How Does Intermittent Fasting Work and Which Method Should You Choose?

There are different methods of timing your intermittent fasting.

Historically, ancient and modern societies have practiced fasting from certain foods for specific lengths of time for religious or cultural purposes. Today, intermittent fasting is a buzzy topic for media outlets and talk shows as a popular weight loss strategy where dieters eat by the clock. You may have heard about intermittent fasting for weight loss and are considering trying it to propel the pounds away. But how does intermittent fasting work for weight loss exactly? 

Read on to find out.  Plus, you’ll get familiar with intermittent fasting methods, benefits, and possible drawbacks.

What Is Intermittent Fasting?

Put simply, intermittent fasting is a diet approach consisting of alternating between eating and fasting periods throughout the day. Instead of focusing on what you eat, the intermittent fasting diet plan is more about when you eat. Essentially, intermittent fasting limits your eating to a defined time. Remember though, no fasting schedule will make up for a poor-quality diet. No matter what meal timing pattern you follow, be sure to have nutritious foods to provide your body with the fuel it needs.

How Does Intermittent Fasting Work?

Intermittent fasting can be characterized by taking extended breaks from eating, which may result in lower calorie intake. Eating fewer calories throughout the day can help drive weight loss successes over time. Studies suggest that intermittent fasting not only helps decrease calorie intake, but also induces a ketogenic state which requires the body to use more energy, leading to greater calories burned.

The good news is there’s no one way to implement intermittent fasting into your life. Plenty of fasting styles are out there for your choosing. As you learn about each one, consider your lifestyle and which style best suits you. Finding a system that is practical and fits seamlessly into your life is key to staying consistent. 

Who Should Avoid Intermittent Fasting?

While intermittent fasting is generally safe, it isn’t safe for everyone and can even be harmful. The following groups of individuals should avoid intermittent fasting. Always consult with a medical provider before adopting new eating regimens. 

People who are:

  • Pregnant or breastfeeding
  • Under the age of 18
  • Have blood sugar balance issues 
  • Recovering/recovered from eating disorders
  • Underweight or malnourished 
  • Taking certain medications (ie fast-acting insulin, NSAIDS, and some antibiotics)
  • Struggling with fertility issues or have abnormal menses 

Intermittent Fasting Methods

Intermittent fasting can be flexible to suit different people thanks to multiple fasting methods. It’s best practice to seek the advice of your medical provider before starting any new diet, as some of these methods can cause extreme changes to your regular eating routine.

1. Intermittent Fasting 16:8

A popular type of fasting, the 16:8 method is where you eat within eight hours and fast for the remaining 16 hours of the day. People following this plan often start eating at noon and stop eating at 8:00pm, though you can shift the 8 hour window to meet your needs. 

2. Intermittent Fasting 18:6

More rigid compared to the 16:8 style, the 18:6 method features daily fasting for 18 hours and eating during a six-hour window. A typical schedule might be eating from 12:00 to 6:00pm. 

3. Intermittent Fasting 20:4

The 20:4 method is even more intense and involves fasting for 20 hours and eating for four hours. For those who choose this method, a standard eating schedule might look like 12:00 to 4:00 pm. Remember, the 20:4 method is an extreme way of intermittent fasting that’s not ideal or right for everyone. 

4. The Warrior Diet

The Warrior Diet was created by health and fitness guru named Ori Hofmekler and is the same as the 20:4 method but also includes specific foods.  Hofmeler believes we should pattern our eating after our warrior ancestors who ate fermented, seasonal, and fresh foods infrequently during the day and filled up on foods overnight. While the emphasis on whole, unprocessed foods is a healthy eating strategy, the Warrior diet is highly restrictive, not research backed, and can be extremely difficult to stick with long term. 

5. Intermittent Fasting 5:2

5:2 intermittent fasting is a different approach when you eat as you usually would five days a week. On the remaining two days, this method calls for limiting your calorie intake to 500-600 calories. This may be the only method that would require some sort of calorie counting or at least some general knowledge of how much you’re eating by reading nutrition labels. 

6. Eat Stop Eat

Eat-stop-eat is an intermittent fasting style that consists of one to two fasting days and eating without time restrictions on the other days of the week. While intermittent fasting is generally safe, the eat-stop-eat method is extreme. This highly restrictive eating schedule may not be a safe or sustainable method for most people.

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What Is The Best Intermittent Fasting Method?

While there are several types of intermittent fasting plans, no one fasting method is considered the best. At Form, our team of weight management experts take into account your health, lifestyle and goals in order to help you determine which method is the right fit for you. We believe in helping you find a plan that feels realistic, not overly restrictive, and something that you can see yourself following for the rest of your life. If you want to give intermittent fasting a try, consider consulting with a Form dietitian so you can pick a sustainable method. 

Benefits of Intermittent Fasting

Science suggests many benefits of intermittent fasting to human health and many studies have been done in the short term with small study populations. More research continues on intermittent fasting, but for now, here are a few potential benefits of incorporating it into your lifestyle. 

1. You don’t have to count calories

If you’ve ever tried to count calories to lose weight, you may know that it can be stressful and cumbersome. Before you know it, the whole day has passed you by, and you didn’t have time to log what you ate. Many weight loss seekers fall off the calorie-tracking bandwagon because it’s often not sustainable or practical. Most intermittent fasting types bypass the need to count calories and may be an option you’re more likely to stick to. Bear in mind you may need to track calories if you’re using the 5:2 method for weight loss, though this method may not be as realistic as the others.

2. You may lose weight

Intermittent fasting is a popular method because it organically restricts your calorie intake for the day, which may help you meet your weight loss goals. 

According to a 2020 review examining 27 human research trials of intermittent fasting and weight loss, all studies had weight loss successes of  0.8-13%. Weight loss of more than 5% is considered clinically significant.

3. Intermittent fasting might curb inflammation and disease

While weight loss may be the biggest reason most people intermittently fast, new findings suggest it may also lower inflammation in the body. A 2020 review of 18 studies found that intermittent fasting regimens lowered C-reactive protein (CRP) levels in individuals with higher body weights. CRP is a significant marker of inflammation, which can lead to many chronic disease states. 

4. You could have more effective workouts

Another bonus of intermittent fasting is maximizing your weight loss efforts with exercise. A small 2016 study of 34 resistance-trained males found that working out during fasting times burned more body fat compared to diets with typical eating schedules. 

5. Intermittent fasting may improve cardiometabolic health

Your cardiometabolic health influences your risk for a spectrum of diseases and conditions, including type 2 diabetes, cardiovascular disease, and metabolic syndrome.

Living with obesity can increase your chances of these diseases, but intermittent fasting may help. One 2021 review of 46 studies examined the impact of intermittent fasting on cardiometabolic health. The study found that intermittent fasting groups had lower body weight, fat mass, waist circumference,  blood pressure, fasting blood glucose levels, total cholesterol, and triglycerides than non-fasting groups. 

Drawbacks of Intermittent Fasting

Generally, intermittent fasting is touted as a safe approach to weight loss. But, avoiding food for specific periods can come with side effects, many of which stem from hunger.

How Form Health Can Help You Adopt New Eating Patterns and Reach Your Health Goals

It’s no surprise that many diets are popular in our culture today, including keto and Intermittent fasting. Intermittent fasting is unlike any other diet because it’s based on the clock. By definition, it’s a diet approach that is defined by eating and fasting during specific stretches of time.  According to research, the intermittent approach may help promote weight loss, improve inflammation, prevent disease, normalize heart and metabolic labs, and help burn more fat during workouts, but it is still unclear if intermittent fasting is superior to other weight loss methods.  More high-quality, long term randomized controlled trials are needed. 
If you’re considering adopting an intermittent fasting method into your life, get in touch with Form. We offer personalized support from Registered Dietitians, who know the ins and outs of intermittent fasting and how you can apply it to your lifestyle. You can schedule a call or send a message. If you’re having trouble losing weight even after improving your diet, Form medical weight loss may be right for you.

About the Author

Julia Axelbaum, RD, Director of Clinical Nutrition, CSOWM, LDN

Julia Axelbaum is a Registered Dietitian board certified in obesity and weight management at Form Health. She studied Nutrition and Public Health at New York University and completed her clinical training at Beth Israel Deaconess Medical Center in Boston. Julia worked as a bariatric dietitian at NewStart Bariatrics in St. Louis, MO and went on to become the Bariatric Program Coordinator where she fully launched the center’s first non-surgical, medical weight loss program. Julia is passionate about helping her patients learn how to take control of emotional eating, develop a more balanced mindset and improve their relationship with food.

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