Intermittent fasting (IF) is gaining popularity in the media. With all the exposure, if you haven’t already dug into this, you might be wondering what Intermittent Fasting is all about.

Intermittent Fasting is less of a “diet” and more of an eating protocol. As such, it is more complex in nature than a typical diet would be. There are many ways to “do” intermittent fasting. And your body goes through a lot of changes when adapting to fasting and during fasting. This article is a very high level of intermittent fasting and by no means a complete resource.

Basics of Intermittent Fasting

In intermittent fasting, it is generally considered “fasting” if you abstain from all food. However, not all food is created equal, and non-caloric beverages such as green tea and water are generally considered “safe” for fasting. However, anything that has a caloric content would be considered “food” that shouldn’t be consumed during a fast.

This means, if you are consuming protein shakes, BCAAs, cream in your coffee, or small meals, you are not fasting.

Additionally, research is being conducted on non-caloric sweeteners to see if insulin spikes based on taste alone. There is some evidence that certain non-caloric sweeteners still spike insulin, and for the purposes of fasting for weight loss, would be considered to break a fast.

So, if Fasting is “not eating food”, Intermittent fasting is:

Fasting and not fasting (eating) on and off over some predefined period of time.

Generally, you’ll hear people who practice intermittent fasting talk about their fasting and feeding windows (Or Fasting and Feasting windows… which I prefer because the term feeding brings to mind a swarm of sharks in a feeding frenzy…)

Therefore, intermittent fasting is an eating protocol based on time. And as such, you can practice intermittent fasting with any other sound diet out there. Many people actually combine the keto diet with intermittent fasting. But, it doesn’t have to be keto. Also, it doesn’t have to be any “branded” diet. You could just eat healthy and practice intermittent fasting and still reap the benefits.

Intermittent Fasting Protocols

There are several ways to “do” Intermittent Fasting. These would be considered the IF Protocols, and the main difference between each is the duration and/or timing of the feasting window. I’ll explain.

16:8

The most common protocol for IF is probably 16:8. This means you would fast for 16 hours, and feast for 8 hours. Generally, the time of day that you eat doesn’t matter. Therefore, you can slide your 8 hours wherever you want. The important part is that you have 16 hours of no eating. Most people get 6-8 of these during sleep.

So, you can do your 8 hours from when you get up to 8 hours later, you can start it at noon and go till 8… Basically, you can do whatever you want regarding the TIME you eat, but the duration of your eating window stays at 8 hours.

And for the record, if you eat at noon, and start eating at 8, then your feeding window would technically be longer than 8 hours because you’d be eating still, past 8. This means that generally, most IFers would likely start eating closer to 7 to be done eating by 8 and start their fasting window. So, you can see already that the EXACT timing of fasting/feasting isn’t precise. The good news? It doesn’t have to be.

20:4

Sometimes this is called the “Warrior diet”. It’s a 20-hour fasting window, with a 4-hour feeding window. This is NOT for the beginner faster. In fact, starting fasting can be ….. Challenging. Click here for tips on how to get started Intermittent Fasting.

Typically, the IFer doing 20:4 fasting would eat only 2 meals during their 4-hour feasting window. As you can imagine, depending on the caloric needs of the person, those meals could be rather large or super dense in calories. Granted, MOST of us do not need to consume very large quantities of calories.

But given the short window to get the essential nutrients, it’s often not recommended for high-performance/elite athletes to practice IF. Exceptions could be during an off-season, when the athlete is dialing back on training, focusing on recovery and fat loss.

18:6

This bridges the gap between 16:8 and 20:4. It would be slightly easier to do than the 20:4 and slightly harder than 16:8. But it can be quite common, especially if you’ve been 16:8 for a while, but can’t quite stomach the idea of packing all your calories into a short 4-hour window. Eating for 6 gives you time to have 2 larger meals and a small snack to get all your calories in.

One Meal a Day (OMAD)

OMAD is exactly what it says. It’s eating one meal within a 24 hour period. As with the 20:4 fasting, you can imaging that getting all the calories you need in that one meal… well,… let’s just say, your body will need to adapt…

Alternate Day Fasting

Alternate day fasting would be eating during one 24 hour period and not eating for the next 24 hour period. There are quite a few variations that could be taken on this. The first, would be to eat relatively regularly during the feeding day (so breakfast, lunch, dinner over an 8-12 hour period). The other would be to keep the feeding window shorter on the feeding day (4-8 hours of feeding) and lengthening the fast.

There are benefits to doing longer fasts. However, if these benefits are what you’re after, it is not recommended to do them “all the time”. Maybe do a 24 hour fast once a week and anything over that (36 or 48-hour type fasts) only once a month.

Time-Restricted Eating (TRE)

In my mind, time-restricted eating is just another name for intermittent fasting because essentially in IF you’re restricting the time you’re eating. But in some TRE protocols, you actually eat only during a very specific period of time. For example, first thing in the morning till 8 hours later.

Circadian Rhythm

This fast is supposed to align with your natural circadian rhythm. The fasting period is when the sun is down. You eat when the sun is up. If you’re practicing this method of fasting, you would notice that your eating window would be shorter in winter and longer in summer. You might also notice it’s opposite of the fast Muslim practitioners follow during Ramadan.

What protocol is best?

Well, that largely depends on you. You must consider your goals, your lifestyle, your current eating habits, your family, your culture, your schedule, and your body.

Regardless of what protocol you use, start slow. Ease into the change in schedule by slowly (over weeks) shrinking your current eating window.

What Intermittent Fasting Isn’t

People choose to do Intermittent Fasting for a variety of reasons. Some folks do it for fat loss. Some people fast for the health benefits of fasting. Others use it as an occasional plateau buster. Others, still, do it simply for convenience. Regardless of your goals, it is important to keep in mind several things.

Intermittent fasting isn’t a blank check to “eat whatever you want and whatever quantities you want” during your feasting window. The general energy balance equation absolutely still applies. (ie. If you eat more than you burn, you’ll gain weight, and if you eat less than you burn, you’ll lose weight). Too many people think that they can go all wild on food during the feasting window and still lose weight. However, if your goals are to gain mass, Some intermittent fasting protocols may prove to be too difficult to get enough quality food to support your caloric demands.

IF grants some additional fat-burning benefits. But it doesn’t magically make you burn more calories. (not like exercising or packing on muscle might). It helps change where you get your energy from. If you are fasting, you need to tap into your own energy stores to fuel your body. There’s a big boon with fasting in that your muscle mass is generally NOT used. Your body prefers fat for fuel anyway, and even at 5% body fat, you’d still have plenty of fuel on you to live comfortably for a short fast. It also can aid in muscle building. However, IF alone will not build muscle. Muscle and strength building must be supported by both good nutrition, and appropriate exercise.

There are several “kinds” of fasting out there. Some people will say fasting means you can’t even drink water. Some will say you can eat up to 600 calories a day and still be “fasting”. I would say in general, most practitioners of intermittent fasting do not consume calories during their fasting window. Most consume at least water. However, many studies that are out there appear to study intermittent fasting but often use a protocol that would not be considered “Fasting” by many practitioners. That is, they alternately eat a day of full calories and a day with very low calories. Very low-calorie diets have shown to have many of the same health benefits as IF, however, because one never fully fasts, they never fully reap the benefits of not eating. The most notable is that when you are eating, your body continues to signal your brain to want more food. This hormonal signaling actually diminishes over time when you are truly in a fasted state, so you end up feeling less hungry over time, even when you haven’t eaten for a significant number of hours.

Benefits of Intermittent Fasting

Intermittent fasting has shown to have many benefits. Some of these benefits include:

• Increased Fat Burning
• Autophagy
• Increased Insulin Sensitivity
• Mental Clarity
• Saves Time

Increased Fat Burning

Because the body still needs to sustain itself during a fasted state when no additional calories are coming in, it resorts to using the most readily available source of energy – your fat stores. The body prefers to convert fat to energy over converting muscle or lean mass to energy so the risk of losing muscle is slim. (Provided that you are meeting your nutritional needs to maintain muscle.) If you fast long enough, you can even get into a state of ketosis which is the foundation of the ketogenic (keto) diet. This is where your body uses ketones for fuel (ketones are made from fat). But, with Intermittent Fasting, you don’t need to cut out any food types to get into this state if you fast long enough.

Autophagy

Autophagy is your body’s method of recycling old damaged cells so that it can replace them with new and improved ones. It’s thought to keep you younger by creating these new younger cells. When fasting, the recycled cells may also be used for nourishment to keep vital functions going.

Autophagy at the cell level can remove toxins that may be attributed to neurodegenerative diseases (like Alzheimers and Parkinson’s disease). It’s also getting a lot of press for its role in reducing the risk of, preventing and maybe even curing cancer.

Increased Insulin Sensitivity

Insulin is a hormone that tells your cells to accept energy into them. When you flex a muscle say to pick up something or walk, that muscle is forced to use energy stored within it just to contract. Muscle cells can only store a limited amount of fuel at a time. So, once that is depleted, the body must put it back. If your body is insulin resistant, that means that your cells are not as receptive to insulin signaling and therefore will not replenish their energy stores as efficiently. Over time, this will make you weak and sluggish. And that can start a downward spiral. Diabetics (type 2) are typically insulin resistant. This means their body produces insulin, but the cells aren’t receptive to it.

Intermittent fasting can help your cells become more receptive to insulin. New research shows that intermittent fasting may even reverse type 2 diabetes.

Mental Clarity

Studies have shown that fasting actually increases mental clarity. Many folks report feeling more alert from fasting. Think about how sluggish you might feel after a big meal (like trying to stay awake after Thanksgiving dinner). Studies show that fasting will increase alertness. Perhaps from the hunger affect.

Additionally, animal studies show that IF even improves motor coordination, learning, and memory.

Time-Saving

Because with intermittent fasting, you are eating during a smaller portion of the day. It frees up time that would otherwise be spent preparing and eating meals to do other things. In this way, it can simplify your life. If you’ve ever thought “there aren’t enough hours in the day, just shrinking your eating window or the number of meals can free up precious hours.

Side Effects of Intermittent Fasting

There are some side effects of intermittent fasting that one may or may not experience. I’m putting these out there not to scare you, but to arm you with knowledge just in case you do have any of these. The good news is that most of them are temporary, reversible or completely avoidable. In general, these side effects may be caused by either your body adapting to the changes in eating patterns or poor nutrition. As always, talk to your doctor before starting any new diet or diet protocol.

You may experience any number of the following (Or maybe you won’t experience any):

• Headache
• Diarrhea
• Constipation
• Insomnia & Anxiousness
• Acid Reflux (Heartburn)
• Gout
• Bad Breath
• Feeling Cold
• Nausea (when eating)
• Lethargy or Fatigue
• Hair Loss
• Fainting
• Headache
• Moodiness (Especially in the first few days)

Headache

Headaches – may occur cause your brain needs glycogen, and you need to adapt to fat for brain fuel – temporary

It could also be caused by low levels of sodium. Once we drop insulin, the kidneys get the signal to release excess water. If you are urinating a lot, it’s likely you are losing sodium. Also, because you don’t eat when fasting, it’s quite likely you’re not eating as much as before. And it could happen that you’re not getting enough electrolytes in general (sodium, potassium, and magnesium). To combat, try having some salt, like a pinch of salt under your tongue or added to some water while you are fasting.

Additionally, since fasting actually does cause a stress response and raises cortisol levels, your headache could be a stress headache.

If adding salt isn’t working, go ahead and break your fast a little early. There’s no harm in that. Often, after adapting to the shorter fasts, you will be able to increase the fasting length gradually. Remember this can be a pretty big change to adapt to so easing into it is always best.

Diarrhea

Diarrhea can be quite common for new fasters. It’s especially common if you enter the fast after eating a lot of carbs. The drop in insulin signals the kidneys to excrete the excess water. Along with depleting sodium as described under headaches, it could create watery bowel movements (or unwanted bowel movements). Make sure you are getting enough electrolytes since they are lost in bowel movements just as they are lost with urination. And take some fiber to help bulk up the stool (such as psyllium husk or Metamucil). Make sure you continue to drink a lot of water so that the fiber can do its job.

Constipation

Constipation can be an issue. However, if you aren’t eating, or if you aren’t eating as much, this change in diet may result in a reduction in your bowel movements. Most notably, it could reduce it. So, it’s probably nothing to worry about if you are not feeling uncomfortable. If it does become uncomfortable (and not just weird to be off schedule), then make sure you are drinking enough water. So, drink more especially when you’re thirsty. You can take over the counter meds for constipation. Exercising more can help as well.

Insomnia & Anxiousness

When we fast, we produce more adrenaline. Typically, this energizes us and makes us feel more alert. But, it can also make us more jittery (feel anxious) or more energized and alert when we should be sleeping. Interestingly enough, sometimes the jitteriness is actually interpreted as low blood sugar. It isn’t, it’s adrenaline, and it’s actually signaling fat burning. If you are already anxious, this probably isn’t making your anxiety worse, but it may feel like it. To counter it, try implementing relaxation techniques. Start a bedtime ritual that includes meditation, relaxing baths, or yoga. But if it persists, probably the best thing is to do is to scale back on fasting. As mentioned above, fasting requires adaptation. Think of it as you training your body to physically do things inside itself, just as you would train it to physically do things outside like pushups or running.

Acid Reflux (Heartburn)

Acid Reflux is caused by excessive stomach acid. Fasting increases the acid in the stomach. Most people don’t have enough acid in the stomach and will not have this side effect. If you already suffer from acid reflux, you are at a greater risk for this happening.

You can try taking lemon juice or apple cider vinegar to help neutralize some of the acids. Also, go ahead and eat it may just require a longer adaptation period. Typically, once the body adapts, the symptom gets better than it was before.

Also, if your suffering from acid reflux at night in bed, take note of when you ate last. Sometimes moving your last meal further away from bedtime (move it earlier in the day) will help reduce the symptom at night.

Gout

Gout is caused by excess Uric Acid typically in your feet or toes. Like with acid reflux, generally, folks don’t develop gout from intermittent fasting if they don’t already have a history of it. Uric acid is an antioxidant so isn’t inherently bad. If you develop an excess of it you can add lime juice and take cherry root extract to help. You may also need to alkalize the acid. The best way to do this naturally is to make sure you are getting enough vegetables and fruits (especially ones that contain potassium). Spinach, broccoli, sweet potatoes, avocado, beans, and fruits like grapefruit or watermelon. Additionally fish like tuna, halibut or cod have good sources of potassium. If symptoms persist, scale back your fast. Talk to your doctor. The risks are high for potassium supplementation and may not be recommended.

Bad Breath

Bad breath is caused by the ketones our bodies make when we are in ketosis. It really signals that you are burning fat. But it can be an issue. Try brushing your teeth more, using a tongue scraper and drinking more water. If you want to try oil pulling a few times a week, it may help.

Feeling Cold

May feel cold especially in your hands and feet. This can be caused by the thyroid not having to work as much. Usually, it’s temporary and not a big deal. You may also feel cold as your body burns fat because it actually changes your fat from the normal adipose fat we think of to a more metabolically active fat called brown fat. Other than wearing warmer clothes, there’s not much to be done. Exercising will help warm you temporarily. But just remind yourself you are actually burning more fat.

Nausea (when eating)

Once again, until you adapt to fasting, you may feel nauseated when you eat, especially when you are breaking your fast. This is usually related to a sluggish gallbladder and apple cider vinegar could help. Also, don’t eat so much at any one meal that you feel bloated. Eat good, and enough calories, but refrain from eating too much. You may need to scale your first meal of the day way back to something small and lean like lean protein with little to no fat, or a non-fat carbohydrate like an apple.

Lethargy or Fatigue, Hair Loss, Fainting, or Moodiness (Especially in the first few days)

These side effects are often caused by simply not getting enough nutrients.

When fasting it’s easier to eat less food because the window in which food is consumed is dramatically decreased from a typical schedule. It’s really important to choose good food when fasting (see my Eat Healthy Without Dieting article). Many folks are already deficient in some nutrients (even though you may not know it). And some are in the insufficient stage where you aren’t quite deficient in that nutrient but you aren’t really getting enough. Fasting can magnify nutrient deficiencies and insufficiencies. Since this can cause a wide range of issues, here are the symptoms (Side Effects) generally caused by deficiencies:

Who Shouldn’t Fast?

Pregnant or breastfeeding women, children under 18, anyone underweight (BMI <18.5), and anyone at risk of eating disorders should refrain from intermittent fasting. If you are at risk for hypoglycemia or have a medical condition such as diabetes, have gout, heart disease, kidney disease or liver disease or take prescription medication, talk to your doctor before starting fasting. Fasting may be contraindicated for your condition. You may still be able to try fasting but under supervised conditions.

In Summary

Intermittent fasting is an eating protocol that has a vast amount of benefits with few drawbacks, especially when starting slowly, given time to adapt and combined with a healthy nutritious diet.

Intermittent fasting may not be right for everyone, but it can be incredibly helpful for those it is right for.

As with any diet change, talk to your doctor first. Then if you choose to move forward, ease into it. Strive to create a healthy lifestyle that you can sustain for the rest of your life.

Are you still on the fence regarding a diet? Here’s my overview of popular diets. Or, you can choose to eat healthy without dieting.