6 Possible Reasons Why Your Weight Is Fluctuating

Weight fluctuations can be incredibly frustrating—and confusing. What seemingly helped keep the number on the scale steady last week—whether it was eating a high-protein breakfast, doing a daily HIIT routine, or a combo of both—might bear no difference the next. It can really screw with your mind.

The first thing to note is that a little weight fluctuation on a day-to-day basis is pretty normal, according to Courtney Vickery, R.D., a registered dietitian who specializes in weight inclusivity and eating disorders. In fact, for most adults, it’s considered normal to see weight fluctuations of two to four pounds from day to day. “Some people might even experience up to five- to six-pound fluctuations and still be within a normal range,” she says. 

A number of factors can contribute to these ups and downs—and while many of them are nothing to worry about, some might warrant further investigation. Here are six common reasons why your weight might bounce around, plus how to tell when you should actually be concerned.

• ABOUT OUR EXPERTS: Courtney Vickery, R.D., is a registered dietitian specializing in weight inclusivity and eating disorders. Jenna Volpe, R.D.N., L.D., C.L.T., is a functional dietitian. Kiera Lane, N.M.D., MSAc, L.Ac., Dipl. Ac., is a naturopathic doctor and the director of Arizona Natural Medicine. Charlie Seltzer, M.D., C.S.C.S., is a doctor of obesity and internal medicine.

1. You’re retaining fluids

The human body is made up of about 60 percent water. Given that, it makes sense that changes in your hydration levels can directly impact how much you weigh. “When we eat foods high in sodium, our body retains more water to maintain the right balance of electrolytes, which can cause a temporary increase in weight,” notes Vickery. That’s right, going in on movie theater popcorn can drive your sodium intake up enough to move the needle on the scale.

“On the flip side, if we’re dehydrated from not drinking enough water or are sweating a lot, we might see a temporary decrease in weight,” Vickery adds. Luckily, these types of fluctuations are usually short-lived and your body returns to its usual weight as fluid levels balance out.

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2. You’re constipated 

Naturally, when food waste builds up in our gut without getting eliminated, the number on the scale goes up. As with fluid retention, this is not the same thing as losing or gaining body fat. “When somebody is constipated or not moving their bowels regularly, it can lead to abdominal bloating or distention and a false feeling of weight gain based on the number on the scale,” says functional dietitian Jenna Volpe, R.D.N., L.D., C.L.T. “Somebody who is struggling with looser, more frequent bowel movements, however, could be in a state of dehydration and potentially appear to have lost weight quickly.” Your weight will eventually find its sweet spot as your bathroom habits do the same.

3. You’re yo-yo dieting

If you’re someone who goes on and off diets regularly, you’ll be more prone to extreme weight fluctuations. Unfortunately, erratic eating can have an impact on certain metabolic processes, such as insulin’s ability to move glucose (blood sugar) into the cells where it is metabolized into energy, explains Volpe. “People with a tendency to restrict and then overeat may also be more subject to fluid retention from blood sugar imbalances, since sugar holds onto water (like sodium) in the body,” she adds. 

4. You’re experiencing hormonal changes

Our hormones play a crucial role in regulating metabolism, appetite, and how the body stores fat and fluids, all of which can affect changes in your weight. For example, cortisol, the stress hormone, can lead to weight gain by increasing appetite and promoting fat storage, especially around the abdomen, explains Kiera Lane, N.M.D., MSAc, L.Ac., Dipl. Ac., a naturopathic doctor and the director of Arizona Natural Medicine. “Insulin, which helps regulate blood sugar, can also cause weight changes if the body becomes resistant to it, as seen in conditions like type 2 diabetes,” she adds. Other hormones, like the thyroid hormones, which control metabolism, can lead to weight gain or loss if they become overactive or underactive. 

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That said, some hormonal changes that contribute to weight fluctuations are completely healthy and normal. “In women, hormonal fluctuations during the menstrual cycle, pregnancy, or menopause often lead to water retention and temporary weight gain,” Lane says.

5. You’re taking certain medications

Medications like corticosteroids, which are often used for inflammation, can make you hungrier and cause your body to hold onto water, leading to weight gain, according to Lane. Antidepressants—particularly certain SSRIs—too, can affect mood-regulating hormones and appetite, causing some people to gain or lose weight, she adds.

Meanwhile, “diabetes medications like insulin or sulfonylureas may promote fat storage and weight gain, while medications that influence thyroid function can directly impact metabolic rate, causing either weight gain or loss,” she explains. “Many medications influence changes in weight, so check with your doctor to determine if a medication you’re on might be impacting your weight.”

6. You’re Not Balancing Carbs

Our bodies store carbohydrates as glycogen in our muscles and liver. The thing about glycogen, though, is that it holds onto water, explains Vickery. So, when we eat a lot of carbs, our glycogen stores increase and we hold onto more water, which can cause our weight to creep up a bit. On the other hand, if we slash carb intake (like on a low-carb diet), we might see a quick drop in weight as our body uses up our glycogen stores and releases the water that accompanies them, she says. “This is why people often see rapid weight loss at the beginning of low-carb diets; much of this initial loss is just water weight,” she notes. Again, this is not the same thing as losing or gaining body fat.

When to seek a healthcare professional for weight fluctuations 

Though many of the above factors can influence weight without reflecting bigger health changes or concerns, you know your body best. If you feel suspicious about sudden weight loss or gain, it’s always a good idea to consult a doctor, especially if that weight loss or gain correlated with unusual symptoms like notable swelling or shortness of breath, notes Charlie Seltzer, M.D., C.S.C.S., a doctor of obesity and internal medicines.

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If you’ve noticed a significant change in your weight, even without changing your diet or exercise routine, it’s important get a professional opinion. Other concerning symptoms to look out for include fatigue, weakness, changes in appetite, difficulty concentrating, and hormonal symptoms like mood shifts.

While weight fluctuations are normal—especially for women—a combination of up-and-down weight with other symptoms might indicate underlying health issues, notes Seltzer. If you’re worried about your weight or anything else you’re experiencing, there’s certainly no harm in consulting with a pro.