Weight Fluctuation is Totally Normal, Here are 6 Common Reasons It Keeps Happening

Chances are, as a living, breathing person, you've experienced a weight fluctuation. In fact, it's something that all humans share, regardless of their diet or lifestyle. This is because a weight fluctuation simply refers to your body changing weight throughout the day/week. For humans, this is a completely natural occurrence and something with a number of underlying causes.

'A weight fluctuation simply means an increase and decrease in weight from the norm,' explains Ultimate Performance personal trainer and trainer education manager, Emily Servante. 'It is completely normal for body weight to fluctuate between 1-3% each day, regardless of changes to body composition (the ratio of how much body fat to muscle you have).'

Now, that's not to say that fluctuations in weight are always easy to swallow, if you're trying to lose weight well or lose body fat, it can be frustrating to see the scale shift up and down. Fortunately, there are easily explained reasons for why this could be – with true weight gain low on the list of reasons.

Read on for what to know about weight fluctuations and the six common causes.

Is weight fluctuation normal?

'Fluctuations in weight are completely normal (and there are lots of causes for them).' says Servante.

'While scale weight is an easy-to-use and readily available progress marker, it comes with some inherent flaws. Firstly, scale weight is a proxy rather than a direct measure of fat loss; it tells us how much [weight] rather than what [fat, muscle, water] we have lost, gained or maintained.'

'Secondly, your body weight includes everything physically contained in your body: muscle, bone, organs, tissues, water, the food you ate last night, and so on. Therefore, the scale can only ever offer a very crude representation of your current status.'

So, if you're weighing yourself every day or every other day, remember that the scale is only ever one way to mark change – it doesn't (and can't) ever tell the entire story.

6 causes of weight fluctuations

No day is the same when it comes to our weight. Everything from keeping your water bottle topped up (and drinking it!) to where you are in your menstrual cycle can affect how much you weigh.

'There are many factors which can cause weight to fluctuate. But it’s important to put these into context,' says Servante. 'To have gained an additional 1kg of body fat, you would have needed to have consumed 7,700 calories over and above your maintenance calories. Unless you did (and this is highly unlikely) you can be pretty sure you didn’t gain 1kg in fat.'

Let's break down the main causes of weight fluctuations.

1. You've eaten more calorie-dense foods than normal

Calorie dense foods (aka foods that have a high ratio of calories to size) tend to contain higher levels of sodium (salt). This can cause your body to retain water and show up as an increase on the bathroom scale.

'Many things we do will affect the flow of water in and out of our cells and therefore how much water we store when we drink,' explains registered dietician and founder of City Dieticians, Sophie Medlin.

Weight Fluctuation is Totally Normal, Here are 6 Common Reasons It Keeps Happening

'In very basic terms, it may be helpful to remember that the storage of fluid is all based on how much of a particular substance you have in your blood stream and the need for your body to dilute this. For example, when we eat a lot of salt, our body needs to dilute this in our blood so we feel thirstier and store more water to reduce the circulating and cellular salt levels.'

Now, at WH, we like to advise an approach of 'everything in moderation, including moderation' and this goes double when it comes to calorie-dense foods. There's a time and a place for them (that wicked post-wedding 2-day hangover, for example) but they shouldn't be a staple in your regular healthy diet.

2. You've consumed more carbohydrates

Carbohydrates are an essential macronutrient that humans need to function well. (Any diet that tells you to swerve carbs entirely is one to be wary of, okay?)

However, when we consume them, our bodies put them to work, extracting what they need from the food. With carbs, this can cause a brief fluctuation in weight.

'When you eat carbohydrates, your body breaks them down into glycogen which is shuttled to muscle cells along with water, causing your weight to increase slightly,' says Servante. 'However, this is a perfectly natural and necessary process and doesn’t mean you're not losing body fat.'

3. You haven't drunk enough water

Our bodies are up to 60% water. If you're dehydrated your body works overtime to hold onto the water you already have in your body. Fix this by sipping from your water bottle throughout the day and consuming fluid-rich foods like cucumbers and tomatoes.

Thirst isn't the only symptom of dehydration. Clue up on the other signs to look out for.

4. You're stressed or slept badly

'Poor sleep and too much stress can also increase how much fluid we store in our bodies,' cautions Medlin.

'Stress is characterised by the hormone cortisol. Cortisol increases the amount of a hormone called Antidiuretic Hormone (ADH) which tells your kidneys to keep more water in the body and pee out less. This would have been an excellent survival mechanism when we evolved, as stress would always have meant a lack of food, water or physical danger so storing more water in the body was essential.'

'Sleep also seems to affect our fluid balance with poor sleep driving greater fluid retention. Of course, when we are stressed and/or tired, our diet is often less positive as we look for high energy foods to keep us going and these are often processed and salty. We may also drink less water when we’re stressed and tired which in turn, leads to water retention.'

5. Your period is coming

Not only can PMS bring mood swings, uncontrollable food cravings and a general feeling of malaise, it can also impact how much water and fluid you retain.

'Hormonal changes can cause weight gain by increasing water retention. In the days before your period, oestrogen and progesterone rapidly decrease. This tells your body that it's time to begin menstruation. Oestrogen and progesterone also control the way your body regulates fluid,' explains Dr Natalie Geary of The Light Touch Clinic.

Here's what to know about exercise and your menstrual cycle.

6. You're constipated or experiencing gut irritation

'You’re constipated, or you’re experiencing gut irritation. If you’ve noticed changes to your digestion recently, such as being constipated, it’s not surprising if the scale shows a slightly higher number,' says Servante.

'Equally, if you’re experiencing a gut flare-up, there’s likely to be some inflammation and water retention. In either case, focus on increasing your fibre intake, minimising inflammatory foods, and drinking plenty of water. Once things start moving as usual again, your weight will go back down.'

When are weight fluctuations a cause for concern?

As we've covered, weight fluctuations are for the most part totally normal when taken in context. However, occasionally a fluctuation in weight can be a sign of something within your body that needs addressing. Here's how to know the diff.

'Weight fluctuation is normal, but if the scale rises 5 or more pounds for longer than a day or two, chances are it's more than simply water weight,' says Dr Geary. 'Don't freak out — just pay attention to your body and, if still having trouble, call your doctor. Consulting a professional is always a good idea.'

What about rapid weight gain?

'Weight gain and fluctuations in weight can happen for a variety of reasons. Many people progressively gain weight as they age or make changes to their lifestyle. However, fast weight gain can be a sign of an underlying health condition, such as a problem with the thyroid, kidneys, or heart.'

Again, if in doubt, get in touch with your doctor or a medical professional.

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How often to weigh yourself

How you measure progress is a personal choice. However, whether you prefer to use bathroom scales to see your basic body weight or smart scales to keep an eye on your body fat percentage, there are ways to make sure your task stays as useful as possible.

'If you want to keep an eye on your weight, I typically recommend weighing yourself once a week. If you do it more often than that, you'll probably see more of the day to day fluid and hormonal fluctuations that are often just temporary, and don't paint an accurate picture of your true weight,' advises registered dietician Melissa Mitri.'Once a week is regular enough to catch trends in weight gain or loss in a timely manner, but not too much that you'll drive yourself crazy.'

Great advice.