Fat loss vs Weight loss: The differences you need to know

nutrition Apr 29, 2021
Fat loss vs Weight loss: The differences you need to know


If you’ve made the decision to drop a few pounds, understanding the difference between fat loss vs weight loss can save yourself anxiety when using the scale to monitor your progress.

Unfortunately, the terms weight loss and fat loss are often used interchangeably, but they’re completely different things. This can lead to panic when you see the number on the scale change drastically, despite your best attempts with nutrition and training. In this article, we’ll go through the important differences so you can have a better understanding of your progress and provide some reasons why the scale may not be playing ball (and what to do about it).

What is weight?


Let’s jump right in. Our weight is simply our relationship with gravity. In physics, you learn that weight = mass x gravity. Because gravity is pretty constant on earth, let’s use weight and mass as the same thing for simplicity.

What this means though, is that every time you step on the scale, you are measuring your total body mass. But this isn’t very specific, and I’d hazard a guess to say this isn’t what you’re actually interested in.


Fat loss vs Weight loss: What are you trying to measure?


This is an important distinction. For 99% of you reading this, it’s likely that you want to improve your body composition to promote visual changes.

Your body composition can be broken down into two compartments:

  1. Fat mass
  2. Fat-free mass

Your fat mass is self-explanatory. The visual type of fat we attempt to alter during dieting phases is called subcutaneous fat (the fat directly under our skin).

Fat-free mass, on the other hand, is made up of everything else that carries mass. This includes body water, organs, muscle, bone etc.

So, as you can see – our weight (or mass) encompasses fat, but also fat-free mass. This can cause a few issues when weighing yourself in an attempt to monitor changes in fat mass.

You’re using a non-specific piece of equipment for a specific purpose.

So, before you think your weight has changed 5lb in 2 days, let’s go through a few factors which can influence weight (but not necessarily mean your body fat has changed).


What can cause weight changes?


Fluid changes

Our body is 60% water, making fluid changes an area with potential for large variations. Take the example of someone who is slightly dehydrated following an intense exercise session. They may weigh lighter post-exercise due to fluid losses (increased sweat and respiration during exercise).

The reverse can also affect things too. Take the example of someone who drinks a pint of water before stepping on the scale – they will weigh heavier.

Both of these cases, of either additional input or loss of fluid affect weight. But it’s simply water weight and isn’t reflecting changes to fat mass.



Stress can come from the angle of both physical and psychological causes. For example, it may be psychological stress from work or physiological (physical) stress from dieting/ energy restriction.

Either way, during times of high stress, the bodies primary stress hormone, cortisol is released from the adrenal glands above the kidneys. This forms part of the “fight or flight response.”

In the context of weight change, what’s interesing is that cortisol can interact with aldosterone receptors of the kidney. Cortisol can bind to these receptors and mimic the effect of aldosterone, with one such effect being the retention of water.

This water retention will clearly affect scale weight, while having no indication of fat changes.



This is also the secret as to why low carb diets promote larger weight loss in the short term! Carbohydrate is stored in our muscles as glycogen. This is a primary fuel source for high-intensity exercise. However, for every gram of carbohydrate, 3g of water is also stored.

When you consider that the average storage capacity of glycogen is around 600g, this means 1800g is attached as water when stores are full. So, carbohydrate plus water in the body may total ~2.4 kg. This can be even higher with increased muscle mass. Practically, this means that day to day variation in carbohydrate intake can also cause changes to weight.



Salt in the diet is made from sodium and chloride. Sodium can bind to water in the body and has the potential to cause water retention. So, recent intakes of high salt sources such as processed food, salted snacks and table salt may be something to consider when contextualizing your weight.



While fibre is an important nutrient for health, undigested plant matter can sit in the intestines until excreted, which can add additional weight. Soluble fibre also draws water into the intestine, which again may cause weight changes. For this reason, combat sports athletes sometimes reduce fibre intake for a short period of 2-3 days in an attempt to reduce their weight temporarily. This highlights fibres relationship with the number you see on the scale and can also be considered as a factor influencing scale weight.



This will be no stranger to most gym goers. Creatine is one of the most popular and well-studied supplements on the market. But, a common side effect of creatine is intra-cellular water retention. This can be in the region of 1-2kg weight increase once creatine has saturated muscle. If you’re taking creatine during a dieting phase, it may, therefore, disrupt your weight data and should be a consideration.


Muscle mass

While the capacity to form new muscle tissue may be reduced when you restrict energy intake, it is possible to occur. This is known as body recomposition. Increases in muscle mass are unlikely to entirely counterbalance weight loss due to the fact muscle gain is a slower process than fat loss. However, for some individuals, it potentially be a small influence.


Food volume

This is a relatively simple one. It takes time for food to pass from one end of our gastrointestinal tract to the other. During this time, the food is in our system and will carry mass. Consuming heavier foods before stepping on the scale will affect the reading you get. The weight of the food you have eaten in the previous 24 hours may even affect weight if it hasn’t been passed yet.


Weighing conditions  

Are you weighing yourself under consistent conditions? Think about the clothes you’re wearing. Are you wearing jeans or shorts? This will affect the number on the scale. Have you gone to the toilet before weighing? There’s some pounds lost that we don’t care about. Are you weighing at the same time of day? First thing in the morning is usually best before you eat or drink anything!


Your scales

Another factor to consider is whether your scales are accurate and precise. Accuracy is whether or not your scales show the correct value. Precision, on the other hand, is the repeatability i.e. will your scales show the same value if you weigh something multiple times. A simple test you can use is getting a dumbbell of specific weight (e.g. 10kg), then weighing and comparing to what your scales say (of course we are assuming the dumbbell itself is the correct weight). As a tip, digital scales are recommended for greater accuracy.


What should you do then?


So, as we have discussed, the scale measures your total mass and there are plenty of factors that can influence this!

Now, there are ways to directly measure fat. However, these methods are typically more expensive, and results can fluctuate under various conditions. No equipment is perfect!

So, for most people, scales are a quick, cheap, and convenient way to monitor progress. But as day to day variation will occur with scale weight, how can we attempt to control this? Instead of asking you to control every aspect that has the potential to change your weight – I have an easier method.

If you are seeing large variations in scale weight when weighing once per week, you can try taking daily weights and use the weekly average. You can then assess trends on a week to week basis and see if your weight is changing or not.

An alternative method would be to simply go off visual changes. If the thought of daily weights stress you out, then monitoring appearance may be the way to go!

It’s also important to note that factors other than scale weight can also be monitored such as performance, energy levels, mood, confidence etc. These are sometimes as important, if not more important than simply your weight on the scale.


The take-home message


Understanding what the bathroom scale actually measures and it’s limitations is crucial when interpreting your progress.

The bottom line is that scale weight will fluctuate. This is normal and doesn’t necessarily mean there have been changes to your body fat percentage. A scale is an imperfect piece of equipment and just one tool to monitor progress.

So if your weight on the scale has changed unexpectedly – DON’T PANIC. Always assess and see if you can explain why this may be. But equally, if your goal is fat loss, reflect on your diet and training. Ensure you are consuming fewer calories than you burn i.e. are in a calorie deficit. Without this, you can’t expect to lose fat in the first place.

If you have any questions, don’t hesitate to contact me.

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