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What the number on the scales is really telling you

You have been good all week. You managed to get to the gym every day and you even managed to abstain from the cookies that winked at you every day in the staff room as you got your salad out of the fridge.

You weigh yourself on the Friday and so far, so good, your weight loss efforts are on track. The weekend is here and Friday night calls for pizza, in bed, in your pyjamas. One meal, no big deal right? You hop on the scales on Saturday and bam - you have put on 3kg. 

3kg overnight… how is that even possible?

I have heard this time and time again with many people so disheartened that their week longs efforts have gone to waste that they feel like throwing the towel in completely.

What many people need to understand is that short-term fluctuations in bodyweight are caused by factors completely irrelevant to your long-term progress.

Here’s what can often cause fluctuations in weight:


  • Changes in glycogen stores

To put it simply, your body stores energy as fat and glycogen. When you eat carbohydrates in particular, they are broken down into glucose and stored in the muscles and liver as glycogen. The interesting thing about glycogen is that it requires water in order to be stored. Thereby the difference in water weight between a glycogen depleted and replenished state can be quite significant. Kreitzman and colleagues found that glycogen is stored with three to four parts water, thereby glycogen loses or gains could potentially contribute to as much as a 5-kilogram weight change (1)So that pizza you ate has just done a stellar job of replenishing those glycogen stores. 

  • Water retention from sodium

The body has a wonderful way of ensuring that we stay perfectly in balance (also known as homeostasis). When we eat a salty meal (insert Friday night pizza), the balance between sodium and water in the body fluid gets altered. This senses to the body that we need to take on more fluid to balance this back out so there is a decrease in urine excretion via the hormone aldosterone (2). Thereby more water on board resulting in an increase in body weight.

  • Menstrual cycle

More so unrelated to the pizza, but an important thing to note, women do tend to retain water during menstruation (3). Therefore, even the best weight loss efforts can be derailed in the short-term by your hormones. This is completely normal and should normalize after your period.

  • Every other little thing going on in your ‘too complex to completely understand’ body

Alcohol, caffeine, stress, certain supplements or illness are just a small number of the endless things that can have an effect on body weight. Sometimes you just have to accept that the scale is going to move from time to time- completely out of your control.

  • So, what can you do?

Scales can be a measure of progress in the long term but if used excessively will do nothing but weigh your self-esteem. Trying not to get too caught up in the numbers on the scale and focusing on how you feel is a much more sustainable, health-focused way to monitor progress.


1. Kreitzman SN, Coxon AY, Szaz KF. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr. 1992;56(1 Suppl):292S-3S.
2. Bhave G, Neilson EG. Body Fluid Dynamics: Back to the Future. Journal of the American Society of Nephrology : JASN. 2011;22(12):2166-81.
3. White CP, Hitchcock CL, Vigna YM, Prior JC. Fluid Retention over the Menstrual Cycle: 1-Year Data from the Prospective Ovulation Cohort. Obstetrics and Gynecology International. 2011;2011:138451.

Article supplied by Emily White.

Emily White (BSc) is an Auckland based Nutritionist who specialises in breaking down diet culture, and finding peace with food and your body. She consults with an holistic, non-restrictive approach and allows her clients to tune into their own inner wisdom.