Low Carb Intermittent Fasting:

A Complete Guide

Low carb intermittent fasting (LCIF) 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.

If you are not familiar with intermittent fasting and low carb dieting, In the following article, we're going to take a closer look at the concept and the benefits and show you how to get started with a practical example. We will also dispel a few common myths along the way.

How Does LCIF Assist Weight Loss?

There’s a lot of talk about the benefits of intermittent fasting and low carb diets in general but it should be noted that lCIF isn’t a magic bullet for weight loss alone.

To lose weight the human body must be in a caloric deficit.

Weight Loss

What Is A Caloric Deficit?

When you are consuming less energy from food (Calories) than your body requires to maintain your current weight, you are in caloric deficit. The end result is weight loss.

If Caloric Deficit Is The Key To Weight Loss Why Bother With LCIF?

There’s a couple of reasons for this. 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 broken down into three specific groups, known as macronutrients.

These are protein, carbohydrates, and fat.

In simple terms, proteins are the 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. While Carbohydrates are our primary energy source.


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 it has the ability to convert stored body fat into energy through Ketosis. Body fat, otherwise known as subcutaneous fat accumulates when you consume more calories than your body requires to maintain current weight (caloric surplus).

Stored excess calories 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

The longer the body becomes accustomed to converting fat into energy, the more efficient it becomes. You could say by following a low carb diet you are 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, 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 perhaps 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. Most people simply cannot consume as much food 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 carbs) and many people find it easier sticking to an LCIF diet.

Beating The Sugar Crash

Plate of Donuts

Additionally, if consuming a diet high in processed carbohydrates, most of the fibre is stripped from the food when it is being produced. Low fibre combined with high sugar content initiates a rapid insulin response, resulting in the body digesting processed carbohydrates quickly. 

This can leave you feeling hungry sooner and 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.

LCIF Results

So does LCIF 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. Depending on how much you reduce your carbohydrate intake you may also 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.

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 experience a mild reaction. Symptoms typically last between 5 – 10 days.

Is LCIF Safe?

It is safe, and holds numerous health benefits aside from weight loss. 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, 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 of nutrients and consume plenty of vegetables.

Overeating And Weight Gain

You must ensure you are not overindulging during the eating window. Just because you have fasted for 16 hours doesn’t mean you can eat excessively during the eating window as you will put on excess weight if in caloric surplus.

Caffeine Dependency

Black coffee is often associated with fasting and is acceptable during a fasting period due to its lack of calories (2 calories per cup). Some people rely on this excessively and take in too much caffeine. Excess caffeine is detrimental to sleep and may contribute to other health issues such as:

  • Dehydration
  • Dizziness and headaches
  • Insomnia
  • Irregular heartbeat

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


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.

Children should focus on making smarter food choices rather than restrictive diets. Children are in a state of constant development, restrictive diets of any kind are generally not recommended.

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 method of intermittent fasting​.

The truth is there are a number of different approaches to intermittent fasting. But in the majority of cases the 16:8 method (fasting for 16 hours and consuming your food within the 8 remaining hours) is considered the easiest method to get started with.

A 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. 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 this to suit your work schedule. The concept remains the same however. 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 many 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 calculate the number of calories you should consume from carbohydrates. But first, let’s dispel a few commonly held beliefs about carbohydrates.

In Defence Of Carbohydrates

Carbs get a pretty bad rap in today’s nutritional landscape but the fact is not all carbs are created equal. When we mention low carb diets it would 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. In fact they contain many of the micronutrients our bodies requires to remain healthy.

Refined Carbs

Refined carbs such as white bread, pasta, soda drinks, and cakes and biscuits should be 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 isn't a magic number that applies to everyone and it can largely depend on your somatype.



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

Depending on your goals it can be a good idea to adjust your macronutrient intake to suit your somatype. Recommendations are shown in the example graphic below.

Each somatype has different carbohydrate tolerances. For instance endomorphs tend to store more body fat and have a large bone structure. Mesomorphs are athletic and tend to have a faster metabolism. Ectomorphs find it difficult to gain weight. 

Recommended Macronutrient Breakdown Based on Somatype






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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 slow your metabolism and your progress if trying to lose weight.

Your body might just be the most complex thing in the entire universe (yes, it’s true). It helps to remember that it is always seeking equilibrium (Homeostasis). Because of this, the body will make adjustments to any form of caloric restriction by altering your metabolism.

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 our current weight. BMR takes into consideration 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

No deliberate exercise

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 place to start 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 generic 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, start with a lower deficit to preserve lean muscle mass.

A Practical Example of LCIF in Action

The information above can quickly get complicated, and in some cases may put people off the idea of LCIF completely.

To help simplify things let’s walk you through what a typical day would look like for someone undertaking LCIF.

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.


LCIF 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. This give us 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.

Incorporating Intermittent Fasting

This is the simple part (simple, not easy!).

Just stop eating at 8:00pm the previous night and don’t eat again until midday the following day. You can drink black coffee and zero calorie drinks. But remember many of these contain artificial sweeteners 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:




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2200 x .4 = 880 Calories

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2200 x .2 = 440 Calories

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2200 x .4 = 880 Calories

LCIF 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 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 advised to adhere to the following:

  • 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 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. 

A Reliable System That Will Lead To Weight Loss

While many diets are little more than guesswork, LCIF 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 can be a trap to get too caught up in the finer details at the expense of application.

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 an LCIF 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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