IF: The Ultimate Intermittent Fasting Guide

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What is Intermittent Fasting?

Intermittent Fasting (IF) is a type of time restricted eating that's become super popular with the rise of the keto diet. IF means that you restrict eating to a certain time frame every day. For example, you only eat between 10am and 6pm.  This time restricted eating pattern is said to have many health benefits and makes it easier for people to lose weight without purposefully cutting calories.

Intermittent Fasting came onto the recent scene in 2012 with Dr. Michael Mosley’s documentary Eat Fast, Live Longer and his book The Fast Diet. After this, a few others including Kate Harrison (The 5:2 Diet) and Dr. Jason Fung (The Obesity Code) joined the scene and the effectiveness of IF was brewing up a storm.

What are the benefits to Intermittent Fasting?

People claim there are tons of benefits to IF including, lowered insulin levels, increases in human growth hormone (HGH), increased cell repair, weight loss, reduced inflammation, and a ton of other benefits that are based the animal studies they’ve done. If it works on a mouse, it must be true for me too, right???

How do these benefits actually happen? Well, after about 8 hours, the body has used up its glycogen stores and your body slowly begins making small amounts of ketones. Ketones are what your body burns when it doesn’t have carbs/sugar, these ketones allow the body to continue functioning when it no longer has glucose/glycogen from a carb source.

Ketones are made from fats when the body is low on glycogen (what carbs get turned into). This fat can come from dietary fat, if any is left floating around from last night’s dinner, or from your body’s fat stores. This is why people are linking IF with the keto diet. More on this connection later…

What are the downsides?

The biggest downside to IF is that you actually have to be able to do it. Meaning you must have the control and willpower to avoid food and/or calories for a set period of time. This may be harder for some people than others. For me, I can never make it the 16 hours.. around 12 I usually end up giving into my hunger. But hunger and I have never gotten along.

Also, this may not be the best eating plan for people with a history of or a current eating disorder. The restriction that is emphasized in this method can be triggering.

You may also get headaches and cravings for the first couple of days while you adjust to the new schedule. This is normal. You may want to *slightly* increase your salt and water intake to help combat these side effects.

Does it Work Better than Daily Calorie Restriction?

When comparing IF to a typical diet where you restrict calories on a daily basis, there is no difference in weight loss in the long run. Some people find that fasting is hard and choose to eat less daily rather than include periods of fasting. It comes down to personal preference. IF is not a miracle, just another tool in the toolbox.

How do you implement Intermittent Fasting?

Intermittent Fasting is easy enough once you determine your selected schedule. Take a look at the methods below to see if one of these would work for you. Make sure that you choose one that is sustainable for you.  Once you have chosen your schedule, implement it with times that work for you. Don’t choose to eat your last meal at 4pm if you typically have dinner with your family at 7pm. That is going to make it harder to stick with. Stop eating at the time you choose and wait to eat your next meal 16-24 hours later, depending on which method you chose.

16/8 Method

The 16/8 method is one of the most popular methods. This means that you choose an 8 hour window where you eat all of your calories for the day. This method works great for people who like to skip breakfast or for people who are too busy to eat in the morning. An example of this would be not eating anything until 10am and having your last meal before 6pm. Then you fast for the night. Keep in mind that the times can change based on your schedule.

5/2 Method

Another option is the 5/2 method. This is a method where you eat normal calories for 5 days of the week and fast for 2 non- consecutive days. For example, you eat normally on Monday, Wednesday, Thursday, Saturday and Sunday and you fast on Tuesday and Friday.

During the 5 days where you are eating normally, some people like to follow a time restriction for eating, like 16/8, to further enhance the benefits. But this is not required.

20/4 Method

The 20/4 method is harder than the 16/8 because you are fasting for 20 hours and only eating for 4 hours a day. This works great if you like to have one really big meal a day. But it can also create a challenge if you are counting your calories and macros, you need to make sure that you somehow get them all in during a 4 hour period. That can be daunting for some people.

With any of these methods, if your goal is weight loss, then you need to ensure that you are still eating fewer calories than your body burns. IF will not produce weight loss if you are binging during your eating window.

Reverse Fasting: What is it?

So now that we have tackled Intermittent Fasting, there is a new player that I have seen about recently, called reverse fasting. I included this in here because it is very similar to Intermittent Fasting. Reverse Fasting is where you front load your calories, meaning breakfast and lunch are bigger than dinner. Then you fast until breakfast.

This is slightly different from IF in the fact that the times are preset for you. This diet is trying to sync your eating with your circadian rhythm. You eat more when your digestion is stronger (i.e. in the morning) and you finish eating when the sun goes down.

For 2 hours before bed, only water is allowed. This helps your body relax before sleep and ensures that digestion is completed.

If you want to try something like this a schedule might look like:

5am: Get up
6am: Eat large breakfast (protein, carbs, fruits, veggies)
Noon: Lunch (Lean meat, carbs, some fats)
4-6pm:  Dinner (Lean meat, leafy vegetables, fats)

This is a great method for people who love breakfast, or are more active during the day and not as active later in the day.

Do I have to do Keto to do Intermittent Fasting?

With the rise in popularity of the Keto Diet, IF has been on the rise too. People have begun to link Keto and IF as they both promote the use of ketones for energy, even if it is just for a short period of time with IF. Ketones are created when your body runs out of glycogen which is your body’s preferred energy source if you eat a Standard American Diet. Fasting for 14-16 can allow for glycogen storage to be depleted and your body to create ketones. OR you can just not give your body anything to make glycogen with (severely restrict carbs, like the Keto Diet does). As ketones are made from fat, keto encourages larger amounts of higher fat foods.

But just because they have a similarity does not mean that you have to do one to do the other. You can do Keto without doing IF and your can do IF without going Keto.

What Do I eat on IF?

As IF is not a diet plan but more of a method of eating, you can eat whatever you want, with one caveat.. if you want to lose weight, you must restrict calories. No matter what method you choose when it comes to eating, you will never lose weight if you are eating more than you are burning.


With that said, IF does make reducing calories easier. When you only have a certain amount of time to eat, you may end up eating less. For example, if you want to lose weight and use IF, then you could skip breakfast and not add those calories back later in the day. You would continue to eat the same thing for lunch and dinner. Check out the example below of a day using IF vs a day where you only restrict calories.

Daily Calories Restriction Only Intermittent Fasting Day for Calorie Restriction
Breakfast: Eggs and Toast
Lunch: Chicken Salad
Dinner: Steak, potato, and vegetables
Snacks (optional): protein shake/ banana with PB
Water and Calorie free beverages before 10am
Lunch: Chicken Salad
Dinner: Steak, potato, and vegetables
Snacks (optional): protein shake/ banana with PB No food after 6pm

What if I mess up?

If you mess up on IF, it’s no biggie. Just start again the next day. You might be hungrier during your fasting period the next day, but once your body has adjusted to the timeframe when you choose eat, you won’t be very hungry when fasting. Just remember: there will be an adjustment period.


Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical TrialJAMA Internal Medicine, May 2017.
Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolismAmerican Journal of Clinical Nutrition, January 2005.
Intermittent fasting interventions for treatment of overweight and obesity in adults: a systematic review and meta-analysis. JBI Database of Systematic Reviews and Implementation Reports, February 2018.
Metabolic Effects of Intermittent FastingAnnual Review of Nutrition, August 2017.

Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with PrediabetesCell Metabolism, May 2018.