Alternate-Day Fasting 101 — on your marks, get set, go! Alternate-day fasting (ADF) is a type of intermittent fasting. People following this food regimen eat every other day, but this varies depending on the exact regimen.

Those are all pretty legit reasons to consider eating ➔ not eating ➔ eating ➔ not eating ➔ eating ➔ not eating ➔ eating.

Intrigued? Want more than just this little introductory nibble? Then keep on keepin’ on to learn about:

  • what alternate-day fasting is
  • how to do ADF
  • what to eat and drink on fasting days
  • possible results from ADF
  • potential benefits of ADF
  • safety considerations of ADF
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Brook Pifer/ Getty Images

What, that one sentence in the intro didn’t do it for ya?! OK, yeah, we understand.

Fasting 101

Let’s hit the basics first — like what is fasting? Fasting is simply intentional abstinence from consuming calories for some amount of time. For instance, not eating between dinner (6:30 p.m.) and breakfast the next day (8:30 a.m.) could be considered fasting.

Many people opt for a slightly less intense fast like modified alternate-day fasting. This is a form of fasting in which you don’t fully avoid eating and drinking on fasting days but restrict your calorie intake — to 500 calories per day, for example — on those days.

From a physiological perspective, fasting is a metabolic state your body enters once it has completely processed all the food and drinks in your system. Lots of interesting things can happen when your bod’s in fasting mode. (We’ll come back to this.)

According to some research, including a small 2013 study, ADF could be even more effective — better at promoting weight loss, changing body comp, and reducing certain heart disease risk factors — if combined with exercise.

Alternate-day fasting vs. intermittent fasting

Hearing that ADF is one form of intermittent fasting is only helpful if you know WTF intermittent fasting is. Just to be 100 percent sure, it’s like this:

  • Intermittent fasting = a cyclical eating pattern in which you switch back and forth between eating periods and fasting periods. The focus is on when you eat rather than what you eat. There are many variations of intermittent fasting that slice and dice the eating/fasting windows in different ways.
  • Alternate-day fasting = a specific version of intermittent fasting that entails eating one day and fasting the next. So, all variants of ADF are forms of intermittent fasting, but not all flavors of intermittent fasting are ADF. (It’s like saying all purples are colors but not all colors are shades of purple. They should be, though.)

Sample alternate-day fasting schedule

Below is a sample of what your ADF schedule might look like.

Remember how we said you could adopt a modified fasting plan to include some calories on fasting days? You can see how that would fit into your overall ADF regimen. You’d just aim to keep your total daily intake to about 25 to 40 percent of your energy needs, or roughly 400 to 700 calories.

If you aren’t sure what your calorie needs are, you can check the Dietary Guidelines for Americans for a ballpark number. A registered dietitian may be able to give you a more personalized recommendation based on your specific bod and habits.

Whether you’re a fasting purist or a modifier, you should eat normally on non-fasting days — meaning, don’t consume all those calories you skipped while fasting in addition to your regular daily total. The point is to have an overall reduction in your calorie intake.

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Illustration by Wenzdai Figueroa

If you’re sticking to a strict fast, you can have only zero-calorie liquids on fasting days.

BUT if you’re taking a modified approach, you can partake of some chomps and slurps on your fasting days. By the time noon rolls around, you just might be salivating at the mere thought of these delectable options. Nom nom nom!

The things you consume on your modified fasting days should be zero- or low-calorie items, preferably ones that are high in water content, fiber, and/or protein. These kinds of foods and drinks can be lifesavers (figuratively) because they can:

FYI: Fasting regimens can also be incorporated into high fat, low fat, low carb, and other kinds of eating protocols. If you feel like hitting a double-whammy eating plan, talk with your doc first.

F is for foods: Things to eat on modified fasting days

On modified fasting days, look for foods that don’t have many calories or much fat. Remember, your goal is nutritious foods that won’t blow your 500ish-cal-per-day budget.

Your best bet is to channel your inner bunny and graze on fruits and veggies throughout the day. To get your nutritional synapses firing, here are some ideas:

If you want to sneak some protein in there, beans and legumes, lean poultry or fish, and egg whites may work.

A tall drink of (mostly) water: Liquid libations for fasting days

Noncaloric beverages are also allowed when you’re fasting. Water is always a healthful choice, and seltzer may help you deal with sweet cravings.

But doing ADF doesn’t mean you have to give up your coffee! As long as you take your caffeine black — skip the cream and sugar — you’re free to enjoy your chai not-te, caffè america-no, or espress-no.

If you’re doing the modified fasting thing, you can have fluids that contain some calories.

For example, it would be OK to add a tiny bit of milk to your coffee. And, though not it’s necessarily a drink-drink, broth may be one of your BFFs by the end of a (modified) fasting day. Savory, warming, and satiating, clear broths can be a nice break from your regular litany of fast-friendly liquids.

Does it really work? Possibly.

Does ADF help with weight loss and maintenance?

It’s a distinct possibility. Research suggests ADF may help you lose weight and keep it off, but it looks like it’s no more effective than your garden-variety calorie-cutting diet.

But turn that frown upside down!

  • With ADF you might preserve more non-fat weight — aka lean muscle — than with conventional energy-restriction diets.
  • According to a 2017 research review, adults who are overweight or have obesity could lose 2.5 percent of their body weight when following ADF for 3 weeks. A small study back in 2007 also suggested folks could lose 8 percent of their weight in 12 weeks with ADF.
  • ADF could help you win the battle of the belly bulge. A small 2013 study found that participants’ waist circumferences decreased by up to 7.3 cm in 8 weeks.

Does ADF help change body composition?

Hmm. The available information is mixed. Some studies suggest ADF might be better at helping you lose fat (as opposed to body weight from non-fat tissue) than traditional continuous caloric restriction.

Other studies haven’t found significant body composition changes with ADF as compared with ye olde regular diet. But there’s always emerging research that shines more light on this weighty matter.

But overall, you’ll likely lose body fat with ADF, which means your body composition would shift and reflect a lower body mass index (BMI).

And — given that ADF might help with that stubborn-as-all-heck midriff.. uh… padding — you could see a difference in your body’s contours due to the change in body composition.

Does ADF help reduce hunger pangs?

That sensation of hunger really bites. No joke — it can have you looking longingly at dessert-shaped erasers… or kinda almost licking those fruity-tooty scratch-and-sniff stickers on your notebook. The struggle is real.

As with any calorie-limiting eating plan, you may get a serious case of the hangries, which could make you feel even hungrier on non-fasting days.

This is one of the things that can make ADF so darned challenging.

It’s also what motivates most ADF followers to choose a modified fasting routine. Bet that snack sack of crudités is sounding pretty mouthwatering now!

However, some studies report that fasters may be rewarded with improved satiety over time. This means that if you can stick it out, the hangries might not set in as often and may become less severe. You’ll feel fuller longer.

Set aside those weight- and body-comp-related results for a moment. Let’s take a gander at what else is happening inside your hot bod. According to research, ADF may serve up a buffet of health benefits.

ADF and diabetes

Type 2 diabetes and prediabetes are common in the United States. Of the 34.2 million Americans with diabetes, at least 90 percent have type 2. More than one-third of American adults have prediabetes, and the percentages go up with age.

That’s pretty striking.

ADF might help strike back, in a few ways. Losing weight with intermittent fasting is the biggest lever. This weight loss may help reduce or even reverse diabetes symptoms or risk factors.

Research from 2014 suggests ADF could also help lower fasting insulin levels. But again, there’s not enough clinical evidence to suggest that ADF is superior to daily calorie restriction.

ADF and heart health

You might want to sit down for this one. But what we’re gonna tell ya just might be shocking (given the trajectory this article’s been taking thus far): ADF might be a boon for cardiac wellness. Did you see that coming?

Maintaining a healthy weight can positively impact the well-being of your chest ticker. The Centers for Disease Control and Prevention (CDC) says so, so you know it’s too legit to be bullsh*t.

As we’ve established, ADF could be an effective and sustainable way to get into and stay in that target weight range.

ADF may also nudge other heart health biomarkers in the right direction. Here’s what ADF might be capable of doing for your 💓, according to various studies:

ADF and autophagy

Auto-wha?!?! We hear ya!

Autophagy is a natural body process. It’s your body’s way of breaking down and recycling old pieces of cells. (Imagine you have a ♻ on your cells!)

This function contributes to the prevention of diseases, chronic health conditions, and other illnesses. Autophagy is also associated with the aging process.

Data from a slew of animal studies suggests ADF may boost autophagy and correlate to:

Is ADF beneficial for people in a moderate weight range?

Abso-freakin’-lutely! As we’ve highlighted above, alternate-day fasting offers a cornucopia of potential health benefits.

Some studies have specifically explored ADF’s influence on people with moderate body weight. Here’s what they have to report:

  • In a small 2005 study in 16 people without obesity, participants lost 2 to 3 percent of their body weight, and their fasting insulin levels went down about 57 percent.
  • Another small study from 2013 found that participants in a “normal” weight range not only lost weight but also reaped cardio-protective perks.

The main bummer is that people who are at a moderate weight may still endure intense hunger levels on fasting days.

Since ADF could lead to some unneeded or unwanted weight loss, a slightly modified fasting practice (say, eating one small meal on fast days) could be a more manageable or sensible option.

Alternate-day fasting is generally considered “safe and tolerable.” If you’re a healthy adult, it could be perfectly A-OK for you to hop on the ADF bandwagon, at least for a test drive.

Unintended consequences of ADF

You might think that, with ADF, your chances of regaining lost weight or fat jump like they might with starvation or very low calorie diets.

There’s no proof of this. Actually, existing research suggests there’s no difference between ADF and regular reduced-calorie eating patterns when it comes to putting weight back on.

Other research has looked into ADF’s impact on disordered eating behaviors. A small 2015 study found that when participants followed a modified ADF plan (in which they ate at least some food every day), depression and bingeing went down, while controlled eating practices and body image improved.

(Note: Anyone who experiences disordered eating behaviors or has an eating disorder should *not* do alternate-day fasting without the consent and supervision of a qualified medical professional.)

ADF: Not appropriate for all

As with anything else related to health and wellness, approach ADF carefully. There are definitely scenarios in which fasting is not a good idea. Doctors don’t recommend ADF for:

  • kiddos
  • folks who are pregnant or nursing
  • folks with clinically low body weight
  • people who have certain medical conditions or take certain medications
  • anyone with an eating disorder

When in doubt, it’s always a good idea to consult a medical professional.

Fasting involves avoiding consuming calories for a given amount of time.

ADF is a form of intermittent fasting in which you eat only every other day. Modified versions of ADF that permit some calories on fasting days are also extremely common.

ADF can have health benefits like improved biomarkers for metabolic well-being, heart health, and aging. It can also promote weight loss. Some of these effects are more noticeable in people with higher body weights.

Some benefits may get a boost when you pair ADF with exercise. The kinds of foods you eat on non-fasting days (such as high fat or low carb foods) may also change the effects of the plan.

Alternate-day fasting is safe for most people. But it’s not suitable for kids, pregnant or nursing folks, or those who have clinically low body weight or eating disorders.

If you have any health conditions or are taking medication, check with your doctor before trying ADF.