By: Lisa Spriet, Registered Dietitian

Diet trends come and go and while we at NutriProCan don’t subscribe to any ‘diet dogmas’ or specific diets unless clinically indicated, we have jumped on the intermittent fasting bandwagon with some clients. Why? Two reasons: 1) The human body is built to go long periods of time without eating and 2) both recent studies and clinical experience with our clients have shown some potential benefits. 

That being said, intermittent fasting is NOT for everyone and the research in humans is just getting started. Additionally, we now see the emergence of other types of fasting, such as time restricted eating, fasting mimicking diets and some other fairly over-the-top interpretations of fasting, such as extended fasts, water fasting, air fasting… the list goes on. 

In this article, we’ll focus on a few of the most common types of fasting and let you know what they are, if and what the potential benefits are, what the potential risks are, and finish with a guide to choosing, planning and executing each type of fasting. 

What is Intermittent Fasting and Time Restricted Eating?

In short, fasting is for going extended periods of time without eating. There is no true, scientific definition, but here is an overview of each type:

Intermittent Fasting (also known as IF)

This type of fasting is going for 12+ hours without eating, and for some this could be 36-48 hours without eating. IF can be done on an irregular basis or regular basis and depending on the type of fast, it may or may not include non-caloric beverages such as water, black coffee and tea. 

Time Restricted Eating

With this type of fasting, there is a specific eating window and specific non-eating window, which are usually repeated on a regular basis, if not every 24-hours. Examples of this would include ratios of eating hours to non-eating hours of 12:12, 14:10, 10:14, 8:16, and so on. For those who observe Ramadan, you’re likely very familiar with this type of fasting. 

Fasting Mimicking or Modified Fasting

This type of fasting includes periods of usually a few days where calories are very restricted, usually to less than 750 kcal per day. This can be repeated on a weekly, monthly, quarterly or yearly basis. This type of fasting was created by and has subsequently been studied by a key researcher in the field, Dr. Valter Luongo. 

What are the Potential Benefits of Fasting?

This is where you should ask yourself – what are my health and performance goals? Just because something is good for one person or health outcome, doesn’t mean it is good for all, or good for you. As Laurent Bannock says ‘you could, but should you?’ 

Well, let’s see and dig into the potential benefits for each type of fasting. 

1)Health and longevity

Most of the data that explores intermittent fasting on health and longevity has been done in animal models, which is hard to translate to humans. In animal models, both intermittent fasting and time restricted eating, combined with decreased caloric intake (usually as a result of fasting) does show benefits in terms of reducing cellular signs of aging and perhaps even extending lifespan. Research on the Fasting Mimicking Diet have shown molecular benefits that may promote anti-aging and longevity, but the actual effect on aging and lifespan is not yet known. 

2)Weight loss

Most human studies show a moderate weight loss ranging from 2.5-9.9%, most of which is fat loss (versus muscle or other tissue), from various types of fasting. However, most of these studies are less than 6 months in duration, the average being 3 months, so the long-term effects are not known and are likely dependent on how long one can continue with the fasting regime. All three types of fasting have shown short-term benefits for weight loss. 

3)Blood sugar and insulin levels (diabetes risk)

When we fast, our blood sugar levels initially drop, which tells our bodies to start using stored glycogen and fat for energy. Lower blood sugar levels also leads to lower insulin levels, and while insulin is an important hormone for metabolism and health, having too high of levels, combined with high blood sugar levels, increases your risk for diabetes.  It seems intuitive that fasting would lower your blood sugar and insulin levels, which it does in the short term. However, the real question is whether continual fasting regimes lead to long-term benefits on blood sugar levels, insulin levels and risk of type two diabetes. All three types of fasting have shown beneficial effects on blood sugar and insulin levels over a 3-6 month period. These effects seem to be seen even if the study participants don’t lose weight, which is pretty cool. Additionally, some studies have shown that intermittent fasting can even correct type two diabetes if the fasting leads to weight loss. 

4)Digestive health

The theory behind fasting and improved digestive health is that when our gastro-intestinal tract is empty, it is more effective at cleaning and repairing. While this is partly true, there really is very little research looking at the effects of fasting on the gastro-intestinal tract. What do we know? If you are prone to reflux (heartburn), stopping eating 2-3 hours before bed can help manage symptoms. We also recommend fasting or consuming only liquids when there is a lot of gastrointestinal inflammation happening, like with gastritis or diverticulitis. At this time, intermittent fasting for overall improvements in digestive health just isn’t founded in science, but some people find it does help (speak to a dietitian if you are having digestive issues before trying this!). 

5)Sports performance

We are seeing more and more athletes experiment with intermittent fasting. To date, there is no research that supports fasting as having a benefit on performance, unless perhaps it leads to fat loss, which may have a benefit in some sports for some athletes. Energy and nutrients are needed for top performance! Where a bit of research is starting to emerge is using low carbohydrate availability training, which may have some benefits for endurance athletes. Note however, that this is not NO carbohydrates and that having low carbohydrate  foods (i.e. having proteins and/or fats) can lead to these benefits, as long as the relative amount of carbohydrates is low as compared to energy needs. If you’re a distance athlete looking at trying this, speak to a dietitian first. 

What are the Potential Risks of Intermittent Fasting?

I really believe the risks of various types of fasting are really overlooked both by research and practitioners. 

Risks include:

1. Low energy levels
2. Macro (protein, carb and fat) and micronutrient deficiencies
3. Alterations in hormone levels, including increased cortisol (stress hormone) levels and changes in female hormones, which may also affect fertility
4. Increased risk of disordered eating and/or recurrence of disordered eating
5. Hypoglycemia (low blood sugar levels), especially in those who are on medication for blood sugar control
6. Trouble sleeping and anxiety, likely due to changes in hormone levels

Because of the risks we HIGHLY recommend that you speak with a professional before trying any type of fast, including intermittent fasting.

Okay, so maybe you’re ready to give fasting a try. Here is our guide for those new to fasting. Before you start, take these two steps:

1. Speak to a professional. Honestly, make sure that fasting is safe for you!
2. Nail the basics of healthy eating. Fasting is not a cure-all and overall good nutrition matters.

Five Steps to Intermittent Fasting:

1. Pick the type of fast you’ll try. We recommend starting with time-restricted eating before jumping into longer fasts. 
2. Pick an eating window
   1. Start slowly, like a 12:12, where you will not eat for 12 hours, which can include sleeping time
   2. Decide on the day(s) of the week you’ll try your fast. To start, perhaps try one day per week and then increase from there. 

3. Do the planning and prep
   1. I know you’re thinking ‘prep for what? I’m not eating anything, what do I need to prep?’ Make sure that you’ve done your food prep for after your fast. Prepping food while fasted is not recommended! Additionally, if you are doing a fasting mimicking diet, you’ll need to plan for about 750 kcal of low carbohydrate meals or snacks to have throughout the day.
   2. Make sure that you have adequate fluids ready to go. Make herbal teas, and so on, which are still fine to have with intermittent fasting.
   3. In terms of planning, plan your fast around activities or work (no one wants a hangry surgeon or pilot), as well as when you take medications that may require food. For females, you may not want to try your first fast during your menstrual cycle. 
4. Execute! Here are a few ground rules:
   1. Drink adequate fluids. This can include black/calorie-free teas and coffee, in addition to water. 
   2. Moderate physical activity, especially if you’re new to intermittent fasting. Unless you are an athlete, training in a fasted state is fine and may have additional benefits in terms of fat loss. However, if your workout is lack-luster without eating before, perhaps only plan on doing light activity and saving your harder training sessions for when you have food energy available. 
   3. Don’t plan to fast for too long after physical activity, especially if you’re doing weight resistance training with the goal of increasing lean mass. 
   4. Break your fast ANY time. If you feel light-headed or unwell, don’t hesitate to break your fast. Know when your body has had enough.
5. Reflect, revise and re-plan
   1. How did your fast go? Did you pick a good time of day or day of the week? Was your fast too long? Too short?
   2. Did you end up so hungry that you ate everything in sight after your fast? Perhaps some adjustment is needed. 
   3. Keep in mind that sometimes we need to try a few times before we get comfortable with fasting, so don’t write it off altogether if the first fast didn’t go as planned
   4. What are your next steps? Are you going to introduce a weekly longer fast? Or perhaps shorten your daily eating window to 10, 8 or 6 hours. 

Intermittent Fasting FAQs

1. Can I still drink coffee when intermittent fasting?
   1. Yes! Though it isn’t technically fasting, you can still get most of the benefits of fasting if you have black coffee or tea. Hydrating is important, so have lots of water as well.
2. Can I workout while intermittent fasting?
   1. Yes, but this depends on you. When you’re first starting, take it easy on fasted workouts. If you are an athlete or looking to increase lean muscle mass, fasted training likely isn’t the best choice for you. If you’re looking to lose weight or improve blood sugar levels, fasted exercise may be beneficial. 
3. What should I eat to ‘break’ my fast?
   1. Good food. For real, fasting is not an excuse to then down a large pizza and sundae. Not only are you not getting energy while fasting, but you also are not getting micronutrients either. Choose a healthy, well-balanced meal with adequate protein, healthy low-glycemic carbs such as veggies and whole grains, and healthy fats. A meal like this will also leave you satiated and less likely to overeat