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Why the scale fluctuates and how to really judge fat loss

Have you ever wondered why you weigh yourself one day and the next day your weight is up by 4 lbs? Or maybe you weigh yourself in the morning, and notice the scale tells you you’re 8 lbs heavier in the afternoon.

One of the most common frustrations with our clients is scale fluctuations.

I get it! But, I’m here to take away all your frustrations…. well, maybe not all… but I’ll shed some light on why this happens.

First and foremost, I want you to understand that the increase you’re seeing on the scale is NOT an increase in fat. It is virtually impossible to eat that many calories in one day to gain 4 lbs overnight. You’d have to have consumed over 14,000 calories.

In this universe, I’m going to go out on a limb to say that you did not eat 14,000 calories. Am I right?

So why the scale fluctuations?

We, as humans, eat food, retain water, make gasses, make waste, and don’t always eat the same calories or the same foods in any given day.

One of the most common reasons is water retention.

Eating, drinking, urination, bowel movements, exercise, hormones and medications all have an effect on water retention.

Let’s look at the two most common of these in detail.


When we consume too many packaged foods or foods that contain sodium, our bodies will hold onto water, hence the scale weight will be higher.

So, if you ate fast food, at a restaurant, or a pre-packaged meal at any of your meals the day before, the next day, you may be holding onto 2-4 lbs of water retention. This does not mean that you gained 2-4 lbs of fat, you’re body is just holding onto water.

Also, if you’ve eaten a high carbohydrate meal, you will weigh more on the scale the next day.

When we consume carbohydrates, our bodies will store this as glycogen. For every gram of carbohydrate your body stores as glycogen, 3 grams of water will also be stored. 

This is why people who eat low carbohydrate plans will lose more scale weight at the beginning.


Strength training causes micro tears in the muscle fibers. Our bodies will fill these tears with water to help repair the muscle. Over time, with proper nutrition, our muscles grow, hence adding a toned appearance.

So, if you did an intense workout the day prior, expect to weigh a little more on the scale the next day. This “weight gain” is caused by the inflammation and water stores in the muscles and is not from fat.

How to use the scale to judge fat loss.

As you can see, the scale is a terrible tool for judging fat loss. However, it can give us some helpful information on your progress with the help of a few other measurements.

When we look at your scale weight, in combination with your abdomen/waist measurement and strength, we get a better understanding of your actual fat loss progress. 

Abdomen & Waist measurements

At Nerdy Girl Fitness, we measure our members once a month. Two of the measurements we want to see a change in are the abdomen and the waist. If the scale is staying the same, but these two measurements are going down, that’s a good indication that your body is burning fat at the same time as muscle. Especially if your strength is improving.

Measure your abdomen right around the belly button, and then measure two inches above or below the navel. Track that measurement for a few weeks.

Also, keep a note of your personal bests. Are you able to do one more push-up than before. Are you able to list more or squat more weight? In essence, are you feeling stronger. If the answer is yes, that’s great! If no, then we need to do some adjustments.

Here is a little chart we use to help you determine if your program is working for you.

Weight Abdomen Strength Interpretation Recommendation
Decreasing Decreasing Increasing Experiencing Fat Loss Keep doing what you’re doing
Increasing Increasing Decreasing Fat gain is happening Lower calories and look at how much/little you are training
Decreasing Increasing Same Fat lost is likely happening Keep doing what you’re doing and recheck in two weeks
Same Decreasing Increasing Losing fat at the same time as gaining muscle Consider increasing your calorie deficit either by adding in an additional training day, or decreasing calories by 250 – 500/day.

Now, one note we should mention. If you’re experiencing rapid weight loss (on the scale), then you could be losing muscle as well. Healthy, and sustainable, weight loss is 1-2 lbs a week. Any more than that, and you may not experience lasting results.

If you’re experiencing too many fluctuations in scale weight and getting frustrated, please schedule an in-person Success Session with me. We will review what you are currently doing and give you a plan to start seeing results!


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