Everything You Need to Know About Alternate Day Fasting

Everything You Need to Know About Alternate Day Fasting

Alternate-day fasting is one type of intermittent fasting. Some people use it to lose weight without counting calories but nutrition experts are wary that it’s just another diet fad that’ll leave you disappointed. “Intermittent fasting can be effective for weight loss but the best diet is one that you will enjoy the most and can follow for years to come,” says Samantha Thoms, MPH, RDN and owner of Budget Dietitian,

Ask yourself: Can you make this a lifestyle change? Read this alternate-day fasting guide to find out if the answer is yes.


What is Alternate-Day Fasting?

Alternate-day fasting (ADF) is a type of intermittent fast where you cycle between feeding and fasting days. On feeding days, eat and drink whatever you want within reason, but you’ll eat nothing or close to nothing on fasting days. A popular version is the 5:2 diet where you limit yourself to 500-600 calories on fasting days.

For our purpose, let’s assume that:

  1. ADF is eating 0 to 25% of calorie needs on fasting days and
  2. Fasting days happen every one to two days. This doesn’t include a multi-day fast where you don’t eat for more than two days.


What Are the Benefits of Alternate-Day Fasting?

ADF has similar benefits to classic calorie restriction. It helps with weight loss, getting lean, and better blood work (e.g., blood sugar, cholesterol). There’s evidence that it can protect against neurodegenerative diseases like Alzheimer’s and Parkinson’s. Fasting kickstarts autophagy, a body-wide process that breaks down and disposes of old, damaged or useless proteins.

A benefit not related to health: Less meal prep, cooking, and fewer dishes means more time to do other things in life.

empty plate- alternate day fasting

How to Start Alternate-Day Fasting

The easiest way to do ADF is fast one day and then eat what you want the next. This approach is easy to say, but may not be easy to do. Unsavory side effects of fasting are hunger, dizziness, lightheadedness, low energy, feeling cranky, reduced ability to focus, and feeling cold. However, these side effects may become less profound as your body becomes more accustomed to fasting, and ultimately you may find that on fasting days you have increased energy.

Choosing a fasting plan, schedule, and the right foods can help fasting feel more bearable. If you’re still concerned if fasting is for you or want to know how to tailor a fast to your particular situation, please talk to a dietitian.

1. Fasting Plan

Fasting plans vary in how restrictive they are. A complete ADF fast plan involves a whole-day fast, which means giving up all food and caloric beverages on fasting days. But a modified plan, like the 5:2 or others, allows for consuming up to 25% of your total calories needs on fasting days.

If you’re new to fasting, try to steer clear of a no-food fast. Let yourself have that 25%-of-your-daily-calorie-needs wiggle room. According to Angel Planells, MS, RDN, CD, FAND and spokesperson for the Academy of Nutrition and Dietetics, “The 5:2 method is easier to implement since it is two days per week of reducing intake to 500 to 600 calories. It can be done on a Monday and Thursday and allow a person to still maintain a regular schedule.”

For those who are already doing shorter fasts (8 to 16 hours) but not seeing results, a whole-day fast could be the next big leap.

2. Fasting Schedule

With ADF you’ll fast 2 to 3 days per week — let’s see how they fit into your weekly schedule. Your physical and mental energy may tank on a fasting day. Consider these questions before you plop fasting days onto a calendar:

  • What are your busiest workdays? If you fast on these days you’ll spend less time eating while mindless or distracted. Staying busy may also keep your mind off food.
  • Do you want to fast on the weekend? Fast during the week if your weekend is packed with social eating.
  • What days do you normally work out? A handful of you may enjoy fasted-state training, but the rest of you may be happier keeping your muscles well-fueled during workout days. Try fasting on non-workout days or try playing around with your workout routine, perhaps on fasting days you just go for a long but slow walk.

3. What to Eat and Drink

Drink as many calorie-free beverages (e.g., water, unsweetened tea, black coffee) as you want on a fasting day. Even mild dehydration can drain your energy and cause you to think less clearly. If you eat on a fasting day, enjoy 500 calories in one big meal or divide it into two small snacks. No matter what you do, include foods high in protein and fiberto keep you satiated after eating.

Here’s a 500-calorie meal plan filled with fiber and protein:

  • Egg scramble (2 eggs, 1 cup raw veggies) with a cup of berries on the side
  • Tuna salad (1-2.5 pouch/can tuna with 2 teaspoons mayo) with veggie sticks and a small apple

For non-fasting days, you can technically eat whatever you want. And yes, food should bring you joy. If that means savoring a small piece of chocolate cake on a non-fasting day, go for it. But don’t exclude tasty fruits, veggies, lean meats and whole grains from the menu. These foods are high in vitamins and minerals that keep you from becoming malnourished. Highly processed or refined foods are delicious, but they also make it easy to eat a lot of calories in one sitting without giving you many nutrients in return.

4. Dealing with Hunger

Hunger is a normal response to fasting and a big reason why people can’t stick to it for long. So you may wonder if it gets better with time. Unfortunately, we don’t know. Studies show mixed results. A 2010 study published in Nutrition Journal suggests that hunger fades the longer you fast, yet an earlier study published in the American Journal of Clinical Nutrition suggests it’ll hang around no matter what.

People respond differently to hunger. As you do ADF, pay attention to how hunger makes you feel. Your hunger may be uncomfortable but it shouldn’t be accompanied by unbearable weakness, shakiness or anxiety. These may be signs of hypoglycemia (aka low blood sugar). It’s a sign to quit your fast and talk to a doctor before you resume. Try keeping snacks handy just in case you need to quickly break a fast.


woman smiling- alternate day fasting

What Types of Results Can I Expect from Alternate-Day Fasting?

ADF can help with weight loss and reaching a leaner body composition, but it’s no diet miracle. You’ll still need to create a calorie deficit to lose weight. And research shows you might not need to go to these fasting extremes. A 2017 study compared intermittent fasters to those who followed a basic, reduced-calorie diet and the results showed that both groups lost similar amount of weight but participants had a harder time sticking to the fasting regimen.

Is Alternate-Day Fasting Safe?

Planells says, “Intermittent fasting is safe. Many people have implemented fasting throughout the years in many regions of the world. But I would urge caution against fasting to anyone who is underweight, pregnant, lactating, has issues regulating their blood sugar, diabetes or low blood pressure.”

Other experts are also concerned that ADF could trigger an eating disorder in those who are susceptible to it. They don’t believe it’s worth endorsing especially if there’s not enough research to say it’s any better than plain old calorie restriction.

Still interested in ADF? If you think fasting may work for you but are worried that ADF is too drastic or just want to ease into the practice, give 16/8 fasting a try.