Weight Loss Slow vs. Fast: Implications for body composition and performance


When some individuals set out on their weight loss journey the primary focus may be to see the numbers drop on the scale and fast! However, it is important to consider the quality of such weight loss, with preferably a decrease in fat mass and maintenance/increase in muscle mass.

The importance of muscle should not be overlooked. When we think of muscle, thoughts may immediately turn towards aesthetically pleasing physiques or performance. However, the maintenance or development of muscle mass should also be considered important from a health perspective. The greater the amount muscle mass an individual holds the greater the contribution to resting metabolic rate (typically the biggest contributor to energy expenditure). Furthermore, muscle is a glucose disposal and lipid (fat) oxidation site. Additionally, sarcopenia is a condition commonly seen amongst older individuals with a progressive loss of muscle mass and function with ageing.

Rate of Weight Loss

Regarding the rate of weight loss within athletes, when opting for a slower (0.7% loss of bodyweight), compared to a faster rate (1.4% loss of bodyweight), weight loss approach individuals were able to preserve, or in some instances enhance, muscle mass and performance, with greater fat mass loss – see the image above. With regards to increasing muscle mass within a deficit, this is dependent upon an individuals training status/size of calorie deficit/current body fat%/protein intake. Individuals who are resistance trained/low body fat % may be more concerned with trying to preserve muscle mass, compared to the gains that can be made by an individual new to resistance training. Furthermore, there may be certain instances where a higher rate of weight loss may be required, for example individuals that hold larger amounts of fat mass.

As you are reading this article, I assume you are interested in decreasing your fat mass. Below are the suggested rates of loss based upon the guidelines put forward by Alan Aragon. There will be inter-individual variation with regards to rate of of fat/body mass loss, especially in certain individuals who may be able to increase muscle under such conditions. Those who may wish to lose at a quicker rate than suggested may find that this comes with a greater risk of muscle mass loss.

A typical strategy to decrease body mass is to utilise a weekly 3500kcal deficit to lose 0.5kg (1lb) of fat/body mass per week. Alternatively, some individuals may opt for a more aggressive strategy via a 1000kcal daily deficit. However, caution must also be used with the utilisation of a higher than required deficits, as there is a risk that such an increase could result in increased lean mass loss in athletic individuals, especially those already lean. Based upon Alan Aragon’s suggested rates of loss outlined in the table above, I would encourage you to individualise any nutritional strategy.

Monitoring Progress

It is important that once you have implemented your nutrition strategy you then regularly track your progress. Within a previous post I covered methods of tracking progress, so if this is something of interest I recommend you take a look at this. The data derived from tracking body mass and body composition can highlight whether kcal intake needs to be increased, decreased or kept the same according to how you have progressed thus far. I would encourage all individuals to track progress (both body composition and training), whilst additionally some individuals may also wish to track daily wellness data to provide further insight. I have created a spreadsheet which can log daily/weekly body mass progress, as well as monthly body composition testing (click here to download).

Structure of Daily/Weekly Energy Intake

It is important to stress that consistency is needed when implementing such a nutritional strategy for the achievement of daily targets, and ultimately your weekly targets. It is is easy to sell yourself short by not being consistent with energy intake and therefore not progressing at the expected rate. It is therefore important to opt for a dietary setup that you will be able to adhere to, whilst suiting your individual schedule. I shall now talk through two example structure options:

(1) Linear

This would be considered a linear approach, as kcal intake is the same each day of the week. For example, if your maintenance kcal intake is 3000kcal and you are looking to lose 0.5kg per week then you would need to decrease weekly intake by 3500kcal. This on average over the week would require a 500kcal daily deficit, which would bring your average daily intake to 2500kcal.

(2) Non-Linear

This would be considered a non-linear or undulating approach, as kcal intake varies across the days of the week. For example, if your maintenance kcal intake is 3000kcal and you are looking to lose 0.5kg per week then you would need to decrease weekly intake by 3500kcal. As above, this on average over the week would require a 500kcal per day reduction from maintenance daily intake, which would bring your average daily intake to 2500kcal. However, the intensity/volume of your training sessions (e.g. weights, conditioning) or rest day would require varying amounts of daily energy intake. Therefore, you could vary your energy intake over different days to accommodate this, but when averaged out over the week you would still be in a 3500kcal deficit.

A common problem I hear of is slow dieting progress due to a lack of dietary adherence, even thought the individual may protest their innocence! Let’s take the above infographic. This individual keeps on top of both training and diet Monday to Thursday. But wow, come Friday it all seems to escalate and quickly. Friday night drinks with colleagues after work, Saturday night out and take-away to end the night and a Sunday hangover feasting on anything they can get their hands on (or order).
Some quick maths on this individual:
To maintain their current weight this individual would have to consume 3000kcal per day or 21000kcal per week.
Therefore, to lose their target of 0.5kg per week the individual had a planned weekly deficit of 3500kcal – target intake 17500kcal.
However, the actual deficit was only half of that planned. The result, weekly weight loss was 50% slower! With such a lifestyle it could even be possible to fully erase the deficit or even go into surplus!

When putting your dietary approach together it is therefore important to remember to opt for a diet that you can consistently adhered. Within this dietary approach set a rate of progress that is achievable and in line with your desired body composition goals.

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