The Fat Loss Equation

Spartanomics' Fat Loss Equation:

FL = Energy expenditure (Training + NEAT) - Energy intake (Nutrition)


Diet-related adaptations (BMR + TEF + NEAT)

Fat loss can seem like a simple process, but simple doesn’t necessarily mean easy. While on the surface, it may simply look like a case of training more, eating less, and the energy balance between them, or the expression; ‘calories in vs calories out’.

If we take a deeper look beyond the surface, there’s a multitude of processes occurring for fat loss to occur. Understanding these can give us a better idea of first how to achieve fat loss, but also how to maximise our efforts in doing so, and lastly, how to maintain the end result.

The Mechanisms of Fat Loss:

Before we delve into the process of achieving fat loss, lets first understand the mechanisms taking place in the body to create that change.

The foods we consume, contain macronutrients (protein, carbohydrates, fats) in some form of ratio and amount. The food we consume first gets chewed into smaller parts to start the process of digestion, before reaching the stomach where enzymes break it down into the required molecules.

This is a vital part of the process.

This process relies not only on a what we swallow, but more importantly what we digest and absorb. Some of the food swallowed will be lost to digestion and excretion, but the food that make it, release nutrients into the bloodstream where they can now be used by the body.

These nutrients face 2 potential fates; burned for energy or stored somewhere to be used at a later time when required e.g. in the muscles, liver or fat cells.

You might be wondering how the body decides the fate of these nutrients. Well, if the intake of these nutrients is less than the output (what we burn), the body will pull on stored energy within the body and there will be some loss of tissue (e.g. fat, muscle, etc.).

The opposite also rings true here whereby if intake of nutrients is greater than the amount we burn, we store them.

If the 2 are equal, there will be no change. Therefore:

Energy Expenditure – Energy Intake = Change in Stored Energy

Still with me?

Okay, lets go one step further and understand HOW we actually burn that fat.

The ‘burning’ of fat is essentially the cells burning fuel to be utilised for energy production. This is broken down into 3 parts:

  1. Breakdown - to burn this fuel, we need to get the fatty acids OUT of the fat cells and released into the bloodstream.

  2. Transportation - once we’ve extracted these fatty acids into the bloodstream, they can now be transported or re-stored depending on their requirement

  3. Burning - once in transit, we can now oxidise or ‘burn’ the fatty acids to generate energy for other tissues to use e.g. the muscles.

So, how and where are we burning calories?

If we take a brief look at human metabolism in terms of an energy expenditure, we can see the following:

  • Basal metabolic rate (BMR): these are the calories we burn at rest just to maintain bodily functions - this makes up approximately 70% of the calories we burn.

  • Thermic effect of food (TEF): these are the calories used to process and digest the food we consume - this makes up approximately 10%.

  • Physical activity (PA): these are the calories burned from planned physical activity - this makes up approximately 5%.

  • Non-exercise activity thermogenesis (NEAT): these are the calories burned from non-planned exercise i.e. general daily movement - this makes up approximately 15%.

You’ll notice the word ‘approximately’ for all the above. Thats because all of these are subject to an individual.

A bigger and heavier person will have a greater requirement of calories to be burned via BMR compared to a smaller person simply because they have a larger body.

An individual with a higher calorie intake will have a greater requirement of calories to be burned via TEF as there is more food to be processed and digested. This is also dependant upon the macronutrients of the foods consumed.

An individual with greater training demands will burn more calories via PA.

A more active individual will burn more calories via NEAT than a more sedentary individual.

BMR and TEF will be more difficult to influence in order to create a fat loss effect. However we can have a much greater impact on PA and NEAT to change the energy balance we mentioned above.

As a result, the biggest factors in our control to tip the energy balance towards fat loss are nutrition, training and physical activity.

Energy Balance - Nutrition

While theres a number of factors affecting nutrition, our big rocks are going to be total calories consumed, and the macronutrient breakdown of the calories. With regards to fat loss, looking back at the energy formula we need to ensure that our energy intake is less than our energy expenditure to impact stored energy or in other words, consuming less calories than we burn.

So, step 1; lets figure out how many calories we require to maintain our current body mass, and how many calories are required to create a deficit to burn fat tissue.

The easiest way to calculate our maintenance intake is to use the following calculation:

Lets clarify a little more at step 3:

We're working out an estimate...yes this is just an estimate. Our tracking + changes in weight will tell us if we’re in the right ballpark here.

So when we're calculating a deficit, we use our maintenance figure, and then figure out how much we need to subtract to create a deficit.

To do so, we need to know how many calories make up 1lb of fat tissue.

1lb of fat = 3500 kcal.

Again, it’s not quite as concrete in practice due to changes in glycogen, water, sodium, etc, which can affect the weight change. In addition, not all of the weight loss necessarily comes from fat. For example if it came from muscle; 1lb of muscle requires around 600kcal, so if 10% of the weight lost was from muscle, that means now only 90% of the loss was from fat.

Therefore to lose 1lb of PURELY fat, we’d need an additional 10% deficit (assuming this additional loss even comes from fat). So without trying to confuse you, what I’m saying is, its not quite as crystal clear as 3500kcal.

With that said, it is a good place to start as part of our estimated calculations.

So lets continue:

3500kcal deficit / 7 days in a week = 500kcal per day deficit.

So lets take the upper end of our maintenance figure at 3168kcal - 500kcal = 2668kcal per day to lose ~1lb of fat.

This takes into consideration weekly training and activity level, however the deficit doesn’t need to fully come from nutrition, we can create that with cardio for example. We’ll touch on that in the training section.


While the calories have the biggest impact on the energy balance and resulting fat loss, the macronutrient composition of those calories can have a significant role in determining the distribution of weight loss in terms of muscle and fat, energy levels, performance and satiety among other factors.

Each macronutrient plays a different, but important role for fat loss:

Energy Balance - Training

On the other side of the energy balance equation, we have training. The primary goal of training in a fat loss phase is preservation of muscle mass to ensure the majority of the weight lost will be coming from body fat.

The secondary goal is simply to burn calories however that should just be more of a bi-product of your training, rather than a specific focus. Too much focus on calorie burning during resistance training could cause a loss of intensity (in terms of weight lifted) or begin to compromise recovery if performing too much volume.

The calorie burning is however an important part of the process in the energy balance and so we may consider utilising a form of cardio work to burn more, without compromising recovery. Your options regarding cardio will be a slower, steady state cardio vs a high intensity interval training (HIIT).

A higher intensity version may seem like an obvious answer due to its time efficiency whereby you’ll burn more calories per minute of work, however you wont be able to work as long as with steady state cardio. Consequently, the end result of calories burned may be the same, but performed faster with HIIT. However, if we go back to our primary goal of training, which is to preserve muscle mass, then we must consider the effect of cardio. HIIT will be somewhat more similar to resistance training with regards to the stress and intensity on the body therefore potentially interfering with the recovery element and compromising future sessions.

Considering all of the above, the calories actually burned via resistance training and cardio are generally significantly less than most expect. On average, 300-400kcal in a resistance training session, and 300-600 per hour in a steady state cardio session. Of course, these numbers will be largely variable, but the consideration is…with the resistance session being essential, and a relatively fixed output from week to week, is it easier to increase caloric output via cardio or the diet?

To weigh up the best option, consider the following:

Energy Balance - NEAT

When looking at the elements of energy expenditure above, rather than focusing on the physical activity, let’s look at another option; NEAT.

We defined it above as ‘calories burned from non-planned exercise i.e. general daily movement’. NEAT can account for 15-50% of an individual’s daily energy expenditure. Yes, this is massively variable, which is based on numerous factors, with the main one being occupation. For exmaple, a manual worker will burn significantly more calories than an office-based worker. These differences can amount to as much as 2000kcal per day differences, which will undoubtedly have a large impact on energy balance.

When you consider that your gym time only accounts for 1-2 hours of your day, and removing 6-8 hours of sleep, that leaves us with at least 14 hours to either support or hinder your efforts in the gym.

Despite NEAT being somewhat ‘unplanned’, we can take matters into our own hands and use it as a tool for increasing energy output in those 14 hours.

How, I hear you ask?

  • Track daily step count - increase over time as needed

  • Go for a walk

  • Take the stairs

  • Park further from work/gym and walk the rest

  • Stand up + move around every hour or so if you’re in a sedentary job

These may sound insignificant but done consistently can make a huge difference to daily calories burned and may just save you from needing to add more cardio time at the gym or making calorie cuts.

Energy Balance - It’s Dynamic

We’ve spoken about the formulas and numbers for setting up a training and nutrition plan that creates a deficit to ensure a fat loss effect, however…the energy balance is not fixed. The training and nutrition that help you lose fat in week 1, will not be the same in week 12.

But thats not necessarily a bad thing, it shows that you’re on the right path.

When you lose weight, you have a smaller body, and a lighter body. A smaller and lighter body burns less calories. As a result, BMR changes as your body now requires less calories to maintain the bodily functions of a smaller body.

Another element of energy expenditure which is affected by a deficit is the thermic effect of food. TEF is directly related the amount of food you consume. While the effect size is minimal, (as TEF only accounts for approximately 10% of calories burned) as food is reduced, the calories burned to metabolise that food, is also reduced. Further evidence, that the energy balance is indeed dynamic.

In addition, we start to see and adaptive element to hormones in response to the reduced intake, increased output and burning of body fat which can impact the deficit.

The stress that is involved in these hormonal changes, as a result of the changes in energy balance factors, can also lead to changes in NEAT. More exercise and less food can lead to less movement later in the day. If that 500 calorie reduction we spoke about earlier to create a deficit, is now met with a 200 calorie reduction in movement due to diet-related stressors leading to reduced NEAT, that very deficit is now reduced to only 300 calories, and potentially see a smaller change in weight.

However, unlike the above factors, you can feel a sense of empowerment knowing that NEAT, physical activity and nutrition are very much in your own control. So, if you notice a smaller change in weight than expected or a stall in your fat loss changes, you simply have to be as dynamic with your decision-making, as your body is with the energy balance.

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