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Alternate Day Fasting

by | Jun 7, 2020 | FASTING METHODS | 0 comments

The Big Idea

Deprivation diets don’t work. No matter how much weight you can lose, the rigmarole of counting calories and food stress is more than most people can tolerate for days let alone months. Alternate-day fasting (ADF) is an appealing alternative that helps you lose weight without all the tedium of traditional dieting.

The idea behind ADF is simple – eat one day, don’t eat the next. And because it’s so easy to follow (spoiler alert: you can even have food on your ‘fast’ days), alternate-day fasting has become one of the most popular and widely-researched branches of intermittent fasting.

 No adverse effects have been reported in ADF’s numerous studies. And if you can endure slight discomforts like mild headaches and hunger for a week, scientists say that alternate-day fasting actually decreases overall hunger while increasing your sense of fullness.

What it is

 As the name implies, ADF is a continuous cycle of fasting one day and eating the next. But it’s a little deeper than that. The parameters for alternate-day fasting studies include a 36-hour fast followed by a 12-hour refeeding period. This means that even on off days, you’re still practicing intermittent fasting to some extent.

 One of the reasons that alternate-day fasting has a greater adherence rate than calorie-restricted diets is that you can eat whatever you want during your eating days, also known as ‘feast’ days. But the really cool part of this fasting method is that you can eat up to 500 calories on your fasting days and still reach all the benefits. Sort of similar to the Fasting Mimicking Diet.

 You might worry that such an on-again-off-again relationship with food could either cause or worsen an eating disorder. But there’s no need to fear: a study of 59 adults showed no increase in disordered eating behavior after eight weeks of alternate-day fasting.



While calorie-restricted diets force you to scrutinize every bit of food you take in – calorie logs…are you serious? – ADF is mostly hands-off. This means you can enjoy a night out with friends, have a glass of wine, and feel like a human even when you’re in the process of losing weight. No more, “I wish…but I’m dieting” excuses. You just have to plan your social activities for fast days.

May reduce inflammatory bowel disease

Studies in both mice and humans have shown that alternate-day fasting and other intermittent fasting methods can reduce inflammatory bowel disease. Scientists have observed an increase in beneficial bacteria in the course of these fasts, which produce short-chain fatty acids that repair the gut lining. 

Long-term weight loss

 Weight loss is one of the most widely reported benefits of alternate-day fasting. While people tend to scoff at the YouTube videos highlighting 100+ pounds of weight loss, study after study shows that ADF is a reliable way to lose weight and keep it off. (This applies to both the obese and non-obese.)

Though long-term weight changes are similar to calorie-reduction study groups, the fat mass/lean mass ratio was more favorable in alternate-day fasting groups. This suggests that ADF spares lean muscle mass better than calorie restriction.         

Cardiovascular health

Several studies show that ADF is associated with cardiovascular disease prevention. It’s not known exactly why, but research indicates that several markers of inflammation are lowered on fasting days, notably the inflammatory amino acid homocysteine.


No moderate or serious risks have been reported in alternate-day fasting studies to date. That said, slight dizziness, headaches, and fatigue have been reported. Doctors say that hunger is normal during a fast, but they recommend stopping a fast if you start to feel unwell in any way.

Always consult your doctor before starting a fasting regimen, especially if have these conditions: 

  • Heart disease
  • Liver and kidney disease
  • Epilepsy
  • Pregnancy
  • Eating disorders

How to do it

Alternate between fast and feast days.

On day one, fast the whole day. On day two, eat all your snacks and meals into a 12-hour window, and don’t consume more than 500 calories. Studies show that it doesn’t matter whether you graze throughout the day or eat all 500 calories at once, so you can experiment with what works best for your appetite. 

Doctors and fasting experts recommend drinking plenty of water during your fasting days. And lucky for you, coffee and tea are allowed. (Just go light on the sweetener and cream!)

  • Day 1: fast. Eat no more than 500 calories worth of food in a 12-hour window
  • Day 2: feast. Eat whatever you want, and enjoy it
  • Coffee and tea are allowed


Key Experts:

Krista Varady, Ph.D.

Krista Varady, Ph.D.

Krista Varady, Ph.D., professor of nutrition at the University of Illinois, is regarded as the foremost authority on alternate-day fasting. She discovered alternate day fasting when she had an extra 15 pounds to lose after giving birth to her first child, and has since been the lead author on many ADF studies.

“I found daily restriction very difficult to stick to,” she said about traditional dieting, “since it required me to vigilantly monitor all of my calorie intake ALL day long.” Varady quit within a week and started ADF. “I had plenty of energy and my mood improved considerably. In addition, I lost about 1 pound (0.45kg) per week.”

Thomas Delauer

Thomas Delauer

Thomas Delauer is one of the biggest champions of intermittent fasting for health and body composition. And he’s one of the few science-backed voices that stands behind dry fasting. “The process of autophagy – the body recycling old, useless cells – happens so much faster during dry fasts because the metabolic need is that much more,” he said on his YouTube channel. “All the strong cells survive; all the weak cells get recycled. This helps your body to perform at its peak.”

About The Author

Fast Forward Editors

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