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Intermittent Fasting 101 & FAQs

Intermittent fasting (IF), also known as time-restricted eating, is the method of eating only during certain times of day—or certain days of the week—and fasting for others.1 There are many different approaches to IF, and there is quite a bit of room for personalization depending on each individual and their goals. This intermittent fasting guide will provide Atkins' viewpoint for FAQs plus tips for making intermittent fasting successful for you.

How does Intermittent Fasting Work?

Intermittent fasting works much like a low carb diet. When you increase the time between meals, you force your body to rely on stored fuel for energy. Depending on what you are eating between fasts, and how long you are going between eating periods, you may even begin to produce ketones as a by-product of burning fat. One demonstrated benefit of IF is that when you go longer than a few hours between eating, your blood insulin levels go down. This ultimately allows your body to burn stored body fat and may improve insulin sensitivity.

What is the Science Behind Intermittent Fast?

While there is data suggesting that IF can be beneficial, a major limitation of this data is many studies use a variety of approaches to fasting, which makes the research difficult to summarize. Some studies show a benefit of 14:10 time restricted eating, while others look at the benefits of alternate day fasting. One important thing to note is that in general, the clinical studies using IF tend to be shorter than 2 years, so the long term sustainability of this approach remains to be determined. Furthermore, it is not clear whether all of the benefits of IF come directly from fasting, or indirectly from weight loss. 

What are the Benefits of Intermittent Fasting?

Studies indicate that IF may be effective for weight loss and maintenance in addition to improving markers of metabolic health, digestive function, and circadian rhythm. Other research shows that overall, IF reduces caloric intake, which can help people lose weight, support healthy blood sugar levels, and regulate inflammation. Some researchers have suggested that when IF results in weight-loss it may help support cognitive functions or even help break food addiction.

What are the Types of Intermittent Fasting?

There are many types of IF but they can generally be grouped into 3 different categories.

  • Time restricted eating – This type of intermittent fasting breaks the 24 hour day into fasting and feeding windows. Popular forms of time restricted eating include: 16:8, 12:12, and 20:4.
  • Alternate-Day Fasting –  While this may sound like you are supposed to fast every other day, this is actually the term used to describe a method of eating normal one day, and the next day consuming very few calories (usually around 500 calories). Another form of alternate day fasting is the 5:2 method, where you eat normal for five days, but fast or eat a very low calorie diet the other 2 days of the week.
  • Longer fasts – As people become more acquainted with IF, they may start to read about 24+ hour fasts. We don't typically encourage people to follow this protocol, simply because we believe that low carb is a beneficial way of eating that provides a complete nutritional profile that doesn't require you to deprive yourself of food for days on end. We encourage anyone who is planning on doing a longer fast to consult with a healthcare professional who specializes in this approach.

How Long Should I Fast?

If you are interested in trying intermittent fasting, we suggest starting with a 14:10 or 16:8 approach. This gives you a chance to get your body used to relying on its own energy stores, without being overly taxing from the get-go. Data supports that even these shorter fasts can be beneficial for weight-loss and improving markers of metabolic health. We also suggest using IF as a way to get back on track, rather than an all-the-time diet.

When Should I Fast?

IF is probably best used when you know you have excess blood sugar and insulin to clear out. This could be post-holidays, or after a week or two when you know that you haven't been eating low carb.

We suggest starting with a 16 hour fast, after dinner. Ideally, you would finish dinner between 6-7 p.m. on Monday and you would not consume your next meal until 10-11 a.m. on Tuesday. During your fasting period, we recommend making sure to stay hydrated and consuming adequate electrolytes.

You can stick with your chose fasting approach for as long as you would like, one day or one year. some people like to fast when they feel bloated or overate at dinner the night before, while others use it as a lifestyle. Pay attention to how you feel, and personalize it how you see best.

What Should I Eat When I'm Not Fasting

Most of the research around IF does not provide strict guidelines around what to eat during your feeding window. But no matter which type of fasting you choose, make sure you're eating sufficient, quality calories during your feeding window. Reach for healthy foods such as fiber-rich carbs, healthy fats, and protein (approximately 12-18 ounces per day), you should also avoid sugar and refined carbs.

Because fasting elicits some of its beneficial effects through reducing insulin production, it has become popular to pair IF with a low carb or keto approach. We recommend eating high quality goods when you're not fasting, for inspiration, we recommend browsing our low carb recipes.

What Should I Eat to Break My Fast?

When you are ready to start eating after a shorter fast, we suggest that you try not to undo all the metabolic benefits you've gained from your fast. This means staying away from junk food and sugar, instead breaking your fast with low glycemic foods like cooked veggies, berries, or poultry/fish. If you’ve been doing a longer fast, it is often a good idea to slowly awaken your digestive system with something that is easy to digest, like a smoothie, or a broth/soup.

What are the Side Effects of Intermittent Fasting?

Just like a keto diet, when you begin IF, the decrease in circulating insulin levels and carb intake can result in water and electrolyte loss. For some people this manifests in flu-like symptoms, headaches, or low blood pressure/dizziness. It’s also possible to experience low blood sugar levels if you are not adapted to IF or are taking blood sugar lowering medications. Pay attention to how you feel and don’t be afraid of breaking your fast early if you start to feel unwell.

Remember that IF is not for everyone. If you have diabetes, your medication must be carefully monitored by a physician because you are at risk for becoming hypoglycemic, which can be very dangerous. IF is also not recommended for anyone who has struggled with an eating disorder, with preexisting conditions, under the age of 18, or who is pregnant or nursing.

As with starting any new diet or exercise routine, consult with your doctor or healthcare provider for guidance on whether intermittent fasting is right for you.

How Do I Combine Fasting with Atkins 20?

While we do not suggest that you combine these two approaches. However, if you are keen on combing the two, we recommend starting your low carb diet for 2–3 weeks prior to fasting so that you can safely and completely adapt your body.

We do suggest pairing intermittent fasting with an Atkins 100-type approach, which allows for a few more fiber-rich carbohydrates each day. This can reduce some of the stress that may occur when strict carbohydrate restriction is paired with IF. Atkins 100 also more closely resembles the research that has combined low carb eating with fasting.

Can I Exercise During the Fasting Period?

Some people can exercise while fasting, while others report dizziness or low blood sugar/blood pressure. We recommend starting off with light-intensity exercise and keeping a close eye on how you feel during your workouts. 

Additional Tips for Intermittent Fasting

  • Strive for 12-16 calorie-free hours.
  • Avoid snacking between meals and at night to let your body burn fat between meals.
  • Stay active throughout the day to help build muscle.
  • Drink water or a calorie-free electrolyte beverage during fasting times to help you stay hydrated and reduce cravings and hunger.
  • If coffee or tea is part of your normal routine, you can consume them during your fasting period.
  • Don't binge after fasting, eat to satiety, but don't overdo it.
  • Ride out the hunger periods, they will pass!

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Learn more healthy tips, find inspiration and motivation, and connect with our online community when you start your Atkins journey today. For more information on intermittent fast, check out our intro to intermittent fasting and these Atkins-approved IF meal plans.

1 Before starting IF, consult with your doctor or healthcare provider for guidance on whether IF is right for you.

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