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Typical Timescales for Fat Loss Phases

Performance Training Personal Training

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Our first two insights, Effective Body Composition Changes and Upper and Lower Limits on Weekly Fat Loss, explored the importance of understanding why some attempts at weight loss ultimately fail, and why structure is needed to maximise potential outcomes over time.

In both articles we also looked deeply at why the preservation of muscle mass is fundamental in preventing a decrease in performance, and maintaining positive levels of health and immunity during phases of intended fat loss.

In Upper and Lower Limits of Weekly Weight Loss, we further developed some recommendations in terms of the amount of weight we can expect to loose within a weekly time course at rates that take all of these considerations into account. Concluding that aiming between 0.5-1% of bodyweight per week was a safe target range for body weight changes to maintain muscle, health and sustainability over time course.

In this insight we will continue further and look at the total length of a fat loss phase and whether there are upper and lower limits to consider when mapping out this overall plan.

As a quick review, our overall goal within a fat loss phase is to reduce the amount, and size, of fat cells that we have. For this to occur we need the Fractional Synthetic Rate (FSR) of fat tissue to be lower than the Fractional Breakdown Rate (FBR) of fat tissue. We know that our metabolism, regular levels of daily activity (NEAT), partaking in intentional exercise (EAT), adequate sleep and low stress levels are all contributors in creating a higher FBR. Whilst ensuring sufficient calorie intake control (i.e. eating less total calories than we consume…) is the main contributor to lowering the FSR.

Taking all this into consideration, when it comes to starting a fat loss phase, how many of us have ever really thought through and planned out the process in terms of timescale with a clear end date in mind?

Or do we simply jump in head first on the next available Monday morning, and hope it will eventually end when we reach the body composition we desire?

From what we now know in terms of rates of body weight loss (0.5-1% per week), we can at least begin to have a general starting point in understanding how long it may potentially take to reach a body composition target. 

As a practical example to demonstrate, Client A weighs 80kg and wants to lose 10kg in total to reach an eventual target of 70kg. At the most accelerated target rate (1% = 0.8kg), Client A can expect to lose the total amount in approximately 12-14 weeks of caloric restriction. At the lower rate (0.5% = 0.4kg) this would be more towards 24-28 weeks total to reach the 10kg amount. There is of course a spectrum of rates of weight loss between these two numbers that are possible (eg. 0.75%), however we at least have a starting time course for our individual.

However, potential rate of loss isn’t the only component to consider. We have secondary factors that need to be taken into account along the way.

As we mentioned in Upper and Lower Limits of Weekly Weight Loss, there are potential trade-offs and downsides in fat loss especially when it comes to spending too long an overall period of time trying to lose body fat. 

The physical and psychological fatigue associated with body composition changes is likely to be barrier that we are increasingly pushing against.

When aiming to lose at faster rates, the consistency and accuracy day-to-day of our calorie intake control, movement and exercise needs to be much higher. 


Because we need this level of commitment, consistency and control in place to prevent excessive variability. Things need to be the roughly the same day after day. Everything needs to be directed towards the intended outcome.

This requires more cognitive oversight and likely higher levels of physical effort.

Over time this is both stressful and ultimately fatiguing physically and mentally. Maintaining step count, getting in resistance sessions, possibly weighing and tracking food are tasks that require physical and mental effort.

Individuals who have tried to lose significant amounts of weight over long time courses will have experienced just how challenging it is to remain in a hypocaloric environment for extended periods.

Alongside the associated fatigue accumulation, whilst our goal is always to retain as much muscle mass as possible during a fat loss phase, we inevitably have to accept that some degree of muscle will be lost during the process.

Consuming less calories than the body needs to maintain its natural balance, results in a need for energy creation from our own internal sources. We therefore consume what we have available to us. Whether that be our own body fat stores, muscle glycogen or even the muscles themselves. We knowingly accept along the way that we will lose some muscle inevitably, however we can control the extent of this to some degree.

Associated with this, a loss of muscle mass is likely to be a subsequent loss in strength. If improved performance is a factor in your “Why?” for body composition changes, this could be a big negative if we allow for time courses to extend too far.

Spending significant periods of time in a hypocaloric state is also likely to lead to a large-scale rebound in hunger levels once a diet period ends. Many individuals within their attempts at losing body fat are simply trying to drop the same 10-15lbs that they cyclically put on again throughout the rest of the year.

Having a structure to the time course matters for these reasons. Losing at a rate that is sustainable, over a time period that is manageable, are both components that make the entire process possible without resultant weight gain.

Over time, the process of being in a calorie restricted state, requires the body to adjust and adapt to try to regulate the conditions as best as possible. As a result we tend to see a subconscious decrease in daily physical activity.

With less calories on board for fuel, our brain naturally makes us become more sedentary to prevent any further expenditure. Our metabolism slows and we pull energy away from short term non-essential systems (disruption or potential loss of a women menstrual cycle, for example). 

If our goal is to continue to push a sustainable rate of weight loss over time, it therefore becomes MORE difficult to lose weight the longer a single phase lasts.

Within the first week of a fat loss phase, individuals may tend to experience heightened rates of change in scale weight. With the removal of a lot of processed carbohydrates (hopefully…) from daily intake, we see significant alterations in body water and stored glycogen without any real fat loss actually occurring.

Individuals can be mislead by these early shifts in body water into thinking dramatic fat loss has taken place. This becomes most prevalent in those who aim to lose weight in very short periods of time i.e. 2-3 weeks through dramatic calorie restrictions, most often in the lead up to an event/holiday etc.

Our immediate issue here, is that we haven’t truly seen any worthwhile or long term change in body composition. In much the same manner as a boxer may fast from eating and dehydrate themselves in the lead up to a weigh-in to meet a certain target weight before rehydrating and restoring glycogen levels, this is a temporary measure with limited long term outcome.

Within approximately a month of sustained attempts at fat loss, we begin to see noticeable changes outside of fluctuations in body water and glycogen. At this point we can assume that weight loss changes on the scales are actually taking place from a reduction in overall fat levels.

At our upper limit, within a time period of 2-3 months meaningful changes can be made. Using our previous example from above, 80kg individual looking to drop 10kg, we would likely have seen between 8-10% body weight change over this maximal time course. This is a significant and sustainable amount lost over a sufficient time period.

To provide greater context, Client B is an 100kg individual who would like to eventually reach a the same target weight of 70kg, a 30% reduction in body weight. Based on what we’ve discussed so far, we can begin to now see how the psychological and physical restraints we may encounter could become an issue down the road in attempting this type of loss in a single phase.

A bodyweight loss of 30% would require between 30 (at 1%) and 60 (at 0.5%) weeks of total time spent in a calorie deficit when purely considering the mathematical numbers. That’s reaching potentially well over a year in total, at  rates of loss that are sustainable in preventing subsequent rebound and maintaining muscle mass and health preservation. However the likelihood of encountering fatigue, loss of muscle, loss of strength, power, speed, endurance, radical hunger, lowered daily activity, possible disordered eating patterns and increasing difficulty in loosing further weight, are all very, very real possibilities if we ran this purely on the maths in a single phase.

When we’re approaching large total amounts of intended fat loss, such as our 30% example, there is going to need to be long term structure and specific phases of fat loss and maintenance of body weight. We may need 3-4 distinct phases of intentional fat loss at a time, interspersed with periods spent maintaining the new body weight. An example is outlined below of how this may be structured.

  • Starting weight of 100kg
  • 8-10 weeks aiming to lose 8-10% body bodyweight (targeting 1% per week)
  • 4-6 weeks of maintenance of new bodyweight
  • 10-12 weeks aiming to lose 6-8% body bodyweight (targeting 0.75% per week)
  • 4-6 weeks of maintenance of new bodyweight
  • 10-12 weeks aiming to lose 6-8% body bodyweight (targeting 0.75% per week)
  • 4-6 weeks of maintenance of new body weight
  • 10-12 weeks aiming to lose 4-6% body bodyweight (targeting 0.5% per week)
  • Maintenance of new body weight for life

This may now be a process that takes 9-12+ months in total of targeted weight loss that match the individual and the challenges they may face along the way.

However the goal is to ensure maximal retention of muscle mass through a process that limits the trade-offs and downsides associated with not only extended periods of fat loss, but the process of losing fat in general.

Our goal is always to make fat loss manageable and sustainable, both during the process and after, by providing structure and guidance to make sure an individual can maintain the desired body composition long term.

We now have some key considerations in place to start to map out the journey…

  • A targeted rate of between 0.5 and 1% of bodyweight loss per week is optimal to maintain muscle mass and health status
  • Our metabolism, daily activity, intentional exercise, calorie intake control, adequate sleep and stress level management are all contributor to fat loss. Ensuring sufficient and appropriate levels of each provides an optimal balance. Caloric restriction is not the only component at play.
  • Fat loss phases lasting less than 1 month are likely to result in a lack of meaningful changes to body composition long term.
  • Fat loss phases of 2-3 months are likely to result in meaningful and sustainable rates of change (5-10% total body weight loss)
  • Shorter fat loss phases (6-8 weeks) can be approached with greater percentages of body weight loss (0.75-1%), whilst longer phases can hold lower rates of body weight loss (0.5-0.75%) for a greater period of time.
  • The rate of body weight loss is directly proportionate to the consistency and adherence needed. More intensive rates require greater accuracy and adherance. Lower rates allow for more flexibility in meeting outcomes.
  • Overall amounts of total fat loss greater than 10% in a single phase, may require multiple phases of fat loss, interspersed with periods of weight maintenance. This is due to our goal of maintaining muscle mass and health status, without encountering significant physical and psychological issues associated with extended periods of hypocaloric food intake.

In our next insight, we will begin to break down the components of Calorie and Macronutrient intake to establish a starting point for where to begin in setting up daily targets based on an individuals needs.

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