Intermittent fasting has caught on in a way I honestly didn’t expect. I think part of its success is that the concept is so easy to understand, and do. There is no prep required – you can start today if you wanted to. It’s also super popular in the keto diet community…which is as popular and controversial as ever.
However, we need to talk about the fact that there is a healthy – and a less healthy – way to do intermittent fasting. As a dietitian, you know which one I’m about… so let’s talk about how to do intermittent fasting the healthy way.
What is intermittent fasting?
Intermittent fasting, simply put, is cycling periods of eating and not eating. We all already do this when we sleep – intermittent fasting just takes this one (or three!) steps further.
Types of intermittent fasting
- 5:2 This type of fasting involves eating less than 500-600 calories on two days a week and eating ‘normally’ the other five days.
- Alternate day This type of fasting means only eating every second day. Another form of this is Eat-Stop-Eat which does two 24 hour fasts each week. I’m not a huge fan of this one as it is hard on your body and might not have much benefit.
- 16:8 This type of fasting – which seems to be most common right now – is where you extend the overnight fast to 12, 14 or 16 hours, shrinking your daily eating window in kind.
How to do intermittent fasting, the healthy way
Before I go any further, I want you to know that if you have any pre-existing health condition or you are on medications, you need to talk to your doc before you start intermittent fasting. Dietitian’s orders!
In my opinion, successful intermittent fasting has a lot to do with what you eat when you’re not fasting. Surprised? Here’s why.
- If you are eating less often, you put more pressure on what you’re eating to be nutritious enough to meet all of your needs. The tighter your eating window is, the more nutrient-dense every single morsel you eat needs to be. If you eat a lot of hyper-processed or refined foods, intermittent fasting can result in a lot of deficiencies that hinder optimal cellular function. Like your hair, skin and nails looking amazing? Want to still crush your workouts? Stay nourished, my friend!
If you are taking a 5:2 approach, food choice matters a lot on your minimal days. It’s pretty easy to make a single food choice that rings in at 500-600 calories these days. For example, you could eat one cheeseburger all day long and feel awful – or a kale salad with hemp dressing, some raw nuts for a snack, and a small green protein smoothie at breakfast. Much better!
- What’s more, if you consume a lot of refined flour and sugars, or skimp on protein, fiber or healthy fats at a meal, your blood sugars will be pretty erratic, leading to blood sugar lows that mess with your appetite and make you hangry as hell.
First step to healthy intermittent fasting: balance your meals well to keep your blood sugars balanced for fasting
What does this look like? It’s simple: you’re going to want to make the bulk of your intake whole, single ingredient plant foods like hemp seeds, green vegetables, berries and legumes. Eating more plants will ensure that you are getting plenty of vitamins, minerals and phytochemicals that flood your cells with the nutrition they need. White flour, granola bars and sweetened coffee drinks won’t cut it.
When it comes to meal time, make half your plate vegetables, get 15-30 grams of protein, include healthy fats like olive oil, nuts, seeds or avocados and then a moderate amount of high fibre whole grains like kamut, barley or buckwheat. The combination of fat, fibre and protein will activate hormones that moderate appetite while they help elongate your blood sugar curve and keep you from getting the hangries later on.
If this is not what your meals typically look like – or your diet is typically more processed or high in sugar, I recommend you work on your diet for at least 1-2 weeks before attempting intermittent fasting. Set yourself up for success by eating more plants…I’ve got a cookbook to help you do just that.
Second step to healthy intermittent fasting: start slow and pay attention to your body
I don’t recommend that you start fasting with a more intense technique such as alternate day fasting or 16:8. The reason for this is that the body loves routine and needs time to adapt to new feeding patterns happily. Heck, even your gut bacteria appear to be on a daily rhythm. So don’t freak them out, okay?
Instead, take a more moderate approach, such as not eating anything after dinner and maintaining the fast for 12 hours. Not eating between 7:30PM and 7:30AM? Not such a big deal! If this agrees with you, and you feel a benefit, then try to extend to 14 hours. Really tune in to how you’re feeling. Energized…or sluggish? Relaxed in your appetite…or starting to get preoccupied with food? Blood sugars going down…or up?
It’s important to remember that we all have individual constitutions and metabolisms. Just because it worked for your partner, or coworker, doesn’t mean your body will respond in the same way. Honour that.
For many women, I recommend you cap it at 12-14 hours as our bodies are designed to be extra sensitive to external stressors. In one trial in women with obesity, 24 hour (such as alternate day type) did not appear to improve insulin sensitivity.
However, if you’re still feeling good, you may wish to continue at 12-14 hours or extend the fast to 16 hours, which means that all of your eating will occur in an 8 hour window.
Best hours for intermittent fasting
I am a fan of a flexible and realistic eating window. There is no sense in setting your dinner time at 6PM if you are rushing in the door from work at 5:45. What’s more, setting the window too early can make it difficult to socialize, if that is a big part of your habits.
However, if you can during the week, choosing hours that can become more of a routine, at least Sunday – Thursday, can help your body adjust and expect the behaviour. So, if you like to eat dinner at 7PM, set the beginning of your fast window to 8PM and then continue it for 12-14 hours. If you eat later on Saturday night, or sleep in a bit more on Sunday, not to worry. Just modify your window accordingly.
Some may advocate for earlier or later windows to account for seasonal variation or to be more in line with our natural circadian rhythms and if that works for you – there is no harm in it!
Common Questions about Intermittent Fasting
Best foods for breaking an intermittent fast?
As I’ve mentioned above, what you eat during your eating window matters. Make your breakfast nutrient-dense, whole food and not too high in sugar. In fact, it might be most important that breakfast be high in protein, fibre and healthy fats and lower in starches and sugars to help send a strong message to your metabolism to keep blood sugars in check. My easy chickpea scramble is a five minute meal that checks all of those boxes.
It’s also important that you prepare to break the fast ahead of time. If your eating window begins after you are already at work, make sure that you are preparing a healthy breakfast and taking it with you so you have a solid, nutrient-dense meal waiting for you when you are ready to eat. A muffin from starbucks isn’t your best choice.
What’s more, don’t break your fast with an all out feast. Plan a meal size that is normal for you. Enjoy it and give yourself at least an hour before eating again so you can truly assess hunger and avoid A) overeating and B) putting too much of a load on your digestive tract.
Can you eat or drink during your fasting hours?
Fasting hours are meant to be without food but you should, by all means, stay hydrated. Coffee and tea are no problem either. However, when you eat, blood sugars rise and the process that is providing energy to your body will shut down. Carbohydrates and proteins will cause more of a blood sugar rise than fat. As a result, health professionals who work a lot with intermittent fasting seem to recommend no more than 40 calories, preferably fat. So if you want to drink your coffee with a spoonful of almond or coconut butter blended in, that is okay too.
Common mistakes in intermittent fasting
Pushing the fast too far and not properly nourishing yourself
For those with a history of dieting or disordered eating, I caution against intermittent fasting. The reason for this is that intermittent fasting can become one more way of exerting control over your intake – even if you feel you have a healthy relationship with food – and it might encourage you to push the fast longer than is good for your body.
Pushing the fast too far can not only harm your metabolism and your relationship with food but set you up for deficiencies that might result in low energy, risk of injury for those who are active, or loss of fertility. More is not always better.
Making less healthy choices, or overeating, during your eating window
Pushing the fast too far can also have an outsized effect on your hunger, leading to less healthy choices. When you are really hungry, the body may drive your hunger for less healthy foods that are high in sugar, salt or fat.
Particularly if you are eating within an 8 hour window, it puts a lot of pressure on your food choices to get all of the nutrition your body needs in a day, including vitamins and minerals. So a half rack of ribs and garlic mashed potatoes followed by cheesecake at lunch isn’t likely to optimize your health or your experience of intermittent fasting.
Ignoring the signs that intermittent fasting isn’t right for you
I do not typically recommend greater than a 16 hour fast, and I don’t recommend alternate day fasting. I don’t care what Jack Dorsey does, it’s not healthy and I’m genuinely concerned that he has established disordered eating habits.
I also do not recommend intermittent fasting for anyone who is pregnant, breastfeeding or trying to conceive along with those who suffer from anxiety, thyroid issues or hormonal imbalance like period loss. Those with a history of eating disorders and those with type 1 diabetes or insulin-dependent diabetes should steer clear unless under specific direction from their medical team.
Signs that intermittent fasting isn’t right for you
- Dizziness, headaches + fatigue
- Difficulty concentrating
- Feeling cold all the time
- Feeling really irritable or more anxious
- Having problems sleeping
Alternatives to intermittent fasting
If you find that intermittent fasting isn’t for you…what’s next?
In my practice, I talk a lot about knowing the difference between needing to eat and wanting to eat. Because many of us have been told to eat every 3-4 hours to ‘boost our metabolism’…but what that really does is keep you in the fed state.
And now, we’ve become such a nation of snackers that some of us eat every 1-2 hours. And we probably don’t need to.
So, I recommend that you start playing with eating (mostly) when you are hungry. If you aren’t hungry in between meals, why snack? It will allow you a more natural balance between the fed and fasted state over the course of a normal day. Leaving 4-5 hours between a meal will also assist in activating your migrating motor complex (MMC) which I feel is quite beneficial for those with digestive health issues such as ulcerative colitis and irritable bowel syndrome.
You could also decide to close the kitchen after dinner, unless you feel a strong stomach hunger. You probably don’t need the extra energy. However, at the end of the day – or the beginning of it – if you’re hungry, you should eat. Full stop.