There are a lot of factors that go into how much you weigh, including your body composition and even what you eat and drink on any given day. But if you’ve been keeping an eye on the scale and noticed a lot of variation, it’s understandable to mull over the question of “Why does my weight fluctuate so much?”

It’s important to get this out of the way upfront: Some weight fluctuation is normal for everyone. Still, if you find that you’re experiencing large weight fluctuations, you probably have some questions about what, exactly, could be going on. Here’s the deal, according to nutritionists.

Why does weight usually fluctuate?

Again, some weight fluctuation is normal. “Things in the body are constantly moving in and out of equilibrium,” says Scott Keatley, R.D., of Keatley Medical Nutrition Therapy. Your weight has likely fluctuated to some degree your entire life—you just may not have noticed it if you haven’t been tracking it closely.

Your weight tends to shift on a daily basis “primarily from hydration status and the contents of your colon,” says Sonya Angelone, R.D., a spokeswoman for the Academy of Nutrition and Dietetics. “So, weight can fluctuate with the amount of food you eat and how much is still in your colon based on how often you have bowel movements, how much you urinate, the amount of salt or sodium in your diet—water follows sodium so more sodium the more water you hold on to—and how well hydrated or dehydrated you are.”

Bloating can make you gain weight, while excessive sweating from exercise can make you lose it, points out Keri Gans, R.D., a nutritionist and author of The Small Change Diet. “Medications can also cause weight gain or weight loss,” she adds.

How much weight fluctuation is normal?

It depends. Gans says it’s important to keep in mind that weight fluctuations are “totally normal” and that some people will fluctuate by as little as two pounds, while others may see differences of up to eight pounds.

“Women are known to gain upwards of five pounds when they are menstruating,” says Vanessa Rissetto, R.D., the CEO and co-founder of Culina Health. And, if you eat more sodium from one day to the next, you may also see a bigger shift. “Sodium also can adversely affect the numbers on the scale,” because it typically encourages water retention, Rissetto says.

“Even the amount of carbs can cause weight to fluctuate,” Angelone says. “Every gram of glycogen or stored carbs in muscles holds on to three times its weight in water. If you eat a low-carb diet, then eat a pasta dinner, for example, your weight will go up just because your muscles gained more glycogen from the carb-rich dinner and is holding on to water.” This, she says, is partly why people tend to see weight loss of five pounds or so when they switch to a low-carb diet.

In general, Keatley says that most people can expect to fluctuate up to 2% of their body weight, provided they’re not doing excessive sweating or making any huge dietary changes.

When should you be concerned about weight fluctuations?

If your weight keeps fluctuating outside of that 2% range, it’s worth keeping an eye on it, Keatley says. Conditions like kidney disease or heart disease can lead to buildup of fluid in the body and consequential weight gain, he says, and gaining large amounts of weight in a short amount of time could signal a more serious issue. Conditions like hypothyroidism can also cause weight to fluctuate fairly quickly, Angelone says.

“If your weight changes more than a few pounds in a short period of time and you have not changed your food consumption or exercise routine, see your physician or other healthcare professional to rule out any health issue,” Angelone says.

What to do if you have large weight fluctuations

You don’t need to panic if you notice your weight seems to be fluctuating, but experts say it’s definitely something to investigate. “Large weight fluctuations should signal you to consider the amount of salt or sodium in your diet,” Angelone says. “You should also be sure you are having regular bowel movements. For many people that means once or twice a day.”

You also may want to factor in when you’re weighing yourself (your weight will be heavier later in the day after you’ve had several meals and plenty liquids, for example), what your exercise habits have been on any given day, and how well hydrated you are, she says.

But, again if your weight is changing a lot and you’re not sure what’s going on, it’s time to seek professional care, just to be safe. “If you notice huge shifts that don’t seem to add up, definitely make sure to see your doctor,” Rissetto says.

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