7 reasons why your weight fluctuates so much

Seeing daily weight fluctuations on the scales and wondering what it means? Our expert has the answers...

Woman weighing herself
(Image credit: Getty Images)

So you invested in a set of the best bathroom scales to monitor progress on your health and fitness journey, but you're finding that your weight fluctuates massively by the day - or even the hour.

If that sounds familiar, fear not. Whilst no-one enjoys feeling heavier some days than others or seeing a number creep up on the scale, daily weight changes don’t always mean fat gain - and there's likely a simple explanation.

Stuart Jack is a nutritionist and co-founder of MuscleMary protein powder. He says that for many, the number on the scales is part of their identity.

‘It’s a figure lodged in the mind that dictates if life is moving along the right path or not. 

'At its best it can be used as a motivator to introduce healthier habits or serve as a tool to illustrate if a weekend indulgence has gone a bit too far. 

'But at its worst it can create a strong feeling of self-loathing and lead to an entirely unhealthy relationship with food and exercise. Even to the extent that a single pound movement on the scales can influence the choices made that day and determine if it is going to be a good or a bad day.’

However, he also explains that it actually takes an excess consumption of 3,500 calories above your Total Daily Energy Expenditure (TDEE) to gain one pound of fat.

In other words, if you haven't consumed 3,500 calories above your TDEE (whatever that may be), then it is more than likely that the increase in the scale weight is due to another factor and not excess stored fat.

Seven such causes of weight fluctuation are listed below. But first, a word from Stuart, who advises that if you find yourself constantly checking your weight on the scales, it might be wise to take a step back.

‘Be kind to yourself, step off the naughty step and relieve yourself from the judgmental burden of the daily weigh-in,' he urges.

It's also worth noting that the reasons outlined below will usually balance out given time. Anyone who experiences sudden and sustained weight loss or gain should consult a doctor.

1. Your carb intake has been high

Stuart explains that for every 1g of carbohydrates consumed, the body retains 3g of water.

‘Carbohydrates are the body’s primary go-to fuel source for energy, the most common sources of which are pasta, rice, potatoes, and bread,' he says.

‘A high carb diet will increase water weight and fluctuate the scales. It explains why diets such as the ketogenic diet are often referred to as strong weight loss diets due to the limitation of carbohydrates.’

So next time you eat a delicious bowl of pasta and your instantly weight increases, don’t worry! It’s not fat gain, rather just water weight which will soon leave your body. And it's definitely not a reason to cut carbs, which are a key component of healthy eating.

2. You’ve exercised a lot

Exercise can cause the body to lose a significant amount of water as the body seeks to naturally cool down by sweating, particularly following cardiovascular exercise such as running, cycling or a HIIT workout.

‘This loss of water will cause the scale weight to drop but ultimately as the water is replaced the scales will move upwards,’ says Stuart.

It makes sense, as up to 60% of our weight is water. So when we lose water through sweating, naturally our weight decreases.

Therefore it's not unusual for your weight to drop after a long, but then steadily rise again as your body rehydrates.

3. You’ve consumed a lot of salt

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(Image credit: Getty Images)

Salt, aka sodium, causes the body to retain water. 

‘Thus, a diet rich in food with sodium can cause weight to fluctuate,' Stuart explains. 

'This does not necessarily have to be in the form of table salt; often frozen meals, canned soups and savory sauces will have a high sodium content.'

Removing such foods may cause a drop in scale weight but remember this is just a loss of water.

The Dietary Guidelines for Americans recommend limiting intake of sodium to less than 2300mg per day, whilst British NHS guidelines state that we should be eating no more than 6g of salt a day; less than one teaspoon. Some ready meals alone can contain half this amount! So be salt aware and learn more about how to reduce your sodium intake.

4. You haven’t pooped

Bowel movements are a big contributor to our weight. Naturally, when you’re constipated, or unable to poop, your body is holding on to more weight.

It’s often clear that your body is holding on to the weight, as bloating may occur, which can lead to considerable discomfort.

In fact, a study published in medical publication GastroJournal found that the median daily stool weight was 106g for healthy UK adults. However, around the world, this weight varies from 72g per day to a staggering 470g per day.

Struggling to go? Ways to alleviate constipation include eating enough fibre (at least 25g daily), drinking herbal teas such as peppermint or dandelion, drinking plenty of water and gentle, relaxing exercise such as walking or yoga. So keep your gym water bottle and best yoga mat to hand!

5. Your weight fluctuates during your menstrual cycle

That feeling during period week is an uncomfortable one, and can result in all sorts of weight fluctuations.

Stuart explains: ‘Studies have shown that fluid retention is at its highest on the first day of the menstrual cycle and lowest during the mid-follicular phase. Therefore, the weight on the scales will be higher during the early stages of the menstrual cycle.’

An increase in appetite often occurs during this stage too, which could lead to an excess of calories, which in turn can lead to an increase on the scales. However, over the course of a month this often evens out as appetite normalizes.

6. Your food hasn’t digested yet 

When you eat, your food needs to be digested before it’s used by the body or excreted by the body. Naturally, your weight will increase as you consume food.

‘The body works to digest all the food that it eats. However, this will take time depending on the type of food ingested, the body’s genetics and ability to digest foods and how much water is being held by the foods consumed.’

Generally speaking, it takes around six to eight hours for food to be digested, and bout 36 hours for food to move through the entire colon. So don’t spend any time worrying about weight fluctuations after a meal - it’s natural and normal.

7. Alcohol has made you bloated

Alcohol is a diuretic, meaning it makes you wee more than usual as the body seeks to expel the toxins taken in. This can lead to weight loss.

But, as Stuart explains, alcohol is often consumed in combination with foods high in salt and dense in calories, which has the opposite effect - eventually leading to an upward movement on the scales. As mentioned previously, high salt intake can lead to weight fluctuations.

Want to limit the damage of alcohol? Alternate alcoholic drinks with water and try to keep salty, calorie-dense foods out of reach, so you’re not tempted to consume them.

Lucy Gornall
Lucy Gornall

Lucy is Health and Fitness Editor at various women's magazines, and also Editor of Woman&Home Feel Good You. She has previously written for titles including Now, Look and Cosmopolitan. She lives and breathes all things fitness; she works out every morning, and mixes it up with runs, weights, boxing and endless box jumps. She is also a Level 3 personal trainer and teaches classes at various London studios, primarily Digme Fitness. Lucy is pre- and post-natal trained and helps new mums get back into fitness after the birth of their baby. Lucy claims that good sleep, plenty of food, and a healthy gut (seriously, it's an obsession) are the key to maintaining energy and exercising efficiently. Saying this, she's partial to the odd Negroni on the dance floor with her friends.