Is Weight Fluctuation Normal?

Is a daily weight fluctuation normal? If you weigh yourself every morning, you probably notice that the number on the scale can change significantly from one day to the next.

Sometimes, the reason for the daily weight fluctuation is obvious. Perhaps you indulged in a big meal before bedtime that resulted in weight gain, or you did a very sweaty workout that resulted in weight loss. But there are other reasons that weight fluctuations occur from day to day.

If you are trying to lose weight or change your body composition, you might be tempted to believe that the daily weight fluctuation is due to fat loss or fat gain. That is a possibility. But there are many other factors that affect your weight from day to day.

Endocrinologist Kathleen Wyne, MD, says that a five-pound weight shift is typical for most people day-to-day but that the number on the scale can change by as much as 20 pounds depending on your body size. So why the big swing? And what causes these frustrating weight fluctuations from day to day? These factors contribute to an increase or decrease on the scale.

Weight fluctuation causes — Verywell / Jiaqi Zhou

Why Does Weight Fluctuate?

Factors like sodium and carbohydrate intake, exercise, food intake, bowel patterns, a person's menstrual cycle, medications, and alcohol can all contribute to daily swings in the number on the scale. Stepping on the bathroom scale weekly rather than daily can help you get a broader view of the changes in your body weight. Here is a closer look at some of the factors that influence weight fluctuation.

Weight Fluctuation From Sodium

High-salt foods can cause water retention. The extra water adds up to pounds on the scale. Some people are very sodium-sensitive and may retain more water, while others are less sensitive.

Many of us don’t overuse the salt shaker at mealtime. But sodium can hide in unexpected places. Cold cuts, frozen meals, and savory sauces are often high in sodium. Canned soup is another common culprit. Many varieties of low-calorie soups are very high in sodium.

Even homemade soups can have a lot of added salt. If you are trying to cut back on big meals and you replace a meal with low-calorie soup, you might notice an increase in the scale—even though the weight is simply water retention.

Weight Fluctuation From Carbohydrates

If you love bread, pasta, rice, and other starchy carbs, the weight gain you see on the scale may be related to your carb intake. For every gram of carbohydrate you consume, your body retains about three grams of water in order to store the fuel source.

For that reason, if you eat a very high carbohydrate meal, your body weight is likely to increase because of the water weight, not because of increased fat. In addition, many refined carbohydrate foods are also high in sodium. For example, a spaghetti and meatball meal with Parmesan cheese may cause you to retain water due to the high carbohydrate and salt content.

Weight Fluctuation From Food Weight

Of course, food intake will cause your weight to increase slightly while your body processes the food. The food you consume can weigh a few ounces per meal, up to a few pounds per day. The water in food can cause your weight to increase as well.

According to some experts, consuming two cups of water—from beverages or water in food—increases your weight by one pound.

So what happens to all of that weight? Well, it doesn’t automatically stick to your thighs. Instead, the calories in food are used to fuel your body’s natural processes, or the energy is stored to be used later. And any waste products are processed and excreted by your body in the form of urine and stool (bowel movements).

Weight Fluctuation From Bowel Movements

You’re likely to see some fluctuations on the scale due to bowel movements. How much does your poop weigh? In a research study, investigators found that you might produce 125 to almost 170 grams of stool per day. That’s less than a half-pound of poop.

However, other studies report the average daily stool weight to be roughly 106 grams per day—less than a quarter pound. Even so, additional sources report that you might poop up to one ounce per day for every 12 pounds of body weight.

Nonetheless, when you lose stool weight, there will still be digestible material in transit. Normal physiological fecal transit time is estimated to vary between 40 and 60 hours, with an optimal whole gut transit time of 24 to 48 hours. Transit time is improved if you consume more dietary fiber.

Normal bowel habits vary, but you won’t see significant weight fluctuations from bowel movements alone.

Weight Fluctuation From Exercise

Exercise can cause you to sweat and lose water weight. In fact, exercise experts estimate that the average person loses approximately 25 to 45 ounces of fluid per hour during exercise, especially intense cardiovascular activity.

Of course, that number can vary greatly based on weather conditions and other factors. However, fluids lost from sweat shouldn’t make a difference on the scale since these fluids lost during exercise are immediately replaced.

If you notice that you lose weight consistently after exercise, you may want to come up with an improved hydration plan.

Other forms of exercise can cause daily weight fluctuations as well. Lifting weights or any form of strength training can cause your muscles to retain water. Why does this happen? When you participate in strength training, you create tiny tears in the muscles. Your muscles store and use water to repair the damage. When you create and repair these micro tears, your muscles become more prominent and stronger.

Weight Fluctuation From Medication

Certain medications may cause you to gain weight. Some increase your appetite, some may cause you to retain water, and according to the Obesity Action Coalition (OAC), “others may affect how your body absorbs and stores glucose, which can lead to fat deposits in the midsection of your body.”

If you are on medication to treat conditions including diabetes, high blood pressure, mood disorders, seizures, or migraines, you may notice an increase of up to several pounds per month. The OAC reports: “Some people may gain a few pounds throughout the course of a year, while other people can gain ten, twenty, or more pounds in just a few months.”

If you notice a sudden increase on the scale after you start a new prescription, don’t stop taking the medication. Instead, talk to your doctor or pharmacist. Sometimes, the weight gain is normal and to be expected, but other times it may be an indication that something is wrong.

Weight Fluctuation From Your Menstrual Cycle

Most women notice some degree of bloating from fluid retention immediately before and during their menstrual period. Studies have shown that fluid retention peaks on the first day of menstrual flow. It is lowest during the mid-follicular period (the middle phase of your cycle) and then gradually increases over the eleven days surrounding ovulation.

Some researchers have found that fluid retention was not linked to ovarian hormone changes. However, other studies have linked fluctuations in estradiol and progesterone (your ovarian hormones) to changes in binge eating and emotional eating.

So, hormonal changes may not cause weight gain. The cravings you get before your period may mean you eat more or eat different foods than you would typically eat—causing increased fluid retention and possibly an increase in weight from food and water intake.

If you are trying to lose weight during your period, it's important to be aware of and manage these menstrual eating patterns. A few days of high-calorie, high-fat eating can easily undo a few week’s worth of consistent dieting.

Weight Fluctuation From Alcohol

Alcohol is a diuretic, so it is possible that you could notice an immediate weight decrease if you end up urinating more than usual while drinking. In fact, researchers have found that alcohol can produce urine flow within 20 minutes of consumption, leading to urinary fluid losses and possible fluid imbalance.

However, this imbalance may also cause your body to retain fluids from the beverages you consume and from the food that you eat. Many drinkers eat or overeat salty foods that cause water retention. The end result is that it is very possible to see a weight increase after drinking.

When Will My Weight Go Back to Normal?

There are many reasons that a daily weight fluctuation may occur. Most of the changes can be linked to changes in water weight and normal bodily functions. So there really is no "normal weight." You probably don't need to worry if you see a small shift from day to day. You can even buy a scale that measures the percentage of water in the body to see how your fluid levels change throughout the month.

When should you be concerned about daily weight changes? If the number on the scale continues to increase or stays elevated for more than five to seven days, then it may be an indicator of a medical concern. Or it may show increased body mass. But keep in mind that both muscle and fat increase your mass, so your weight gain may be due to muscle growth.