What Is Intermittent Fasting?

How to safely adopt this trendy — and often effective — diet

While most diets focus on what you eat, intermittent fasting is about when you eat.

“Intermittent fasting is any kind of eating pattern where you strategically divide up your time into hours of eating and hours of not eating,” says Naomi Parrella, MD, a medical weight management physician at RUSH University Medical Center.

Historically adopted for religious and cultural reasons, intermittent fasting has become a trendy way to lose weight — because it’s inexpensive and frequently effective.

It can also make you feel better, Parrella says, and help with other health matters like diabetes, sleep and cognitive decline.

How does intermittent fasting work?

Here’s how it works: Every time you have a routine break in digestion — while you’re sleeping, for example — this sends signals to your body to clean up, recover and heal.

"As humans, we’re designed to get stronger and better during and after fasting times. You’re letting your body decompress and prepare for newer, better things moving forward."

So how long should you fast?

It depends, Parrella says, on the person and their health concerns — but a routine that fits your lifestyle usually is the most effective.

Here are a few common intermittent fasting plans:

  • Alternate day fasting: Fasting every other day, eating about 25% of your usual calorie intake on fasting days and then what you want the alternate day.
  • Time-restricted fasting: Fasting every day for 12 hours or longer and eating during the remaining hours. A popular example is the 16-8 method, which features a daily 16-hour fast and an 8-hour eating window.
  • The 5:2 fasting diet: Two days of the week you eat a low number of calories, and the rest of the week you eat normally.

What should you eat on an intermittent fasting diet?

Even though intermittent fasting is about when you eat, you should still consider the types of foods you eat when you break your fast.

Parrella recommends eating healthy proteins and veggies and avoiding starchy carbs and sugars.

“Some people start with a soup or stew, or something else light,” she says. “The key is to have some vegetables with some proteins. This is a better way to break a fast and gives you more energy, especially if it's been a prolonged fast.”

It’s important to work with a dietitian or health care provider to help you create a meal plan that works for you.

Is intermittent fasting safe?

To determine whether intermittent fasting is safe for you, consult with your doctor or a dietitian.

“Intermittent fasting can have significant effects on the body. Your current health plays a huge factor,” Parrella says. “And depending on your health status, intermittent fasting may not be right for you or even dangerous. When in doubt, ask your health care provider if it’s right for you”

Intermittent fasting is not recommended without medical supervision, especially for people with heart problems, high blood pressure or high blood sugar, or with those who are pregnant, breastfeeding or have a history of eating disorders. Medical supervision is also suggested for people taking certain medications as adjustments may be needed.

Tips for intermittent fasting

Although often effective, intermittent fasting can be challenging. Your health care provider can help you know if the diet is right for you and be a guide.

Here are some other tips to help you stay on track:

  • Stay hydrated. Drink lots of water throughout the day (roughly two to three liters). A registered dietitian or health care provider can advise if you need to add electrolytes to your water.
  • Incorporate rest. Avoid intense workouts on fasting days, especially if you just started intermittent fasting. Light workouts, such as yoga and walking, and mindfulness practices may be beneficial.
  • Have a good support system. Create a group of trusting and safe family members and friends to provide emotional support during your fast. For example, ask them to not place enticing foods in visible places that make it hard to resist.
  • Plan activities for when you’re fasting. Engaging in activities can be a helpful distraction when you’re fasting, such as talking to someone, going on a walk, painting, drawing, listening to music, volunteering or playing with your pet.
  • Use reliable resources. “There is a lot of misinformation about intermittent fasting, so make sure your resources are creditable,” Parrella says.
  • Be careful not to fixate on your fast. “The minute the diet starts getting stressful, it's no longer giving you the benefit it's supposed to and can potentially lead to problematic eating habits,” Parrella adds.

If you’re interested in intermittent fasting, consult with your doctor or schedule an appointment with our Weight Management team to determine whether the diet is right for you.

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