The Ultimate Guide to Intermittent Fasting II – Not All Fasts Are Created Equal


The Ultimate Guide to Intermittent Fasting II – Not All Fasts Are Created Equal

Interested in Intermittent Fasting? Grab my book on it here: Feast.Fast.Fit. – Train Your Body to Torch Fat, Build Muscle, and Never Diet Again

Part I –  The Ultimate Guide to Intermittent Fasting I – Feast vs. Famine

When you hear the word fasting you either recognize it from its spiritual origin or when your doctor makes you starve before a blood test.  Either way it doesn’t sound inherently fun.  I mean, you don’t eat any food during a fast so, how could it be fun?  Well, believe it or not, there really are a lot of reasons to at least toy with fasting even for the anti-aging and longevity benefits alone.

Clearly, health in this country has hit an all-time low so taking any precautions you can should be a priority.  Caloric restriction, intermittent fasting and alternate day fasting are three forms of dietary interventions that can be used to improve your health and physique.

By properly implementing and utilizing fasting you can potentially:

  • Lose fat
  • Live longer
  • Improve health
  • Reshape your physique
  • Improve your muscle to fat ratio
  • Improve insulin sensitivity, cholesterol, blood glucose levels and more

              That’s a lot to promise from simply not eating for a few hours, right? It sure is, but if you look closely at what happens in the body during fasts you will start to understand how this is possible.

It’s well established that caloric restriction (reducing calorie intake without malnutrition) extends lifespan, provides anti-tumor effects, delays the onset/severity of chronic diseases (cancer for example), and has positive effects on cognition [1]. To this day, caloric restriction remains the most potent dietary factor in preventing aging and maximizing lifespan [1].

As one group of researchers put it:

“Few environmental manipulations have been reported to consistently extend the lifespan of multiple species. CR (Caloric Restriction), the reduction of macronutrient intake while maintaining sufficient micronutrient intake, is one notable exception.” [1]

Restricting your calories doesn’t sound too thrilling though, especially in today’s day and age.  Luckily, intermittent fasting and alternate day fasting have been shown to exhibit a lot of the same benefits as CR (caloric restriction), and still allows you to eat the calories you are accustomed to.

It’s important to recognize the difference between intermittent fasting, alternate day fasting and calorie restriction; though a lot of the benefits are the same.

  • Intermittent Fasting (IF) – refers to periods of no food followed by a pre-determined window of food intake. Ramadan is an example of intermittent fasting, those who follow this will abstain from food during the day and then have a large dinner at night. Common examples of this are the 16/8, 18/6, and 20/4 fasting and feeding windows.
  • Caloric Restriction (CR or DR) – refers to taking your normal daily required caloric intake and reducing it by a certain percentage (15-60%). However, during calorie restriction there is still a need for sufficient micronutrient intake to avoid malnutrition.
  • Alternate Day Fasting (ADF) – is a form of IF and is exactly what it sounds like; you have a feed day followed by a fast day. This type of eating allows for more leniency on your feed days in terms of the food choices. This is a more radical approach and should only be used by advanced dieters in my opinion as the hunger pangs can be tough at first.
  • Modified Alternate Day Fast (mADF) – Similar to an alternate day fast, this style of dieting has a feed day and a fast day. However, on the fast day you will break the fast with one small meal, 300-700 calories. Ideally, you’d like this to be a balanced meal.  Your feed day will supply the majority of your calories.

Common fasting variations you may have heard of:

  • 16/8 – 16 hour fast followed by an 8 hour feeding window – often referred to as “lean gains”
  • 18/6 – 18 hour fast followed by a 6 hour feeding window
  • 20/4 – 20 hours of fasting or “under-eating” in some practices, 4 hour feeding window – often referred to as the “warrior diet”
  • Once a week 24 hour fast
  • Twice a week 24 hour fast
  • Every other day feeding and then fasting
  • Feed day followed by a long fast and 1 meal on the fast day
  • Using fasting periods for a “detox”

The point here is that there are many ways to fast. If you find one that fits your lifestyle and it makes adherence much easier, then go for it. But please be wary of people who bash fasting while grouping them all together. All of these forms of fasting have their own results to offer, from fat loss to life extension. So what style of fasting should you use? First, define your goals.

What Can Your Fast Do For You?

Whether you are starting a new training block or diet, you need to determine what the goal of said program is. For this plan, let’s look at what we want to achieve from our fasting period. Different forms of intermittent fasting can be included in any sort of a program, from mass gain to trying to shed body fat. Dependent upon the goal, you can tweak the timing, frequency and length of your fasting periods.


Fasting for Fat Loss:

If your current goal is a reduction in body fat, there are a lot of ways you can implement fasting into your routine. In this circumstance, the fasting period is the catalyst for igniting fat loss. During your stretches of low food intake/low insulin levels, you want to burn energy, specifically fat. You are also trying to teach your body how to run smoothly and efficiently on its stored fat.  By using this fuel more often and limiting the refilling these fat stores, you can work towards a steady loss of body fat until a leaner equilibrium is reached.

In order to accelerate fat loss, you need to create an environment where fatty acids are freed and utilized. This can be done by extending your overnight fast until lunch (12 or 1pm), or stretching that fast even longer. The theme here is making sure you allow some periods where insulin remains low.

Some fasted cardio or activity during the fast, followed by some additional fasting afterwards, is a perfect way to jump start fat burning that day. Fasted exercise has been shown to lead to greater mobilization and utilization of fat for fuel as opposed to fed exercise [2] and has been shown to burn 20% more fat [3].  For more information on fasted exercise read my previous article – Fasted Cardio for Fat Loss.

This doesn’t need to happen every single day. All lengths of fasts can be useful here but I’d recommend starting at 11-14hr fasts (including your overnight fasting hours) at first. So if you have never tried a fast, wake up and don’t eat for 2-4 hours to ease your way into it. As you get more comfortable or begin to desire even greater fat loss, you can add hours to your fast.

However, it’s important to remember that what you are doing during your feeding window is equally as important as what you do during the fasting period. Remember, it’s all a part of a larger plan. The calories aren’t being forgotten, only shifted around.

How it helps:

– Control appetite and therefore successfully reduce calories

– Improve carbohydrate metabolism through increases in insulin sensitivity

– Allows stored fat to potentially be released and used for energy


Anti-Aging and Health:

fasting for fat loss

If your interest in fasting stems from hearing of its purported longevity effects, you want more than just the reduction in fat stores. Even though shorter fasts still offer health benefits, it’s what happens deep into the fast period that those looking for longevity are after. In the later stages of fasting, 24-36+ hours, there are a host of unique hormonal changes that I’ll discuss in more detail later on.

Aging and certain diseases like cancer occur as a result of cellular damage and the body’s response to these dysfunctional cells. The long fast is a potent stressor to the cells and the body. That doesn’t sound good, why do we want that?

It’s this stressor that boosts the resiliency of our cells to oxidative stress – this is good. This can be viewed as a potent defense mechanism that the body employs to boost our chance of survival. During this time you want damaged cells to undergo repair (through a process called autophagy), increases in neuro-peptide y (NPY), and activation of certain “longevity” genes like SIRT1.

Fasting has been linked to potentially protecting against Alzheimers [4], Cancer [5], Type II diabetes [6], Cardiovascular disease [7] and more. There are also beneficial effects seen from intermittent fasting, calorie restriction and alternate day fasting in regards to improving LDL particle size/distribution [8], lowering LDL levels [9], and reducing the risk of atherosclerosis [10]. Another recent study found that 10-12 hours of fasting in pre-diabetic patients led to LDL (bad cholesterol) being pulled from fat cells and used for energy [11].  With the ever increasing use of statins I think these protocols deserve more research.

Even more recently, a study out of the University of Southern California found long stretches (up to 72 hours) of fasting to trigger stem cell regeneration of the immune system [12]. In their terms, the fasting shifted stem cells from “a dormant state to a state of self-renewal.” [12] They also found that fasting prior to chemotherapy treatment could prevent toxicity and limit the damage done to the immune system.

Knowing this, I think you should appreciate how easy it is to reap these benefits, simply don’t eat for a few hours. If there was a pill that showed all of the promise that fasting does, it would be a best seller. Stop and think about that for a second. Dr. Oz is on tv selling supplements that are literally proven to be utterly useless, yet people are rushing out to buy them. On the other end of the spectrum, fasting has been a part of our life (intended or not) since the inception of mankind and unlike 99.9% of supplements, actually has research supporting it’s effectiveness.

Caloric Restriction is another option when you are searching for a diet aimed towards “longevity.”  The problem becomes compliance and assuring you are getting proper macronutrient and micronutrient intake. This is why intermittent fasting gives you the best of both worlds. When comparing the two, CR to IF, fasting typically leads to more lean muscle mass being retained. This is why fasting is likely to be a better option for sustainability and progress.

So, for those with these specific goals, a once or twice a week 24-36 hour fast (or longer) can be used effectively.

How it helps:

– Autophagy (cellular degradaton process)

– Activiation of certain “longevity genes” (SIRT1, NPY, AMPK)

– Increases the cells ability to tolerate stress


Muscle Gain:

Why would you use fasting when trying to gain muscle? Mainly because it can help keep your cells sensitive to insulin, increase growth hormone, improve nutrient repartitioning and keep body fat in check. A fast is a useful way to resensitize your body’s response to nutrients because it serves as a break from your constant surplus of calories. Usually when people think “muscle gain,” they think that they need a lot of food. While a powerful training stimulus + adequate nutrition is necessary for muscle gain, superfluous calories and excess body fat is NOT.

Yes, fasting is technically catabolic in nature, but your understanding of catabolism is skewed. You aren’t looking to gain muscle during the fast period, but you’ll be surprised to learn the benefits some stretches of catabolism will serve you.  For starters, it’s a good idea to allow your body to get rid of some of the defunct tissue that you don’t need and may become problematic in the future.

Critics will say, “Well when you’re trying to get big you can’t do it in less meals.”  Just because YOU can’t do it, doesn’t mean nobody else can. Some people prefer large, less frequent meals. Get over it. Nobody is forcing you to try it. The other criticism is the over-hyped “muscle loss,” I will cover this a bit later. Where does the truth lie? Somewhere in between.

Some research suggests that having periods where anabolic processes are shut off will allow for the replenishment of satellite cells. Satellite cells are vital in our muscle building efforts as skeletal muscle can’t regenerate without them [13]. That coupled with increased resting glycogen stores, are part of why fasting can be useful when gaining muscle is the goal.

If you are looking to gain muscle but want to use fasting you just need to time it appropriately and keep the focus on having productive workouts and ingesting the proper amount of protein and calories. For this, I’d recommend keeping fasting limited to non-workout days only. I really believe that periods of low caloric intake or fasting during “bulks” can be highly effective at keeping body fat at bay.

How it helps:

– Increase in resting glycogen stores

– Replenishes satellite cells and increases mitochondrial biogensis

– Improves nutrient repartitioning

– Increases in growth hormone

In the next part of this series I will start to breakdown what is happening at a deeper level during times of fasting and low caloric intake.


[1] Minor, Robin K., Joy W. Chang, and Rafael De Cabo. “Hungry for Life: How the Arcuate Nucleus and Neuropeptide Y May Play a Critical Role in Mediating the Benefits of Calorie Restriction.” Molecular and Cellular Endocrinology. U.S. National Library of Medicine, n.d.

[2]  Dohm, G.L. “Metabolic Responses to Exercise after Fasting.” Metabolic Responses to Exercise after Fasting. Journal of Applied Physiology, n.d.

[3] Javier T. Gonzalez, Rachel C. Veasey, Penny L. S. Rumbold, Emma J. Stevenson. “Breakfast and exercise contingently affect postprandial metabolism and energy balance in physically active males.” British Journal of Nutrition, 201

[4] Z, Guo. “Intermittent Fasting and Caloric Restriction Ameliorate Age-related Behavioral Deficits in the Triple-transgenic Mouse Model of Alzheimer’s Disease.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d.

[5] Lee, C., and VD Longo. “Fasting vs Dietary Restriction in Cellular Protection and Cancer Treatment: From Model Organisms to Patients.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d.

[6] James E. Brown, Michael Mosley and Sarah Aldred. Intermittent fasting: a dietary intervention for prevention of diabetes and cardiovascular disease? British Journal of Diabetes and Vascular Disease, April 2013

[7] Varady, KA. “The American Journal of Clinical Nutrition.” Alternate-day Fasting and Chronic Disease Prevention: A Review of Human and Animal Trials. American Society for Clinical Nutrition, n.d.

[8] Kroeger, CM. “Result FiltersAlternate Day Fasting Increases LDL Particle Size Independently of Dietary Fat Content in Obese Humans.”National Center for Biotechnology Information. U.S. National Library of Medicine, n.d

[9] MC Klempel, and CM Kroeger. “Intermittent fasting combined with calorie restriction is effective for weight loss and cardio-protection in obese women.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d.

[10] Fontana, Luigi. “Long-term Calorie Restriction Is Highly Effective in Reducing the Risk for Atherosclerosis in Humans.”

[11] Intermountain Medical Center. “Fasting reduces cholesterol levels in prediabetic people over extended period of time, new research finds.” ScienceDaily. ScienceDaily, 14 June 2014. <>.

[12] Chang, CW. “Prolonged Fasting Reduces IGF-1/PKA to Promote Hematopoietic-Stem-Cell-Based Regeneration and Reverse Immunosuppression.”

[13] Relaix, F. “Satellite Cells Are Essential for Skeletal Muscle Regeneration: The Cell on the Edge Returns Centre Stage.” National Center for Biotechnology Information. U.S. National Library of Medicine, n.d.

9 Responses to “The Ultimate Guide to Intermittent Fasting II – Not All Fasts Are Created Equal”

  1. Nick


    I am new to the IF and trying to understand the basics. During the feeding window, do I eat normally or do I try to eat more? (assuming I am hungrier). Goal is to cut weight and I am on a 2,300cal diet- 40% protein, 30% CHO, 3O% Fat. Weight= 220lbs, 30%BF.

    How many days a week do you recommend for the IF and do those calorie goals make sense?

    • Fred

      Nick, How much you eat during your window is dependent upon what your caloric goal for that day/week is. There are many ways to do this but my clients typically have low calorie days on fasting days and high calorie days on lifting days. I’ve found this to be a good set up for body recomposition. If pure fat loss is your goal you can be more aggressive with the amount of low calorie days you have. So while your average for the week may be 2,300, you don’t need 2300 on every single day. Certainly don’t need the same amount of energy on a day you train vs. an off day, right?

      The numbers you picked might work but it’s individual at the same time. At 30% body fat you aren’t in a prime position metabolically so don’t be surprised if you need to lower calories more or the weight loss is slow. If you are new to fasting I’d start with 1-2 per week and see how long you can push the fast.

  2. Martin

    I’ve been doing 16-8 fasting twice a week for a while now. On fasting days I do HIIT followed by about twenty minutes of aerobics (one of the fitness experts I follow says that free floating fatty acids reattach if you don’t follow HIIT with slow sustained exercise. Don’t know if it’s true, but I like how it makes me feel). Last year, I tried to add to days of IF a week, but I started having gout symptoms. I’d love to go back to fasting more. Any suggestions?

    Also, you said in one article that you don’t use any supplements besides whey, but in another you say you use leucine.

    Would love to read more about protein meal replacements for breaking fasts.

    • Fred Duncan

      Martin, Thanks for reading.

      I’m not aware of any research on aerobics post HIT in this regard, but that doesn’t mean it may not exist. I imagine they mean you wouldn’t want to release fat into the blood stream and then not match your activity to make use of it. I agree with that. Though I wouldn’t quite say you “need” to do aerobics post resistance training or HIT training in a fasted state. It depends how you structure the day.

      However, I rarely recommend HIT during fasting anymore. I use a different set-up that I’m outlining in my ebook coming up. I also give examples of meal breakdowns and what to eat on days you fast. Might be of interest to you. I’m not saying that you can’t have some success with it, but I prefer other methods.

      I experimented with and used leucine for a very long time – so I’m pretty familiar with it. At the moment, I’m not using any. It’s still something that I may recommend or bring up to specific clients depending on their goals. I may begin using it again shortly.

      Lastly, Were you staying hydrated? How long did you try and go? Could be your set-up. Hard to know without seeing big picture.

      • Martin

        Thanks for answering so quickly. No, I wasn’t drinking enough water afterwards. Definitely helps when I’m better about that. I should have mentioned that I’m 62 years old. I do intervals twice a week. By the scale I’m ten pounds overweight, but I want to cut fat. I’m certainly open to tweaking or even changing my routine and will buy your book when it becomes available.

  3. Chandrika

    Fred, I’m 52, Female, thin, vegetarian. (But eat eggs)
    I’m doing dry fasts for the anti-inflammatory effect and to build muscle and strength.
    My first 24 hr dry fast was good; I felt energetic, did stretches, did a normal day’s work in 43 centigrade heat. Then I did a 4 hour eating and water window. But my second day fast dehydrated me, and I experienced exhaustion and increased pain. So I’ve to tweak this down to a weekly 24 hour fast, and more hydration. Any food recommendations? I eat some homemade probiotics (so flavonoids and polyphenols), one egg, fruit, and some vegetables.



  1.  What Happens When You Fast?
  2.  Intermittent Fasting - What the Research Says
  3.  The Ultimate Guide to Intermittent Fasting I - Fred Duncan

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