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Why Does My Weight Fluctuate?

9 Reasons Why And What To Do

By: Zack Mathews, NASM - CPT, CES, & PES, PN-L1

One day your weight is going down and the next day it’s trending up, leaving you to ask the question, why does my weight fluctuate?!

The good news is that weight fluctuations are completely normal and everyone experiences them.

If you weigh yourself constantly, it’s important to know the scale will not move in a linear fashion.  In a perfect world, if you are trying to lose weight and doing all the right things, the scale would go down everyday.

But as we know, the world isn’t perfect!

Since you now know that weight fluctuations are normal, let’s get into what could be causing them.

Why does my weight fluctuate? Here are 9 reasons why.

Why Does my Weight Fluctuate Graph of weight loss progress

Your Weight Fluctuates Depending On How Many Carbs You Eat

Out of the 3 macronutrients; protein, carbs, and fats, carbohydrates will make you hold onto more water than the other two.

That’s the reason why so many people give up carbs when they are trying to lose weight.

Less carbs  = less water weight.

See how I didn’t mention anything about FAT loss.  That’s because the amount of carbohydrates you consume does not make you lose fat any faster or slower.

We know from research that when we eat carbs, some of those carbs are stored as glycogen, which is your energy stores for later.  For every gram of glycogen, you’re going to have about 3 grams of water with it.

The next time you question why your weight fluctuates, think about your carb intake.

Some common form of carbohydrates are rice, potatoes, pasta, bread, fruit, chips, crackers, desserts.

If you weight went up the day after eating any of those items, it’s probably from the excess glycogen you are holding onto.

You Had More Salt Than Usual

One of the most common reasons why your weight will fluctuate is based on how much salt you eat.

Anytime a client brings up that their weight spiked, my first question is to ask if they prepared their meals at home or went out to eat.

The amount of sodium used in take out is usually far more than the amount of salt you would use at home.  It’s very common for your weight to spike when you go out to eat.

The reason that this happens is because your body wants to maintain an optimal sodium to water ratio.  If you spike your salt intake, your body will hold onto water to keep that ratio in check.

You Need To Use The Bathroom

If you’re backed up and need to use the bathroom, you can expect your weight to fluctuate.

Your average bowel movements takes around 33 hours to be processed and weighs between a .25-1 pound.

Are you backed up and haven’t gone to the bathroom in a couple days?  Expect that scale to spike.

Ideally, if you are weighing yourself daily, you will step on the scale first thing in the morning after you use the bathroom.

That’s not going to always happen, so it’s important to have progress trackers in place.   Check out my article How To Track Your Weight Loss Progress for a full list of efficient ways to monitor body changes.

You Ate Later Than Usual

You just learned that it takes 33 hours for food to be fully processed so depending on what time of the day you eat, your weight may fluctuate.

If you eat dinner at 8 PM when you normally eat at 6 PM, that two hour gap can make a big difference on a normal morning weigh in.

It doesn’t only have to be at night either.

Just switching up the times you eat will change your body’s digestion time, so be aware of when you eat.

Menstrual Cycle Weight Fluctuations


During a women’s period, there are a lot of hormone fluctuations that could lead to weight fluctuations.

The two main hormones in play during a women’s period are estrogen and progesterone.  The former is highest right before a period and will cause bloating and water retention.

Progesterone will be higher towards the second half and will have the similar response that estrogen does.

Your period is going to happen each month so there is no reason to be upset of a weight spike during that time.  It’s totally normal and means your body is doing the right things!

Lifting Weights Can Lead To Scale Fluctuations

A fact that most people don’t know about lifting weights is that you are causing damage to your muscles.  Once they're damaged, they start to repair and can grow if your nutrition is right and you are putting adequate stress on those muscles with your workouts.

To get that recovery process going, your body will hold onto water.   For the muscles that you worked, your body starts sending fluid to those areas so they can start the recovery process.

Don’t think you can get fat and gain weight from lifting weights.  It’s not possible!  Well it is, but you would have to be eating A LOT of food for that to happen.


I know what you’re thinking.  If I’m lacking water, why would my weight fluctuate up?!

The main reasons is when your body is lacking adequate water, your body isn’t going to be moving nutrients and waste as fast as it normally will.

Being dehydrated can cause constipation, and as we learned a couple points earlier, lack of a bowel movement will lead to weight fluctuations.

Lack Of Sleep & Increases In Stress


Two areas of your transformation that often go overlooked are sleep and stress.

In my initial consultation with a new client, I always ask about these two things.

Lack of sleep and increases in stress lead to your stress hormone, cortisol, being raised, which can make you hold onto excess water.

What To Do When Your Weight Fluctuates?

Relax.  Accept it for what it is.

That’s what I tell my clients.

When you weigh yourself everyday, it’s important to be able to see that number as a form of data and not let it dictate your mood for the day.

The main thing you shouldn’t do is to try and “fix” it by eating less.

As long as you are consistent, your body will do the right things to align with your goals.

You got this!