Low Carb Intermittent Fasting: A Complete Guide

Low carb intermittent fasting is a term used to describe low carb diet combined with intermittent fasting. When combined with a caloric deficit it forms a powerful approach to weight loss that offers a number of advantages over a regular weight loss diet.

If you don’t know anything about intermittent fasting, low carb or caloric deficit, In the following article, I’m going to explain the concept, the benefits, show you how to get started with a practical example and dispel a few myths along the way.

How Does Low Carb Intermittent Fasting Assist Weight Loss?

It’s easy to get the wrong idea, there’s a lot of talk about the benefits of intermittent fasting and low carb diets in general but it should be noted that low carb intermittent fasting isn’t a magic bullet for weight loss on its own. The fact is to lose weight the human body must be in a caloric deficit.

What Is A Caloric Deficit?

This occurs when you are consuming less energy from your intake of food (Calories) than your body requires in total energy (Calories, again) to maintain current weight. The end result is weight loss.

If Caloric Deficit Is The Key To Weight Loss Why Bother With Low Carb or Intermittent Fasting?

There’s a couple of reasons for this. And, while there are conflicting opinions on just what the most beneficial aspect is, one of the most compelling involves how we utilise sugar in the blood stream for energy. To really get a grasp on the concept it’s important to understand how the body digests and absorbs nutrients from the food we eat.


Our food is typically be broken down into three specific groups, known as macronutrients. These are protein, carbohydrates, and fat.

In simple terms, proteins are building blocks of the body, used to build and repair tissue, make enzymes and hormones. Fat is used to store energy in the body and assist with chemical processes.

Carbohydrates on the other hand are our primary energy source.

Low Carb Intermittent Fasting and Pasta

The Role Of Carbohydrates

When consumed carbohydrates are broken down into glucose in the bloodstream. Excess glucose is converted into glycogen (the stored chain form of glucose) and stored in the muscles and liver; where it can be broken down to glucose as required by the body for energy.

In an average person the liver holds 100 grams of glycogen while our muscles hold approx. 500 grams.

This is where things get interesting….

When the body has insufficient glucose to draw upon for energy e.g. as is the case when your diet is very low on carbohydrates it converts stored body fat into an energy source through the process of Ketosis. Body fat (subcutaneous fat) accumulates when you are consuming more calories than your body requires to maintain its current weight (caloric surplus) and can be thought of as reserve energy. When your energy demands are higher than your caloric intake, your body taps into these reserve energy stores.

Sugar V Fat

Importantly, the longer the body becomes accustomed to converting fat for energy as opposed to sugar, the more efficient it becomes at it. You could say by following a low carb diet you are theoretically training your body to become better at burning body fat instead of sugar. The ‘Ketogenic Diet’ utilises a very low carbohydrate approach with the aim of keeping the body in ‘ketosis’. Ketosis occurs when the energy demands of the body are not being met from glycogen (glycolysis) resulting in the liver producing ketones from stored fatty acids to provide energy to the body.

What Is Insulin?

Insulin is the hormone that is responsible for removing excess glucose from the bloodstream. It is produced by the pancreas. Type 2 diabetics suffer from insulin resistance in many cases (but not always) due to diet and lifestyle e.g. an unhealthy diet, high in sugar combined with a sedentary lifestyle. Over time the body becomes resistant to insulin and high levels of glucose remain in the bloodstream.

Type 1 Diabetics, on the other hand, do not produce Insulin or produce an insufficient amount due to an autoimmune condition which destroys the cells of the Pancreas.

Both groups require insulin supplementation.

Calorie Control

The second and for some even more compelling reason low carb intermittent fasting is effective is calorie control.

When undertaking intermittent fasting your window for consuming food is narrower than the standard 12-14 hours most people operate within. This approach tends to lead to a natural reduction in caloric intake as most people simply cannot consume as much food as they would throughout a standard day within this smaller period of time.

Combine this with the fact that limiting carbohydrate intake generally means increasing your protein intake (protein is more satiating than carbohydrates) and many people find it easier sticking to an LCIF diet.

Beating The Sugar Crash

Refined Carbs - Sugar Spike

Additionally, if consuming a diet high in processed carbohydrates, most of the fibre is stripped from the food during processing. Low fibre combined with high sugar content initiates a more rapid insulin response than normal, resulting in the body digesting processed carbohydrates much faster, leaving you feeling hungry sooner and subsequently low in energy. This is also referred to as a ‘sugar crash’. Alternatively, foods high in soluble fibre tend to slow digestion resulting in a more balanced insulin response.

Low Carb Intermittent Fasting Results

So does low carb intermittent fasting help you lose weight?

In short, yes. It has a proven track record, regardless of whether the main perceived benefit is simply calorie control.

Will it work for you? The most effective weight loss methods are the ones we can sustain.

Most people report some hunger early on and depending on how much you reduce your carbohydrate intake you may experience what is known as ‘low carb flu’. But as the body adjusts the hunger pains and flu-like symptoms diminish making it far more sustainable for most people.

What Is Low Carb Flu?

When the body transitions from using sugar (glucose) as energy to fat it’s normal to experience flu-like symptoms as the body adapts. These symptoms include but are not limited to fatigue, an inability to focus, headaches, muscle aches and in some cases nausea. While some experience quite severe symptoms, the majority of people will only suffer from a mild reaction or no reaction at all. Symptoms typically last between 5 – 10 days.

Is Low Carb Intermittent Fasting Safe?

It is safe. But there are a few things you need to be aware of before starting:

  • Eating Disorders

If you have experienced an eating disorder in the past such as Anorexia or Bulimia, any form of fasting should be discussed with your doctor. The fast/feast mentality can have a psychological impact and push someone towards a pre-existing eating disorder.

  • Maintaining A Balanced Diet

You must ensure you maintain a balanced diet even when on a restrictive diet. Changing the way we eat can sometimes force changes we might otherwise not consider. Always focus on a healthy balance and consume plenty of vegetables.

  • Overeating And Weight Gain

You must make sure you are not overeating during the eating window. Just because you fasted for 16 hours doesn’t mean you can eat everything in sight during the eating window as you will put on excess weight if in caloric surplus.

  • Caffeine Dependency

Black coffee is often associated with Low Carb Intermittent Fasting and is perfectly acceptable during a fasting period due to its lack of calories (2 calories per cup). Some people rely on this a little too much however and take in too much caffeine. Excess caffeine is detrimental to sleep and may cause health issues such as:

  • Dehydration
  • Dizziness and headaches
  • Insomnia
  • Irregular heartbeat

I recommend the following groups seek professional medical advice before undertaking LCIF:

  • Diabetics
    While low carb intermittent fasting may hold benefits for diabetics I would advise speaking to your doctor before undertaking major changes to your diet.
  • Mum’s to be
    Studies demonstrate that pregnant women who fast may have issues with their children’s development, both physically and cognitively.

How To Get Started

Step 1) Introduction To Intermittent Fasting

For the purpose of this guide, I recommend starting with a variation of the 16:8 approach to Intermittent Fasting.

The truth is there are a number of different approaches to intermittent fasting that you can read more about here. But in the majority of cases the 16:8 method (Fasting for 16 hours and consuming your food in the 8 remaining hours) would be considered the easiest method for beginners.

But, I don’t recommend coming out of the blocks on day one with a 16 hour fast. Intermittent Fasting takes time to adjust and therefore I recommend a 12 hour fasting window to begin with and then increase the fasting window to 16 hours.

A simple and practical way to get started is to simply skip breakfast.

16:8 Intermittent Fasting

The most popular approach to the 16:8 diet is to consume your calories between midday and 8:00pm, however, this can be difficult when starting out so instead allow yourself to eat as you normally would in the evening for the first 1-2 weeks before gradually reducing this to 8 pm.

For shift workers you may need to alter things to suit your work schedule however the concept remains the same. Stop eating before you go to bed and do not consume calories until you normally would have your second meal of the day.

Isn’t Breakfast The Most Important Meal Of The Day?

Disregarding for a second the fact that most people do not consume a healthy breakfast to begin with e.g. most breakfast cereals are high in sugar. The truth is there really is no reason you can’t skip breakfast. There is also no evidence that suggests eating breakfast is beneficial with regard to weight loss or improved metabolism.

Step 2) Combining Low Carb And Intermittent Fasting

Once your fasting window is established it is time to factor in the number of calories you will consume from carbohydrates. But first, let’s dispel a few commonly held beliefs about carbohydrates.

In Defence Of Carbohydrates

Low Carb Intermittent Fasting encourages eating vegetables

Carbs get a pretty bad rap in today’s nutritional landscape but the fact is nothing about nutrition is ever completely black and white and not all carbs are created equal. When we mention low carb diets it would perhaps be, more accurate to refer to low (processed or refined) carb dieting, but to be fair it just doesn’t have the same ring to it.

In any case, carbohydrates from cruciferous vegetables, sweet potato, brown rice, nuts, beans and many fruits should not be avoided and in fact contain many of the micronutrients our bodies requires to remain healthy.

Refined Carbs

Refined carbs on the other hand such as white bread, pasta, soda drinks, and cakes and biscuits are best avoided and are in large part responsible for the obesity epidemic we are witnessing along with lack of sleep and a more sedentary lifestyle.

How Many Calories Should I Consume From Carbohydrates?

There really is no magic number that applies to everyone when discussing carbohydrate consumption and it can largely depend on your somatype.


What’s a Somatype you ask?

While not an exact science, we can place most people into three specific body type groups. Ectomorph, mesomorph and endomorph.

Depending on your goals (in this case weight loss) its best to adjust your carbohydrate intake to suit your somatype as each have different carbohydrate tolerances.

For instance endomorphs tend to store more body fat and have a larger bone structure, whereas mesomorphs are more naturally athletic and tend to have a faster metabolism. Ectomorphs on the other hand are naturally skinny and find it difficult to gain weight. In the majority of cases if your somatype was ectomorph you would be less interested in weight loss.


Naturally Thin


Ectomorph recommended macronutrient ratio


Naturally Athletic


Mesomorph recommended macronutrient ratio


Naturally Thickset


Endomorph recommended macronutrient ratio

Step 3) Incorporate A Caloric Deficit

Once you have established your eating window and carbohydrate intake you can start calculating your caloric deficit.

Don’t Go To Extremes

Studies demonstrate that eating too little e.g. creating an excessive caloric deficit over an extended period will only serve to slow your metabolism and ultimately your progress if trying to lose weight.

Your body might just be the most complex thing in the entire universe (yes, it’s true) and it helps to remember that it is always trying to reach a state of equilibrium (Homeostasis) and will make adjustments to any form of caloric restriction by altering your metabolism. Therefore when approaching weight loss in a practical sense, slow and steady is always the most effective approach.

BMR – Basal Metabolic Rate

To calculate a caloric deficit we need to do some math. Specifically, we need to know our Basal Metabolic Rate, otherwise known as our BMR. This number indicates the total number of calories our bodies require each day to maintain current weight, taking into consideration our gender, age, height starting weight and activity levels.

The formula most often used to calculate this total is known as the Harris–Benedict equation which is as follows:



BMR = 66.5 + (13.75 × weight in kg) + (5.003 × height in cm) – (6.755 × age in years)


BMR = 66 + (6.2 × weight in pounds) + (12.7 × height in inches) – (6.76 × age in years)



BMR = 655.1 + (9.563 × weight in kg) + (1.850 × height in cm) – (4.676 × age in years)


BMR = 655.1 + (4.35 × weight in pounds) + (4.7 × height in inches) – (4.7 × age in years)

Don’t feel like doing all the math yourself? Don’t worry. I’ve included a free calculator below that calculates your BMR, establishes your caloric deficit and even works out your required amount of protein, carbs and fat.

Deliberate Exercise

Once we have an established BMR it’s simply a case of increasing this total amount to take into account your current activity levels (calories used by the body during deliberate exercise).

I’ve listed the level of activity beside the amount you should increase your total BMR below.

Activity Levels

Completely Sedentary

Multiply your total BMR by 1.2%

Light Active

(light exercise 1-3 times per week)

Multiply your total BMR by 1.375%


(moderate exercise 3-5 times per week)

Multiply your total BMR by 1.55%

Very active

(heavy exercise 6-7 days a week)

Multiply your total BMR by 1.725%

Extremely active

(very heavy exercise 6 – 7 days per week)

Multiply your total BMR by 1.9%

Once you have factored in your activity levels the next step is to reduce your total BMR by your chosen caloric deficit.

The Ideal Caloric Deficit

It’s best when considering your caloric deficit to calculate in percentages. For most people a good starting point is a 20% reduction in calories.

A percentage based approach is most effective because it takes into account different weight ranges e.g. the more overweight a person is the more body fat they have to lose and the less likely their bodies will consume muscle tissue while in caloric deficit.

Simply providing a number e.g. 400 calories might be effective if you are around 200 pounds but if you are much heavier, a larger deficit would be recommended, or your progress will be slow and may affect your motivation.

Alternatively, if you are quite lean, to begin with you would definitely want to start with a lower deficit to preserve lean muscle mass.

A Practical Example of Low Carb Intermittent Fasting

Ok, so the information above can quickly get complicated. And in some cases may put people off the idea of low carb intermittent fasting completely.
To help simplify things let’s walk you through what a typical day would look like for someone undertaking low carb intermittent fasting.

For the purpose of this example, let’s consider our test subject to be a 42-year-old male, endomorph weighing 210 LBS at 6ft tall. The subject is mostly sedentary e.g. works behind a desk and his only form of deliberate exercise is walking his dog a couple of times each week. The subjects goal is to lose at least 20LBS of weight, predominantly body fat.


Low carb intermittent fasting is perfect for this type of goal. First let’s establish the subjects BMR.

For our test subject this results in the following:

BMR = 66 + ( 6.2 × 210 ) + ( 12.7 × 72 ) – ( 6.76 × 42 ) = 1998.48 Calories

Deliberate Exercise

We now have the subjects BMR, which is 1998.48 Calories. Next, we need to establish the subjects deliberate exercise into the equation.

As the subject’s only form of deliberate exercise is to walk his dog 1-3 times per week, we can consider the activity levels to be light active.

This means we multiply the subjects BMR by 1.375 which results in a total of: 2747.91 Calories per day to maintain current weight.

Now that we have established the total calories required for the subject to maintain his current weight we simply need to reduce this by 20% to provide us a caloric intake that will result in steady weight loss.

2747.91 x .2 = 549.582 Calorie Deficit
2747.91 – 549.582 = 2198.328 allowed daily calories

We can round this up to 2200 calories for the sake of practicality.

Intermittent Fasting

This is the simple part (I said simple, not easy).

Just stop eating at 8:00pm the previous night and don’t eat again until midday the following day. In the meantime you can consume black coffee and zero calorie drinks, although remember many of these contain artificial sweeteners and additives that have a dubious record when it comes to health.

In general the occasional zero calorie drink probably won’t do you any harm but I’d recommend against relying on them too heavily or making them a normal part of your day.

Low Carb Diet

Next we can establish how many carbohydrates the subject should consume per day, taking into account the subjects Somatype.

As our test subject is an Endomorph the recommended starting point for Macronutrient ratio is as the following:


Naturally Thickset


Endomorph recommended macronutrient ratio

Based on our recommended caloric intake this would result in the following calories recommended for each Macronutrient:

Protein2200 x .4 = 880 Calories
Carbohydrates2200 x .2 = 440 Calories
Fat2200 x .4 = 880 Calories

Low Carb Intermittent Fasting Calculator

Now that you understand the general concept it’s not at all that important to do the calculations listed above manually. In fact using a spreadsheet or specifically formulated calculator will save you a lot of time.

I have included a handy calculator below that calculates your BMR including deliberate exercise, desired caloric deficit and then lastly the ideal macronutrient breakdown for your body type.

Summing Things Up

In the example above, our test subject would be undertaking the following regimen:

    • No food after 8:00pm until midday the following day
    • 2200 calories allowed per day
    • 880 calories from Protein, 880 Calories from Fat, 440 Calories from Carbohydrates


While this can take some working out if new to LCIF dieting the fact is if sticking to the above our test subject would lose weight.

How much weight you ask?

1 LB of fat is approximately 3,500 calories. Therefore, if sticking to a caloric deficit of approx. 550 calories per day, we could reliably predict weight loss of more than 1lb of fat each week. No ifs or buts.

A Reliable System That Will Lead To Weight Loss

While many diets are little more than guesswork low carb intermittent fasting incorporating a caloric deficit is a reliable system that leads to weight loss. And while there is more we could dive into including the thermal effects of food, cheat meals, micronutrients and metabolism, it is often a trap to get too caught up in these details.

It’s always better, once you have an understanding of the concept to just begin, so my question to you is are you ready to start on a Low Carb Intermittent Fasting program and lose weight? The only thing stopping you is your ability to adhere to this approach and ultimately that will come down to how committed you are.

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