Why Do I Weigh More at Night? Fluctuations Throughout the Day

If you're watching your weight, it's tempting to step on the scale several times a day. But resist the urge — these frequent checks can be frustrating and misleading, as weight naturally fluctuates throughout the day. So if you're wondering why you weigh more at night, rest assured that's normal.

Indeed, there's usually a several-pound difference in your weight morning versus night (more on that soon). Here's everything you need to know about daily weight changes.

Weight-loss statistics show on average, daily weight can fluctuate from 1 to 2 kilograms (2.2 to 4.4 pounds), per a July 2017 article in ‌Physiological Reports‌. So if you notice you do weigh more at night, that's normal: Body weight is typically a bit lower in the morning because you eat less food and fluids overnight and lose water through sweat and breathing, per the American Physiological Society.

But not everyone is the same, and above-average weight fluctuations can occur in people with more muscle mass, or related to changes in diet and exercise. So if you're wondering why you weigh less at night and more in the morning, these may be the reasons why.

Water makes up around 75 percent of muscle mass, according to an August 2019 review in ‌Nutrients‌. So people with higher amounts of muscle mass could experience weight fluctuations of several pounds per day as they undergo changes in muscle mass.

What's more, runners can lose several pounds of water weight after a several-mile run, and fluid replacement is essential for safety and performance, according to the Academy of Nutrition and Dietetics.

Drastic changes to diet can also affect how much more you weigh at night by causing weight loss or gain that exceeds the daily average of 2.2 to 4.4 pounds, per the Mayo Clinic.

For example, if you nearly eliminate carbohydrate foods from your diet, the body uses glycogen stores for energy — which can lead to weight loss of 10 or more pounds in a week and may influence how much heavier you weigh at night.

Resuming a diet that includes carbohydrate foods after a brief fast or low-carb diet can also lead to several pounds of weight gain, as the glycogen stores are restored.

Daily changes in weight are normal, although shifts in body water — not body fat — explain most of the daily fluctuations, according to a July 2017 article in ‌Physiological Reports‌. Because an average of 60 percent of an adult's body weight comes from water, per the Academy of Nutrition and Dietetics, even small losses of water can show up as weight loss on the scale.

Here are some of the key factors that could cause the number on the scale to shift from a.m. to p.m.

The water in your body shifts from morning to night. Body water is lost through sweat, respiration, urination and with bowel movements, according to Harvard Health Publishing.

Exercising and being in hot temperatures cause an even greater loss of body water. Illness, including symptoms of diarrhea, fever and vomiting, can also cause water loss — and a temporary drop in weight, according to the Merck Manual.

Body water is replenished by drinking beverages and eating water-containing foods.

The loss or gain of glycogen — the storage form of glucose found in the liver and muscles — is another cause of short-term weight fluctuations. Glycogen is stored with up to 3 or 4 parts water, so when this energy source is broken down, the body also loses extra water — and weight, according to the article in ‌Physiological Reports‌.

Glycogen can be quickly depleted — and weight can be lost — from extended exercise, or as a result of very low-carbohydrate or fasting diets, per an April 2018 article in ‌Nutrition Reviews‌.

On the other hand, someone who has depleted glycogen stores from dieting or exercise can regain weight after eating carbohydrate foods and glycogen stores are built back up.

This factor makes intuitive sense: Your weight will temporarily change when you eat or drink because your body now contains what you ate. Just drinking 16 ounces of water can spike your weight by about a pound. This temporary weight of food and liquids stays with you as your body digests and absorbs water and nutrients, until it sends waste out of the body via urine and stool.

Even as stool is in your intestines, it adds to your weight. The average daily weight of stool in humans is 128 grams — or 0.28 pounds — according to September 2015 research in ‌Critical Reviews in Environmental Science and Technology‌.

But rest assured, these weight changes are temporary and when you urinate or have a bowel movement, your weight will go down a bit.

Other factors can explain short-term weight fluctuations. For example, if you are dehydrated, your weight will be lower. If you tend to retain water, a condition known as edema, you can gain weight.

Edema can occur in pregnancy, in premenstrual syndrome, or due to other medical conditions such as liver, kidney or heart disease, per the Mayo Clinic. Taking in too much sodium, a mineral important for water balance, can worsen edema, according to Harvard Health Publishing.

Certain medications can also lead to water retention, per the Mayo Clinic. Steroids and some blood pressure and diabetes medicines are common types of drugs that can cause puffiness or swelling.

Alternatively, diuretics or "water pills" can lead to weight loss, as these medications remove extra body fluid. Taking any of these drugs can cause weight fluctuations between morning and night.

If you are tracking your weight, you may be more interested in changes to muscle and fat weight instead of the temporary fluctuations from fluids, foods and intestinal contents. Changes to fat and muscle mass occur more gradually, as these are influenced by the calories and nutrients in your diet along with your physical activity.

To assess these weight changes, there's no hard and fast rule for when you should weigh yourself. Instead, be consistent: Weigh yourself at regular intervals (like once a week) at the same time (like morning), on the same scale, wearing similar clothing, according to the Cleveland Clinic.

That way, your weigh-ins will more accurately reflect your routine rather than providing random snapshots of your weight fluctuations throughout the week, as it's possible to gain weight in an hour without eating or drinking due to factors like an inaccurate scale, wearing heavy clothing or fluid retention.

You asked, we answered: Here are some common questions about daily weight changes.

Bowel movements are comprised of all of the waste material left over from the digestive process, according to the U.S. National Library of Medicine. And expelling that waste from your body will result in small amounts of temporary weight loss — 0.28 pounds on average, per the ‌Critical Reviews in Environmental Science and Technology‌ research.

However, more frequent bowel movements aren't a weight-loss strategy. Instead, you need to lose weight sustainably by burning excess fat through a combination of nutritious eating and regular exercise, according to the Mayo Clinic.

Your body processes excess fluid overnight, which you eliminate in the morning when you pee, according to Johns Hopkins Medicine. Shedding this water weight is often the reason why you weigh less in the morning or soon after waking up.

The same goes for morning bowel movements, which can further contribute to a lower weight early in the day.

Your body size may get smaller while your weight goes up if you're becoming more muscular.

For instance, activities like strength training can help you burn fat while building lean muscle mass, according to the Mayo Clinic. And because muscle is more compact than fat, it takes up less space on your frame even while increasing your weight, per the Baylor College of Medicine.

Similarly, if you're visibly losing weight but the number on the scale isn't budging, that's likely because you're burning fat while also gaining lean muscle mass, according to the Baylor College of Medicine.

If you're new to an exercise program, your body retains extra fluid to help repair micro-tears in your muscle, according to the Cleveland Clinic. As a result, you may temporarily weigh more after exercising until your muscles heal and your body adapts to the activity.

Weight changes that are lower or higher than the average of 2.2 to 4.4 pounds a day could be related to medications or health conditions.

Let your doctor know if you are experiencing weight fluctuations outside of the average range or outside of the range recommended by your doctor, particularly if you are being treated for any medical conditions or if you are taking any prescription medication.