Intermittent fasting—Yay or Nay?


Behind the Keto Diet, Intermittent Fasting (IF) seems to be a very popular “diet.” But what is IF? Is it really safe to do? What are the benefits? What are the disadvantages? Let’s dive into all of those questions and more.

What is IF?
It’s when you only eat within a certain window of time each day vs. eating whenever you want/feel like it. It’s not about what you eat, but when and for how long.

Is there only one way to do IF?
Nope. It’s common for people to fast for 12-14 hours (overnight) and then eat within that 10-12 hour window only. Another common timeframe is the 8-hour eating window, where you fast for the other 16 hours. And another kind of IF is eating a low number of calories (500-600) two days per week and then your normal eating habits the other five days.

So which type should I choose?
Well, first and foremost, you need to figure out why you’re considering IF in the first place. Is it to lose weight? Get your blood sugar under control? Depending on your health history, it’s a good idea to talk to your primary care physician (PCP) first.  

If you’re a mostly healthy person, there are studies to suggest that fasting for 12-14 hours is good for your digestive system.

What does IF do?
It can affect your body on a few different levels. Your body can adjust its hormone levels to make stored body fat more accessible, and it can also cause your cells also initiate important repair processes and change the expression of genes. Another big effect IF can have on the body is on your insulin sensitivity. It can improve insulin sensitivity as well as allow your levels of insulin drop, which makes stored body fat more accessible. Intermittent fasting can have many benefits for your body and brain. It can cause weight loss and may reduce your risk of type 2 diabetes, heart disease, and cancer. Some studies suggest IF may even help you live longer.

Who isn’t IF good for?
If you have a medical condition, you should consult with your doctor before trying IF, particularly if you:

  • Have diabetes
  • Have problems with blood sugar regulation
  • Have low blood pressure
  • Take medications
  • Are underweight
  • Have a history of eating disorders
  • Are a woman who is trying to conceive
  • Are a woman with a history of amenorrhea
  • Are pregnant or breastfeeding



What do dietitians say about IF?
I reached out to my friend and colleague, Taylor VanDyk, MS, RDN, of Taylor’d Nutrition, and here’s what she had to say about IF!

What do you think about IF?
Like any other diet, there is nothing magical about IF. The reason people do have some success with it is because eating for shorter periods throughout the day generally leads to eating fewer calories, which can lead to weight or fat loss. However, there is also some research about fasting in regards to the anti-inflammatory lifestyle, in which case it may be beneficial when done correctly. 

I definitely would not recommend IF for anyone with a history or chronic dieting or disordered eating. However, for someone who has a good relationship with food and can withstand the fast, it would be fine to try something like IF.

If someone decides to do it, what version do you suggest they try?
I would recommend whatever version is closest to what your body naturally does. For instance, if you're not hungry in the morning, it may be okay to start your meals later on. Or if you like to go to bed early, it may be beneficial to shift your fast to earlier in the day. The most common version of IF is 16:8 (16 hours of fasting and 8 hours of eating), I think that any eating window shorter than that would be too restrictive for most people.

Any do's and don'ts you have regarding IF?
If you are into fitness or have physique goals, I recommend having your eating window near your workout time. The 30-60 minutes after a workout is a prime time to refuel your body. If you work out during the fasting period, you won't have time to refuel, which could lead to soreness, low energy, and lack of muscle growth.