Intermittent Fasting Guide for Complete Beginners

energy restriction eating for fat loss

You have probably heard of intermittent fasting by now. It is a new dieting trend that has upended the traditional three-meals-a-day mentality.

People who practice intermittent fasting claim that this diet helps them burn fat, lose weight, and simplify their lives without counting calories or eating any specific foods. 

Are you interested in intermittent fasting but aren’t sure if it’s right for you? Or are you curious but don’t know where to get started? If so, then you have come to the right place. 

The following article will give you a comprehensive overview of intermittent fasting, the different types of fasting plans, and what you need to consider before starting. 

Think of this as your ultimate beginner’s guide to intermittent fasting.

What Is Intermittent Fasting?

Intermittent fasting (IF) is an umbrella term used to describe various diets that cycle between periods of fasting and eating.

Unlike most traditional diets, intermittent fasting does not specify what or how much you should eat, but rather, it is about when you should eat. For this reason, many people classify intermittent fasting as more of an eating pattern compared to conventional diets, which generally count calories or macros.

In theory, you could eat unlimited fast foods during the eating period while following this diet, since intermittent fasting does not have a traditional calorie restriction. However, we’ll discuss why that might not be a good idea later in this article. 

There are multiple variations of IF cycles, with the 16:8 diet being the most popular version. The 16:8 plan involves eating all your meals and snacks during an 8-hour window while abstaining from food for the remaining 16 hours every day. Most of the time, this plan involves skipping breakfast and not eating anything after dinner.

A typical 16:8 schedule looks like the following:

  • 7:00 am – Alarm clock goes off
  • 7:30 am – Skip breakfast but non-caloric, unsweetened beverages are permitted 
  • 12:00 pm – Lunch
  • 3:00 pm – Snack
  • 6:00 pm – Dinner
  • 7:45 pm – Snack
  • 8:00 pm – Begin 16-hour fasting

While the 16 hours fast is one of the more popular plans and is an excellent place to start for people new to fasting, there are different types of intermittent fasting diets. Depending on which intermittent fasting method you choose, the fasting period can be anywhere from a few hours per day to a full day. We will discuss the different fasting plans in more detail later in the article. 

The takeaway: Intermittent fasting is a short-term, time-restricted eating plan where you limit your food intake to a designated period of time and allow your body to fast for the remaining time window. It is not a traditional calorie restriction diet and does not have any food rules. Instead, it is a dietary pattern that designates when to eat and when not to.

Intermittent Fasting for Weight Loss

Female reading about IF diet for fat loss

There is growing research that intermittent fasting is at least as effective for weight loss as other diet plans (1). There is also evidence that fasting may help boost metabolism and could be a useful tool for weight management (2, 3).

One review study found that intermittent fasting plans resulted in a 3 to 8% reduction in body weight over 3 to 24 weeks. Study participants also had a 4 to 7% decrease in waist circumference, meaning that they lost belly fat (4).

A more recent systematic review from 2020, found that intermittent fasting resulted in a weight loss ranging from 0.8% to 13% of starting body weight. Waist circumference also decreased by 3 to 8 cm (or about 1 to 3 inches) among intermittent fasting participants in the studies that had a duration of four weeks or longer. Additionally, the researchers noted that most of the body weight loss from intermittent fasting was from body fat loss (3).

The reason why intermittent fasting can help with weight loss is two-fold.

The first and foremost reason that intermittent fasting helps you lose weight is by decreasing your daily food consumption to create a calorie deficit. A calorie deficit occurs when you burn more calories in a day than you eat. 

In general, people practicing IF skip meals and snacks to some extent because they limit their food intake to a defined eating window. Therefore, you end up consuming fewer calories than usual, as long as you are not overcompensating by consuming much more during the eating periods. 

Additionally, your body also adjusts hormone levels during a fast to make stored body fat more accessible to use as energy. To understand these changes, we first need to discuss the impact that eating has on the body. 

When you eat, your digestive tract or gut releases enzymes to break down food into smaller molecules that can be absorbed into the bloodstream. In particular, carbohydrates, or carbs, are broken down into glucose (aka sugar), a preferred energy source for your body tissues and brain cells.

In this fed state, glucose enters your cells with the help of a pancreatic hormone known as insulin. Basically, insulin signals to your cells to absorb glucose and burn it as fuel. Insulin also communicates with fat cells and tells them to absorb excess glucose to be stored as fat. 

During a fast, insulin and glucose levels decrease. This decrease sends signals to your body to start utilizing fat for energy instead of blood sugar. Essentially, when your body is cut off from the energy found in food, it will start burning fat as its primary source of fuel. Therefore, you are not only losing weight, but a portion of that weight loss will be from body fat storage.

Potential Benefits of Intermittent Fasting

The idea of intermittent fasting or time-restricted eating is not new. In fact, fasting has been around since the dawn of our species. 

During ancient times, our hunter-gatherer ancestors did not have access to unlimited food supplies and likely went without eating for hours or days at a time. As a result, humans evolved to survive without food for extended periods. 

Fasting is also a part of religious and spiritual traditions and is practiced in Islam, Judaism, Buddhism, and some denominations of Christianity.

Additionally, there may have been moments in your life where you “fasted” by intentionally or unintentionally skipping a meal.

This is all to say that the human body is equipped to handle short-term fasts, such as intermittent fasting. However, the concept of fasting as a health and fitness trend is relatively new. So why should you consider intermittent fasting as a lifestyle choice? 

Fasting periods have been shown to impact the body in several ways. Some changes that occur during a fast include:

  • Lower insulin levels and increased insulin sensitivity – During a fast, insulin levels decrease which results in lipolysis—the breakdown of fat. This makes stored fat more accessible to use as energy (5).
  • Increased human growth hormone – Human growth hormone (HGH) has been linked to higher fat burn and increases in muscle mass. Research has shown that HGH levels increase during a fast (6-8). One study found that two days of fasting caused a 5-fold increase in the rate of growth hormone secretion among participants (8). 
  • Elevated norepinephrine – During a fast, norepinephrine levels rise in the body. Norepinephrine is a hormone released by the central nervous system which tells the body to release stored body fat (2, 9).
  • Changes in gene expression – Some preliminary research has suggested that fasting may change gene expression. 

In particular, fasting has been linked to the expression of genes that are associated with longevity, anti-aging, circadian rhythm, and protection against certain conditions such as Alzheimer’s disease and Parkinson’s disease (10-12). However, further research is needed to explore the relationship between fasting and gene expression. 

These changes at the molecular and cellular levels may lead to health benefits, including:

Weight Loss: Weight loss relies on creating a calorie deficit. Basically, you lose weight when you eat fewer calories per day than you burn. Intermittent fasting makes it easier to eat fewer calories without calorie counting by limiting the amount of time you spend eating. 

Decreased risk of developing type 2 diabetes: Intermittent fasting may reduce insulin resistance by lowering blood glucose and insulin levels. A reduction in insulin resistance can help prevent the development of type 2 diabetes. 

One review study found that intermittent fasting decreased fasting blood sugars by 3 to 6% and fasting insulin levels by 20 to 31% in people diagnosed with prediabetes (4). 

Improvements in heart health: Intermittent fasting may reduce the risk factors associated with heart disease. Research has shown that fasting may lower “bad” LDL cholesterol, blood triglycerides, and insulin resistance (13, 14). 

Reduced inflammation: Research shows that intermittent fasting may reduce oxidative stress, which could lead to decreased inflammation (10).

Potential anti-cancer effects: Preliminary research trials conducted on mice and rats suggest that IF may slow the growth of tumors and prevent the development of certain cancers (15, 16). 

Anti-aging and increased lifespan: Animal studies have shown that intermittent fasting helps rats live longer. One study found that fasted rats had an 83% increase in life expectancy compared to those on a regular diet (17). 

It’s important to keep in mind that research studies using animals are considered preliminary research, and many questions still need to be answered using high-quality, human studies among people.

The takeaway: Intermittent fasting may cause weight loss by creating a calorie deficit in which you consume fewer calories per day than you burn. It may also help with type 2 diabetes prevention by increasing insulin sensitivity and improving blood sugar control. There is some exciting but preliminary evidence that IF may alter gene expression and increase longevity. However, future research is needed to further investigate these findings. 

Intermittent Fasting Protocols

There are multiple ways that you can intermittent fast. Below, you will find a list of some of the common intermittent fasting schedules.

The 16:8 Fasting: The 16:8 diet, sometimes referred to as the Leangains protocol, is a popular version of time-restricted eating. Many people find that the 16:8 plan is the simplest version of intermittent fasting, and it may be an excellent place to start if you are a beginner.

It involves eating all meals and snacks during a designated 8 hours while abstaining from food for 16 hours every day. A typical eating timeframe on the 16:8 fast is from 12 pm to 8 pm. Generally, this plan involves skipping breakfast and not eating anything after dinner. 

24-Hour Fasts: This is sometimes referred to as the eat stop eat plan. On the 24-hour plan, you fast for 24-hours once or twice per week. For example, you could finish dinner at 6 pm one day and fast until 6 pm the next day- a full 24-hours. 

The 5:2 Method: The 5:2 method restricts your intake to 500 to 600 calories for two fasting days per week while following a typical eating pattern on the other five days per week. 

Alternate Day Fasting: For the alternate-day plan, you fast every other day of the week. Several different versions of this fast exist, with one plan allowing 500 calories during the fast days and others recommending to fast for 24 hours. Completing a full 24 hour fast every other day can be a challenge, and this method may not be ideal for long-term success. Side effects of alternate-day fasting include feeling hungry multiple days a week.

The Warrior Diet: This version of intermittent fasting entails eating small amounts of fruits and vegetables throughout the day and one meal in the evening. 

Remember that the best intermittent fasting plan is the one that you can sustain in the long run. Before starting any intermittent fast, you may want to consider your current eating pattern and try to select the one plan that fits with your lifestyle.

As with all diets, intermittent fasting should not be an all-or-nothing approach. Perhaps you are hesitant to commit to a full 16 hour fast? If that is the case, try starting with 12 hours and increasing your fast if it feels right. 

Another option is to skip meals occasionally if you do not feel hungry. Even engaging in sporadic or occasional fasting will create a calorie deficit for most people.

Who Should Avoid Intermittent Fasting?

Many people find that intermittent fasting is an effective strategy to lose weight and simplify their eating habits. However, this diet has some drawbacks and is not appropriate for everyone.

As you might imagine, the most common side effect of intermittent fasting is hunger. Additional side effects may include weakness, fatigue, and headaches during the fasting window, especially when starting an intermittent fasting plan. Overeating during the eating window can also occur while practicing a fast. 

In general, intermittent fasting is considered safe for most well-nourished adults. However, it may not be right for all people. This includes individuals who are underweight or who have been advised to gain weight by a healthcare professional. Additionally, people with a history of eating disorders, such as anorexia, may want to avoid intermittent fasting, as this regimen may not provide enough flexibility to support treatment and recovery.

You may want to avoid intermittent fasting if:

  • You are pregnant or breastfeeding
  • You are trying to become pregnant    
  • You have a history of an eating disorder 
  • You have low blood pressure 
  • You are underweight, or you have been advised to gain weight by a health professional 
  • You have a history of amenorrhea 

Additionally, make sure to speak with a healthcare professional before starting intermittent fasting if any of the following apply to you:

  • You are taking certain medications
  • You have certain medical conditions or health issues, such as diabetes 
  • You have a history of hypoglycemia or low blood sugar

Intermittent fasting is only one of many approaches that can help people lose weight. If you find that you are uncomfortable with the idea of fasting, then this may not be the best approach for you. Ultimately, fasting isn’t for everyone, and that is okay. The best diet is the one that you can maintain in the long run.

Takeaway: Side effects of intermittent fasting may include hunger, weakness, and fatigue, especially if you are new to fasting. People with a history of eating disorders or who are underweight may want to avoid intermittent fasting. When in doubt, consult with your physician or a registered dietitian before starting an intermittent fast. 

Got Questions Before You Start?

Do you have additional questions about intermittent fasting? Below, you can find answers to the FAQs about fasting.

What Can I Drink During the Fast?

Intermittent fasting allows for unsweetened, calorie-free drinks during the fast. These include water, unsweetened green tea, and black coffee. 

Drinking water helps maintain adequate hydration and should not be limited to your eating schedule. In addition to preventing dehydration, noncaloric beverages may play a crucial role in decreasing hunger cues. Drinking plenty of fluids may help increase feelings of satiety, meaning that you will feel fuller.

How Can Skipping Breakfast Be Healthy?

It is not necessarily true that skipping breakfast is unhealthy. There are many studies that show that people who eat breakfast tend to be healthier. However, this may have less to do with meal timing and more to do with the fact that breakfast eaters typically engage in healthier lifestyle habits compared to people who don’t eat breakfast (18, 19). 

Be sure to focus on diet quality during your eating windows to get the most out of your meals.

Can Supplements Be Taken While Fasting?

Yes, you can take vitamin supplements when you are fasting. However, fat-soluble vitamins are better absorbed when taken with food. Be sure to check the label and follow the supplement instructions in this regard. Also, consider speaking with a healthcare professional for more individualized advice on the timing of supplements and medications while fasting. 

Can I Work Out While Fasting?

Yes, you can work out while in the fasted state. Your body can adapt to meet energy needs during a workout by burning fat as an energy source versus blood sugar. However, as with all workouts, be sure to stop if you begin to feel light-headed, dizzy, or faint.

Will I Lose Muscle Mass While Fasting?

The short answer to this question is yes. All weight-loss diets indeed result in some loss of muscle mass. However, you can minimize muscle loss while dieting by consuming enough protein and doing strength training exercises, such as weight training.

Additionally, some research suggests that intermittent fasting may result in less muscle tissue loss when compared to calorie restriction diets (1).

Will Fasting Slow My Metabolism?

No, it shouldn’t. Many people have heard that going without food for too long can cause the body to enter “starvation mode,” which results in a slower metabolism. However, research suggests that this happens with fasting that lasts more than three days (20). Additionally, some research shows that short-term fasting may actually boost metabolism (2).

Can I Fast While On a Diet?

Yes, since intermittent fasting is more of an eating pattern, it can be combined with other dietary plans.

However, you may want to review your daily calorie intake when following other diets to ensure that you are getting enough to eat. Keep in mind that a fast already restricts your energy intake by limiting your eating window. It may not be a good idea to combine a fast with an overly restrictive eating plan or diet. 

Generally speaking, whether you’re on the Paleo diet or the high-fat, low-carb keto diet plan, intermittent fasting can increase these plans’ effectiveness. Additionally, healthy eating patterns, such as the Mediterranean diet, can easily fit with intermittent fasting and offer various health benefits.

How to Get Started

As previously mentioned, intermittent fasting is associated with potential health benefits, including a reduced risk of type 2 diabetes, decreased inflammation, and improved heart health. Intermittent fasting can also help you lose weight and has been shown to be at least as effective for weight loss when compared to calorie restriction diets (1). 

If you feel comfortable with the idea of fasting and find it to be sustainable, then it can be an excellent weight loss program and may improve your health. 

So are you ready to try an intermittent fasting plan?

Begin by selecting a plan that will set you up for long term success. Consider your goals, lifestyle, current eating pattern, and appetite when choosing the fasting schedule that best suits your needs. 

Additionally, keep in mind that intermittent fasting is not a replacement for healthy lifestyle changes.

It is still recommended to limit processed and junk foods during your eating windows, as these foods are associated with obesity, weight gain, and increased risk of certain diseases. Even while intermittent fasting, you will want to focus on a balanced diet, which includes plenty of fruit and veggies, whole grains, legumes, fish, healthy fats, and lean proteins. Healthy habits such as exercise and getting enough sleep are also important for health.

As always, the best diet strategies are the ones that you can maintain for an extended period. This means that intermittent fasting will be a natural fit for some people, but not for others. Perhaps the best way to find out if it is right for you is to try a fasting plan and see how you feel. 

Consider using the tools, tips, and resources outlined in this article to get started or speak with a healthcare professional to determine if intermittent fasting is right for you. 

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