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What is intermittent fasting, and should I try it?

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Monica Matys
Written by Monica Matys

There have been a lot of stories in the news about intermittent fasting and time restricted feeding. Registered Dietitian Janna Guberman helps us figure out what to make of it all.

What is intermittent fasting?

It’s a dietary pattern that includes a period of time where you are fasting and a period of time where you are eating. There are a few different types. One is alternate day fasting (days when you eat regularly and others where you calorie reduce or don’t eat), whole day fasting or time-restricted feeding (ranges between 16-20 hours of fasting and 4-8 hours of eating every day).

Why have we been hearing more about these approaches lately?


There is definitely more research around these ideas. Also, there are always new trends and discussions around diets, and some of them recycle themselves as time goes on.

What does the new research tell us about when to eat?

There was a systematic review and meta-analysis of about 40 studies done on intermittent fasting that showed there was a benefit for weight loss and some other factors in the short term. Weight loss was equal to regular calorie restriction, but in terms of maintaining lean muscle mass, there may be some benefit to intermittent fasting. Because you are able to eat regularly, just at different times, there may be a chance to get more protein into your diet. Protein is important because it can help you feel fuller, longer.

If you want to try intermittent fasting, is it about eating your normal diet within a shorter period of time, or eating less within a shorter period of time?


There are a lot of variations! So for alternate day fasting, you might be eating like you normally would on some days and for the other days you might be completely fasting or eating with a caloric deficit, or one small meal. With other types of intermittent fasting, you might be fasting for part of the day, and then eating a lot more than you normally would in a shorter period of time.

Is one approach easier than another to stick to?


Some people do see intermittent fasting as a bit easier because you’re not restricting your diet every single day. You’re just eating everything in a shorter period of time, so that’s where some people see the benefit. Truly though, it’s about choosing an approach that you feel you can stick to. And to reap the benefits for your overall health, it’s always important to avoid processed foods and load up on fresh fruits and vegetables.

What happens physiologically to the body when we fast?

A number of things. After a typical meal, your body will break down starches and sugars into glucose, which is what the body usually uses for energy. When we use up our glucose stores, the body uses fat for energy. The last resort following that process is when the body breaks down muscle for protein. Keep in mind that when you don’t eat for a long period of time, you might feel hungry, fatigued and maybe even irritable. Fasting can also cause our metabolism to slow down, making weight loss harder in the long-term.

So who should try intermittent fasting, and who should avoid it?

If you are pregnant, have other health issues or a history of eating disorders, I wouldn’t recommend it. Also, people who have diabetes and require insulin, or people taking medications requiring them to eat at certain times during the day, should avoid intermittent fasting.

For a healthy diet, I would personally recommend focusing on eating balanced meals, and snacks if needed, throughout the day, everyday. But if you are someone without any health conditions, and you haven’t had success with other weight loss strategies, you could try intermittent fasting. Just be sure to consult with a Registered Dietitian to make sure you are doing it safely.

* This interview has been edited for length and clarity.

About the author

Monica Matys

Monica Matys

Monica Matys is a Communications Advisor at Sunnybrook.

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