Fasting and Intermittent Fasting

20/4 intermittent fast

Intermittent fasting TiesIt seems everywhere you look these days there is a fasting challenge or information on fasting and intermittent fasting. Is this the newest trend and will it disappear the way the shake weight did and step aerobics, hip hop, abs, insanity etc. 

What is Fasting and Intermittent fasting? 

Although it’s currently trending, fasting has a long rooted tradition in many regions dating back as far as recorded history. Fasting is simply not eating or drinking calories for a specific period of time. So we all fast while we sleep, hence the term breakfast for the morning meal. Intermittent fasting is simply having a set time for feeding, and the remaining time is spent not feeding or ingesting calories. Snacking throughout the day is a fairly recent phenomenon. Growing up, my grandfather had a small farm where work was very physical and the workers needed many calories. They had three square meals prepared every day on the farm, as it was a long walk back to the house just to get a little snack. These days most work is performed sitting at a desk where it’s so easy to grab the unhealthy snack that you packed the night before. 

There are different types of fasts – dry fast, water fast, liquid calorie only fasts and  calorie restricted fasts.

Dry fasting – Is consuming no liquids at all. Some religions have dry fasting as part of their practice. From a health standpoint there is no benefit to restricting water so we won’t spend much time on dry fasting. 

Water fast – A water fast is consuming no calories and only drinking water. This can be done for any number of hours but the most common is 24-72 hours. 

Non-Caloric Liquid Fast – is consuming zero calorie liquids such as tea and coffee in addition to water. Some people feel the caffeine in coffee and tea give them more energy than a water fast. This can be done for any number of hours, but again, the most common is 24-72 hours.

Caloric-Liquid fast – this would be consuming bone broth or small amounts of vegetable juice or smoothies. Calories are kept very low 300-500 / day and the idea is to give the digestive system a break. It is often done to correct other health issues and heal the gut biome. These fasts can last from hours to multiple days as there is some nutrition being consumed. This is best done with guidance from a health practitioner. 

Restricted calorie fast – consuming a small amount of food on a fast and often specific foods to combat certain health problems. As there are some calories being consumed, these fasts tend to last longer and are used for targeting gut microbiome or specific health problems. Also, best done with guidance from a health practitioner.

Often people combine various types of fasts such as a 24 hour water fast, followed by 48 hours of Caloric Liquid fast such as bone broth and green tea. The purpose of explaining the various types of fasting is so we can discuss fasting and know if we are talking about consuming only water, nothing at all or green tea and water etc. 

Intermittent fasting is simply having a pre-set feeding window followed by a fasting window. The most common fast is to do a water fast followed by a window in which you eat. Sixteen hours of fasting and eight hours of eating, so eating between 11 am and 7 pm and not eating again until 11 am the next day. 

Fasting Benefits

One of the main benefits of all forms of fasting is decreasing insulin sensitivity. When you eat your body releases insulin. Consuming sugary foods produces an insulin spike and a resulting dip that will require more food or sugar to get your blood sugar back up. Continuous spikes and drops can lead to diabetes and increased insulin sensitivity. The more often insulin is released, the more likely your body will eventually develop a tolerance. Meaning in the future more is required to get the job done. By having a set feeding and fasting period your body can decrease its insulin sensitivity which means it will require less, going forward when it is released. 

Fasting allows a break from digestion:

Which allows your body to focus energy on other areas such as recovery and immune system health. Fasts over 24 hours are said to produce autophagy, which is a cellular clean up.

Fasting can also improve appetite regulation:

Gherlin is the hormone responsible for hunger and Leptin is the hormone responsible for feeling satiated or full. Fasting has been shown to regulate Gherlin which allows Leptin to settle as well. From personal experience fasting can shrink your stomach making it harder to over eat during your feeding window. 

Fasting can improve energy: 

Studies show that mammals tend to be energized when hungry and sedentary when fed. Many people report increases in both physical energy and mental clarity.

Fasting can improve productivity: 

When you really think about it, it’s  surprising how much time is spent thinking about what you’re going to make for meals, prepping and even eating what you just made. In a 24 hour fast, if you are only drinking liquids, for example, water and green tea – fasting can free up your time so you’re more productive at work. 

Fasting can aid in weight loss: 

Not eating creates a caloric deficit and from a willpower perspective some people find it easier to be disciplined for one 24 hour period in which you are also sleeping, than to be constantly disciplined so that all your meals still end up in a caloric deficit. From a fueling standpoint doing low intensity exercise while fasted is more likely to burn fat as a fuel which also aids in fat loss / weight loss. 

Is fasting for everyone?

 Definitely not. Women should not fast around their cycle; they need to consume more carbohydrates and iron-rich foods. Athletes should not fast unless it’s planned around their training and competitive cycle. High intensity training is more difficult when fasted so athletes may see a drop in output during training or competition when fasting. Extended fasting can be stressful and produce a cortisol response so people with high stress in their life may want to avoid fasting or limit it to times when stress is lower. 

How to get started? 

I would suggest a shorter fast to start such as an 18 hour fast with a 6 hour feeding window  18/6 or a 20 hour fast with a 4 hour feeding window 20/4. Plan in advance so you have lots of water on hand and other no calorie beverages like green tea that will not break your fast. Plan meals in advance that you will have when you break your fast. I recommend something easier to digest like bone broth to break the fast and then a balanced meal a few hours later. 

Common questions?

The most common question is, does this food or drink break a fast. Short answer yes, if it has calories it breaks your fast. If your goal is weight loss, you could break a fast with something that is not going to spike your blood sugar such as bone broth and continue to fast for weight loss or go from a water only fast into a low calorie fast and extend the time by only consuming a few calories of non insulin spiking foods like bone broth or BCAA powder etc. 

If you want the health benefits of fasting and specifically want autophagy or cellular clean up, then you need to go over 24 hours of only having water and things that do not require your digestive system to engage, like black coffee or green tea. 

My personal recommendations:

Protein Sparing Modified FastOne fast I enjoy is the protein sparing modified fast. This requires knowing your daily protein requirement. This is the most common for people who are active and weight train and is 1g per pound of body weight. I weigh 175lbs so I need around 175g of protein per day. If I am eating three times per day that is just under 60g of protein per meal. So for a protein sparing modified fast, I would take the protein I am missing for that day by fasting and split it into the other meals. For example, if I am going to fast from 4:00pm today to 4:00pm tomorrow, instead of having 60g of protein at each meal I would have 90g at my two meals today and 90g at my meal tomorrow. This makes for an easier fast as protein helps you feel satisfied. Also psychologically it is easier to spread the 24 hours of fasting into two different calendar days in which you are eating both days. I find 1:00pm – 1:00pm and 4:00pm to 4:00pm to be easier fasting windows. 

I also practice a 20 / 4 fast on days when not training. It’s an easy way to limit calorie consumption on an inactive day. Example, finish eating by 7:00pm one day and only have green tea the next morning. You will likely be hungry by noon or one pm. You only need will power until 3:00pm. I will make a light lunch and have this as I am preparing dinner. In this example a bowl of soup works great or even half a sandwich and I give the other half to my kids. 

If you are not at your desired body weight, fasting is definitely a tool that can help you get in a caloric deficit and help you burn fat as a fuel source by reducing insulin and insulin sensitivity. Additionally, it can have positive effects on both longevity and immunity. Why not give it a try! 

If you would like help with your nutrition planning or guidance with fasting Craig Boyd at Precision Athletics is able to help. You can reach out to him here at [email protected] 



Precision Nutrition Definitive Guide to Fasting



Craig Boyd is a personal trainer and nutrition coach, in Vancouver, B.C. with over 25 years experience. He Co-Founded Precision Athletics with a goal to help as many people as possible reach their health, fitness and wellness goals.

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