What Is Intermittent Fasting and Does it Work for Weight Loss?

In recent years, intermittent fasting has become one of the hottest trends within the health and fitness community.  In fact, it’s even made its way into the mainstream, with everyone from celebrities to the average social media influencer raving about it.  

As opposed to a short-term diet plan, intermittent fasting is an eating lifestyle that’s routinely followed over an extended period of time.  Also in opposition to the average diet, which relies on 3 meals per day, with intermittent fasting, you’ll be skipping a meal or two each day.  Here’s how it works.  

What is Intermittent Fasting?

Intermittent fasting is an eating routine most commonly used for weight loss.  It consists of taking extended breaks in between meals as opposed to following the average 3-meals-a-day eating schedule.  

Most people who regularly perform intermittent fasting, follow a relatively strict eating schedule -- e.g. consuming food only between the hours of 12 pm and 6 pm and then waiting until the next day to repeat the routine. 

For instance, if you were to skip breakfast today, you’d technically be intermittent fasting from the time you had dinner yesterday until you eat lunch today -- that’s somewhere in the vicinity of an 18 hour fast.  

Another approach to intermittent fasting is to skip eating for an entire day and then return to a regular meal schedule the next day.  This could then be repeated every other day or every third day and so on.

What Are the Different Methods?

When it comes to intermittent fasting, there’s no one-size-fits-all template.  In fact, there are lots of different approaches to this popular dieting routine.  In this section, we’ll be going over a few of the most popular intermittent fasting plans.  

It’s important to point, however, that you’re free to come up with your own approach;  you don’t have to settle on any of the methods we’ve discussed here if you’d like to try something different.    

While there are all kinds of options when it comes to finding an intermittent fasting routine that works for you, you’ll want to speak with your doctor before making any drastic changes to your diet, especially if you have any medical issues or preexisting conditions. 

16:8 Fasting

One of the most popular approaches to intermittent fasting is known as 16:8 fasting.  Simply put, it consists of skipping one meal a day, which leaves you with an eating window of 8 hours and a fast of 16 hours -- hence the name 16:8.      

In most cases, about half of your fast will be spent sleeping -- the average person sleeps for 8 hours a night -- which makes it one of the easier approaches, especially if you’re just getting started with intermittent fasting.  

Within that 8-hour eating window is when you’ll be taking in all of your daily calories.  One of the benefits of doing it this way is that for most people, you’ll end up consuming less than you did on a normal 3-times-a-day meal schedule.  

As long as you’re eating window is 8 hours, it technically doesn’t matter where you put it in your daily schedule, although many people like to skip breakfast and have their window start somewhere around or slightly after lunchtime. 

5:2 Fasting

5:2 fasting is another relatively easy approach to intermittent fasting. It involves dropping your food intake to about 500 calories per day twice a week.  The other five days you’ll be consuming your normal amount of calories, which is why it’s referred to as 5:2 fasting.   

For example, on Tuesdays and Thursdays, you could cut your calories to 500 a day and then go back to your standard eating schedule the other 5 days of the week.  

However, it’s important to mention that you should be eating healthy, unprocessed foods on your normal eating days; it’s not an excuse to dive into junk food or consume an excessive amount of calories.  

While the two days you’re heavily restricting your calories may be challenging at times, the five days a week where you can eat freely makes it a relatively easy approach to stay consistent with.  

24 hour fast

The 24 hour fast is pretty straight forward.   It consists of eating one meal per day and waiting 24 hours until your next meal.  So for instance, if you eat dinner at 6 pm you’d wait until the following day at the same time to have your next meal.  

While it might be straight forward, it’s not for the light of heart.  If you’re just starting out with intermittent fasting, you may want to work your way up to 24-hour fasting.   

Does Intermittent Fasting Work For Weight Loss?

When it comes to weight loss, there’s only one thing that’s absolutely essential: a calorie restriction, which happens when you take in fewer calories than your body burns off in a day.  

With that being said, many studies have compared the effects of a continuous calorie restriction to intermittent restrictions such as the 4:3 and 5:2 fasting methods.  Most research has ultimately demonstrated that both approaches produce similar results in terms of weight loss.^(1)(2)(3)(4)

For instance, a randomized 2018 study published in Nutrition, Metabolism and Cardiovascular Diseases compared the effects of intermittent fasting to a continuous energy restriction over the course of six months.⁽⁵⁾ The intermittent fasting group consumed around 500 calories two non-consecutive days per week. The continuous energy restriction group took in a reduced amount of calories (26-28% reduction) every day.  

At the conclusion of the study, the researchers found that weight loss was similar in both groups -- the fasting group lost an average of 8kg compared to 9kg for the continuous restriction group.  On top of that, they also observed similar reductions in waist circumference in both groups.      

While research suggests that intermittent fasting and regular dieting can both lead to significant amounts of weight loss, that doesn’t mean that they’re entirely equal.  Several studies have demonstrated that compared to regular dieting, intermittent fasting can help to preserve more lean muscle mass during weight loss.⁽⁶⁾

 Ultimately, that means that it may offer certain advantages that regular dieting does not when it comes to body recomposition. For example, a 2011 study published in Obesity Reviews evaluated the effects of intermittent fasting (IF) versus a daily calorie restriction (DCR) on weight loss.⁽⁷⁾

The researchers ultimately found that over the course of 12 weeks, both groups lost similar amounts of weight (11 -16% weight reduction for the IF group vs 10-20% for the DCR group).  However, they also found that those in the intermittent fasting group, on average, lost less fat-free mass in comparison to those who’s calories were restricted for the entirety of the study. 

Other Intermittent Fasting Benefits

From lowering your risk of coronary artery disease to reducing the chances of type 2 diabetes, there are several other benefits that intermittent fasting has to offer on top of just helping you to lose weight.    

Reduce Inflammation 

Several studies have illustrated that intermittent fasting can help to reduce inflammation in men and women of all ages.  For example, a 2012 study published in Nutritional Research examined the effects of a one month fast.⁽⁸⁾ The study was conducted during the month of Ramadan, where participants did not consume any food between sunrise and sunset for 30 days.  

At the conclusion of the study, the researchers ultimately found that compared to before participants started fasting, their levels of proinflammatory cytokines -- signaling molecules that set off the inflammatory process -- were significantly lower following a month of fasting.   

Reduce Insulin Resistance and Risk of Type 2 Diabetes

Other research has also demonstrated that intermittent fasting can help to reduce insulin resistance (IR) as well.  IR is a central feature of type 2 diabetes and occurs when there’s too much glucose in your blood, which, in turn, impinges on the ability of your cells to absorb and convert blood sugar into energy.  

A 2014 study published in Translation Research ultimately found that participants who fasted for 1-3 days a week (they ate freely on the other days) ultimately saw significant reductions in insulin resistance.⁽⁹⁾ The researchers ultimately concluded that intermittent fasting is a promising method when it comes to reducing type 2 diabetes risk factors.   

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Decrease LDL Cholesterol

On top of decreasing insulin resistance, intermittent fasting may also help reduce low-density lipoproteins (LDL) cholesterol levels, especially in combination with cardiovascular exercise.  LDL is usually referred to as “bad cholesterol” because it can cause build-ups in your arteries at high levels.  

A 2013 randomized study published in Obesity explored the effects of alternate-day fasting on 64 subjects over the course of 12 weeks.⁽¹⁰⁾ Compared to the control group who saw no changes at all, subjects who intermittent fasted and exercised saw significant reductions (12%) in their LDL cholesterol levels.  

Lower Blood Pressure 

Research also shows that intermittent fasting can help to lower both your systolic and diastolic blood pressure, helping to reduce your risk of having a stroke or heart attack.  

For example, a 2015 study published in the Journal of Ayub Medical College, measured the blood pressure of participants before and during the Month of Ramadan (MOR), during which individuals fasted between sunrise and sunset.⁽¹¹⁾

During the MOR, researchers ultimately saw an average reduction of 7.61 mmHg in systolic before participants ate their daily meal and 2.72 mmHg afterward.  On top of that, participants’ diastolic blood pressure also dropped by an average of 3.19 mmHg over the course of the study.

Wrap Up

When it comes to weight loss, numerous studies have shown that intermittent fasting can be just as effective as a continuous calorie restriction.  On top of that, intermittent fasting may actually help you to maintain more lean body mass during a weight cut.

In addition to helping with weight loss, intermittent fasting may also help to reduce some of the risk factors associated with coronary artery disease and type 2 diabetes.  

There are several different approaches to intermittent fasting, ranging from the popular 16:8 routine to the challenging warrior diet.  Determining which one is right for you ultimately depends both on your level of experience and personal preference.  

• References
  1. “Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial.”Sundfor, T.M., Svendesen, M., Tonstad, S. Nutrition, Metabolism, and Cardiovascular Disease. Jul. 2018.
  2. “Do intermittent diets provide physiological benefits over continuous diets for weight loss? A systematic review of clinical trials.” Seimon, R., Roekenes, J.A., Zibellini, J., Zhu, B., Gibson, A.A., Hills, A.P., Wood, R.E., King, N.A., Byrne, N.M., Sainsbury, A. Mollecular and Cellular Endocrinology. Dec. 2015.
  3. “Intermittent energy restriction and weight loss: a systematic review.” Davis, C.S., Clarke, R.E., Coulter, S.N., Rounsefell, K.N., Walker, R.E., Rauch, C.E., Huggins, C.E., Ryan, L. Europoean Journal of Clinical Nutrition. Mar. 2016.
  4. “Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?” Varady, K.A. Obesity Reviews. Jul. 2011.
  5. “Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial” Sundfor, T.M., Svendesen, M., Tonstad, S. Nutrition, Metabolism, and Cardiovascular Disease. Jul. 2018.
  6. “Intermittent energy restriction and weight loss: a systematic review.” Davis, C.S., Clarke, R.E., Coulter, S.N., Rounsefell, K.N., Walker, R.E., Rauch, C.E., Huggins, C.E., Ryan, L. Europoean Journal of Clinical Nutrition. Mar. 2016.
  7. “Intermittent versus daily calorie restriction: which diet regimen is more effective for weight loss?” Varady, K.A. Obesity Reviews. Jul. 2011.
  8. “Intermittent fasting during Ramadan attenuates proinflammatory cytokines and immune cells in healthy subjects” Faris, E., Kacimi, S., Al-Kurd, R.A., Farerjeh, M.A., Bustanji, Y.k., Mohammad, M.K., Salem, M.L. Nutrition Research. Dec. 2012.
  9. “Intermittent fasting vs daily calorie restriction for type 2 diabetes prevention: a review of human findings” Barnosky, A.R>, Hoddy, K.K., Unterman, T.G., Vardy, K.A. Translation Research. Oct. 2014.
  10. “Alternate day fasting and endurance exercise combine to reduce body weight and favorably alter plasma lipids in obese humans.” Bhutani, S., Klempel, M.C., Kroeger, C.M., Trepanowski, J.F., Varady, K.A. Obesity. Jul. 2013.
  11. “Effects of Ramadan Fasting on Blood Pressure in Normotensive Males” Samad, F., Qazi, F., Pervaiz, M.B., Kella, D.k>, Mansoor, M., Osmani, B.Z., Mir, F., Kadir, M.M. JAMC. 2015.