What is Intermittent Fasting?

What is Intermittent Fasting?

Publish Date March 17, 2023 6 Minute Read
Author Marcella Ranieri (RDN, LD, CLC)

From keto to paleo to intermittent fasting and beyond, there are so many different eating patterns that exist. Because of this, it can be hard to keep track of what each eating pattern involves, let alone know if it’s right for you. While it’s important to keep in mind that one style of eating might not work for everyone, here’s the scoop on Intermittent Fasting.

What is Intermittent Fasting and How Does it Work?

Intermittent fasting, also called time-restricted feeding, focuses more on when you eat instead of how much you eat, and is commonly used as a means for weight loss.1 Intermittent fasting is broken up into 2 parts: fasting and feeding. During the fasting time, food and beverages with calories are to be avoided, while beverages with no calories, such as water and black coffee, are allowed. And during the feeding window, there’s no set restriction on what you eat or how many meals you have. There are a few different ways to do intermittent fasting, with fasting time ranging from 12-36+ hours.

While there are many types of intermittent fasting, let’s explore the 3 most common ways2:

Daily: The most common form of intermittent fasting is a daily fast for 12 to 16 hours. For a 16-hour fast, this would result in an 8-hour feeding window during a 24-hour period. A “16:8” fast might look like eating breakfast at 11am and finishing dinner by 7pm. There’s no set number of meals or calories to eat within this window.

“5:2”: For those who prefer longer periods of fasting, a 5:2 schedule results in 5 days of following your normal meal pattern, paired with 2 days of 24-hour fasts each week. Another form of the “5:2” diet is practicing extreme calorie restriction 2 days per week where only 400-500 calories are consumed.

Alternate Day Fasting: This form consists of alternating days of no restrictions with days where just 1 meal is consumed. On fasting days, individuals consume approximately 25% of their calorie needs.

How Do I Start?

When considering such an involved meal pattern like intermittent fasting, it’s important to consult your doctor and/or dietitian first. Interested in intermittent fasting? Here are some tips to help get you started:

Start Small: Begin your fasting period at 12 hours, and slowly increase the hours in your fast every few days. This can help with any unwanted side effects of fasting, like hunger or moodiness.

Fast Overnight: Create a schedule so that most of your fast occurs while you sleep. For a 12-hour fast, this could look like finishing dinner at 7pm and eating breakfast at 7am the next day. To extend your fast, delay your breakfast or have dinner earlier. For 24-hour fasts, eat breakfast and lunch and then refrain from eating again until lunch the next day.

Work with a Registered Dietitian: A nutrition professional can help you plan an intermittent fasting schedule that’s right for you. You can even meet with a registered dietitian online by scheduling a telenutrition appointment.

What Should I Eat During My Feeding Window?

While it may be appealing to “eat whatever you want” during the feeding window, it’s still important to eat a healthy, balanced diet that includes:

  • Vegetables
  • Fruit
  • Lean proteins
  • Whole grains
  • Low-fat dairy

Also keep portion sizes in mind. For more information about a healthy, balanced diet, talk to a registered dietitian today.

What Are the Benefits of Intermittent Fasting?

Intermittent fasting may have the following potential benefits:

  • Improved blood sugar levels4
  • Improved blood pressure4
  • Improvements in thinking and memory1
  • Improved tolerance to bodily stress4
  • Decreased inflammation4,5
  • Improvement in inflammatory conditions and autoimmune disorders5,6
  • Increased lifespan7
  • Cell/tissue repair7
  • Liver disease prevention8
  • Less severe complications from COVID-199

Intermittent fasting, like any dietary change, is not an overnight fix, and may take 2-4 weeks to start seeing any benefits.1 More long-term research, specifically on humans, is needed to explore the validity of the health benefit claims from intermittent fasting. Research is also needed to compare the different time frames and types of fasting. A more diverse population needs to be represented in this research as well.

What Are the Safety Considerations?

As with any diet, it’s best to talk to your healthcare provider before starting a fasting regimen, especially if you have any chronic health conditions requiring medications.

Intermittent fasting is not recommended for:

  • Pregnant women, breastfeeding women or women trying to get pregnant10
  • Type 1 diabetes
  • Type 2 diabetes with insulin and/or medications
  • Ages under 18
  • Those diagnosed with hypoglycemia
  • Those who have a current eating disorder or a history with eating disorders
  • Those who have kidney stones5
  • Those with gastroesophageal reflux disease (GERD)5

It’s important to keep in mind that limiting intake too much or too frequently could prevent your body from getting the fuel needed for daily functions, and it could put you at risk for vitamin and mineral deficiencies.11 There is also a risk of creating a disordered relationship with food. If you find that intermittent fasting is changing your feelings or relationship with food, or if it doesn’t feel right, you should discontinue and speak with your healthcare provider. Taking charge of your health and nutrition can be overwhelming. Talk to a registered dietitian to help you take the first steps toward a healthier future.

Disclaimer: This information is educational only and not providing healthcare recommendations. Please see a healthcare provider.


1. John Hopkins Medicine. “Intermittent Fasting: What Is It, and How Does It Work?” Johns Hopkins Medicine, 2021.

2. Harvard School of Public Health. “Diet Review: Intermittent Fasting for Weight Loss.” The Nutrition Source, 19 Jan. 2018.

3. University of Adelaide. "Intermittent fasting could improve obese women's health." ScienceDaily. ScienceDaily, 8 January 2019.

4. Sutton, Elizabeth F et al. “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes.” Cell metabolism vol. 27,6 (2018): 1212-1221.e3.doi:10.1016/j.cmet.2018.04.010

5. Mundi, Manpreet. “Is Intermittent Fasting Good for You?” Mayo Clinic, 21 Apr. 2020,

6. Choi, In Young et al. “Nutrition and fasting mimicking diets in the prevention and treatment of autoimmune diseases and immunosenescence.” Molecular and cellular endocrinology vol. 455 (2017): 4-12. doi:10.1016/j.mce.2017.01.042

7. Bagherniya, Mohammad et al. “The effect of fasting or calorie restriction on autophagy induction: A review of the literature.” Ageing research reviews vol. 47 (2018): 183-197. doi:10.1016/j.arr.2018.08.004

8. University of Sydney. "How intermittent fasting changes liver enzymes and helps prevent disease: Research on mice reveals surprising impact on fat metabolism." ScienceDaily. ScienceDaily, 10 March 2020.

9. Intermountain Healthcare. "People who practice intermittent fasting experience less severe complications from COVID-19, study finds." ScienceDaily. ScienceDaily, 7 July 2022.

10. University of Illinois Chicago. "How intermittent fasting affects female hormones: New evidence comes from study of pre- and post-menopausal obese women on the 'warrior diet'." ScienceDaily. ScienceDaily, 25 October 2022.

11. Gordon, Barbara. “What Is Intermittent Fasting?” Academy of Nutrition and Dietetics, 7 May 2019.