Alternate-day fasting (ADF fasting) is the granddaddy of intermittent fasting regimens. With 36 hours between feeding periods, it's not a subtle intervention.
Adopting an alternate-day fasting schedule is like diving into the deep end of a freezing cold pool. Even if you know how to swim, your dip may be uncomfortable.
If you're considering alternate-day fasting for weight loss or other reasons, you're in the right place to learn the straight truth. You'll learn how ADF works, how to structure fasting and feeding days, potential benefits, risks, and more. Then you can decide if ADF fasting makes sense for you.
First, though, let's cover some fasting basics.
Intermittent Fasting Basics
Intermittent fasting (IF) means taking regular breaks from calories. If you've ever gone 12 hours or more between bites, you've done it.
Pausing your feeding schedule can be beneficial. When you hit pause, you flip a metabolic switch that activates fat-burning mode.[*]
Modern society doesn't encourage this switch. With 24/7 food access, you're never far from a hyper-palatable snack that raises blood sugar, spikes insulin, and promotes fat-storage mode.
It wasn't always like this. Our Paleolithic ancestors would oscillate between fasting and feeding periods, often going days between meals.
Consequently, they were fat-burning machines. Obesity wasn't a thing back then.
But it is now. Fortunately, structured food breaks (intermittent fasting) can help us return to our ancestral state. (With less body hair.)
Intermittent Fasting Schedules
The main flavors of intermittent fasting are:
- 12/12—also called overnight fasting
- 16/8—a 16-hour daily fast
- OMAD—one meal a day
- 5:2—two non-consecutive fasting days per week
- ADF—fasting every other day
Read this article for a practical guide on building your ideal IF schedule. (One takeaway: start slow.) Let's drill down on ADF now.
What Is Alternate Day Fasting?
Alternate-day fasting is the final rung on the intermittent fasting ladder. Because it involves 3–4 fasting days per week, it's a relatively intense form of caloric restriction.
To practice alternate-day fasting, you fast every other day. Monday you fast, Tuesday you eat normally, Wednesday you fast, etc.
Some ADF regimens allow about 500 calories daily on fasting days, while others promote a zero-calorie approach. Consider favoring the low-calorie version to make your life easier.
Unsurprisingly, ADF tends to be effective for weight loss.[*] When you skip full days of feeding, you tend to lose fat and muscle.
What You Can and Can't Eat
With ADF, your menu alternates with the dawning of each new day. Here are some pointers.
Your fasting day menu depends partly on your ADF regimen. If you're allowing 500 calories, choose nutrient-dense whole foods (meat, fish, vegetables, etc.) to keep your body happy. If not, stick to noncaloric options.
Generally, any noncaloric food, beverage, or sweetener is acceptable. Coffee, tea, water, multivitamins, bone broth, and a bit of MCT oil won't meaningfully disrupt your fast.
Don't overthink it. The fasting police aren't patrolling if you sneak a few calories. For more on this topic, see this simple guide to what breaks a fast.
On feeding days, optimize for nutrient density. Eat whole foods with plenty of protein, vitamins, minerals, essential fatty acids, and other compounds vital to human flourishing.
If you eat junk food on feeding days, you'll probably lose weight. But you won't be doing your long-term health any favors.
Alternate Day Fasting Results and Benefits
Researchers have published many studies on alternate-day fasting. Rather than review them all, let's review the review.
The review in question is a 2020 meta-analysis of ADF studies analyzing seven randomized controlled trials with 269 participants, many of whom were obese.[*]
Here were some statistically significant ADF benefits gleaned from this data:
- Weight loss (nearly 10 pounds more than control groups, though controls consumed more calories)
- Lower triglycerides
- Lower LDL and total cholesterol
- Lower blood pressure
Interestingly, ADF didn't improve HDL, blood sugar, or insulin resistance markers compared to controls.
Downsides and Who Should Avoid ADF
When you restrict calories, you don't just lose fat. You lose muscle too.
You don't want to lose muscle. Lean mass keeps you functional, prevents injuries, and makes you look better naked.
As you age, it gets harder and harder to maintain muscle. Age-related muscle loss (sarcopenia) is a leading cause of morbidity in older adults.[*]
Understand: unless you have significant fat to lose[*], ADF will sap your muscle reserves. ADF fasting isn't for lean people.
And a final disclaimer. Pregnant and nursing women, growing children, underweight people, and folks with eating disorders should avoid fasting entirely.
4 Quick Tips for Trying ADF
Mind these tips before plumbing the depths of the IF pool.
#1: Know your goals
Do you have considerable fat to lose? Consider a temporary, 4-8 week ADF program under the guidance of a medical professional.
But if you don't—if you're seeking some nebulous "longevity benefit" of fasting—ADF is probably too aggressive. You'll lose muscle while feeling cold, tired, and hungry 50% of the time.
#2: Prioritize protein and strength training
If you want to build and maintain muscle, these two factors matter most:
- Adequate protein intake (1.2 to 1.6 grams of daily protein per kilogram body weight[*])
- Regular resistance training
On ADF, you'll likely lose muscle regardless. But you'll minimize losses if you're smart about protein and strength training.
#3: Track your progress
You can be smart about protein, exercise, fasting, sleep, and much more by using the Carb Manager app. For instance, the IF tracker lets you choose your fasting protocol (ADF, OMAD, 16:8, etc.), set custom feeding windows, and count down your next meal. All the while, you'll be logging foods to ensure optimal nutrition calibrated to your health goals.
#4: Start smaller
Doing ADF without prior fasting experience is like embarking on a silent retreat without meditation experience. You won't be ready for what's coming.
A better strategy is to start with an overnight fast and work your way up. Find an easeful protocol that fits your schedule and health goals.
Remember, the goal isn't to lose weight as quickly as possible. The goal is to build a sustainable regimen that promotes all aspects of health.