Once again weight loss is at the top of everyone’s mind. Guest Blogger William Law looks at the problems with using weight as a guide to progress

There are better and worse ways to start a day.

And for many people, the day begins with dragging yourself out of bed (after hitting snooze on the alarm 3 times), going into the bathroom, and stepping on the scales… and there’s nothing worse than waking up and seeing the number a few pounds higher than you remember it being the day before, especially when you thought you’d been following your nutrition plan well and weight loss was bound to follow.

There’s certainly an obsession with the concept of ‘weight loss’ in fitness. Losing weight is undeniably one of the main reasons people begin to exercise in the first place, but the problems arise when the focus on the pure weight, the number on the scale, becomes so precise and laser-focused that other elements like how you feel, or how easy it is to carry yourself, or even how you look in the mirror, start to lose their importance.



And the problem with this is that the number on the scale can be very, very deceiving.

The issue with taking someone’s raw weight as a measure for their progress is that it’s far too general to draw specific conclusions from. Yes, our bodies are made up of fat and muscle, but there’s far more to it than that. You often hear phrases like “25% body fat” being thrown around, and of course, that’s referring to the proportion of weight in the body attributed to a certain type of tissue.

Typically, for a 20-39 year old woman, body fat percentage lies somewhere within the range of 22-33%, and muscle mass percentage between 63-75.5%. Surprisingly, bone mass usually only comprises around 3-5% of body mass.1 Despite these numbers being plastered all over the place, they’re actually not closely related to the small fluctuations on the scale that we get so worked up over.


These small daily fluctuations are often due to much, much smaller chemicals.


The first of these, and the less influential of the two, is salt. Sodium ions are crucial for many of the processes performed by the body, including filtration and reabsorption in the kidneys, and movement of electrical impulses through neurones (I’m really trying to pull something out of A-Level Biology here…), but the idea of homeostasis – that is, the idea that the environment within the body needs to be kept constant – means that the concentration of sodium ions in cells needs to remain the same.

Sodium ions exist in aqueous solution (dissolved in water) in the body, so in order to keep the concentration constant, if there are more sodium ions in the body, there needs to be more water to dissolve them, and if there are less sodium ions, there needs to be less water. We obtain sodium ions from salt – sodium chloride – so if we eat more salt in one day, it follows that the body will keep more water in order to balance out the increased amount of sodium ions, and less water will be lost through urine. Therefore the next day, we’ll likely be carrying more water weight, and this will inevitably show up on the scales. The increase in the number you see isn’t down to suddenly and instantly putting on pounds of fat – that’s quite literally an impossible task. It’s down to the body retaining more water in order to keep the sodium ion concentration at its ideal value – and this change will be reverted back to normal within a matter of hours.



I previously said sodium was the less influential of two factors which affect fluctuations in weight, but the truth is the other factor relies on the idea of water weight as well. When we exercise – or, in fact, perform any action for which our muscles need energy – the first source we use is carbohydrates: specifically, carbohydrates in the form of glycogen.


Glycogen is a complex carbohydrate made up of made rings of a simple sugar with 6 carbon atoms called α-glucose, joined together into a long chain with many branches. When the body needs energy, the bonds linking the α-glucose molecules are broken and the individual glucose molecules can be used in a process called respiration, yielding energy which we can use to move. On average, we carry around 350 grams of glycogen in our muscles, and a further 80 grams in our liver. We can use up all of the glycogen in our liver when we need energy, but in the muscles, some always remains. Glycogen is a form of carbohydrate, so we obtain it from foods containing carbohydrates, like bread or pasta. Glycogen, however, has a key attribute which means it can hugely affect bodyweight on a day-to-day basis: for every gram of glycogen stored in the body, at least 3 grams of water is also stored.2 This means that your weight one morning can be hugely affected by what you ate the previous day: if you’d eaten carb-heavy meals like pizza or pasta, it’s likely that much of this would be stored as glycogen and would carry a significant amount of water with it, potentially leading you to be a pound or two heavier the next morning. Conversely, if you’d eaten a very low amount of carbs the previous day, you could wake up lighter.

Regardless, these changes in weight are absolutely temporary and have nothing to do with long term weight loss: as soon as you return to eating a ‘regular’ amount of carbs, water will begin to be carried more or less depending on whether your carb intake was increasing or decreasing, and your weight would return to how it was before.


The Low Carb Crash Diet

This is precisely why low-carb crash diets are so common – and can often seem so convincing. Such a diet may offer promises of ‘losing 3 pounds in a week’, or something similar. And it’s made even more persuasive when, due to changes in glycogen levels and water weight, this promise seems to come true after a week of following the diet. However, it’s crucial to remember that this is an illusion: you’re not losing any fat, only water weight, and as soon as you return to a ‘normal’ diet your weight will return accordingly.


The only way to lose weight, and to keep it off, is by using a calorie deficit – that is, consuming less calories than you are burning on a daily basis – so that fat is burned for the spare energy your body needs.


Therefore, small fluctuations in weight are really nothing to worry about, and the truth is it’s pretty normal to lose or gain even pounds of weight literally overnight. The numbers that really matter are the averages – a far better way of monitoring weight is to weigh yourself once or twice a week, as then the small fluctuations caused by water weight will likely be cut out and you’ll be able to see actual progress.

weight loss


1 https://www.menshealth.com/health/a27242669/what-your-body-composition-metrics-say-about-your-health/

2 https://pubmed.ncbi.nlm.nih.gov/25911631/