Why Does my Weight Fluctuate?

By Shelby Nolan

Maybe you were told to weigh yourself at the same time and under the same circumstances, but you’re not sure why.

Maybe you have had to weigh yourself multiple times a week and noticed drastic differences and were confused.

Maybe you’re really trying to lose or gain weight, but the scale’s numbers are all over the place and going the wrong direction sometimes, even when you’re “on track”, and you’re getting frustrated.

There are many reasons to weigh your self. It can be important data for your doctor, personal trainer, and for yourself to know. While weight is NOT the only indicator of health, it is related to cardiovascular disease and other serious medical issues. If you are trying to lose fat, for instance, weight can be one of the many sources of data. 

But, as you probably have noticed at some point, your weight is far from static. It can vary wildly even across a single day. It goes up and down every day of every week, no matter what you’re doing in the kitchen or in the gym. It can be so frustrating if you’re trying to lose or gain a certain amount of weight.

So why is that? Why does your weight fluctuate?

Spoiler alert: It is not fat loss or gain! It is HIGHLY unlikely you put on five pounds of fat overnight, no matter how much all-you-can-eat sushi you devoured.

Here are some reasons your weight may change:

Water retention – Things like salt and carbs cause your body to hold onto more water. Exercise does as well, as the water helps to repair muscle damage and remove waste products from your muscles. Medication can affect this as well.

What goes in and out – Be this food, beverage, feces, or urine, your weight will change by adding to or eliminating products from your body. If you drink 8 oz of water, you added 8 oz of water to your body, some of which will exit later. Alcohol makes you need to go more often, but it also makes you crave food, especially salty food.

Menstruation – The lovely monthly bloat accompanied by changes in your hormones that make you more likely to eat and change what you’re craving. Also, did you know the number of calories you need to stay alive (Basal/Resting Metabolic Rate) is the highest when menstruating and lowest about a week before ovulation? You crave food when on your period because your body actually NEEDS more calories! You also burn more calories, so it evens out.

Your body weight fluctuates all the time, so it’s difficult to know for certain what you weigh, but we can notice the trends. If you aren’t negatively affected by weighing yourself daily, you can chart your weight to see the trend. Assuming your schedule of eating, going to the bathroom, sleeping, and exercise is relatively consistent, your body will be in a similar state around the same time of day each day, such as when you first wake up. Each day you step on the scale, record that data point on an app or chart, and watch to see how the data points change over time. If, across several weeks, the trend is going more or less down, then it is safe to say you are, indeed, losing weight, be it fat or muscle or both. Here is an example from my own Garmin app earlier this year when I was regularly weighing myself:

The data points (each weigh-in) vary a lot. Up and down, sometimes by a little, sometimes by a lot, but from the first of June to about three weeks into the month, the trend overall was downward. Gaining 4 or 5 pounds in one day absolutely does not mean you’re “failing” at weight loss, if that’s your goal. It can be totally normal and nothing to worry about. Weight is just data. Up isn’t bad and down isn’t good, or vice versa. It is just your body reacting to various stimuli. Don’t sweat the small stuff, like a big meal or big workout affecting the number on the scale, and focus on the overall trend over time.