The 5:2 Fasting Diet – A Beginner’s Guide
With the 5:2 diet, you reduce your calorie intake by following a weekly fasting protocol: on 5 days you eat maintenance calories, and on 2 days (referred to as the fast days) you eat about 25% of that.
It’s one of the many diets out there that promise sustainable fat loss without making major efforts.
Does the diet live up to its claims, though?
Is it effective, healthy and safe?
How does it compare to other diets out there, and is it better than them?
Let’s find out.
What Is The 5:2 Diet Exactly?
The 5:2 diet is a fasting diet, in which you follow a specific weekly fasting/calorie reduction schedule, and, as a consequence, you are in a caloric deficit by the end of the week.
The diet has been around since 2012 when a book about this diet by Michael Mosley was first published, and, together with intermittent fasting and other styles of fasting, its popularity has been growing.
When you do the 5:2 diet, you eat within your normal calorie range for 5 days a week. Aiming to eat healthy, whole food is not a prerequisite, but will make the diet easier overall.
In the other 2 days, referred to as “fast days”, you eat at around 25% of your calories, or around 500-600 calories (there aren’t any days where you don’t eat anything at all).
How Do You Do The 5:2 Diet?
For 5 days a week, you eat maintenance calories, i.e. the calories that would allow you to sustain your weight. This is also known as your Total Daily Energy Expenditure (TDEE).
Your TDEE depends on a few factors, such as age, height, weight, and activity level. For most women, it’s between 1800 to 2000 calories, and for most men, it falls within the range of 2200-2400 calories.
The official 5:2 diet website has a calculator that you could use to estimate your TDEE, and people who either have a smaller frame, or are already lean, or people who have a lot to lose, or a lot of muscle, could be either under or above that range.
If you know your TDEE from experience (i.e. from logging your food and observing how your body weight fluctuates based on the food you’re eating), you could use that number as a starting point. If not, you could use a calculator to estimate it.
On the two fast days, you eat 25% of your maintenance calories. If your TDEE is of 2000 calories, then on the fast days you’d eat 500 calories. Those calories could be split up between 2 to 3 small meals, or you could have them at once.
The two fast days are usually done with at least a day or two of normal caloric intake in between, although they can also be done consecutively.
There isn’t a strict rule about when to have them exactly. They can be on Monday and Thursday, or on Tuesday and Friday, and so on. You could also have your fast days on different days each week – feel free to adapt the diet to your schedule, as needed.
What Can You Eat On The 5:2 Diet?
There aren’t any strict guidelines about what you can and cannot eat, or about the macros or the ratios between the different macros.
As with any diet, it’s a good idea to eat whole, natural food, in order to manage hunger successfully, but apart from that, as long as it is within your calorie budget, you can eat plenty of different foods.
While you could eat anything on fast days, too, for the best results in terms of satiety and appetite control, it’s a good idea to prioritize your meals with vegetables and protein (in the form of lean meat, fish, or eggs), and to avoid processed carbohydrates, which tend to spike blood sugar and will soon leave you feeling hungry again.
During non-fast days, you might still be hungrier than usual because of the caloric deficit you’re in. That’s normal for any diet, and weight loss does come with some mild to moderate discomfort.
In order to stay on top of your hunger, prioritize food that is high in volume, fiber and essential micronutrients, while being low in calories.
Vegetables and some low-calorie fruits fit that description well. Additionally, protein is essential, so you need to be getting enough of it, too – the best sources of it are meat, seafood, eggs, dairy.
Is The 5:2 Diet Safe & Healthy?
As long as you get the necessary micro- and macronutrients from the food you eat, the 5:2 diet isn’t likely to result in deficiencies, and the diet will likely be safe for most people.
Fasting for 20-24 hours (or more) might actually carry additional benefits in terms of cellular health, as autophagy is thought to begin around that time.
On this diet, you could be having fasting periods of around 20h or more on your fast days, if you decide to have all of your calories for that day in a single meal (which is what many people do). It could also drive your cortisol levels up, though.
Fasting for many hours on an end, and having days with such a low energy intake might disturb hormonal function in some women, even if it’s done only once or twice per week.
For that reason, we recommend easing your way into fasting, and starting with fasts of 12-14 hours to see how you feel and how your body reacts to them.
If you notice any symptoms that could be related to your diet, such as frequent headaches, sluggishness, hair loss, missed or delayed periods, and a general lack of energy, then it might be time to switch to another diet that is better tolerated by your body.
Additionally, this diet is not recommended to anyone who has a history of disordered eating, or to women who are pregnant or breastfeeding.
People who have diabetes type 1 or 2 or any other major health conditions should consult their doctor before starting a fasting diet.
If you are prone to developing gastritis or other stomach problems, you should keep in mind that coffee or tea on an empty stomach will be irritating for the stomach lining.
Is The 5:2 Diet An Effective Way To Lose Weight?
It can be, but will ultimately depend on a few factors:
#1. On your actual caloric needs and whether the TDEE estimate that you’re starting with is correct.
Let’s do the math on this one: on this diet, most women would be eating around 1800-2000 calories for 5 days, and 500 for two (in fact, that’s the example you’d see mentioned the most often).
Let’s say that your maintenance calories are around 1900. If you eat at maintenance (i.e. 1900 calories each day of the week), then for the whole week you’d be eating 13300 calories.
If you follow the 5:2 diet and eat 1900 calories for five days and 475 calories for two, you would be eating 10450 calories for the week, and therefore having created a deficit of 2850 calories weekly.
At this rate, you could expect to lose approximately a pound every one to two weeks. The actual weight loss will depend on plenty of factors, including your monthly cycle, water retention, stress, activity levels, etc., and it’s never a linear process.
However, if your actual maintenance calories are around 1600 (which is definitely possible for smaller women who don’t have a lot to lose and who aren’t working out on a regular basis), and you begin dieting with the assumption that your TDEE is 1900 calories, then your weekly maintenance calories would be 11200 calories (7×1600), and if you’re actually eating 10450 calories (or 5 days of 1900 calories and 2 days of 475 calories), then your deficit would be of only 750 calories, which would likely be too small to make a difference (and could be easily offset by errors in tracking).
#2. On how well you manage to follow the 5:2 diet.
This is a diet that requires a fair amount of dedication and might be difficult to get used to, especially if you don’t have experience with low-carb dieting and aren’t fat-adapted.
If you have done keto prior to that and are fat adapted as a consequence, it will be easier to stick to such a low amount of calories on fasting days, because appetite control is much easier when you’re eating low-carb.
Even if you’re not experienced with low-carb dieting, you could still follow a 5:2 diet – it might just be more challenging in the beginning and take a while until you get used to it.
If you often find yourself hungry on it, we recommend cutting back on the processed carbs and adding more vegetables to your diet, for their fiber & volume. Getting enough protein in is also essential for satiety.
#3. On whether you track your food accurately.
People are notoriously bad at estimating their calorie consumption – eating what you believe is 500 calories could very well be closer to 900, and what you assume is 2000 calories might just as well be 2500, if you’re relying on visual estimation and on measuring cups of food and serving sizes according to the label.
Instead, to be successful, you need to weigh your food with a food scale and track everything you eat. While tracking is not a must, according to the creators of the 5:2 diet, we strongly advise you to do it, if you want to see good results. Otherwise, with the deficit, your hunger will go up, and you might end up eating more calories than what you believe you’re eating.
Will You Be Able To Keep The Weight Off After You Stop Following The 5:2 Diet?
This will depend entirely on the eating habits you have in place, prior to starting the 5:2 diet, or that you establish while you’re on it.
If you don’t build up a system of sensible, easy to stick to & healthy eating habits that help you to manage your weight, then the fat loss will likely only be temporary, and the weight will slowly creep up once you go back to the way you were eating before.
If you are just trying to lose weight for a specific event (such as a wedding or a reunion), then this strategy might be good, or at least as good as any other that puts you in а similar caloric deficit.
There might be diets that will feel easier and more pleasant, but if 5:2 is something you’d like to try, it’s as good as any other method out there that puts you in a moderate deficit.
If you actually want to keep the fat off – and who doesn’t! – then things become more difficult. You cannot go “on a diet” for a couple of weeks, and then go back to your previous habits and expect weight loss to be sustainable – it won’t be, and you’ll feel hungrier than before (because of the weight you just lost) which will make you eat more and gain the fat back.
To put it bluntly, if your previous eating habits are what made you gain weight in the first place, why would it be any different after the diet is over?
In order to manage your weight successfully, you need to make a number of lifestyle changes, and these start with nutrition.
It’s essential to learn to not overeat on a regular basis, but instead to eat adequate amounts of food for the activities you’re doing, and to provide your body with all micro- and macronutrients it needs for optimal health.
A general understanding of nutrition and of your macronutrient needs will help you build a stable basis for good habits, which is why we advise tracking accurately your food at least for some amount of time, regardless of the specific diet that you choose to follow – and for the 5:2 diet, that would be advisable anyway.
By tracking your food, you learn to be accountable, to not overeat and to manage your portions. You also get to know how many calories are in different foods, and how they are distributed between the different macronutrients that a given food contains. You can use that information to accurately assess your maintenance calories, as well as the way different proportions between the three macros (protein, fat, and carbs) affect you.
Additionally, it’s always a good idea to stay active. You cannot outrun a bad diet, but activity will drive your energy expenditure up, so you’ll be able to eat slightly more than if you’re sedentary (unfortunately, the difference is never as big as we’d like it to be – but it’s still there).
If you learn to fuel your body properly for the physical activity you’re engaging in (without systematically over- or underfeeding it) you’re on the right track.
Another equally important part of weight management is sleep and the way you deal with stress in your life. To put it simply, stress and insufficient sleep make it more difficult to lose fat, and that would be true for any diet out there.
If you combine those 3 principles (eating healthy, staying active, and getting enough sleep & time to relax) with a fasting diet, such as the 5:2 diet, you’ll definitely see results, and you’ll also be able to keep them.
Once you achieve your goal, you could go off the diet and just stick to your maintenance calories – as long as you establish healthy habits in the process of losing weight, you’ll be able to keep it off.
How Does The 5:2 Diet Compare To Other Diets?
The 5:2 Diet Vs. Other Intermittent Fasting Diets (16:8, 20:4, Etc…)
The 5:2 diet is essentially a fasting strategy, and as such, looks somewhat similar to other fasting protocols.
It might be more difficult to stick to than daily intermittent fasting, due to the very low amount of calories you’d be getting 2 days out of 5, and also more of a mental challenge than traditional intermittent fasting. Intermittent fasting usually goes very well with keto.
Similarly to the 5:2 diet, fasting diets might not be suitable for women whose hormones easily get out of balance – if you notice hair loss, fatigue, or missed periods, fasting might not be for you, or you might have to cut back on the duration of the fasts.
The 5:2 Diet Vs. Keto
In theory, the keto diet could be combined with a 5:2 eating schedule, and this could improve overall diet adherence, as your appetite and hunger will be easier to control on keto.
In fact, if you decide to do both fasting and keto, it’s advisable to first let your body become fat-adapted, and then to add fasting to your eating habits.
Besides that, the two diets don’t have that much in common – the 5:2 diet doesn’t give any specific guidelines regarding the food you should be eating, while the keto diet is all about eating specific foods while limiting others and tracking your macros precisely.
Overall, the keto diet would be easier to sustain in the long run than a 5:2 diet and is less likely to give you side effects.
Alternatively, if you don’t feel you could commit to a ketogenic diet, you could try a low-carb diet (where your carb limit is set higher than for keto), or paleo. You could combine all of those with the 5:2 diet, or with other fasting protocols.
Fasting is most commonly used as a means to control appetite and hunger, and to keep you in a moderate caloric deficit; other benefits of fasting, such as autophagy, could be experienced with longer fasts.
The 5:2 diet could be a successful strategy for some people, or feel unnecessarily difficult for others – if you feel it could work for you, you could give it a try. It will require a few weeks to get used to, and fasting days might be particularly unpleasant, if you’re not used to fasting or if you aren’t fat-adapted.
In order to make the weight loss from the 5:2 diet sustainable, you need to make changes to your lifestyle and eating habits that go well beyond dieting, and not just “go on a diet” for a couple of weeks and forget about it.