What to Know About Alternate Day Fasting

Health Line

22-05-2025

Alternate-day fasting may help promote weight loss and may help lower risk factors related to heart disease and type 2 diabetes.
Alternate-day fasting is one way to do intermittent fasting. On this diet, you fast every other day but eat whatever you want on the non-fasting days.
The most common version of this diet involves 'modified' fasting, where you can eat around 500 calories on fasting days. Here's a detailed beginner's guide to alternate-day fasting.
How to do alternate-day fasting
Alternate-day fasting (ADF) is an intermittent fasting approach. The basic idea is that you fast on one day and then eat what you want the next day. This way, you only need to restrict what you eat half of the time.
On fasting days, you're allowed to drink as many calorie-free beverages as you like. Examples include:
If you're following a modified ADF approach, you're also allowed to eat about 500 calories on fasting days, or 20–25% of your energy requirements.
The most popular version of this diet is called 'The Every Other Day Diet' by Dr. Krista Varady, who has conducted most of the studies on ADF.
The health and weight loss benefits seem to be the same regardless of whether the fasting-day calories are consumed at lunch or dinner or as small meals throughout the day.
Some people may find that alternate-day fasting is easier to stick to than other types of diets.
However, a yearlong study found that adherence to alternate-day fasting (where calorie intake was reduced to 25% of energy needs on fasting days) was not superior to everyday calorie restriction.
Most studies on alternate-day fasting used the modified version, with 500 calories on fasting days. This is considered much more sustainable than doing complete fasts on fasting days, but it's just as effective.
In this article, the terms 'alternate-day fasting' or 'ADF' generally apply to the modified approach with about 500 calories on fasting days.
Alternate-day fasting and weight loss
Although ADF may help promote weight loss, studies have suggested that this type of calorie restriction is no more effective for weight loss than traditional daily calorie restriction.
Studies among adults with overweight and obesity show that engaging in ADF may help you lose 3–8% of your body weight in 2–12 weeks. Research suggests this method is not superior to traditional daily calorie restriction for promoting weight loss.
Although ADF may offer benefits for fat loss, research shows that ADF is no more effective than traditional calorie restriction for promoting weight loss or preserving muscle mass.
Furthermore, like other types of calorie restriction, weight loss during ADF may be accelerated when combined with increased physical activity.
For example, combining ADF with endurance exercise may cause twice as much weight loss as ADF alone and six times as much as endurance exercise alone.
Regarding diet composition, ADF seems to be equally effective whether it's done with a high or low fat diet.
Alternate-day fasting and hunger
The effects of ADF on hunger are somewhat inconsistent.
Some studies show that hunger ultimately goes down on fasting days, while others state that hunger remains unchanged.
However, research agrees that modified ADF with 500 calories on fasting days is much more tolerable than complete fasts on fasting days.
One study comparing ADF to calorie restriction showed that ADF increased levels of brain-derived neurotrophic factor (BDNF) after 24 weeks of follow-up.
BDNF is a protein that plays a role in energy balance and body weight maintenance.
Researchers concluded that ADF may induce long-term changes in BDNF and that this may promote improved weight loss maintenance.
However, the researchers found that BDNF levels did not correlate with body weight changes in this particular study and suggested that these findings be interpreted with caution.
Human studies have not shown significant effects of ADF on hunger hormones.
Another factor to consider is compensatory hunger, which is a frequent downside of traditional daily calorie restriction.
Compensatory hunger refers to increased levels of hunger in response to calorie restriction, which cause people to eat more than they need to when they finally allow themselves to eat.
Studies have shown that ADF doesn't seem to increase compensatory hunger.
In fact, many people who try modified ADF claim that their hunger diminishes after the first 2 weeks or so. After a while, some find that the fasting days are nearly effortless.
However, the effects of ADF on hunger most likely vary by individual.
Alternate-day fasting and body composition
ADF has been shown to have unique effects on body composition, both while you're dieting and during your weight-maintenance period.
Studies comparing traditional calorie-restricted diets and ADF show they're equally effective at decreasing weight and fat mass.
Some studies have suggested that ADF may be more beneficial for preserving muscle mass than other types of calorie restriction,
However, results from a 2016 study suggest that ADF is no more effective for preserving muscle mass than traditional calorie restriction.
Health benefits of alternate-day fasting
ADF has several health benefits aside from weight loss.
Type 2 diabetes
Type 2 diabetes accounts for 90–95% of diabetes cases in the United States.
What's more, more than one-third of Americans have prediabetes, a condition in which blood sugar levels are higher than usual but not high enough to be considered diabetes.
Losing weight and restricting calories is usually an effective way to improve or reverse many symptoms of type 2 diabetes.
Similarly to continuous calorie restriction, ADF seems to cause mild reductions in risk factors for type 2 diabetes among people with overweight or obesity.
ADF may also help reduce fasting insulin levels, with some studies suggesting that it may be more effective than daily calorie restriction.
However, not all studies agree that ADF is superior to daily calorie restriction.
Having high insulin levels, or hyperinsulinemia, has been linked to obesity and chronic diseases, such as heart disease and cancer.
Reducing insulin levels and insulin resistance should significantly reduce the risk of type 2 diabetes, especially when combined with weight loss.
Heart health
Many studies have shown that ADF is a good option to help individuals with overweight or obesity lose weight and reduce heart disease risk factors.
The most common health benefits include:
Alternate-day fasting and autophagy
One of the most common effects of fasting is the stimulation of autophagy.
Autophagy is a process in which old parts of cells are degraded and recycled. It plays a key role in preventing diseases, including cancer, neurodegeneration, heart disease, and infections.
Animal studies have consistently shown that long- and short-term fasting increase autophagy and are linked to delayed aging and a reduced risk of tumors.
Moreover, cell studies have confirmed that fasting stimulates autophagy, resulting in effects that may help keep you healthy and live longer.
This has been supported by human studies showing that ADF diets reduce oxidative damage and promote changes that may be linked to longevity.
The findings look promising, but the effects of ADF on autophagy and longevity need to be studied more extensively.
Does alternate-day fasting induce starvation mode?
Nearly all weight loss methods cause a slight drop in resting metabolic rate.
This effect is often referred to as starvation mode, but the technical term is adaptive thermogenesis.
When you severely restrict your calories, your body starts conserving energy by reducing the number of calories it burns. This can cause you to stop losing weight and feel miserable.
However, ADF doesn't seem to cause this drop in metabolic rate.
One 8-week study compared the effects of standard calorie restriction and ADF.
The results showed that continuous calorie restriction significantly decreased resting metabolic rate compared to ADF.
Is it also suitable for people who are within a normal weight range?
ADF is not only beneficial for weight loss, but it can also offer health benefits for those who don't have obesity.
A 3-week study analyzed individuals with average weight following a strict ADF diet with zero calories on fasting days.
The researchers found that it resulted in increased fat burning, decreased fasting insulin, and a 4% decrease in fat mass.
However, hunger levels remained relatively high throughout the study.
They speculated whether a modified ADF diet with one small meal on fasting days might be more tolerable for people who don't have obesity.
Another controlled study involved individuals with overweight and average weight.
It showed that following an ADF diet for 12 weeks reduced fat mass and produced favorable changes in risk factors for heart disease.
That said, ADF generally provides much fewer calories than you need to maintain weight, which is the reason you ultimately lose weight.
If you're not looking to lose weight or fat mass, or have average weight to begin with, other dietary methods will probably suit you better.
What to eat and drink on fasting days
There's no general rule regarding what you should eat or drink on fasting days, except that your total calorie intake shouldn't exceed around 500 calories.
It's best to drink low calorie or calorie-free drinks on fasting days, such as:
water
coffee
tea
Some people find it best to eat one 'big' meal late in the day, while others prefer to eat early or split the amount between 2–3 meals.
Since your calorie intake will be severely limited, it's best to focus on nutritious, high protein foods and low calorie vegetables. These will make you feel full without many calories.
Soups may also be a good option on fasting days, as they tend to make you feel fuller than if you ate the ingredients on their own.
Here are a few examples of meals that are suitable for fasting days:
eggs and vegetables
yogurt with berries
grilled fish or lean meat with vegetables
soup and a piece of fruit
a generous salad with lean meat
You can find numerous recipes for quick 500-calorie meals and healthy low calorie snacks online.
Is alternate-day fasting safe?
Studies have shown that alternate-day fasting is safe for most people.
It doesn't result in a greater risk for weight regain than traditional, calorie-restricted diets.
Some think that ADF increases your risk of binge eating, but studies have found that it may help reduce binge eating behavior and decrease depressive symptoms.
It may also improve restrictive eating and body image perception among people with obesity. However, more research on the effectiveness and safety of ADF in people with disordered eating tendencies is needed.
That said, ADF is likely not appropriate for certain populations.
These include children, pregnant and lactating women, people who are underweight, and those with certain medical conditions that may be exacerbated by fasting, like Gilbert Syndrome.
Although some research suggests that ADF may help reduce symptoms of binge eating, this dietary pattern is likely not appropriate for people with eating disorders, including anorexia nervosa or bulimia.
Be sure to consult a healthcare professional before trying this eating pattern if you have a medical condition or are currently taking any medications.