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Intermittent Fasting For Weight Loss: 5 Common Questions Answered by a Medical Expert

By Stephanie Eng-Aponte Reviewed by Dr. Pamela Peeke, MD, MPH, FACP, FACSM Science-Backed

If your 2020 goals involve weight loss, you’re probably familiar with many of the leading dietary trends. From the ketogenic diet to paleo to intermittent fasting for weight loss — there seems to be a different plan for everyone. But how can you tell if a program is more than just a fad? 


We spoke with Dr. Pamela Peeke, MD, MPH, FACP, FACSM, lifestyle medicine expert and chair of the Jenny Craig Science Advisory Board, to talk about the new science of intermittent fasting and five basic things you need to know, plus why it’s so important to eat in alignment with your body’s natural rhythm.


We’ll take a look at intermittent fasting (IF) for weight loss and the science behind Jenny Craig’s innovative Rapid Results program to answer common questions about this popular weight loss and health strategy.


Here’s why when you eat could make all the difference when it comes to reaching your weight loss goals — and the real research that supports it. 

1. What is intermittent fasting?

Don’t let the word “fasting” scare you: If you’ve eaten dinner, slept through the night and woken up for breakfast, you’ve already done it!


Intermittent fasting is an eating pattern that encourages you to transition between periods of eating and fasting. When you practice intermittent fasting, you’ll start paying attention to when you eat: You’ll eat meals during certain hours of the day and take a break for the remaining hours to let your body rest and digest. This is quite different than what so many people are currently doing, which is eating chaotically, whenever, whatever and however. That’s a sure-fire way to gain weight. The body relies upon a regular nutrition routine, not disorganized eating behavior.



The ideal nutrition blueprint is found with intermittent fasting which works in sync with your natural 24-hour circadian rhythm — the physical, behavioral and mental changes your body goes through each day. When you eat during the first 12 hours of the day and then take a 12-hour break, you’re following your body’s innate rhythm.


During a 12:12 intermittent fasting schedule, you’ll:


  • Focus on a daily eating timeframe with an evening break to allow your meals to digest.
  • Eat within a 12-hour window (say, 7 a.m. to 7 p.m.) each day, which is the eating pattern on Jenny Craig’s Rapid Results Complete Weight Loss Plan.
  • Enjoy breakfast, lunch and dinner (and even snacks!) over the course of 12 hours.



“Following 12-hour periods of eating and resting are what you’re supposed to be doing naturally,” Dr. Peeke states. “With intermittent fasting, we are circling back to our natural, primal rhythm where going 12 hours without eating was something our ancestors expected.”

Photo by nortonrsx on iStock



Other types of intermittent fasting can be more prohibitive and require you to go longer periods without consuming any calories:1


  • 5:2 fast: You’ll eat normally for five days. For two days of the week, you’ll limit your calorie intake to 500-600 calories a day. 
  • Alternate day fast: You’ll eat 500-600 calories one day, and then whatever you wish the next. This is very difficult to implement as the average American eats, drinks and snacks their way through 15 hours of every day — which could make sticking to an eating schedule like this very challenging.
  • 24-72 hour fast: Advocates of this water-only fasting for up to three days face great challenges when trying to socialize as well as manage fatigue and hunger. Clearly, this approach is not feasible or desirable for most people.


If these methods sound intimidating, following a 12:12 intermittent fasting schedule may be more manageable.


Eating and fasting in 12-hour blocks works closely with your natural circadian rhythm. Your rhythm runs on a “12 hours on, 12 hours off” schedule, where you’re typically awake and active for 12 hours and resting or asleep for the remainder. Intermittent fasting works hand-in-hand with these 12-hour periods to maximize your metabolism’s efforts to burn calories, which is great news if you’re trying to lose weight.2

2. Why is it important to pay attention to when and what I eat?

If intermittent fasting works with your metabolism, then eating your favorite candy bar every afternoon shouldn’t matter, right? Unfortunately, not quite. For IF to work, you’ll need to make smart food choices. Only eating deep-fried or sugar-packed foods for most of your meals won’t supply your body with the nutrients it needs or help you reach your health goals, no matter how well your meal timing works with your metabolism.


Support your intermittent fasting schedule with these great foods for the best results:

  • Plenty of non-starchy vegetables and water;
  • A moderate amount of lean proteins;
  • And a small amount of whole grains, healthy fats (like avocado and nuts) and fruit.


Photo by Ella Olsson on Unsplash

IntermittentFasting_WhatandWhen_Photo by Ella Olsson on Unsplash.jpg


Eaten in moderation, these nutrient-packed foods will help you feel satisfied without weighing you down during the 12 hours when you’ll allow your body to rest. Jenny Craig offers delicious, balanced meals and snacks you can enjoy on an intermittent fasting schedule, all while supporting your weight loss goals. View our new healthy meal plans starting at just $12.99 a day.

3. Can I eat breakfast?

When you’re trying to maintain a 12-hour eating window and finish your last meal no later than 8 p.m., then breakfast naturally occurs the next morning and should include a mix of high-quality protein and healthy carbohydrates such as vegetables, fruits and nuts. After you have fasted for 12 hours, you’ll probably find that your hunger and appetite will be more manageable. This is great news and allows you to be more in control throughout the day, eating balanced and thoughtfully-portioned meals.


And don’t forget, snacks are important, too! Eating a healthy snack in between each of your meals will keep your appetite in check and help prevent the urge to overeat. Try choosing snacks under 200 hundred calories to avoid filling up before your main meal.


Some of our favorite Jenny Craig snacks include White Cheddar Popcorn and our Chocolate Peanut Butter Bar — both filled with beneficial protein and fiber.

4. Does fasting work because my body stops digesting food at night?

The body typically digests food within 24 to 72 hours and doesn’t “shut off” while you sleep.[3] While it’s true that you’re not actively eating for 12 hours when following an intermittent fasting plan, waiting to eat isn’t the only reason it’s effective. According to Dr. Peeke, this is also a period that has important health benefits:



“The rejuvenation window is a critical period when your body regroups, resets and regenerates after a busy day metabolizing your food and then using it to fuel your daily activities. One benefit of allowing your body this renewal time is that your body fat, especially belly fat, can decrease.4 This is good news, as excess belly fat is associated with obesity and an increased risk of Type 2 diabetes.5


While you take a break from eating meals, your body is still hard at work, but in a different way. By giving your body 12 hours to rest, you’re giving it the best opportunity to help support your weight loss efforts.

Photo by Adene Sanchez on iStock


5. Could intermittent fasting boost my immune system?

A recent review showed that intermittent fasting may help to stimulate autophagy,6 a biological process that allows the body to break down and recycle cellular materials to regenerate healthier cells.7 Autophagy doesn’t just reduce and reuse cell materials, it also plays a part in immunity and defends cells against disease-causing threats.7 So, while intermittent fasting isn’t necessarily a cure for illness, it may help to boost immune function.

Intermittent fasting for weight loss

Incorporating intermittent fasting into your day doesn’t need to be difficult — just remember, 12 hours on, 12 hours off. Eat your meals within the first 12 hours and rest for the remaining 12 hours to sync with your circadian rhythm. Combine this effective nutrition strategy with healthy meals to work toward your weight loss goals!


Jenny Craig’s Rapid Results Complete Weight Loss Plan makes it easy to combine the innovative science of intermittent fasting with delicious, nutritionally-balanced meals. Connect with a weight loss coach to learn more about the benefits of following a 12:12 eating schedule and get chef-crafted meals delivered to your doorstep today!





[1] https://www.healthline.com/nutrition/what-is-intermittent-fasting#section3

[2] Longo, Valter D., and Satchidananda Panda. “Fasting, Circadian Rhythms, and Time-Restricted Feeding in Healthy Lifespan.” Cell Metabolism, vol. 23, no. 6, 14 June 2016, pp. 1048—1059., doi:10.1016/j.cmet.2016.06.001

[3] https://www.medicalnewstoday.com/articles/319583.php

[4] https://www.sciencedirect.com/science/article/abs/pii/S1550413119306114

[5] https://www.health.harvard.edu/staying-healthy/abdominal-fat-and-what-to-do-about-it

[6] https://www.gwern.net/docs/longevity/2019-decabo.pdf

[7] https://www.britannica.com/science/autophagocytosis


Stephanie Eng-Aponte



Stephanie Eng-Aponte is a copywriter for Jenny Craig and has written for the health and wellness, tech, and environmental industries. Stephanie graduated from Rutgers University with a Bachelor of Arts degree in Journalism and Media Studies. They employ an “eat first, write later” approach to food blogging and enjoy the occasional Oxford comma. Outside of writing, you can find them photographing a muttley crew of rescue pups, brewing kombucha, or exploring San Diego.

Favorite healthy snack: green apple slices with sunflower butter


Dr. Pamela M. Peeke, MD, MPH, FACP





Dr. Peeke is chairman of the Jenny Craig Science Advisory Board, Pew Foundation Scholar in Nutrition and Metabolism, Assistant Clinical Professor at the University of Maryland, School of Medicine, and a Fellow of the American College of Physicians. She is an internationally recognized expert, physician, scientist and New York Times best-selling author in the fields of public health, nutrition, fitness and weight management.





This article is based on scientific research and/or other scientific articles and was written by an experienced health and lifestyle contributor and reviewed by certified professionals.


Our goal at Jenny Craig is to provide the most up-to-date and objective information on health-related topics, so our readers can make informed decisions based on factual content. All articles undergo an extensive review process, and depending on the topic, are reviewed by a Registered Dietitian Nutritionist (RDN) or Nutritionist, to ensure accuracy.


This article contains trusted sources including scientific, peer-reviewed papers. All references are hyperlinked at the end of the article to take readers directly to the source.


Edited by Elisa - Jenny Craig

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