10 Intermittent Fasting Rules (And One Tip That Changed Everything)


Intermittent fasting can be hugely beneficial. That said, there are some rules you’ll want to follow to ensure that you’re fasting correctly and reaping all of the benefits.

I’ve covered 10 of the most important intermittent fasting rules below.

One thing I want to mention upfront. What works for some, might not work for others. With any new diet or workout regimen, it’s important to figure out what works best for you. While many of the rules are backed by science (sources included), you might find a slightly different strategy works best for you.

That’s okay! These are just the rules I follow, and they’ve worked incredibly well.

10 Intermittent Fasting Rules


The following set of rules aren’t in any particular order. All 10 of these rules have been instrumental in my ability to successfully implement intermittent fasting in my life. I’ve spent a great deal of time researching each of these topics, too.

I’m hopeful this information will help you get the most out of your intermittent fasting journey.

1. Eat nutritionally balanced meals

While intermittent fasting does provide some flexibility in what you’re able to eat, it doesn’t mean you should be eating whatever you want.  Being “nutritionally responsible” and making sure you’re eating well-balanced meals should be a priority.

As with most diets, sticking to whole, unrefined foods is a good rule to follow. Things like lean proteins (chicken, turkey, fish, etc.), vegetables, fruits, complex carbohydrates, and healthy fats should be the staples that your meals are built around.

And, try to avoid processed foods that provide little to no nutritional value. Especially foods which are high in sugar. Sugar has actually been linked to increased appetite which can make fasting significantly more difficult.

“…what’s happening is the sugar is absorbed into your bloodstream as soon as you eat your food. To bring down this instant surge in blood sugar, your body secretes high levels of insulin. The insulin does its job to decrease your blood sugar, but pretty soon you feel hungry again.” – Dr. Ozgen Dogan

If you do find yourself craving something sweet, check out our list of 30 Healthy Junk Foods. These are a great way to satisfy cravings while not completely ruining your diet for the day.

2. Don’t overeat (target a slight caloric deficit)

A common misconception about intermittent fasting is you’re able to eat as many calories as you want, as long as its within your predefined eating window. Following this advice can make it difficult to see any significant results, especially in terms of weight loss.

Intermittent fasting does not offset calorie intake!

To lose weight, you still need to achieve a calorie deficit (consuming less calories than you burn). There is no way around this, regardless of if you’re fasting. Calories absolutely matter.

Additionally, avoiding big meals later in the day is usually best. The metabolism slows down when we sleep, burning fewer calories. Nighttime eating, in particular, has been linked to both diabetes and obesity.

“Eating a large meal before bed is probably the worst thing you can do when it comes to weight loss” – Dr. John Morton

So, if you can, try to start your day with a larger meal and eat lighter in the evenings. Like the old saying goes; breakfast like a King, lunch like a Prince, and dinner like a Pauper…

3. Consistency is key

To reap all the benefits associated with intermittent fasting it’s critical you stay consistent. This is probably one of the most important, if not the most important, rules to follow.

The body takes time to adjust, be patient.

You should expect to feel a little sluggish your first 5 or 10 days of intermittent fasting. Many people experience hunger pangs initially, which can be a nuisance. This is primarily due to your body being used to having an abundance of glucose (sugar) at its disposal, which it burns for energy.

Things will get better though, I promise.

Once your body adjusts to its new eating schedule, once it realizes there isn’t always a surplus of glucose around, your body will begin burning stored fat for fuel, instead. This is one of the many great benefits of intermittent fasting.

And, you’re not always going to be perfect. You’ll have off days every once in a while, just like me, and just like everyone else. As long as you don’t allow an off day to turn into an off week, and an off week into an off month, you’ll be just fine.

Lastly, don’t get discouraged if you’re not seeing results immediately, results take time. Stick with it, be consistent, and you’ll be glad you did.

4. Only water, black coffee, or tea during fasts

Knowing what you can and cannot eat during a fast is another important rule to be mindful of. It’s also one of the more debated topics of intermittent fasting. Not everyone agrees on what you’re “allowed” to consume in a fasted state.

For me, I usually err on the side of playing it safe. I’d rather be confident knowing I’m still fasting, than eat something that could potentially break my fast.

Certain people think that a small or low-calorie snack during your fast doesn’t break the fast. There’s also some experts that suggest consuming healthy fats, like MCT oil, doesn’t break your fast.

The research overwhelmingly says otherwise.

The generally accepted rule of thumb, when it comes to fasting, is any food or drink that contains calories is off limits if you want to remain in a fasted state.

Even having milk and sugar with your morning coffee will immediately break your fast.

This leads me into the next intermittent fasting rule…

5. “Juice Fasting” is not fasting

While I’m personally not a big fan of juice fasts, I’ve heard from people who’ve experienced great results and swear by them. The problem I have with juice fasts, however, is the use of the word “fast”.

Many juice fasts are not actually fasts, at all.

What they’re really referring to is a diet consisting of only liquid. They don’t typically prohibit you from eating for an extended period of time, but rather prohibit you from consuming any solid foods while you’re on it.

This can be confusing for someone who isn’t as experienced with fasting.

For example, consuming juice during a fasted state will break your fast just the same as eating a sandwich or bag of chips would. It’s important to know the difference.

And, not to go off on a tangent here, but there’s also a lack of scientific evidence supporting the health benefits many of these juice cleanses claim to provide.

“Juice cleanses specifically lack fiber, which helps control your appetite and helps your body ‘cleanse’ itself. Any weight lost is likely to be gained back and enjoying only juices will likely leave you feeling hungry.” – Kelly Plowe, MS, RD

Anyway, just remember, a juice fast and intermittent fasting are two different things.

6. Avoid taking more than a 2-day break

I’d say it’s virtually impossible to fast every single day, or for all your meals to be 100% balanced and nutritious. And honestly, that sounds somewhat miserable anyway.

There will be days when you don’t feel like it, or days when you just want some pizza. And that’s okay! “Cheat days” are actually super healthy and a great way to reward yourself for all the work you’ve put in.

What you don’t want to do, is allow yourself to get off track for more than a couple days.

Once your body has adjusted to the intermittent fasting regimen it’s significantly easier to maintain. By taking more than a 2-day break, your body will need to readjust which can cause weight fluctuation and have you feeling lethargic.

The best way to avoid this is by setting more realistic goals.

Fasting for 6 days each week and having 80% of your meals be balanced and nutritious is a more realistic approach, initially. And it’s going to be so much easier to sustain.

7. Make sure to exercise

Intermittent fasting is not a replacement for exercise. Read that again…

Not only is it important to exercise in conjunction with intermittent fasting, but there are also some very real benefits that come from working out while fasting. For one, your body’s ability to burn fat is greatly increased.

When you’re in a fasted state your stored carbohydrates (or stored glycogen) is going to be more or less depleted. So, instead of burning carbohydrates for fuel your body will tap into its stored fat to keep you energized.

This is a huge win if you’re looking to lose weight!

That said, there are some caveats to fasted exercise. One of the cons to working out while fasting is the potential for your body to break down muscle to fuel your workouts. You may also find you don’t have as much energy to push yourself as hard.

“While exercising in a fasted state, it’s possible that your body will start breaking down muscle to use protein for fuel… Plus, you’re more susceptible to hitting the wall, which means you’ll have less energy and not be able to work out as hard or perform as well” – Chelsea Amengual, MS, RD

The benefits clearly outweigh the potential downside, though.

8. BCAAs and Collagen technically break your fast

knowing which supplements will break your fast is another important rule of intermittent fasting.

This is something I didn’t learn until more recently. For the longest time I would take several supplements before working out in the morning. Little did I know, some of the supplements I was taking were actually breaking my fast.

Two of the more popular supplements that do this are BCAAs and Collagen.

While neither Collagen or Branched-chain Amino Acids (BCAAs) have any significant caloric value, they’re both proteins and will break your fast.

With that said, it seems the benefits of taking BCAAs while fasting (if you’re going to workout) outweigh the downside of breaking your fast. BCAAs have been shown to help preserve muscle during a fasted workout, while also helping with muscle fatigue.

So, do what’s right for you. Just know that you’re technically not fasting once you consume your BCCAs.

As far as Collagen goes, it’s best to wait until your eating window to consume these.

9. Electrolytes are important

One of the often-overlooked rules of intermittent fasting is remembering to replenish your electrolytes.

When you think of fasting, the exhaustion of your body’s electrolytes typically isn’t what comes to mind first. It’s absolutely something you should be mindful of, though.

“Electrolytes – essential minerals such as potassium, calcium, sodium, and magnesium – play crucial roles in cellular function. Fasting can deplete the body’s stores of electrolytes, especially during prolonged fasts or during periods of exercise” – Dr. Rhonda Patrick

With many of the more common intermittent fasting schedules, such as an 18:6 or 16:8, you can get away with replenishing your electrolytes during your eating window.

For longer fasts, it’s usually a good idea to supplement electrolytes during your fast.

 There are a variety of mineral and electrolyte supplements available, so it’s not something that requires much effort. It’s definitely something you should be aware of, though.

10. Sustainability matters

Beginning a new workout regimen or diet can be exciting. It can also be tempting, initially, to be overly aggressive in your approach. And, while that’s great, it’s important not to bite off more than you can chew.

Sustainability is key when it comes to any diet, especially intermittent fasting.

This goes for both the duration of your fasts and your calorie intake.

An 18 or 24-hour fast, right off the bat, is going to be difficult to sustain. Try starting out with a 14-hour fast and see how you feel. For me, I utilize the 16:8 method. Eating 8 hours every day and then fasting for 16. It took me some time to build up to that, though.

Regarding calorie intake, make sure to eat enough calories throughout the day. Trying to sustain a 1000 or 1500 calorie deficit, consistently, is going to be nearly impossible to sustain. Ease into your calorie deficit.

There was a study done, comparing the dropout rates of alternate day fasting and daily calorie restriction. They found that the fasting group had a higher dropout rate (38%) than the group restricting their calories (29%).

I share this with you, not to scare you off, but to reinforce how important it is to practice a diet and eating pattern that is sustainable, long-term.

One tip that changed everything for me

To wrap things up, I’d like to share one final tip with you.

Coming from someone who has been practicing intermittent fasting for several years, it’s really easy to beat yourself up if you occasionally fall short of your goals. This can lead to an unhealthy cycle of guilt and feelings of inadequacy.

We’re not perfect, nor will we ever be.

The focus shouldn’t be on being perfect, but rather improving little by little. And I’m not just talking about improvements on the scale or in the mirror. The biggest, and probably most impactful improvement you can make is the relationship you have with yourself.

Throughout this journey (yes, it’s a journey), it’s important to be kind to yourself when you mess up or when you make mistakes. If you’re unable to forgive yourself, it can make it really difficult to get yourself back on track.

If you can do that, it’s not a matter of IF you hit your goals, but rather WHEN…

Will Holmes

Former personal trainer and athlete, currently working full-time as a health and fitness writer. Getting in shape, losing weight, and eating better, isn't always easy. It helps to have a friend... that's me, I'm the friend! Sincerely, Your biggest fan

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