Alternate-Day Fasting: a Comprehensive Beginner's Guide

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.

Alternate-day fasting may help promote weight loss and may help lower risk factors related to heart disease and type 2 diabetes.

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:

• water
• unsweetened coffee
tea

Alternate-day fasting cycles between days of fasting and normal eating. The most popular version allows for about 500 calories on fasting days.

Alternate-day fasting and weight loss

Although ADF may be helpful for promoting 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 that this method is not superior to traditional daily calorie restriction for promoting weight loss (3, 6, 8, 9, 10).

Studies have shown that ADF and daily calorie restriction are equally effective at reducing harmful belly fat and inflammatory markers in those with obesity (11).

Although ADF may offer benefits for fat loss, recent research shows that ADF is no more effective than traditional calorie restriction for promoting weight loss or preserving muscle mass (6, 12).

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 than ADF alone and six times as much weight loss as endurance exercise alone (13).

Regarding diet composition, ADF seems to be equally effective whether it’s done with a high or low fat diet (14).

Alternate-day fasting may help you lose weight. However, research has shown that it’s likely no more effective for promoting weight loss than traditional daily calorie restriction.

Alternate-day fasting and hunger

The effects of ADF on hunger are rather inconsistent.

Some studies show that hunger ultimately goes down on fasting days, while others state that hunger remains unchanged (5, 9, 15).

However, research agrees that modified ADF with 500 calories on fasting days is much more tolerable than full fasts on fasting days (15).

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 (16).

Human studies have not shown significant effects of ADF on hunger hormones.

However, animal studies have shown that modified ADF resulted in decreased amounts of hunger hormones and increased amounts of satiety hormones compared to other diets (17, 18, 19).

Another factor to consider is compensatory hunger, which is a frequent downside of traditional, daily calorie restriction (20, 21, 22).

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 (5, 23, 24).

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 (5).

However, the effects of ADF on hunger most likely vary by individual.

The effects of alternate-day fasting on hunger are inconsistent. Studies on modified alternate-day fasting show that hunger decreases as you adapt to the diet.

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 that 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 recent, high-quality study suggest that ADF is no more effective for preserving muscle mass than traditional calorie restriction (6, 8, 16, 25, 26).

Studies suggest that although ADF may help preserve lean muscle mass during weight loss, it’s no more effective than other methods of calorie restriction.

Type 2 diabetes

Type 2 diabetes accounts for 90–95% of diabetes cases in the United States (27).

What’s more, more than one-third of Americans have prediabetes, a condition in which blood sugar levels are higher than normal but not high enough to be considered diabetes (28).

Losing weight and restricting calories is usually an effective way to improve or reverse many symptoms of type 2 diabetes (29).

Similarly to continuous calorie restriction, ADF seems to cause mild reductions in risk factors for type 2 diabetes among people with overweight or obesity (30, 31, 32).

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 (6, 33, 34, 35).

Having high insulin levels, or hyperinsulinemia, has been linked to obesity and chronic diseases, such as heart disease and cancer (36, 37).

A reduction in insulin levels and insulin resistance should lead to a significantly reduced risk of type 2 diabetes, especially when combined with weight loss.

Alternate-day fasting may reduce risk factors for type 2 diabetes. It can reduce fasting insulin levels in people with prediabetes.

Heart health

Heart disease is the leading cause of death in the world and responsible for about one in four deaths (38, 39,40).

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 (1, 4, 8, 41).

Studies on the subject range from 8–52 weeks and involve those with overweight and obesity.

The most common health benefits include (1, 8, 13, 14, 42, 43):

• reduced waist circumference (2–2.8 inches or 5–7 cm)
• decreased blood pressure
• lowered LDL (bad) cholesterol (20–25%)
• increased number of large LDL particles and reduced number of dangerous small, dense LDL particles
• decreased blood triglycerides (up to 30%)

Alternate-day fasting may reduce waist circumference and decrease blood pressure, LDL (bad) cholesterol, and triglycerides.

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 (44, 45).

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 (46, 47, 48, 49).

Furthermore, fasting has been shown to increase lifespan in rodents, flies, yeasts, and worms (50).

Moreover, cell studies have shown that fasting stimulates autophagy, resulting in effects that may help keep you healthy and live longer (51, 52, 53).

This has been supported by human studies showing that ADF diets reduce oxidative damage and promote changes that may be linked to longevity (9, 15, 52, 54).

The findings look promising, but the effects of ADF on autophagy and longevity need to be studied more extensively.

Alternate-day fasting stimulates autophagy in animal and cell studies. This process may slow aging and help prevent diseases like cancer and heart disease.

Does alternate-day fasting induce starvation mode?

Nearly all weight loss methods cause a slight drop in resting metabolic rate (55, 56).

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. It can make you stop losing weight and feel miserable (56).

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 by 6% when calculated relative to lean mass, while ADF only caused an insignificant 1% reduction (16).

What’s more, after 24 unsupervised weeks, the calorie restriction group still had a 4.5% lower resting metabolic rate than at the beginning of the study. Meanwhile, the ADF participants experienced only a 1.8% reduction.

Alternate-day fasting may not decrease metabolic rate in the same way as continuous calorie restriction.

Is it also good 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 (15).

However, hunger levels remained quite 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 (8).

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.

Alternate-day fasting increases fat burning and reduces risk factors for heart disease in people with average weight.

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

Most 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, as well as 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 (57, 58).

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.

There are no strict guidelines regarding what to eat and drink on fasting days. It’s best to stick to high protein foods and vegetables, as well as low calorie or calorie-free beverages.

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 (16).

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 (59).

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 (60).

Although some research suggests that ADF may be helpful for reducing 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 provider before trying this eating pattern if you have a medical condition or are currently taking any medications.

Alternate-day fasting is safe for most people. Consult a healthcare provider to learn if alternate-day fasting is right for you.

The bottom line

Alternate-day fasting is a very effective way to lose weight for most people. It is not recommended for children, people with eating disorders, or those who are pregnant, lactating, or living with rare disorders like Gilbert Syndrome.

It may have benefits over traditional calorie-restricted diets in some cases. It’s also linked to major improvements in many health markers.

The best part of all is that it’s surprisingly easy to stick to, as you only need to “diet” every other day.