Fitness Facts: Intermittent fasting

January 08, 2020 / by / 0 Comment
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By Liz Cook
Registered Dietitian, Canyon Health and Wellness Clinic

It’s January, which means pretty much everyone is re-evaluating their eating habits. You probably hear various terms, such as intermittent fasting, keto and vegan, and maybe even wonder if you should try them. I always recommend getting all the facts before making any major changes, so let’s dive into intermittent fasting.

What is intermittent fasting?

Intermittent fasting is essentially having set time periods when you eat and set time periods when you fast (don’t eat). Intermittent fasting dictates specifically when you eat, not necessarily what you eat.

There are a few different approaches to intermittent fasting:

  • Time-restricted fasting: This is the most popular form of intermittent fasting, which involves having set hours of the day when you eat and set hours of the day when you fast. The most commonly practiced version is an eight-hour eating window paired with a 16-hour fasting interval – for example, eating between 11 a.m. and 7 p.m. However, these intervals can vary in time and in length depending on the person.
  • Alternate-day fasting: This is eating normally one day, completely fasting the next day and repeating this cycle. There is no restriction involved on the days when you eat, but on fasting days there are very few to no calories taken in.
  • Modified fasting: This is a set schedule of eating days and fasting days each week. The most popular schedule is five days of normal intake, two days of very low intake. On eating days there are no restrictions. On fasting days, the goal is to consume only 20-25% of your estimated calorie needs (approximately 500 calories per day).

How does intermittent fasting work?

For reference, our bodies have a circadian rhythm, which essentially is an internal 24-hour schedule that we run on. Intermittent fasting is thought to alter this rhythm, but it is still to be determined if this is a good thing or a bad thing. Another idea behind this eating pattern is that it might change our gut microbiome, otherwise known as the bacteria in our gut. The third reason used to support intermittent fasting is that it can cause changes to some daily lifestyle behaviors, including diet, exercise and sleep.

Pros and cons

Now that we have some background information, let’s talk about the potential benefits and drawbacks of intermittent fasting. Some of the touted benefits include weight loss and improved metabolic factors that may decrease the risk for cardiovascular disease, diabetes, cancer and other diseases. While these benefits sound promising, there are also some potential drawbacks, including increased hunger and decreased energy when fasting, and the potential to develop disordered and/or obsessive thoughts surrounding food.

What does the science say?

As with many things in science, we need more research. The research currently available on intermittent fasting mostly has been done on animals (mainly mice and rats), collected in observational studies (not very controlled) and/or with a very small number of people (not reliable). Unfortunately, it isn’t necessarily the best quality data. Additionally, there is no research out there that looks at the ideal timing of eating and/or fasting intervals, so the jury is still out on that as well. Finally, one other thing to note is that in the studies that showed weight loss with intermittent fasting, overall calorie intake also was reduced, which makes it hard to determine which factor is responsible for the weight loss.

Should I try it?

Strictly based on science, no. Until there is more evidence on intermittent fasting, science says stick with a more moderate approach. However, most of us know someone who has tried intermittent fasting and experienced success, which makes it tempting to try.

The important thing to remember here is that there is no one-size-fits-all approach to “dieting,” and what works for your co-worker, sister or friend might not work for you. If you decide you need to try it right now, here are a few pieces of advice:

First and foremost, listen to your body. Listen when your body tells you it’s hungry and it’s full, listen when it asks for water, and respect the signals it sends to you.

Second, while intermittent fasting tells you exactly when to eat, it lacks guidance on what to eat. Make sure you are filling your eating window with healthy foods, including plenty of fruits and veggies, whole grains, lean proteins and healthy fats. Nourishing your body with healthy items is key no matter when you are eating.

And finally, if you feel you need some more personalized guidance, sit down with a registered dietitian or a physician to find out what is right for you!


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