14 Sneaky Offenders That Cause Weight Fluctuations

Stepping on the scale can be a stressful experience when you’re trying to lose weight (or even just maintain your weight). Every little up and down can feel like it makes a big difference.

When you’re working toward a weight-loss goal, it’s normal to be watching the number on the scale like a hawk waiting for any changes that might occur. But if you’ve been tracking your weight for even a few weeks, you’ve probably noticed fluctuations are common. Still, they can be frustrating to see when you’re working hard to get into your best shape ever.

But, here’s some good news: Day-to-day fluctuations are usually the result of water loss or retention. That means if you’re suddenly a couple of pounds up or down from one day to the next, you’re probably not dealing with fat gain or loss. “It’s important not to let these temporary blips on the radar worry you, because at the end of the day, your weekly weight average is much more important and means more than daily fluctuations,” explains Kia Khadem, a clinical exercise physiologist, nutritionist and online personal trainer.

It’s a good idea to use an app like MyFitnessPal to track your weight trends over time instead of stressing over the daily ups and downs. Here are 14 surprising things that can affect your weight loss to keep in mind:

It’s true that staying well-hydrated is a good move if you’re trying to lose weight, but the first few days of upping your water intake could actually cause the number on the scale to creep up, too. “Let’s break down what weight really is,” says Megan Ware, RDN. “It is not just the measurement of fat in the body. It is the weight of your bones, organs, muscles, fluid and waste. When you’re dehydrated, you weigh less, but that doesn’t mean you are healthier. Let’s say you don’t drink much fluid one day, and the next morning you wake up and your weight is down. Then you drink a ton of water, and the next day, it looks like you gained 2 pounds. That does not mean you gained 2 pounds of fat; it just means that your body was depleted of water the day before.”

Salt and carbohydrates both cause water retention, driving your scale weight up temporarily. And when you pair them together, it’s a double whammy. This is especially likely to happen after a meal out, since restaurant foods tend to contain more salt and carbohydrates than foods we might cook at home — even when we try to make healthy choices. “Sodium without adequate hydration causes the body to hold on to water,” explains Kylie Ivanir, RD. “And when carbs are stored in the body, they are stored with water. So, when you combine these two together, you get a large amount of water being retained in the cells.”

Ever noticed your weight spikes the day after a hard weightlifting workout? Here’s why: “When you strength train, your muscles will fill with blood and water to help repair the tissue you’ve damaged,” says Rachel MacPherson, a certified personal trainer. That damage is actually the good kind. It leads to bigger, stronger muscles, but it can cause a temporary rise in scale weight in the process.

Hitting the weights isn’t the only gym activity that can cause a brief weight boost. “Doing cardio causes an increase in blood volume, which can cause a small jump on the scale after exercise,” notes Tim Liu, a certified strength and conditioning coach. “This is normal and will drop back down after a few hours.” But, if you happen to weigh yourself in the meantime, don’t stress.

Though carbohydrates are not the enemy of weight loss, eating a lot more than you normally do over the course of one day or even a few days can make it seem like you’ve gained weight. “Carbohydrates are another type of food that can result in water weight showing up on the scale,” explains Alexia Lewis, RD. “This is why people lose weight faster initially on a lower-carbohydrate diet. The body doesn’t hold onto the extra water. It’s also why people gain weight quickly when they eventually go off that lower-carbohydrate diet; that water weight comes back, and the scale bounces up.”

Surprise weight gain can also happen due to certain medications, especially if you just started them, according to Deb St. Cyr-Paul, RD. “Calcium-channel blockers, which are medications for high blood pressure, can cause fluid retention in lower legs and hands, also known as peripheral edema, in many people who take them,” she explains. Non-steroidal anti-inflammatory drugs (NSAIDs) and birth control pills can also cause fluid retention, she adds.

“Certain supplements, such as creatine, hold water and glycogen in the muscles, causing your weight to be higher than it normally would,” MacPherson says. This is the same reason your muscles might look fuller or “swole” when taking creatine.

If you’ve ever wondered why you weigh less when you’re sick or right after recovering from a short cold or flu, there’s a pretty simple explanation. “Even mild illnesses can cause a slight dehydration and quick drop in weight,” says Lisa Hugh, RD. “After the illness, people often complain that they have gained weight. But almost always, it’s really just a dehydration followed by rehydration.”

“Being constipated can add pounds,” says Jamie Hickey, a certified personal trainer. “I know this isn’t a topic people want to discuss, but your waste adds weight to the scale, and if you haven’t been able to empty your bowels for a couple days it will add up.” Once you go to the bathroom, you should see the scale drop back down. Constipation is more likely to happen when you overhaul your diet, eat more fiber than usual or aren’t drinking enough water, Hickey adds.

During certain times of the month, women might notice scale changes. “It’s normal for women’s weight and fluid levels to fluctuate in accordance with their menstrual cycle,” says Hugh. But these fluctuations can make it tricky to determine if you’re really losing weight. One way to better understand if you’re making progress is to track body composition (your ratios of muscle, fat, water, bone, etc.) instead of weighing yourself, notes Hugh, who recommends women do these tests right after their cycle ends each month. “This is usually the time [women] have less fluid retention, so the test gives a pretty accurate result.”

Ever notice you weigh more when the temperature rises? “When it’s hot and humid, there’s a tendency to get bloated and retain water, driving that scale number up,” notes Allison Jackson, a certified personal trainer. Once things cool down, you should be back to your baseline.

If you’ve been feeling more stressed than usual, you might see that play out on the scale. “Stress increases cortisol — a steroid hormone that can boost your appetite and make it all the more tempting to reach for your favorite comfort foods,” explains Sheri Vettel, MPH, RDN. This can cause water retention in the short term. And if you stay stressed over a long period, high cortisol levels are also associated with weight gain, Vettel says, especially around the midsection.

Yup, really. “One small study in first-shift Monday to Friday workers found that people’s weights tended to go down during the workweek, hitting their lowest point on Friday morning,” Lewis says. “Weights went up over the weekends to their highest point on Monday mornings.” People who lost weight overall still followed this pattern; they just lost more weight during the week than those who remained the same or gained weight over the course of the study. “While this is one small study, and it cannot be applied to the population at large, it does allow some insight into normal weight patterns,” she says. “Understand that even though the scale is going up and down, over time, overall weight can change.”

Sometimes yesterday’s weight can affect today’s weight for reasons that are all in your head. “Some people cannot get on the scale without judging themselves for the number they see,” Lewis explains. “If the number is up, they decide they have failed, feel bad and resolve to eat less and work out more. If the number is down, they decide they are a success, feel great, and decide they can eat more and work out less.” Ideally, you’d behave the same each day when dieting, and over time, your weight would start to trend downward, despite the normal fluctuations, but for many people, this is easier said than done.

“If the scale makes you think this way, consider weighing yourself less often, so you don’t see the natural ups and downs,” she suggests. It may also be worth considering adding some alternative tracking methods to your routine, like weekly measurements and progress photos. That way, your weight is just one of the many ways you keep track of how you’re doing, and suddenly, the inevitable peaks and valleys don’t seem like such a big deal.

Originally published December 2017, updated with additional reporting

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