What Is Intermittent Fasting?

Intermittent fasting is a dietary approach that focuses on time-restricted eating - fluctuating between specific periods of fasting and ‘allowed eating’ time. Fasting encourages our body to rely more on burning fat for fuel, releasing ketone bodies into our bloodstream.

At first glance, fasting may seem a bit odd, but in all reality, fasting has been around for a long time.

When you think about it we often fasted before the times of refrigeration and convenience food. Only in the past 50-60 years has it become more common to eat continually throughout the day, which isn't always a good thing. Overeating and imbalanced diets play a large role in the development of chronic diseases such as diabetes and heart disease. 

Intermittent fasting mainly focuses on when you eat but what you eat during your non-fasting period is just as important.

Are There Health Benefits from Intermittent Fasting? 

Intermittent fasting can teach us some important lessons when it comes to crafting intentional eating patterns and building healthy eating habits like: 

• Reducing your consumption of sugars and refined grains 
• Eliminating mindless snacking during the day and before bed 
• Avoiding making unwanted food choices and planning a healthy diet 

Along with building healthy habits, some studies suggest that adopting this practice may help with weight loss, improve memory and mental performance, cardiovascular health, type 2 diabetes, and the effectiveness of cancer treatments (1,2). 

Is it Safe?

Fasting may not be appropriate for individuals with type 1 diabetes, pregnant and breastfeeding women, elderly individuals with eating disorders, and those who need regular food intake to take medications (3).

If you have a medical condition, talk to your doctor to make sure it's safe to try intermittent fasting as long periods of fasting can lower your blood sugar levels and leave you feeling lightheaded, dizzy, with headaches and/or nausea.  

6 Intermittent Fasting Methods

One of the first styles of intermittent fasting, the 5:2 approach, was popularized by British journalist Michael Mosley in late 2012 in the UK and Australia, it was during this time that intermittent fasting began to gain popularity as a trendy diet thus prompting scientists to begin investigating the potential health effects. 

There are many types of intermittent fasting. Some people intermittent fast for prolonged periods of time, aka on a recurring basis a few times a week, and others try out periodic fasting, only practicing fasting or fasting-mimicking diets lasting for up to a month.

There isn't a right or wrong answer when it comes to how long you practice intermittent fasting as it all depends on your health goals, lifestyle, what you eat, and current health condition. 

These are some of the most common intermittent fasting methods that have been used in scientific studies investigating the potential health benefits of fasting (4,5):

1. The 5:2 Method  

5:2 intermittent fasting consists of reducing or limiting your caloric intake to 25% or less of your total calories for two non-consecutive days within the same week. 

This usually means eating between 500-600 calories, but if you're unsure of what you're total caloric intake per day is try out our free calculator, as this will help you calculate what 25% of your daily needs would be: 

 

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• Pros: If you tend to stay busy during the day this might be a great way to try out intermittent fasting as you're body may already be used to a slight caloric deficit. You can also focus on eating normal healthy meals on your non-fasting days, meaning you may not have to stress about being in a continuous caloric restriction and reduce the risk of extreme hunger or other issues that could arise with restrictive dieting. The 5:2 fast has also been called an alternate day fast and has been shown to be effective for short-term weight loss within normal weight and overweight individuals (6). 

• Cons: Many people experience headaches and irritability when drastically cutting their caloric intake.  Weight loss associated with this style has only been studied short-term and may plateau within 6 months so focusing on weight maintenance and eating a well-balanced diet along with regular exercise should be prioritized with any fasting regime (6).

2. The 16:8 Time-Frame 

This consists of prolonging your nightly fast and consuming an early dinner then not eating anything until lunch the next day. You eat all your meals within an 8-hour window. For example, you could eat between noon and 8 p.m, 9 a.m. to 5, or 10 a.m. to 6 p.m.

• Pros: A prolonged extension of your nightly fast is flexible and most of it is done while you are sleeping. This style can be done every day or once or twice per week depending on how you feel and your health goals. The hours are flexible and adaptive for any kind of lifestyle or work schedule. 
• Cons: If you're having trouble cutting out late-night snacking or setting aside junk food, this may be a harder fasting style to implement. Might not be the best style to attempt first hand, but something to work up to. 

3. The 12:12 Method 

Similar to the 16:8 approach this approach, except you only fast for 12 hours, so you could eat dinner at 7 pm and then consume a normal breakfast after 7 am the next day.  This may be easier for anyone looking to try out intermittent fasting as it's not as extreme as the 16 hours; your nightly routine and sleep schedule may already cover a 12 hour period. 

It's an ideal amount of time to give your body a break from digestion and focus instead on resting and repairing, completing processes like autophagy in which your cells go through and clean out any unwanted waste products. 

• Pros: You may not have to put much effort into this fast, considering it's just an extension of your nightly fast. A good option for beginners. 
• Cons: There aren't many cons to this style of fasting, beyond taking the steps to plan out healthy meals during your non-fasting period so you aren't feeling hungry before bed. 

4. The 24 Hour Fast

A 24 hour fast involves completely abstaining from eating for a full 24 hours. This is usually done 1-2 times a week, but you should continue to drink non-caloric fluids during your fasting period to stay hydrated such as water and unsweetened tea. For example, you'd eat dinner at 7 pm then fast until dinner the next day, around 7 pm as well. 

• Pros: The longer the fast may encourage your body to adapt more quickly to burning fat as fuel (7). Can do this during the workday or week and save time and money not having to meal prep or worry about breakfast and lunch for a day a week. 
• Cons: This type of fasting can cause fatigue, irritability, and headaches, although these tend to go away after prolonged practice, starting with a 12-16 hour fast and working up to a 24 hour fast may help reduce these symptoms which could be caused by dips in your blood sugar. Always consult your healthcare provider if you have serious medical conditions or diabetes before attempting to prolong fast, as these practices may not be safe for everyone. 

5. Time-Restricted Eating

This type of intermittent fasting restricts eating hours to a 7-hour window or less, for example, eating between 1 pm and 6 pm or 11 am to 6 pm. Some will even restrict their eating window to a 4-hour slot in the 24-hour day. But remember, the more narrow your time frame for fueling your body, the more consistent and conscious your food choices should be. Focus on eating nutrient-dense foods vs empty calories or processed foods. 

There isn't a set time frame for how often this should be done, but like the other caloric restricted fast 1 or 2 non-consecutive days a week may be a healthy option.  

• Pros: Still reap the potential benefits of intermittent fasting without having to completely skip a full day of meals. 
• Cons: You'll have to be even more intentional as to what you eat during your non-fasting period to prevent unwanted symptoms and feelings of extreme hunger. 

6. Reduced Caloric Fasting 

Similar to the 5:2 method, except this method has you reduce your caloric intake to 30% of your normal needs for 4-5 days consecutively before returning to your normal eating cycle.

This type of cycle isn't meant to be repeated week after week, but rather followed once a month or a few times a year. 

• Pros: You only fast for 4-5 days then return to building a balanced diet vs continually fasting each week.
• Cons: You may not reap the benefits of fasting from this method as there is not enough scientific evidence to say this style of fasting is more effective in terms of weight loss vs sustaining a healthy caloric deficit to lose weight. 

6 Intermittent Fasting Tips for Success and How to Start 

When starting a new healthy habit, it's important to think about what challenges you may face or barriers that may arise during the process. 

This is actually a crucial step in planning SMART goals, a common tool used by health coaches to help clients set achievable goals that last long term. When it comes to intermittent fasting there are a few common challenges or questions that tend to arise: 

• What do I eat during my non-fasting period?
• What happens if I feel dizzy or nauseous?
• Is intermittent fasting safe? 
• How long should I intermittent fast for? 

1. Know Your Why and Look At Your Current Nutrition

Think about what you'd like to accomplish from adopting an intermittent fasting practice: 

• better eating schedule 
• manage blood glucose 
• weight loss
• create intentional eating habits like eating more mindfully

2. Choose a TimeFrame That Fits Your Lifestyle

If you've consulted with your primary care practitioner and/or Registered Dietitian and decided fasting seems like a good choice for you, get as specific as you can when it comes to choosing a style of fasting and timeframe.

There are many types of fasting as your read about so sit down and take a moment to look at your week. Consider your work schedule, sleep schedule, and lifestyle when deciding what type of fasting schedule you’d like.

3. Start Small 

If you’re just starting intermittently fast, start small! 

Pick 1 day a week to try out the style that may work the best for you. Short-term fasting can be a more sustainable approach for many people. Start with an overnight 8-12 hour fast as you can easily work this into your schedule and build up to longer fasting days. 

If you do extended fasting, try choosing a day of the week or period of time that you don’t need to be very active or deeply concentrate.   

4. Stay Hydrated 

Even during your fasting periods, you want to make sure you're staying hydrated with noncaloric fluids, especially water. You can also include unsweetened herbal teas and sparkling waters.

The recommended amount of water to drink per day is half your body weight (in pounds) in ounces. Meaning if you weigh 160 lbs you want to aim for a minimum of 80 ounces of water a day

5. Start a Meal Prep Routine 

If not planned correctly, intermittent fasting can still lead to weight gain. 

Feeling starved during your fasting period might make some people more prone to binging behaviors when they’re not fasting. And eating more calories than what your body burns will lead to a long-term increase in body fat even if you consistently fast for 12-16 hours each day. 

In other words, if you are having trouble maintaining your hunger and end up going completely rogue on your non-fasting periods, you could end up gaining weight. Meal plan ahead to ensure you have nutrient-dense food choices during your non-fasting periods and stay within your calorie limit each day. 

Intermittent fasting doesn’t replace healthy eating, you'll want to consider what kind of meal plan you enjoy during your non-fasting periods. Do you want more vegetarian, vegan, or plant-based meals? Looking to go keto? Or want to meet somewhere in the middle with a flexitarian diet? 

Whatever you decide, plan out what you want to eat during your non-fasting period. 

6. Focus on Balanced Meals  

The quality of your food is crucial and balancing your blood sugar can be a key to success when intermittent fasting. Meal plan ahead to ensure you make nutrient-dense food choices during your non-fasting periods.

Make sure you’re continuing to get all of the nutrients you need to fuel your body through fasting!

Eating meals consistently within your non-fasting period that are balanced with healthy whole foods, proteins, and fats to keep you full and satisfied while minimizing things like processed sugars and processed carbohydrates. 

You can also try intuitive eating that removes the focus away from calories and willpower and focuses your efforts on getting in tune with what your body needs to thrive - regardless of what time of day it is or when your next approved eating window is.

Whatever your reason for wanting to intermittent fast, remember to incorporate basic nutrition principles including calorie control and a balanced diet to set yourself up for success. 

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