8 PM 

    Thursday: Fast

    Friday: Eat 8 AM-8 PM 

    Saturday: Fast

    You get the idea. 

    Fasting every other day is a tall order — you’re asking your body to go without food more frequently than (most likely) you ever have before. 

    Naturally, hunger can be a significant challenge, as can making sure you’re getting enough nutrition overall. This nutritional support is crucial to support your body’s needs, so ADF results in you thriving, physically and psychologically, from the experience. 

    So, here’s a SIMPLE tip.

    You could do ADF strict, where you eat zero calories on fast days. 

    But you don’t have to. 

    And we’d highly recommend you don’t.

    At SIMPLE, we never recommend you go an entire day without food. The risk of not getting the nutrients you need outweighs any potential benefit. So, if you’re into the idea of ADF fasting, here’s a better option:

    Turn your fasts into modified fasts where you eat 500/600 calories on your fast days. 

    This makes ADF a slightly more intense sibling of the 5:2 diet, and much safer. 

    With any fasting plan, you are the boss. And with ADF fasting specifically, this key adjustment can make the difference between feeling great and feeling grody. 

    Much of the research on alternate day intermittent fasting was done on modified ADF and the results stack up well. So don’t worry — this isn’t “cheating” and it won’t stop you benefiting. It’s simply a way of making ADF more doable for real humans with real needs. 

    Alternate day fasting schedule and meal plan 

    Let’s get into how to structure your alternate day fasting meal plan and schedule.

    On a non-fasting day, you can eat:

    • when you want
    • what you want 

    Hunger will be part of your ADF fasting experience (at least at first), so our SIMPLE advice is to build your diet around lean proteins, healthy fats, veggies and fruits, and whole grain carbohydrates, i.e., foods that:

    • satisfy hunger
    • keep you feeling full
    • enrich your energy
    • control cravings

    On a fasting day, if you’re modifying your fast, follow the same principles. 

    If you’re wondering what you can drink while fasting, water, unsweetened tea, and coffee will help you most. When you only have 500/600 calories to play with, you want each one to count, so allocate them to your food and let your drinks take care of hydration. 

    Whether it’s a fasting day or not, time your meals in a way that:

    • gives you sustained energy all day
    • helps you make good choices

    For example, you can experiment with eating more food earlier in the day or later. Having more smaller meals, or fewer larger meals.

    You can drip feed small snacks through your day, open your fast day with a meal to shorten the fasting window, plonk a 500-calorie dinner into the mix, follow a breakfast-lunch-dinner pattern — you can cut it up any way you like. 

    However you play it, make it work for you

    For some support in finding a schedule that suits you, try the easy-to-use SIMPLE quiz to track your meals and fasting hours.

    Alternate day fasting and hunger

    What happened the last time you felt really hungry? Most likely, your stomach growled loudly, your brain filled with fog, and you were disproportionately irritated with the world around you. Maybe you felt a bit woozy, light-headed, shaky, or cold, and your mind filled with incessant thoughts of food.

    However it went down, it wasn’t fun, and you probably would’ve eaten curried cardboard if it had been offered to you in that moment. 

    Hunger is the main adversary of the ADF faster, but all is not lost: There are ways to hack hunger while fasting. Here are some strategies to conquer it.

    • Follow a modified ADF fasting approach (as we recommend). Research suggests that hunger will pass in a couple of weeks with modified ADF, but not with strict ADF. 
    • Drink lots of water. 
    • Distract yourself. Play hopscotch, do a jigsaw, have a game of charades with your cat — whatever you find diverting, productive, and engaging. 
    • Eat good quality, nutritious food. 

    Most of all, expect that hunger will be around, at least in the early stages of your ADF adventure. Be prepared and trust that you can handle it. 

    8 tips for implementing an alternate day fasting diet

    1. Listen to your body

    If you feel tired, irritable, hungry, etc., when you’re ADF fasting, how can you help yourself feel better? Try some things — sleep more, listen to uplifting music, go for a walk, etc. 

    If those feelings persist over several weeks it may mean ADF isn’t for you, and that’s OK. 

    1. Plan ahead 

    Know what and when you are going to eat, so when life gets busy and stressful, you can keep moving forward. Especially on fast days: We all know how loudly take-out food can call your name if you aren’t ready and armed with pre-planned meal ideas. 

    1. Stay hydrated

    Staying hydrated when you’re alternate day intermittent fasting is crucial. If remembering to drink is hard (you’re not alone!), try putting a water bottle close to hand, or setting alarms to remind you to hydrate during fasts.

    To give you even more of a leg-up in the hydration game, take our SIMPLE quiz and get your hands on our hydration tracker (as well as a fasting buddy). We’ll send you reminders to drink, so the only thing you’ll have to worry about is whether you want to add some lemon or mint to that next glass of water.

    1. Modify your fast days

    Make your ADF life easy and modify the fast days from 0 calories to 500/600. It’s what we recommend at SIMPLE because it’s safer and healthier for your body, and it’s just as effective if not more so, because it’s easier to stick to. You’ve heard the adage “the diet that works best is the diet you can do”, so if excessive hunger is getting you down, stop being a hero and modify!

    1. Eat well and enjoy your food 

    Don’t just consume nutritious, filling food, like protein, veggies, whole grains, and healthy fats — enjoy them! No one wants you to live on dry chicken breast and boiled broccoli. Grab your cookbooks, throw on an apron, and get creative with tastying up your ADF diet. 

    1. Know your why

    Why are you doing this? What difference do you hope it will make? Get deep here; really draw out your purpose for embracing the ADF fasting life. Then write it down, paint it, choreograph it into a dance routine — however you express it, make sure you capture it and connect to it often.

    1. Notice how foods make you feel

    Perhaps a bowl of oats and berries in the morning makes you feel comfortable and content on a fast day, but turkey and bean chili makes your stomach grouchy (and gassy, but let’s keep that between us). Just because a food is healthy doesn’t mean it’s good for you, so get curious about what helps you to feel and function well. 

    If some friendly feedback would help here, try logging your food in our free SIMPLE app.

    1. Find what works for you

    Tailor your ADF experience to fit you

    From how you structure your fast / non-fast days, to what you eat and drink, how you manage hunger, and how you measure success — it’s your call.

    Alternate day fasting and weight loss

    If you’re trying to lose some inches and reduce your body fat, research has shown that ADF can effectively help you reach that health goal.

    There are lots of studies that back up ADF’s effects on weight loss, like this review and this trial, both of which suggest that ADF is effective at reducing body weight and body fat.[1,2]

    Other studies suggest that alternate day fasting’s weight loss results are on a par with traditional calorie-restricted diets [3], though this research suggests ADF may have some advantages in terms of fat loss and muscle preservation.[4]

    Clinical dietitian Josie Porter, one of our SIMPLE nutrition experts, adds that ADF may have an edge on other IF approaches, too:

    “Interestingly, of all intermittent fasting regimes, such as time-restricted eating, alternate day fasting appears to have a slight advantage.”

    This study would seem to agree.[5]

    One final interesting thing: Some studies suggest ADF may reduce the compensatory hunger we often feel when restricting calories.[6] This means that feeling where you want to eat ALL THE THINGS because you’ve been eating less doesn’t happen as much with ADF. Cool!

    Alternate day fasting results

    The concrete results are strong: ADF fasting can help people lose up to 6% of their body weight in up to 12 weeks.[2] Krystal, an intermittent fasting advocate (and friend of ours here at SIMPLE), reports glowing health:

    I had my annual checkup a couple of months ago and did blood work. I’m in perfect health! 

    If weight loss is your goal, this study gives some insight into what gets results [7]:

    • solid protein intake
    • feeling satisfied with what you eat
    • keeping hunger under control
    • sticking with your plan

    It’s good advice!  

    To boost your alternate day fasting results even more, this study shows endurance exercise can lead to up to twice as much weight loss than ADF alone![8]

    Health benefits and risks of alternate day fasting

    You are probably wondering if fasting is even good for you. Well, beyond weight loss, alternate day fasting has many benefits.

    Lower risk of diabetes 

    ADF can improve your insulin sensitivity, HbA1c, and insulin resistance, and reduce your fasting glucose and fasting insulin, reducing your risk of developing type 2 diabetes.[9,10]

    Improved cholesterol levels

    Alternate day intermittent fasting can drop your LDL and triglycerides, improving your cholesterol levels.[5]

    Improved heart disease risk factors

    ADF can boost your heart health through better blood pressure, lower cholesterol, and reduced inflammation.[11,12]

    Improved body composition

    As well as weight loss, ADF can help you reduce belly fat, lower body fat overall, and potentially increase muscle mass.[12,13]

    The risks

    As for the risks, hunger you already know about — it can be fierce, but it’s short term and there are ways to manage it. 

    You may also feel tired, cold, grumpy, and have trouble sleeping. Again, these should pass. If they don’t, another intermittent fasting schedule might suit you better

    Is alternate day fasting safe?

    If the idea of fasting every other day sounds extreme and you’re wondering whether it’s safe, we get it. 

    It is safe, but not for everyone. Because the fasting window goes well past 24 hours and happens through the day (rather than just overnight), certain groups of people should steer clear, like those who:

    • have a Body Mass Index (BMI) in the “underweight” category
    • are anemic
    • have (or are at risk of having) an eating disorder, or who have a history of one
    • have diabetes or a thyroid condition
    • are on medications (especially those which affect blood glucose or blood pressure levels)
    • are pregnant, breastfeeding, or trying to conceive
    • have high daily physical activity demands
    • are under 18 and still growing (physically, that is; we’re all still growing as people)

    If you do decide to try ADF, talk to your doctor first and make sure you are fully supported by a health professional.  

    We need to talk about women here, too — particularly, intermittent fasting for women and hormones. Calorie restriction can impact women’s menstrual cycle and heighten the stress response, as female bodies are quite sensitive to changes in energy balance. 

    If this affects you, we’d encourage you to start your intermittent fasting journey with the 12:12 approach, and work up to ADF fasting if it feels good. 

    Alternate day fasting drawbacks & the best ways to avoid them

    You might overeat

    Coming off the back of a fast day, you may feel super hungry and eat too much. In the early stages of your ADF diet, this is to be expected, so don’t sweat it! 

    It takes time to get used to a new way of eating; most likely you’ll make some classic intermittent fasting mistakes. Think of a time you learned something new, like driving a car or even the lyrics of a song you like. You didn’t have it down on day one, right? The same applies here. Be patient with yourself. 

    You might feel sleepy, grumpy, or dopey

    Not that you’ll transform into one of Snow White’s 7 dwarves, but the impact of cutting back significantly on your calories every other day can affect your energy levels, your mood, and your ability to think clearly. 

    Don’t worry — these effects will pass. 

    You might forget that life (and food) is to be enjoyed

    Following a diet like the alternate day fasting diet can make you over-focus on food — especially initially, due to hunger — and get hung up on doing everything “perfectly”.

    Remember: ADF works for you. It’s meant to be a supportive method of achieving your goals. Explore how you can make ADF work, see how you get on, and — if it all feels too much — don’t be scared to try another option.

    Is alternate day fasting right for you? 

    ADF’s approach keeps things simple since all you have to remember is to fast one day and eat the next day. But if this sounds a bit too intense, then a different intermittent fasting approach might be better for you (and that’s totally OK!).

    Now you have all the information, it’s bottom line time:

    Is alternate day fasting right for you?

    Yes, if you:

    • like the simplicity and structure of fasting one day, eating the next
    • can get on with eating 0-600 calories every second day
    • have goals that ADF fasting can help you achieve
    • are not in any of these groups

    Then there’s nothing stopping you — go for it!

    No, if you:

    • think this all sounds rather hardcore and difficult
    • prefer a gentler intermittent fasting approach
    • are represented in this list

    That’s OK. We have other possibilities that might suit you better. 

    ADF fasting vs intermittent fasting 16:8

    With intermittent fasting 16:8, you consume all your calories over 8 hours and fast for the remaining 16. The fasting period is up to you, and it’s far shorter than with ADF, making hunger less of an issue. There’s no need to count calories either. 

    It’s an excellent option for getting used to intermittent fasting, and if 16:8 feels too hard, you could try a different approach, like 12:12 or 14:10. The downside is that 16:8 fasting is something you do every day, and that can be more disruptive to your family or social life. 

    ADF fasting vs the warrior diet

    The warrior diet is a 20 hour fast followed by a four hour eating window in the evening. This time-restricted approach isn’t for the faint-hearted, as the eating window is short (it’s quite tough to get all your food into 4 hours!), but the fasts are shorter than ADF and that may feel more manageable. 

    ADF fasting vs 5:2 fasting

    With 5:2 fasting, you fast 2 days of the week and eat as you typically would on the other 5. Like ADF, not fasting every day might fit your life better and, as there are fewer fasting days per week, hunger is less of a challenge. 

    ADF fasting vs one meal a day (OMAD).

    OMAD requires you to fast for 23 hours and eat all your nutrients in a one-hour window. You can schedule that one-hour window whenever you like, but overall, it’s more restrictive than ADF. 

    ADF fasting vs water fasting. 

    With water fasting, you consume only water for 24-72 hours. It’s a short term option that’s quite extreme and truthfully, at SIMPLE, we don’t recommend you try it. 

    SIMPLE’s expert opinion and final thoughts

    SIMPLE’s nutrition experts agree that if it’s safe for you, ADF intermittent fasting is certainly worth a try. It seems to punch above its weight in terms of health benefits, and people often report it’s pretty easy to stick to. 

    Nourish yourself well, go steady, and always listen to your body. If you need a hand deciding where to start, give our SIMPLE quiz a go

    Frequently asked questions about alternate day fasting

    Your goals will determine how long you should do alternate day fasting. Once you’ve reached those goals, switch out to a higher calorie intake on fast days, or to a different intermittent fasting plan like 12:12 or 14:10, in order to keep the benefits you’ve gained.

    How much weight you can lose on alternate day fasting is similar to traditional diets. The science suggests you can expect around a 4-8% reduction in body weight over 6 to 12 weeks.[12]

    You sure can! For the best results, however, shoot for foods that nourish your body

    What you do afterwards determines what happens when you stop alternate day fasting. If you return to how you were eating before, you’ll likely lose any benefits you gained. However, if you maintain your positive habits, you’ll likely keep them. 

    Whether alternate day fasting is good for you depends on who you are. Some people need to avoid it, like those with diabetes, pregnant people, and those who have eating disorders. For other people, however, ADF fasting can really improve their health

    Your results from intermittent fasting will be influenced by many factors, but your actions are key. Stay consistent, make wise choices, and you’ll find it doesn’t take long to see results with alternate day fasting. 

    Some medication does break intermittent fasting, but medication takes precedence over fasting in terms of looking after your health. And, if you are on medications, always talk to your doctor before starting intermittent fasting. 

    Fair point! For men, intermittent fasting can offer excellent results. If you’re intrigued whether it’ll suit you, try it. It might be right up your alley.

    1. Tinsley GM, La Bounty PM. Effects of intermittent fasting on body composition and clinical health markers in humans. Nutr Rev. 2015 Oct;73(10):661–74.
    2. Varady KA, Bhutani S, Klempel MC, Kroeger CM, Trepanowski JF, Haus JM, et al. Alternate day fasting for weight loss in normal weight and overweight subjects: a randomized controlled trial. Nutr J. 2013 Nov 12;12(1):146.
    3. Trepanowski JF, Kroeger CM, Barnosky A, Klempel MC, Bhutani S, Hoddy KK, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Intern Med. 2017 Jul 1;177(7):930–8.
    4. Alhamdan BA, Garcia-Alvarez A, Alzahrnai AH, Karanxha J, Stretchberry DR, Contrera KJ, et al. Alternate-day versus daily energy restriction diets: which is more effective for weight loss? A systematic review and meta-analysis. Obes Sci Pract. 2016 Sep;2(3):293–302.
    5. Patikorn C, Roubal K, Veettil SK, Chandran V, Pham T, Lee YY, et al. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. JAMA Netw Open. 2021 Dec 1;4(12):e2139558.
    6. Klempel MC, Bhutani S, Fitzgibbon M, Freels S, Varady KA. Dietary and physical activity adaptations to alternate day modified fasting: implications for optimal weight loss. Nutr J. 2010 Sep 3;9:35.
    7. Kroeger CM, Trepanowski JF, Klempel MC, Barnosky A, Bhutani S, Gabel K, et al. Eating behavior traits of successful weight losers during 12 months of alternate-day fasting: An exploratory analysis of a randomized controlled trial. Nutr Health. 2018 Mar;24(1):5–10.
    8. hutani S, Klempel MC, Kroeger CM, Trepanowski JF, Varady KA. Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans. Obesity . 2013 Jul;21(7):1370–9.
    9. He S, Wang J, Zhang J, Xu J. Intermittent Versus Continuous Energy Restriction for Weight Loss and Metabolic Improvement: A Meta-Analysis and Systematic Review. Obesity . 2021 Jan;29(1):108–15.
    10. Nowosad K, Sujka M. Effect of Various Types of Intermittent Fasting on Weight Loss and Improvement of Diabetic Parameters in Human. Curr Nutr Rep. 2021 Jun;10(2):146–54.
    11. Kroeger CM, Klempel MC, Bhutani S, Trepanowski JF, Tangney CC, Varady KA. Improvement in coronary heart disease risk factors during an intermittent fasting/calorie restriction regimen: Relationship to adipokine modulations. Nutr Metab . 2012 Oct 31;9(1):98.
    12. Cui Y, Cai T, Zhou Z, Mu Y, Lu Y, Gao Z, et al. Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis. Front Nutr. 2020 Nov 24;7:586036.
    13. Stekovic S, Hofer SJ, Tripolt N, Aon MA, Royer P, Pein L, et al. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell Metab. 2019 Sep 3;30(3):462–76.e6.