Intermittent Fasting 101: A Comprehensive Guide for Beginners

Most diets tell you what to eat, whereas intermittent fasting puts more emphasis on when to eat. As research on intermittent fasting suggests, timing can play a role in helping people achieve a healthier weight, reduce blood glucose, lower insulin resistance, slowed cancer growth, and more (1)(2)(3). 

But how does intermittent fasting work and can everyone practice it? Here’s a guide that explains this ancient dietary practice. 

What is Intermittent Fasting?

Intermittent fasting or IF is an eating pattern that alternates between periods of eating and fasting. While certain cultures practice fasting as part of their tradition — and in fact, periodic fasting has been used for thousands of years — it has gained more interest among wellness influencers, doctors, and other professionals who want to empower people to live healthier. 

During a fast, you abstain from consuming calories to facilitate a metabolic shift in your body. By not eating food for 12 hours or more, your body shifts to using its stored fat as an energy source. At the same time, autophagy is increased, which allows for cellular repair.  

IF aims to tap into various health benefits, ranging from weight management to reducing your risk of certain cancers.  

Intermittent fasting can be practiced through different methods, such as time-restricted feeding (TRF) or alternate-day fasting (ADF), making it a flexible approach for those seeking to achieve specific health or lifestyle goals.

How Does Intermittent Fasting Work?

Intermittent fasting works by creating periods of eating and fasting, which influence the body’s metabolism and hormone levels. 

During a fast, several physiological mechanisms occur, such as insulin levels dropping to force the body to use its stored fat for energy. 

If fasting continues for an extended period (typically more than 12-16 hours), the body’s primary source of energy shifts from glucose to ketones. Ketones are molecules produced from the breakdown of fat in the liver. The increase in ketone levels is known as ketosis and is a natural metabolic process.

For those who have tried caloric restriction (reducing calorie intake without malnutrition), intermittent fasting can provide some of the benefits associated with it. And yes, IF can lead to a reduction in overall calorie intake, which is why some people use it to achieve fat loss. 

What are the Different Methods of Intermittent Fasting?

There are several different methods of intermittent fasting, each with its own approach to cycling between eating and fasting periods:

  • Spontaneous Meal Skipping: This is a more intuitive and less restrictive way to practice intermittent fasting. With this approach, you only eat when you genuinely feel hungry and skip meals when you’re not hungry. 
  • 12 Hour Fasting: Restrict your eating to a 12-hour window each day and fast for the remaining 12 hours. Note that this includes the time you spend sleeping.
  • 14/10 Method: This is similar to 16/8 fast but with a 10-hour eating window. Let’s say you decide to start eating at 10:00 am. With a 10-hour eating window, you would finish your last meal or snack by 8:00 pm. You would then fast for the next 14 hours until 10:00 am the next day.
  • 16/8 Method: Eat within an 8-hour window and fast for the remaining 16 hours.
  • Alternate-Day Fasting (ADF): This typically involves eating normally on one day followed by a day of fasting or very low-calorie intake (about only 500 calories) on the next. For example, you might eat normally on Monday and then fast on Tuesday, continuing this pattern.
  • 5:2 Method: Eat normally for five days of the week and restrict calories on the remaining two non-consecutive days. For women, it’s recommended to aim for around 500 calories on fasting days. For men, the suggested range is about 600 calories. 
  • 24-Hour Fasting: Fast for a full day, often from dinner to dinner or lunch to lunch.
  • Eat-Stop-Eat Method: Fast for a full 24 hours once or twice a week.
  • Extended Fasting: This involves fasting for more extended periods, typically ranging from 48 to 72 hours or even longer.

It’s important to choose a method based on your lifestyle. What does your daily schedule look like? Do you have commitments that may affect how much time you’ll realistically have for intermittent fasting? 

More importantly, consult with a healthcare professional before starting any fasting regimen, especially if you have underlying health conditions.

How Do I Choose the Right Fasting Method for Me?

Choosing the right fasting method depends on your lifestyle, preferences, and health considerations. 

Beginners can start with spontaneous meal skipping, 12/12, or the 14/10 time-restricted approach, which might be more manageable. 

However, if weight loss is your goal, the 16/8 method could be more effective. 

Those seeking a more gradual approach could try the 5:2 method, while individuals comfortable with longer fasts might explore 24-hour or extended fasting. 

Some individuals struggling with obesity, metabolic syndrome, or insulin resistance may consider extended fasting as part of a comprehensive weight management plan.

What are the Potential Health Benefits of Intermittent Fasting?

Intermittent fasting has been associated with various potential health benefits, including:

  • Weight management: Intermittent fasting can help control calorie intake, leading to weight loss and fat reduction. Evidence from multiple reviews suggests that intermittent fasting helps adults with obesity lose weight successfully and achieve other metabolic benefits (4). 
  • Improved insulin sensitivity: Since you’re reducing the frequency of your meals and snacks, you’ll have fewer dips and spikes in your blood sugar. This can increase insulin sensitivity, which reduces the risk of type 2 diabetes.
  • Cardiovascular health: Intermittent fasting may lower blood pressure, improve cholesterol levels, and lower the risk of heart disease.
  • Cellular repair: Fasting triggers autophagy, a process that removes damaged cells and promotes cellular renewal. Research shows that besides calorie restriction, fasting is a potent stimulus for autophagy to occur (5). 
  • Brain health: Fasting might support brain function by enhancing neural pathways and reducing the risk of neurodegenerative diseases. A review on alternate-day fasting found that intermittent fasting reduces inflammation in the brain, protecting the brain from aging and disease (6). 
  • Cognitive function: Many individuals report improved cognitive performance and mental clarity during fasting periods.
  • Longevity: In animal studies, intermittent fasting has demonstrated some positive effects on lifespan and aging-related markers. For example, an older study reports an increase of up to 80% in the average lifespan of rats that maintained an alternate-day fasting regimen (7). 
  • Cancer protection: Preliminary research indicates that fasting could inhibit the growth of cancer cells and improve the effectiveness of cancer treatments.
  • Gut health: Intermittent fasting might positively impact gut microbiota, contributing to digestive health. A study in Frontiers in Microbiology revealed that IF increases the anti-inflammatory bacteria Lactobacillus and Bifidobacterium while also decreasing disease-causing bacteria (8). 

There may be promising research, but keep in mind individual responses to fasting can vary. This is why speaking with a healthcare provider is a must before getting started. 

Is Intermittent Fasting Safe for Everyone?

Intermittent fasting may not be suitable for everyone. 

While many people can safely practice it, certain groups, such as pregnant or breastfeeding women, those with a history of eating disorders, or those with underlying medical conditions like diabetes or heart issues, and taking medications, should proceed with caution. 

How to Do Intermittent Fasting 

To practice intermittent fasting effectively, follow these steps:

  • Choose the right fasting method: Decide which intermittent fasting approach suits you best, taking into account your daily routine, preferences, and health goals.
  • Set fasting windows: Determine the duration of your fasting and eating windows. For example, in a 16/8 method, you might fast for 16 hours and eat during an 8-hour window.
  • Gradual start: If you’re new to fasting, begin with shorter fasting periods and gradually increase them over time. Remember that it can be a significant change in your eating pattern, and your body may need time to adapt without getting too stressed.
  • Stay hydrated: Drink water, herbal tea, or other non-caloric beverages during fasting periods to maintain hydration. By doing so, you avoid or minimize symptoms like dizziness, headache, and low energy. 
  • Balanced nutrition: Focus on nutrient-dense foods during eating windows to support your body’s needs. Incorporate lean sources of protein and healthy fats. Whole foods include fish, poultry, beef, pork, avocados, nuts, and seeds. 
  • Control portion sizes: Avoid overeating when breaking your fast; listen to your body’s cues of hunger and fullness. Eating too much after a period of fasting can lead to discomfort, bloating, and digestive issues.
  • Meal planning: Plan meals and snacks ahead of time to avoid impulsively breaking your fast with unhealthy choices. Knowing what you’re going to eat in advance saves time and minimizes stress, especially for those with busy schedules. 
  • Stay active: Incorporate regular physical activity into your routine, adjusting based on energy levels during fasting. You can definitely exercise while practicing IF, although you need to find the right timing and intensity that won’t leave you exhausted and extremely hungry. 
  • Sleep and stress management: Poor sleep and high stress levels can lead to increased cravings for high-calorie, sugary, and processed foods. This can make it more challenging to adhere to an intermittent fasting regimen.
  • Track your progress: Monitor changes in weight, energy levels, and other health markers over time. Also, stay patient. Give your body time to adapt to this new eating pattern. 
  • Be flexible: Adjust your fasting schedule as needed to accommodate changes in your routine or health circumstances. You’re always free to do a longer or shorter fast depending on your current situation. 

Remember that the key to successful intermittent fasting is finding an approach that works for you. It has to be something you can sustain in the long term. Your health and well-being are a priority throughout your intermittent fasting journey! 

Frequently Asked Questions

Can I drink water during intermittent fasting?

Yes, you can drink water during intermittent fasting. Staying hydrated is important, and water, herbal teas, and other non-caloric beverages can help you stay hydrated without breaking your fast. Avoid beverages with calories, like sugary drinks or milk, as they can disrupt the fasting state.

Is intermittent fasting effective for weight loss?

Intermittent fasting can be effective for weight loss. By reducing insulin and creating a calorie deficit during fasting periods, your body utilizes stored fat for energy, contributing to weight loss. Additionally, the potential benefits of improved insulin sensitivity and reduced calorie intake can further support weight management goals.

How often should I intermittent fast?

The frequency of intermittent fasting depends on your goals, lifestyle, and personal preferences. Some people practice intermittent fasting daily, while others opt for a few times per week. Focus on finding a routine that works for you and allows your body to adapt over time. If needed, consult a doctor, registered dietician, or nutrition and fitness coach for further guidance. 

Will I lose muscle if I fast?

Fasting alone might lead to some muscle loss, but the extent depends on factors like the duration of fasting and your overall protein intake. However, combining fasting with regular resistance training and adequate protein consumption can help minimize muscle loss and support muscle maintenance during periods of fasting.

Can I exercise while fasting?

Yes, you can exercise while fasting. Light to moderate aerobic exercises like walking, jogging, and yoga are generally well-tolerated during fasting. However, more intense workouts might be better scheduled around eating windows to ensure you have enough energy and nutrients for optimal performance and recovery.

How long does it take to see results from intermittent fasting?

Results from intermittent fasting can vary widely depending on factors like your starting point, chosen fasting method, diet quality, and exercise routine. Some people might notice changes in energy levels and hunger control within a few days, while noticeable changes in weight, body composition, and other health markers might take several weeks to a few months. Consistency and patience are keys for long-term success.

Do I need to count calories during intermittent fasting?

Counting calories during intermittent fasting is not always necessary, especially if your main goal is to manage hunger and eat balanced meals. Fasting naturally restricts your eating window, which can help control calorie intake. However, if your goal is weight loss or specific body composition changes, tracking calories might provide additional insights into your progress and help you maintain a calorie deficit.

Will Intermittent fasting affect my metabolism?

Intermittent fasting can influence metabolism, but the effects can vary. Some research suggests that it might help improve metabolic health by enhancing insulin sensitivity and promoting fat oxidation. However, for long-term success, focusing on balanced nutrition and maintaining an active lifestyle alongside intermittent fasting will help support a healthy metabolism.

The Bottom Line

Whether you do spontaneous meal skipping, a 12-hour fast, 16/8, ADF, or another type of fasting approach, intermittent fasting is a sustainable and flexible diet strategy for many. It may be backed by research, but always approach fasting from a balanced perspective. 

With that, keep in mind that your response from another person’s response might be different. Track your weight and other metrics depending on the goals you have set. Reach out to a health professional, especially if you are diagnosed with a condition that requires special considerations.

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Evidence based

This article is based on scientific evidence, written and reviewed by experts.

The founders of Ketogenic Buddies are health care professionals. As we grow, we include other qualified subject matter experts as part of our content team.

This article contains scientific references. The numbers in the parentheses (1, 2, 3) are clickable links to peer-reviewed scientific papers.