What Is Intermittent Fasting? Explained in Human Terms

By Kris Gunnars, BSc — Updated on March 13, 2023

Intermittent fasting involves alternating cycles of fasting and eating. Depending on the type of intermittent fasting, cycle length and calorie limits can vary.

A phenomenon called intermittent fasting is currently one of the world’s most popular health and fitness trends.

Many studies show that this can cause weight loss, improve metabolic health, protect against disease and perhaps help you live longer (1,2) article explains what intermittent fasting is, and why you should care.

What Is Intermittent Fasting?

Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting.  It does not say anything about which foods to eat, but rather when you should eat them.

There are several different intermittent fasting methods, all of which split the day or week into eating periods and fasting periods.

Most people already “fast” every day, while they sleep. Intermittent fasting can be as simple as extending that fast a little longer.You can do this by skipping breakfast, eating your first meal at noon and your last meal at 8 pm. Then you’re technically fasting for 16 hours every day, and restricting your eating to an 8-hour eating window. This is the most popular form of intermittent fasting, known as the 16/8 method.

Most people already “fast” every day, while they sleep. Intermittent fasting can be as simple as extending that fast a little longer.  Google images.

Despite what you may think, intermittent fasting is actually fairly easy to do. Many people report feeling better and having more energy during a fast.

Hunger is usually not that big of an issue, although it can be a problem in the beginning, while your body is getting used to not eating for extended periods of time.

No food is allowed during the fasting period, but you can drink water, coffee, tea and other non-caloric beverages.

A man on an intermittent fasting planAya Brackett images


Some forms of intermittent fasting allow small amounts of low-calorie foods during the fasting period. Taking supplements is generally allowed while fasting, as long as there are no calories in them.

Why Fast?

Humans have actually been fasting for thousands of years. Sometimes it was done out of necessity, when there simply wasn’t any food available.

In other instances, it was done for religious reasons. Various religions, including Islam, Christianity and Buddhism, mandate some form of fasting.

Humans are well adapted to fasting from time to time, and our bodies are very well equipped to handle extended periods of not eating.

All sorts of processes in the body change when we don’t eat for a while, in order to allow our bodies to thrive during a period of famine. It has to do with hormones, genes and important cellular repair processes (3).

When fasted, we get significant reductions in blood sugar and insulin levels, as well as a drastic increase in human growth hormone (4, 5

Many people do intermittent fasting in order to lose weight, as it is a very simple and effective way to restrict calories and burn fat (6, 7, 8).

Others do it for the metabolic health benefits, as it can improve various different risk factors and health markers (1).

There is also some evidence that intermittent fasting can help you live longer. Studies in rodents show that it can extend lifespan as effectively as calorie restriction (9, 10)

Some research also suggests that it can help protect against diseases, including heart disease, type 2 diabetes, cancer, Alzheimer’s disease and others (11, 12)

Other people simply like the convenience of intermittent fasting.

It is an effective “life hack” that makes your life simpler, while improving your health at the same time. The fewer meals you need to plan for, the simpler your life will be.

Not having to eat 3-4+ times per day (with the preparation and cleaning involved) also saves a lot of  time.

10 Evidence-Based Health Benefits of Intermittent Fasting

Medically reviewed by Katherine Marengo LDN, R.D., Nutrition — By Kris Gunnars, BSc — Updated on May 13, 202

Intermittent fasting may benefit heart health, reduce inflammation, and improve cell repair processes. It may also help burn fat.Anna Bogush/Getty Images

Intermittent fasting is an eating pattern where you cycle between periods of eating and fasting.  There are many different types of intermittent fasting, such as the 16/8 and 5:2 methods.  Numerous studies show that it can have powerful benefits for your body and brain.

Here are 10 evidence-based health benefits of intermittent fasting.

Health Benefits Of Intermittent Fasting infographic with sample data. Vector Illustration.

1. Changes the function of hormones, cells, and genes

When you don’t eat for a while, several things happen in your body.For example, your body changes hormone levels to make stored body fat more accessible and initiates important cellular repair processes.

Here are some of the changes that occur in your body during fasting:

  • Insulin levels. Blood levels of insulin drop significantly, which facilitates fat burning (1 Trusted Source).
  • Human growth hormone (HGH) levels. The blood levels of human growth hormone (HGH) may increase dramatically. Higher levels of this hormone facilitate fat burning and muscle gain, and have numerous other benefits (2 3, 4, 5 Trusted Sources).
  • Cellular repair. The body induces important cellular repair processes, such as removing waste material from cells (6).
  • Gene expression. There are beneficial changes in several genes and molecules related to longevity and protection against disease (7 Trusted Source). Everything You Need to Know About Insulin

2. Can help you lose weight and visceral fat

Visceral fat: Intermittent fasting doesn’t shift belly fat, study warns.

Many of those who try intermittent fasting are doing it to lose weight (8). Generally speaking, intermittent fasting will make you eat fewer meals. Unless you compensate by eating much more during the other meals, you’ll end up taking in fewer calories.

How Many Calories Should You Eat Per Day to Lose Weight?

Additionally, intermittent fasting enhances hormone function to facilitate weight loss.  Lower insulin levels, higher HGH levels, and increased amounts of norepinephrine (noradrenaline) all increase the breakdown of body fat and facilitate its use for energy.  For this reason, short-term fasting actually increases your metabolic rate, helping you burn even more calories (7, 9 Trusted Sources)

In other words, intermittent fasting works on both sides of the calorie equation. It boosts your metabolic rate (increases calories out) and reduces the amount of food you eat (reduces calories in).According to a 2014 review of the scientific literature, intermittent fasting can cause weight loss of 3–8% over 3–24 weeks. This is a huge amount (10). The study participants also lost 4–7% of their waist circumference over 6–24 weeks, which indicates that they lost lots of visceral fat. Visceral fat is the harmful fat in the abdominal cavity that causes disease (10).

What is Visceral Fat and how to get rid of it.

3. Can reduce insulin resistance, lowering your risk for type 2 diabetes .Insulin resistance and diabetes.

Type 2 diabetes has become a very common diagnosis in recent decades.  Its main feature is high blood sugar levels in the context of insulin resistance.  Anything that reduces insulin resistance should help lower blood sugar levels and protect against type 2 diabetes.

Interestingly, intermittent fasting has been shown to have major benefits for insulin resistance and to lead to an impressive reduction in blood sugar levels (10).

In human studies on intermittent fasting, fasting blood sugar has been reduced by 3–6% over the course of 8–12 weeks in people with prediabetes. Fasting insulin has been reduced by 20–31% (10).

One study in mice with diabetes also showed that intermittent fasting improved survival rates and protected against diabetic retinopathy. This implies  that intermittent fasting may be highly protective for people who are at risk for developing type 2 diabetes.

However, there may be some differences between the sexes. One 2005 study in women showed that blood sugar management actually worsened after a 22-day long intermittent 

4. Can reduce oxidative stress and inflammation in the body

Oxidative stress is one of the steps toward aging and many chronic diseases (15).  It involves unstable molecules called free radicals. Free radicals react with other important molecules, such as protein and DNA, and damage them (16).  Several studies show that intermittent fasting may enhance the body’s resistance to oxidative stress (17, 18) Additionally, studies show that intermittent fasting can help fight inflammation in the  body.

Understanding inflammation. What we need to know.

The positive effects of intermittent fasting about healthy life. Fasting regulates cellular and general metabolism by modifying the function of cells, genes and hormones in human body.

5. May be beneficial for heart health

Many studies have shown that intermittent fasting, also known as IF can aid weight loss, improve your metabolic rate, and help you live a longer.

Heart disease is currently the world’s biggest killer (20 Trusted Source). It’s known that various health markers (so-called “risk factors”) are associated with either an increased or decreased risk of heart disease.

Intermittent fasting has been shown to improve numerous different risk factors, including blood sugar levels, blood pressure, blood triglycerides, total and LDL (bad) cholesterol, inflammatory markers.

However, much of this is based on animal studies (10, 21 Trusted Source).  The effects of fasting on heart health need to be studied more in-depth in humans before recommendations can be made.

6. Induces various cellular repair processes

When we fast, the cells in the body initiate a cellular “waste removal” process called autophagy (6).  This involves the cells breaking down and metabolizing broken and dysfunctional proteins that build up inside cells over time.Increased autophagy may provide protection against several diseases, including cancer and neurodegenerative diseases such as Alzheimer’s disease (24, 25).

7. May help prevent cancer

Cancer is characterized by uncontrolled growth of cells.  Fasting has been shown to have several beneficial effects on metabolism that may lead to reduced risk of cancer.  Promising evidence from animal studies indicates that intermittent fasting or diets that mimic fasting may help prevent cancer. Research in humans has led to similar findings, although more studies are needed (26  There’s also some evidence showing that fasting reduced various side effects of chemotherapy in humans (29 Trusted Source).

8. Has benefits for your brain

What’s good for the body is often good for the brain as well. Intermittent fasting improves various metabolic features known to be important for brain health.  Intermittent fasting helps reduce:

Several studies in mice and rats have shown that intermittent fasting may increase the growth of new nerve cells, which should have benefits for brain function (31, 32 Trusted Source).

Fasting also increases levels of a brain hormone called brain-derived neurotrophic factor (BDNF). A BDNF deficiency has been implicated in depression and various other brain problems (33Trusted Source).

9. May help prevent Alzheimer’s disease

Alzheimer’s disease is the world’s most common neurodegenerative disease.  There’s no cure currently available for Alzheimer’s, so preventing it from showing up in the first place is critical.

Studies in rats and mice show that intermittent fasting may delay the onset of Alzheimer’s or reduce its severity (29 Trusted Source).  In a series of case reports, a lifestyle intervention that included daily short-term fasts was able to significantly improve Alzheimer’s symptoms in 9 out of 10 people (38).Animal studies also suggest that fasting may protect against other neurodegenerative diseases, including Parkinson’s disease and Huntington’s disease (29However, more research in humans is needed.



10. May extend your lifespan, helping you live longer

One of the most exciting applications of intermittent fasting may be its ability to extend lifespan.  Studies in rodents have shown that intermittent fasting extends lifespan in a similar way as continuous calorie restriction (41, 42).

Intermittent fasting has also been shown to increase the lifespans of fruit flies (43).  In some of these studies, the effects were quite dramatic. In an older study, rats that were fasted every other day lived 83% longer than rats who weren’t fasted (44).In a 2017 study, mice that were fasted every other day saw their lifespans increase by around 13% (45).  Daily fasting was also shown to improve the overall health of male mice. It helped delay the onset of conditions such as fatty liver disease and hepatocellular carcinoma, which are both common in aging mice (46)

canva photo

Although this is far from being determined in humans, intermittent fasting has become very popular among the anti-aging crowd. Given the known benefits for metabolism and all sorts of health markers, it makes sense that intermittent fasting could help you live a longer and healthier life.

6 Popular Intermittent Fasting Schedules For Weight Loss, Explained By Experts


Plus, which one is most likely to work for beginners.  BY KRISTIN CANNING AND SABRINA TALBERTPUBLISHED: OCT 4, 2022

Intermittent fasting (IF) has become a popular weight-loss tool for a reason: It has amassed a huge following over the years, including celebrities like Vanessa Hudgens and Halle Berry, who swear by this eating plan. There are many different ways to do it, though, and each intermittent fasting schedule works for different people.

ICYMI, intermittent fasting is a type of eating plan that alternates periods of eating and fasting in which you can only consume water, coffee, and tea. During your eating windows, you can generally have what you want, which is why the plan works for a lot of people.

There are plenty of benefits to back the hype of IF, but it is not for everyone, and the last thing you’d want to do is try sticking to a plan that feels impossible because it clashes with the structure of your day.

Intermittent fasting can be difficult to follow if you’re the type who munches on smaller portions or snacks throughout the day. And it’s definitely not a good idea for anyone with a history of disordered eating or diabetes and those who are pregnant or breastfeeding—even if weight loss is recommended, says Dana White, RD. And if your schedule is sporadic or you work out at various times of the day, you might also want to reconsider taking on IF.

But if you tend to overeat at night or are looking for a bit more discipline, intermittent fasting may help prevent mindless eating through the day. It might also be a good option if you’ve tried creating a calorie deficit in the past but it didn’t work.

Google Images.  Which schedule would work best for you?

The 16:8 (more on that below) is the most popular method, according to White. But there are plenty of other options to choose from. Here are six of the most popular IF approaches that people tend to follow for weight loss—and exactly what the current research says about the potential benefits or concerns for each one. Really though, the most successful diet is one you can stick to, so the IF schedule that seems the easiest to follow is probably your best bet.

1. The   16:8   diet

The 16:8 method of intermittent fasting involves fasting every day for 16 hours and restricting your daily eating window to eight hours. For most people, this schedule means not eating anything after dinner and skipping breakfast. You might eat between, say, noon and 8 p.m.

If you like to get your workouts done in the A.M., White suggests opting for a schedule that’s more accommodating than this one (see the 14:10 diet). But if you prefer to get in your workouts during the late afternoon or

after 5 p.m., you’ll still have time to eat after your workout to refuel with a meal.As far as how the 16:8 method fares for weight loss? It could work, the (very limited) research shows. In a small study published in the journal Nutrition and Healthy Aging, 23 obese men and women followed the 16:8 diet for 12 weeks. Compared to a group that had eaten normally and not within a set timeframe, those on the 16:8 diet took in 350 fewer calories per day, lost a modest amount of weight (about three percent of their body weight on average), and lowered their blood pressure. Still, it’s important to note that this was a small study, and there isn’t a ton of research on the 16:8 diet specifically, so it’s tough to say that following the 16:8 diet is a surefire way to shed excess weight.

Interestingly, following this kind of eating plan may help with appetite control. A 2019 study in the journal Obesityshowed that people who ate only during a six-hour window versus those following a normal eating schedule felt less hungry, even though both groups ate the same amount of calories.

2. The  5:2  method

To follow the 5:2 diet, you eat normally five days a week and cut back to 20 percent of your normal daily calorie intake for the other two. Women are supposed to have about 500 calories on fasting days, while men have about 600. If you chose to move forward with this plan, make sure you’re fueling up the day before you fast to avoid overeating when it’s time to eat again.

You burn calories every minute you’re alive, including when you’re sleeping. When you snooze, your body utilizes the glycogen stored in your liver to keep your blood sugar levels stable. So your body is already familiar with the mechanisms of fasting, explains White.

“Your body is designed to compensate when energy is not coming in from food,” she adds. “The concept of something like fasting is to prolong that period where you’re relying on your internal backup system in order to fuel you.”This IF method results in just as much weight and fat loss as those who followed traditional dieting methods, according to a 2021 study published by PLOS ONE.

3. Alternate-day  fasting

As the name implies, this diet involves fasting every other day. There are several different versions of this plan, with some of them allowing about 500 calories on the fasting days, and some encouraging that you eat even fewer or close to zero calories on fasting days.


4. Eat-stop-eat  diet

This method of intermittent fasting involves a full fast for 24 hours once or twice a week. For example, you may eat dinner at 6 p.m. and then fast until 6 p.m. the next day, and you would do this one or two times per week—but not in a row.

Keep in mind that not eating for an entire day can be dangerous under certain circumstances and should not be taken lightly. While the weight-loss potential might be appealing, skipping full days of eating is not sustainable long-term.

“If you are knocking out two full days of eating, I would worry that the longer you do that, the greater at risk you would be for certain micronutrients deficiencies,” says White.

5. The  14:10  diet

This one is similar to the 16:8 method, but involves fasting for a 14-hour window and eating for 10. It’s a little easier to stick to than 16:8 because you have a longer eating window. But that doesn’t mean weight loss is impossible.

A 2021 study in Nutrition & Diabetes found that those who followed the 14:10 diet while incorporating nutritious foods and consistent exercise lost more weight than those who did the 12:12 diet. They also showed a more significant improvement in blood glucose levels after eight weeks.

Given that the fasting period is short and pretty much follows the way people already eat, it may be hard for some people to achieve a calorie deficit with this diet. Still, it could be a good way to ease into IF if you’re new to it and just want to see how you do when you have a specific timeframe for eating and can’t just snack whenever the mood strikes. It’s also a great option if you like to get your workouts in between 8 a.m. and 10 a.m.

6. The  Warrior Diet

This diet is way different from the rest, with the majority of eating happening at night. The Warrior Diet was coined by fitness author Ori Hofmekler. It involves eating only small portions of raw fruits and vegetables during the day, then feasting on one huge meal at night within a 4-hour eating window.

There’s no specific research on the Warrior Diet, but since the fasting periods still allow for some food, it may be more practical for some people. Still, the period when you can have heavier foods is very short, and the diet also involves focusing on paleo foods, so it’s stricter than other forms of IF.

However, like the eat-stop-eat diet, this option is not sustainable long-term. “There’s no way you’re going to meet your nutrient needs eating this little food,” explains White. “Your energy levels would suffer and you’re basically asking to overeat. You’re just going to hurt yourself if you go this route.”

What are the benefits of intermittent fasting?

Although there is limited research, the initial findings are promising. Here are the potential benefits of IF based on recent studies.

So which intermittent fasting schedule is best for weight loss? Whichever one you’ll actually stick to, TBH.

In short, the one that’s easiest for you to follow. “It is all about sustainability for the individual,” says Amanda Baker Lemein, RD, a WH advisor. “If one of these diets work well for you and your lifestyle and preferences, then you will likely see some success. If not, then you’ll likely not see the results you’re are looking for, as the sustainability piece will not be there.” That means picking a diet that work best with all the lifestyle factors you need to consider, like your work schedule, family dynamic, living situation, commute time, and travel commitments, notes Lemein.

It’s worth pointing out, though, that the 16:8 diet seems to be the most doable for a lot of people who are into IF. The 16:8 method also scores points for preventing overeating at night, which can often be a big obstacle for weight loss. And sticking to an eight-hour eating window during daylight hours allows your metabolism to run as it’s supposed to—you fuel up for energy during the day (when you’re most active), and stop eating for rest and recovery at night, per a 2017 article in the journal The bottom line: All intermittent fasting schedules may lead to weight loss if you can follow them sustainably, and the 14:10 method may be the easiest way to follow an IF diet.


Kristin Canning is the features director at Women’s Health, where she assigns, edits and reports long-form features on emerging health research and technology, women’s health conditions, psychology, sexuality, mental health, reproductive justice, wellness entrepreneurs, women athletes, and the intersection of health, fitness, and culture for both the magazine and the website.

What Is 16/8 Intermittent Fasting? A Beginner’s Guide

Medically reviewed by Adrienne Seitz, MS, RD, LDN, Nutrition — By Lizzie Streit, MS, RDN, LD and Rachael Ajmera, MS, RD — Updated on August 1, 2023

Intermittent fasting involves limiting your daily food intake to a certain window of time. It’s become popular for weight loss and overall health improvements. For weight loss, knowing what to eat while intermittent fasting will make a difference.

Fasting has been practised for thousands of years and is an important tradition in many religions and cultures worldwide.

Today new varieties of fasting put a spin on this ancient practice.

One of the most popular styles of fasting is 16/8 intermittent fasting. Proponents claim that it’s an easy, convenient, and sustainable way to lose weight and improve overall health.

This article explains how to do 16/8 intermittent fasting and whether it’s right for you.

woman in bed eating breakfast with coffee and bookValentina Barreto/Stocksy United

What is 16/8 intermittent fasting?

The practice of 16/8 intermittent fasting involves limiting your intake of foods and calorie-containing beverages to a set window of 8 hours per day. You abstain from food for the remaining 16 hours, though you’re still allowed to drink water and other no-calorie beverages, like plain coffee or tea.

You can repeat this cycle as frequently as you’d like — from just once or twice per week to every day, depending on your preference.

The popularity of this fasting method has grown widely among those looking to lose weight and burn fat. 16/8 intermittent fasting is also believed to improve blood sugar control and enhance longevity (1)

While other diets often set strict rules, 16/8 intermittent fasting is simple to follow and may provide measurable results with minimal disruption to your diet. It’s generally considered less restrictive and more flexible than many other diets and works with most lifestyles.

Meal plan and getting started

This is what you need to know to do 16/8 intermittent fasting.

To get started, begin by picking an 8-hour window and limiting your food intake to that time span.

Popular 16/8 time windows include:

  • 7 a.m. to 3 p.m.
  • 9 a.m. to 5 p.m.
  • 12 p.m. to 8 p.m.
  • 2 p.m. to 10 p.m.

Many people prefer to eat between noon and 8 p.m., since you need to fast only overnight and skip breakfast but can still eat a balanced lunch and dinner, along with a few snacks throughout the day.

Others opt to eat between 9 a.m. and 5 p.m., which allows plenty of time for a healthy breakfast around 9 a.m., a standard lunch around noon, and a light, early dinner or large snack around 4:30 p.m. before starting your fast.

However, you can experiment and pick the time frame that best fits your schedule.

It may help to set timers at both the beginning and the end of your eating window to remind you when to start and stop eating.

Foods list and meal plan

Pexels images

To maximize the potential health benefits of your diet, it’s important to stick to nutritious whole foods and beverages during your eating periods.

Filling up on nutrient-rich foods helps round out your diet and supports a healthy weight. Try balancing each meal with a wide variety of whole foods, such as:

  • Fruits: apples, bananas, berries, oranges, peaches, pears, tomatoes, etc.
  • Veggies: broccoli, Brussels sprouts, cauliflower, cucumbers, leafy greens, etc.
  • Whole grains: barley, buckwheat, quinoa, rice, oats, etc.
  • Healthy fats: olive oil and avocados
  • Protein sources: eggs, fish, legumes, meat, poultry, nuts, seeds, etc.

Drinking calorie-free beverages like water and unsweetened tea and coffee, even while fasting, also helps control your appetite while keeping you hydrated.

It’s best to limit ultra-processed foods like packaged snacks, deep-fried items, sugary drinks, and most frozen meals. These negate the positive effects of 16/8 intermittent fasting.

Benefits of 16/8 intermittent fasting

One of the main advantages of 16/8 intermittent fasting is its convenience. It can cut down on the time and money you need to spend on cooking and preparing food each week. It has been associated with a long list of health benefits


Increased weight loss

pexels photo

Restricting your eating window to a few hours per day can cut your calorie intake over the course of the day, which in turn may contribute to weight loss.

In fact, research reveals that fasting may boost weight loss.For example, one review found that 11 of 13 studies on intermittent fasting reported statistically significant weight loss in participants (23

Improved blood sugar control

Intermittent fasting has been shown to reduce fasting insulin and blood sugar levels, potentially decreasing your risk of diabetes (4, 5)

Extended longevity

Evidence in humans is limited, but some animal studies note that intermittent fasting may extend longevity. It’s thought that fasting affects metabolic pathways, improves insulin sensitivity, and leads to behavioral changes that together may lengthen your life span. However, these mechanisms aren’t fully understood (6, 7)

Drawbacks of 16/8 intermittent fasting

Although 16/8 intermittent fasting is associated with several health benefits, it has a few side effects and may not be right for everyone.

Be sure to start your fasting regimen gradually and consider stopping or consulting your doctor if you have any concerns or experience negative symptoms.

Overeating and potential weight gain

Restricting your intake to just 8 hours per day may cause some people to eat more than usual during eating periods in an attempt to make up for hours spent fasting. This may lead to weight gain, digestive problems, and unhealthy eating habits.

Pexels images

Interestingly, current research doesn’t suggest that intermittent fasting leads to any more weight loss than typical diets that recommend overall calorie restriction. Both eating patterns may lead to modest weight loss (3Trusted Source, 8 Trusted Source)

If weight loss is your primary goal, you may therefore prefer to lower your calorie intake, exercise more, eat more whole foods, or sleep sufficiently instead of fasting intermittently to prevent the overeating that may occur when restricting intake to a certain time window.

In addition, weight loss may occur while fasting, but when returning to normal eating patterns, it’s common to regain the weight.

Short-term physical symptoms

The practice of 16/8 intermittent fasting may cause short-term negative side effects when you’re first getting started, such as hunger, weakness, and fatigue — though these often subside once you get into a routine.

Hormonal changes and menstrual cycles

Some animal research suggests that intermittent fasting may lead to hormonal changes and undereating. In people with ovaries, these changes may negatively affect menstrual cycles and fertility (9, 10)Furthermore, postmenopausal individuals may experience different effects from intermittent fasting. Menopause causes changes that can decrease insulin sensitivity and lead to weight gain, and intermittent fasting may help improve these outcomes (11)

Is 16/8 intermittent fasting right for you?

It’s true that 16/8 intermittent fasting can be a sustainable, safe, and easy way to improve your health when paired with a nutritious diet and healthy lifestyle.

However, it shouldn’t be viewed as a substitute for a balanced diet rich in whole foods. Plus, you can still be perfectly healthy if you don’t follow intermittent fasting.

Though 16/8 intermittent fasting is generally considered safe for healthy adults, you should talk with your doctor if you have any underlying health conditions. This is key if you’re taking any medications or have diabetes, low blood pressure, or a history of disordered eating.

Intermittent fasting is likewise discouraged if you’re trying to conceive, pregnant, or nursing.

If you have any concerns or experience any side effects while fasting, be sure to consult your doctor.


Does   5-2  or  16-8  Work Better?

16:8 diet vs 5:2 diet

Comparing different intermittent fasting approaches can help you make an informed decision. Here’s a comparison between the 5-2 diet and the 16-8 fasting method:

  • Calorie Restriction: The 5-2 diet involves calorie restriction for two days per week, while the 16-8 method restricts the daily eating window to 8 hours, with a 16-hour fasting period.
  • Flexibility: The 5-2 diet offers flexibility with its fasting and non-fasting days, allowing for easier adaptation to individual schedules. The 16-8 method provides a consistent daily fasting window, which may suit those who prefer a routine.
  • Weight Loss Potential: Both approaches have demonstrated effectiveness for weight loss. However, individual responses may vary, and adherence plays a significant role in achieving desired outcomes.
  • Personal Preference: Consider your lifestyle, eating patterns, and preferences when choosing between the two methods. It’s important to select an approach that aligns with your needs and can be sustained in the long term.

Ultimately, the effectiveness of either approach depends on various factors, including individual compliance, metabolic differences, and overall lifestyle choices. Experimentation and finding what works best for you is key.

  • Individual Considerations: The 5-2 diet may not be suitable for everyone. Individuals with certain medical conditions, such as diabetes, eating disorders, or other underlying health issues, should consult with a healthcare professional before starting the diet.
  • Nutritional Adequacy: It’s crucial to ensure that both fasting and non-fasting days provide adequate nutrition. Focus on consuming a variety of nutrient-dense foods to meet your body’s needs for vitamins, minerals, and macronutrients.
  • Hydration and Electrolytes: Proper hydration is important during fasting days. Be mindful of drinking enough water and consider replenishing electrolytes through sources like electrolyte-rich beverages or foods.


New research has found that eating within a 10-hour window could stave off diabetes and heart disease.

Researchers from the Salk Institute and the UC San Diego School of Medicine found that a 10-hour time-restricted eating intervention, when combined with traditional medications, resulted in weight loss, reduced abdominal fat, lower blood pressure and cholesterol, and more stable blood sugar and insulin levels for participants.

The pilot study, published in Cell Metabolism on 5 December 2019, could lead to a new treatment option for metabolic syndrome patients who are at risk for developing life-altering and costly medical conditions such as diabetes.

Time-restricted eating (eating all calories within a consistent 10-hour window) supports an individual’s circadian rhythms and can maximize health benefits, as evidenced by previous research published by the Salk team. Increasingly, scientists are finding that erratic eating patterns can disrupt this system and increase the risk for metabolic syndrome and other metabolic disorders, with such symptoms as increased abdominal fat, abnormal cholesterol or triglycerides, and high blood pressure and blood sugar levels.

“Eating and drinking everything (except water) within a consistent 10-hour window allows your body to rest and restore for 14 hours at night. Your body can also anticipate when you will eat so it can prepare to optimize metabolism.

Participants to the study  did not report any adverse effects during the intervention. To reduce food intake to the 10-hour window, most participants delayed their first meal and advanced their last meal each day, so meals were not skipped. Although calories were not recommended to be reduced for the intervention, some participants did report eating less, likely due to the shorter eating window.

Overall, participants experienced improved sleep as well as a 3-4 percent reduction in body weight, body mass index, abdominal fat and waist circumference. Major risk factors for heart disease were diminished as participants showed reduced blood pressure and total cholesterol. Blood sugar levels and insulin levels also showed a trend toward improvement.

“Metabolism is closely linked with circadian rhythms, and knowing this, we were able to develop an intervention to help patients with metabolic syndrome without decreasing calories or increasing physical exercise

How Intermittent Fasting Can Help You Lose Weight

Medically reviewed by Grant Tinsley, Ph.D., CSCS,*D, CISSN, Nutrition — By Kris Gunnars, BSc — Updated on February 26, 2023

The intermittent fasting weight loss strategy involves setting periods of time where you avoid eating. Examples include the 5:2 diet, Eat Stop Eat, alternate-day fasting, and more. Many people find this simplified approach more helpful than counting calories.

There are many different ways to lose weight.

One strategy that has become popular in recent years is called intermittent fasting (1)

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

Most people understand intermittent fasting as a weight loss intervention. Fasting for short periods of time helps people eat fewer calories, which may result in weight loss over time (1

However, 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, 5 Trusted Sources).

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

How intermittent fasting affects your hormones

Intermittent fasting may help you lose weight, but it 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 several changes to make its stored energy more accessible.

Examples include changes in nervous system activity, as well as major changes in the levels of several crucial hormones.

Below are two metabolic changes that occur when you fast (17, 18):

  • 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.

Interestingly, despite what some proponents of consuming 5–6 meals per day claim, short-term fasting may increase fat burning.

Research shows that alternate-day fasting trials lasting 3–12 weeks, as well as whole-day fasting trials lasting 12–24 weeks, reduce body weight and body fat (19 20

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

Another hormone that’s altered during a fast is human growth hormone (HGH), levels of which may increase as much as five-fold (17, 18

Previously, HGH was believed to help burn fat faster, but new research shows it may signal the brain to conserve energy, potentially making it harder to lose weight (21

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

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 be consuming fewer calories.

According to a 2014 review, intermittent fasting reduced body weight by 3–8% over a period of 3–24 weeks (22).

When examining the rate of weight loss, intermittent fasting may produce weight loss at a rate of approximately 0.55 to 1.65 pounds (0.25–0.75 kg) per week (23).

People also experienced a 4–7% reduction in waist circumference, indicating that they lost belly fat.

These results indicate that intermittent fasting can be a useful weight loss tool.

That said, the benefits of intermittent fasting go way beyond weight loss.

It also has numerous benefits for metabolic health, and it may even help reduce the risk of cardiovascular disease (24, 25

Although calorie counting is generally not required when doing intermittent fasting, the weight loss is mostly mediated by an overall reduction in calorie intake.

Studies comparing intermittent fasting and continuous calorie restriction show no difference in weight loss when calories are matched between groups.

Intermittent fasting may help you maintain muscle mass when dieting

One of the worst side effects of dieting is that your body tends to lose muscle along with fat (26)

Interestingly, some studies have shown that intermittent fasting may be beneficial for maintaining muscle mass while losing body fat.

A scientific review found that intermittent calorie restriction caused a similar amount of weight loss as continuous calorie restriction — but with a much smaller reduction in muscle mass (27

In the calorie restriction studies, 25% of the weight lost was muscle mass, compared with only 10% in the intermittent calorie restriction studies (27

One 2011 review also showed that intermittent fasting caused less muscle loss than continuous calorie restriction (11 Trusted Source).

However, a 2020 randomized trial looked at people who followed the 16/8 method. In this diet, you fast for 16 hours a day and have an 8-hour window to eat. The people who fasted didn’t lose significantly more weight than the people who ate three meals a day. After testing a subset of the participants in person, the researchers also found that the people who fasted lost a significant amount of lean mass. This included lean muscle (12

More studies are needed on the effect of fasting on muscle loss. All things considered, intermittent fasting has the potential to be an incredibly powerful weight loss tool.

Intermittent fasting makes healthy eating simpler

For many, one of the main benefits of intermittent fasting is its simplicity.

Rather than counting calories, most intermittent fasting regimes simply require you to tell time.The best dietary pattern for you is the one you can stick to in the long run. If intermittent fasting makes it easier for you to stick to a healthy diet, it will have obvious benefits for long-term health and weight maintenance.

Intermittent fasting has become one of the most popular health trends in recent years, and for good reason. Proponents say that it helps improve overall health, weight loss goals, mental clarity and so much more. However, like with any change to your lifestyle or diet there are potential risks and side effects associated with intermittent fasting.

Intermittent fasting is an increasingly popular way of eating that involves periodic cycles of going without food for a certain time frame. This approach to caloric restriction, which is based on when you eat rather than what you eat, has many potential health benefits.

These may include improved weight management and increased longevity, to name just a couple. Intermittent fasting also appears to have positive psychological effects; it can reduce stress and lead to better sleep patterns. 

While it’s a great strategy for some people, intermittent fasting isn’t necessarily for everyone; you should talk with your doctor or healthcare professional if necessary. before beginning any new diet or health regimen.

With proper execution, however, you may find that these lifestyle changes can help optimize both your physical and mental wellbeing.

 In this article we will discuss 11 possible intermittent fasting side effects you must know about before deciding whether or not this type of approach is right for you!

1- Hunger

Hunger is one side effect of intermittent fasting, a dietary practice which involves intentionally going without food for varying lengths of time. There are many potential benefits to this practice, such as better immune system functioning and weight loss. However, hunger can be uncomfortable and overpowering if not properly managed. Fortunately, there are strategies that fasting participants can implement to control their hunger during times when they choose to fast.

This can include eating foods that have a high satiety level and drinking lots of fluids throughout the day. Additionally, it’s important to distract yourself with activities such as reading or exercising while fasting to take your mind off any potential feelings of hunger arising. With the right approach, intermittent fasting needn’t be overwhelmingly uncomfortable; rather, it can be an effective way to achieve long-lasting good health.

2- Headaches and lightheadedness

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many people experience headaches and lightheadedness as side effects. This is due to the changes in blood sugar levels that come with intermittent fasting.

Intermittent fasting can be an effective way to lose weight and eat healthier in general, however side effects are also common. For example, many people experience headaches and lightheadedness as side effects. This is due to the changes in blood sugar levels that come with intermittent fasting – when blood sugar levels become dramatically lower, it can cause these side effects. Headaches and lightheadedness may not seem like anything much, however if it becomes persistent then it might be a good idea to try adjusting your approach to intermittent fasting or stopping altogether if necessary.

3- Digestive issues

Intermittent fasting is becoming a popular method of eating, but side effects such as digestive issues can occur. This type of eating cycle involves extended periods of time without food, with the average fast typically ranging anywhere from 12 to 17 hours. During this period of restricted calorie intake, side effects like heartburn, acid reflux, or bloating may be experienced due to an imbalance in digestive functions as the body does not have enough resources to work properly in digestion and nutrition absorption.

4- Cravings

We all experience cravings from time to time, but suppressing them can be beneficial for our overall health. Intermittent fasting is a type of diet that involves periods of eating and restricted caloric intake, which may lead to side effects such as intense cravings for certain foods. Cravings are merely a side effect and shouldn’t define our physical or emotional wellbeing.

5- Irritability and other mood changes

Irritability and other mood changes are among the side effects of intermittent fasting. But it’s important to keep in mind that they’re usually caused by lower blood sugar levels due to not eating regularly, so they can be easily prevented by ensuring you stay adequately nourished during your fasts.Making sure to drink plenty of fluids is often enough to reduce or prevent any occurrences.

6- Fatigue

Fatigue is a side effect of intermittent fasting that can often be overlooked. Intermittent fasting let’s you cycle between periods of eating and periods of abstaining from food for certain intervals, and is said to promote health benefits such as improvement in insulin sensitivity and weight loss. While this form of fasting can be beneficial, it can also cause the body to experience side effects such as fatigue. This happens because, when you fast, the body switches from burning glucose for energy to breaking down stored fat for fuel.

During this transition period, your body needs more time or rest to adjust which could in turn lead to feeling fatigued throughout the day. Furthermore, if done incorrectly, intermittent fasting may also lead to nutrient deficiencies which could further add to feelings of exhaustion over time.

7- Bad breath

Bad breath can be caused by side effects of intermittent fasting, even if you maintain good oral hygiene. Common side effects include dry mouth or a decrease in saliva production due to dehydration, which can cause an increase in the number of bacteria living in the mouth that produce odors.

Additionally, when food is restricted for long periods of time, it can cause an imbalance between beneficial and harmful bacteria within the digestive system, resulting in further odor-causing bad breath. If you are engaging in intermittent fasting and notice your breath becoming overly smelly or unpleasant-tasting, it is important to speak with a medical professional about possible solutions.

8- Sleep disturbances

Sleep disturbances are side effects of intermittent fasting that can be quite severe. Changes to circadian rhythms and imbalances in hormones such as leptin, ghrelin and cortisol can all contribute to disrupted sleep patterns, making it hard to get the restorative shut-eye our bodies need.

If you’re fasting, keep a close eye on your sleeping patterns; if you notice difficulty with falling or staying asleep, try taking small steps like avoiding caffeine after 2:00 pm or reading an engaging book before bed to better regulate your sleeping habits.

9- Dehydration

Intermittent fasting, while a popular dieting trend and possible beneficial method of losing weight, can also lead to side effects such as dehydration.fasting disrupts the body’s natural cycle of hydration, leaving you feeling fatigued or lightheaded. Dehydration can also cause headaches, blurry vision, and in serious cases, coma or death.

It’s important to regularly drink water during any period of intermittent fasting – doing so will ensure that side effects such as dehydration are minimized and allow you to get the most out of your chosen diet style.

10- Malnutrition

for those that are trying to lose weight, the side effects can include dizziness, headaches, weakness, fatigue and dehydration.

Additionally, diets rich in proteins and complex carbohydrates should be included in any type of malnutrition treatment plan in order for individuals to obtain the necessary vitamins and minerals required for optimal health.

11- Low energy

Side effects such as low energy can often be experienced. This decrease in overall energy levels can be caused by eating less frequently, reduced calorie intake, and a lack of important nutrients. Low energy will also lead to tiredness and fatigue throughout the day, reducing mental sharpness and physical strength.

Who should avoid intermittent fasting?

Intermittent fasting has become a popular weight-loss option, but it is not suitable for everyone. Anyone with a history of an eating disorder should avoid intermittent fasting as this type of schedule could trigger unhealthy behaviors around food.

Additionally, anyone who experiences side effects like weakness, low energy, irritability or headaches should discontinue intermittent fasting and consult a medical professional. Before beginning any kind of new eating regimen, it is important to consider the side effects and your personal wellness needs in order to make a healthy decision for yourself.

However, research indicates that these side effects may be temporary, and people can eventually adjust their body clock to accommodate intermittent fasting. Additionally, intermittent fasting has been shown to lower blood pressure, reduce inflammation levels and improve metabolic markers – so it could offer real long-term health benefits without the side effects experienced while adjusting.

Is intermittent fasting safe for older adults?

Learn the risks before diving into this experimental eating style.

Intermittent fasting is a popular eating strategy being studied in labs and practiced in kitchens across America. And it’s more than a fad. Restricting your calories or mealtimes may have the potential for many benefits, such as weight loss and reduced risk of various diseases. We don’t have much evidence, however, about intermittent fasting’s effect on the health of older adults.

Intermittent fasting restricts when or how much you eat — and sometimes both. There are several approaches.

In alternate-day fasting, you eat normally every other day. On days in between, you eat just 25% of your daily calorie needs, in one meal. So if you consume 1,800 calories on Monday, Wednesday, and Friday, you’d eat a 450-calorie meal (and nothing else) on Tuesday, Thursday, and Saturday.

In the 5:2 approach, you eat normally for five days in a row; then for two days in a row, you eat just 400 to 500 calories per day.

In the 16:8 approach, each day is the same: you fast 16 hours in a row, and then eat normally within an eight-hour period, like between 9 a.m. and 5 p.m.

While intermittent fasting shows promise, we don’t have solid evidence about the benefits or how fasting might affect older adults. Pexels photos

Benefits and Potential risks

The benefits of intermittent fasting seem to affect many aspects of health and is associated with a longer life span studies  however,  leaves have many unanswered questions.”These effects could theoretically result from the flipping of a metabolic switch.

While intermittent fasting shows promise, we don’t have solid evidence about the benefits or how fasting might affect older adults. Human studies have looked mostly at small groups of young or middle-aged adults, for only short periods of time.

But we do know intermittent fasting could be risky in some cases. “If you’re already marginal as far as body weight goes, I’d be concerned that you’d lose too much weight, which can affect your bones, overall immune system, and energy level,” McManus says.

Dr. Suzanne Salamon, associate chief of gerontology at Harvard-affiliated Beth Israel Deaconess Medical Center, expresses another concern: “People who need to take their medications with food — to avoid nauseaor stomach irritation — may not do well with fasting. Also, people who take heart or blood pressure medications may be more likely to suffer dangerous imbalances in potassium and sodium when they’re fasting.”

Intermittent fasting may also be harmful if you have diabetes and need food at certain times or take medication that affects your blood sugar.

Still want to try it?

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If you’re thinking of trying intermittent fasting, especially if you already have health conditions such as diabetes or heart disease, talk to your physician.

McManus advises easing into the diet. “Slowly reduce the time window for eating, over a period of several months,” she advises.

Also: continue your medication regimen as recommended by your doctor. “Taking medications doesn’t break the fast, and neither does having calorie-free drinks like water or black coffee,” says Dr. Alexander Soukas,

Also: continue your medication regimen as recommended by your doctor. “Taking medications doesn’t break the fast, and neither does having calorie-free drinks like water or black coffee,” says Dr. Alexander Soukas, an endocrinologist and molecular geneticist with Harvard-affiliated Massachusetts General Hospital.

What if you do need food with medication? “Perhaps you can try a modified fast. I suspect it would still do a lot of good for people who are overweight,” Dr. Salamon says. “Just work with your doctor on a plan that will benefit your health without risking it.”

Image: © Gunita Reine/Getty Images

Frequently Asked Questions – Who Should Be Careful Or Avoid It?

Intermittent fasting is certainly not for everyone.

group of friends enjoying lunchGoogle photos

If you’re underweight or have a history of eating disorders, you should not fast without consulting with a health professional first. In these cases, it can be downright harmful.

If you have a medical condition, you should consult with your doctor before trying intermittent fasting.

This is particularly important if you:

  • Have diabetes.
  • Have problems with blood sugar regulation.
  • Have low blood pressure.
  • Take medications.
  • Are underweight.
  • Have a history of eating disorders.
  • Are a woman who is trying to conceive.
  • Are a woman with a history of amenorrhea.
  • Are pregnant or breastfeeding.

All that being said, intermittent fasting has an outstanding safety profile. There is nothing dangerous about not eating for a while if you’re healthy and well-nourished overall.

Here are answers to the most common questions about intermittent fasting.

1. Can I Drink Liquids During the Fast?

Yes. Water, coffee, tea and other non-caloric beverages are fine. Do not add sugar to your coffee. Small amounts of milk or cream may be okay.

Coffee can be particularly beneficial during a fast, as it can blunt hunger.

2. Isn’t It Unhealthy to Skip Breakfast?

No. The problem is that most stereotypical breakfast skippers have unhealthy lifestyles. If you make sure to eat healthy food for the rest of the day then the practice is perfectly healthy.

3. Can I Take Supplements While Fasting?

Yes. However, keep in mind that some supplements like fat-soluble vitamins may work better when taken with meals.

4. Can I Work out While Fasted?

Yes, fasted workouts are fine. Some people recommend taking branched-chain amino acids (BCAAs) before a fasted workout.

5. Will Fasting Cause Muscle Loss?

All weight loss methods can cause muscle loss, which is why it’s important to lift weights and keep your protein intake high. A 2011 study showed that intermittent fasting causes less muscle loss than regular calorie restriction (16

Will Fasting Slow Down My Metabolism?

No. Older studies show that short-term fasts actually boost metabolism (14, 15)

However, longer fasts of 3 or more days can suppress metabolism (36

7. Should Kids Fast?

Allowing your child to fast is probably a bad idea.

Should You Try It?

Intermittent fasting is not something that anyone needs to do.

It’s simply one of many lifestyle strategies that can improve your health. Eating real food, exercising and taking care of your sleep are still the most important factors to focus on.

If you don’t like the idea of fasting, then you can safely ignore this article and continue to do what works for you.

At the end of the day, there is no one-size-fits-all solution when it comes to nutrition. The best diet for you is the one you can stick to in the long run.

Intermittent fasting is great for some people, not others. The only way to find out which group you belong to is to try it out.

If you feel good when fasting and find it to be a sustainable way of eating, it can be a very powerful tool to lose weight and improve your health.


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