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Evidence BasedHow Intermittent Fasting Can Help You Lose Weight

Medically reviewed by Imashi Fernando, MS, RDN, CDCES — Written by Kris Gunnars, BSc — Updated on October 9, 2023

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The intermittent fasting weight loss strategy involves setting periods where you avoid eating. This often results in a calorie deficit and hormonal changes that can help people lose weight.

Intermittent fasting is an eating pattern that involves regular, short-term fasts — or periods of minimal or no food consumption.

Intermittent fasting is often a weight loss intervention. Fasting for short periods helps people eat fewer calories, which may result in weight loss over time (1).

Intermittent fasting may also help modify risk factors for health conditions like diabetes and cardiovascular disease, such as lowering cholesterol and blood sugar levels (2, 3, 4).

This article explores everything you need to know about intermittent fasting and weight loss.

A man on an intermittent fasting plan — A male timing his fast. Aya Brackett

Choosing your intermittent fasting plan

There are several different intermittent fasting methods. Popular options include:

the 16:8 method
the 5:2 diet
the Warrior diet
Eat Stop Eat
alternate-day fasting (ADF)

Health considerations

Whether you start with a modified fasting plan or a full fast, it’s best to maintain a nutritious diet, incorporating high protein foods and a variety of fiber-packed vegetables to help you feel full.

Additionally, eating too many high calorie snacks or processed food products can negate the positive effects associated with intermittent fasting.

It’s also best to talk with a doctor before beginning a fasting plan, especially if you have an underlying health condition. They can help determine if the plan is safe and effective for your health needs.

The 16/8 method

The 16/8 intermittent fasting plan restricts food consumption and calorie-containing beverages to a set window of 8 hours per day. It requires abstaining from food for the remaining 16 hours.

The 16/8 method is flexible and based on a time-restricted eating (TRE) model. You can choose any 8-hour window to consume calories.

Some people skip breakfast and eat from noon to 8 p.m., while others avoid eating late and stick to a 9 a.m. to 5 p.m. schedule.

Research indicates that time-restricted eating patterns such as the 16/8 method may prevent hypertension and reduce the amount of food consumed, leading to weight loss (5).

A 2023 review of research found that the 16/8 method and 16/8 combined with restricting calories were effective strategies for weight control in adults with overweight or obesity. An eating window starting before noon led to greater weight loss than one that began after noon. The researchers also noted it may have positive effects on glucose metabolism. (6).

A 2019 study found that the 16/8 method did not impair gains in muscle or strength in women performing resistance training (7).

The 5:2 method

The 5:2 diet is a straightforward intermittent fasting plan.

Five days per week, you eat as you typically do and don’t restrict calories. Then, on the other two days of the week, you reduce your calorie intake to one-quarter of your daily needs.

For someone who regularly consumes 2,000 calories daily, this means reducing calorie intake to 500 calories per day, two days per week.

According to a 2018 study, the 5:2 diet is as effective as daily calorie restriction for weight loss and blood glucose control among those with type 2 diabetes (8).

Another study found that the 5:2 diet was just as effective as continuous calorie restriction for weight loss and the prevention of metabolic diseases like heart disease and diabetes (9).

With the 5:2 diet, you pick which days you fast, and there are no rules regarding what or when to eat on full-calorie days. However, choosing a balanced diet of nutritious whole foods may help support weight loss and overall health.

Eat Stop Eat

Eat Stop Eat is an unconventional approach to intermittent fasting popularized by Brad Pilon, author of the book “Eat Stop Eat.”

This intermittent fasting plan involves identifying one or two non-consecutive days per week during which you abstain from eating for 24 hours.

During the remaining days of the week, you can eat freely, but it’s recommended to eat a well-rounded diet and avoid overconsumption.

The rationale behind a weekly 24-hour fast is that consuming fewer calories will lead to weight loss.

Fasting for up to 24 hours can lead to a metabolic shift that causes your body to use fat as an energy source instead of glucose (10).

More research is needed regarding the Eat Stop Eat diet to determine its potential health benefits and weight loss properties.

Alternate-day fasting

Alternate-day fasting is an intermittent fasting plan with an easy-to-remember structure. On this diet, you fast every other day but can follow your typical eating plan on the non-fasting days.

Some versions of this diet embrace a “modified” fasting strategy that involves eating around 500 calories on fasting days. However, other versions eliminate calories on fasting days.

Alternate-day fasting has proven weight loss benefits.

An older randomized pilot study from 2016 comparing alternate-day fasting to a daily caloric restriction in adults with obesity found both methods to be equally effective for weight loss (11).

Another study found that participants consumed 37% fewer calories and lost an average of 7.7 pounds (3.5 kg) after alternating between 24 hours of fasting and 24 hours of unlimited eating over 4 weeks (12).

If you want to maximize weight loss, alternate-day fasting and exercise can help and support cardiovascular health (13).

If you’re new to intermittent fasting, ease into alternate-day fasting with a modified fasting plan.

The Warrior diet

The Warrior Diet is an intermittent fasting plan based on the eating patterns of ancient warriors.

Created in 2001 by Ori Hofmekler, the Warrior Diet is a bit more extreme than the 16:8 method but less restrictive than the Eat Stop Eat method.

It consists of eating very little for 20 hours during the day and then eating as much food as desired throughout a 4-hour window at night.

The Warrior Diet encourages dieters to consume small amounts of dairy products, hard-boiled eggs, raw fruits and vegetables, and non-calorie fluids during the 20-hour fast period.

After this 20-hour fast, people can essentially eat anything they want for a 4-hour window, but unprocessed, healthy, and organic foods are recommended.

Time-restricted feeding cycles may have a variety of health benefits. Studies show that time-restricted feeding cycles can prevent diabetes, slow tumor progression, delay aging, and increase lifespan in rodents (14).

A 2020 study determined that fasting with a 4-four feeding window did not have benefits over fasting with a 6-hour feeding window (15).

More research is needed on the Warrior Diet to understand its benefits for weight loss.

The Warrior Diet may lead to disordered eating patterns. It’s best to talk with a doctor to see whether this eating plan is right for you.

Summary
There are many varieties of intermittent fasting, each with its own benefits and challenges. Talk with a doctor to see which option may be right for you.

»MORE:Learn how to lose weight the healthy way, the Wellos™ way

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How intermittent fasting affects your hormones

Intermittent fasting may help you lose weight but can also affect your hormones.

That’s because body fat is the body’s way of storing energy (calories). When you don’t eat anything, your body makes changes to make stored energy more accessible.

Examples include changes in nervous system activity, as well as significant changes in the levels of several crucial hormones, including (16, 17):

Insulin: Insulin levels increase when you eat, and when you fast, they decrease dramatically. Lower levels of insulin facilitate fat burning.

Norepinephrine (noradrenaline): Your nervous system sends norepinephrine to your fat cells, making them break down body fat into free fatty acids that can be burned for energy.

Short-term fasting may increase fat burning. Research shows that alternate-day fasting and whole-day fasting can reduce body weight and body fat (18, 19).

Still, more research is needed to investigate the long-term effects.

Another hormone that’s altered during a fast is human growth hormone (HGH). Previously, researchers believed HGH helped burn fat faster, but new research shows it may signal the brain to conserve energy, potentially making it harder to lose weight (20).

By activating a small population of agouti-related protein (AgRP) neurons, HGH may indirectly increase appetite and diminish energy metabolism (20).

Summary
Short-term fasting leads to bodily changes that promote fat burning. Nevertheless, increasing HGH levels may indirectly decrease energy metabolism and combat continued weight loss.

Intermittent fasting helps you reduce calories and lose weight

The main reason that intermittent fasting works for weight loss is that it helps you eat fewer calories.

All of the different protocols involve skipping meals during the fasting periods.

Unless you compensate by eating much more during the eating periods, you’ll consume fewer calories.

A 2020 review of research determined that in their review of 27 trials, weight loss ranged from 0.8% to 13.0% of participants’ body weight at the start of the trials, which lasted between 2 and 12 weeks (20).

Summary
Intermittent fasting is a convenient way to lose weight without counting calories. Many studies show that it can help you lose weight and belly fat.

»MORE:Learn how to lose weight the healthy way, the Wellos™ way

Wellos is owned by RVO Health. By clicking on this link, we may receive a commission. Learn more.

How to succeed with an intermittent fasting protocol

There are several things you need to keep in mind if you want to lose weight with intermittent fasting:

Food quality: Try to eat mostly whole foods over packaged and processed ones.
Calories: Try to eat normally during the non-fasting periods, not so much that you compensate for the calories you missed when fasting.
Consistency: Just as with any other weight loss method, you need to stick with it for an extended period if you want it to work.
Patience: It can take your body some time to adapt to an intermittent fasting protocol. Being consistent with your meal schedule may help.

Most intermittent fasting protocols also recommend exercise, such as strength training. This can help you burn body fat while maintaining muscle mass.

In the beginning, calorie counting is generally not required with intermittent fasting. However, if your weight loss stalls, calorie counting can be useful for some people.

Summary
With intermittent fasting, you still need to eat healthy and maintain a calorie deficit to lose weight.

»MORE:Learn how to lose weight the healthy way, the Wellos™ way

Wellos is owned by RVO Health. By clicking on this link, we may receive a commission. Learn more.

The bottom line

Intermittent fasting can be a useful weight loss tool. Plans can include:

the 16:8 method
the 5:2 diet
the Warrior diet
Eat Stop Eat
alternate-day fasting (ADF)

Fasting can result in weight loss primarily due to a reduction in calorie intake, but some beneficial effects on hormones may also come into play.

It’s best to talk with a doctor before making drastic changes to your eating habits, especially if you have an underlying health condition.

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Medically reviewed by Imashi Fernando, MS, RDN, CDCES — Written by Kris Gunnars, BSc — Updated on October 9, 2023

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Weight Management

Nutrition

Choosing your intermittent fasting plan

Health considerations

The 16/8 method

The 5:2 method

Eat Stop Eat

Alternate-day fasting

The Warrior diet

How intermittent fasting affects your hormones

Intermittent fasting helps you reduce calories and lose weight

How to succeed with an intermittent fasting protocol

The bottom line

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