8 Reasons Your Weight Fluctuates From Day to Day

Changes in weight can be tricky to gauge. Your weight isn’t static, but rather something that fluctuates during the course of the day depending on things like what you ate and your daily activity. In addition to this daily fluctuation, your weight can also go up or down a few pounds throughout the week due to factors that have nothing to do with gaining or losing mass.

Ideally, to get a sense of your weight, it’s best to weigh yourself at a standard time, wearing standard clothing. For example, the suggestion is to usually weigh yourself first thing in the morning, after you’ve gone to the bathroom, but before you’ve had your breakfast.

Even then, your weight can fluctuate a few kg in either direction, for reasons that have nothing to do with either a calorie deficit or surplus. This can be especially frustrating if you are actively trying to gain or lose weight, or if you are competing in a sport that requires weigh-ins for competitions, when even a small amount of weight gain can be frustrating to deal with.

With that in mind, here are a few reasons your weight may fluctuate from day-to-day.

Eating salty foods

If you’ve been eating a lot of processed foods lately or been especially heavy-handed with the salt shaker, this can cause your weight to go up a little, as sodium causes your body to retain extra water.

Given the amount of sodium in processed food, keeping an eye on your salt intake can be tricky. The recommended daily sodium intake is 2300 mg a day, or about a teaspoon, which adds up fast. For example, a serving of deli meat has about 700 mg of sodium, which is almost a third of the daily recommended amount, while there can be surprisingly high sodium levels in unexpected foods, such as your breakfast cereal or store-bought bread.

However, given that this is all water weight, cutting back on the salt will result in the scale going back to normal.

You drank a lot of alcohol the night before

Alcohol takes longer for your body to process, which means it will stay in your body for a longer amount of time. It also has the effect of slowing down your digestion, as well as causing water retention, all of which means your weight will be a little bit higher than normal after a night of drinking.

So if the scale goes up after a night of drinking, that’s a temporary gain, one that should go back down again within a few days.

Your period is about to start

Depending on where you are in your menstrual cycle, this can cause your body to retain extra water. Most people will notice a slight increase on the first day of their period, which will then drop within a couple days.

You worked out really hard the day before

If you wake up with sore muscles from a tough workout, there’s a good chance the scale will be a little higher than usual. This is because a tough workout causes micro-tears in your muscles, which then need to heal. These micro-tears are a good thing, as this is how your muscles get stronger, however, during the healing process, your muscles will retain extra fluid.

You’ve been eating a lot of carbs

Just like with salt, carbs can cause your body to retain water, leading to a temporary weight gain. The reason for this is that glycogen, our body’s carb storage in our liver and muscles, contains about three grams of water for every gram of carbs. Glycogen storage fluctuates for several reasons, but the major ones are that it gets burned during exercise and replenished when we eat carbs.

You haven’t pooped in a while

If you are constipated, that means that your body is hanging on to a bunch of excess waste. In addition to being uncomfortable, this can cause the numbers on the scale to go up, at least until you can find a way to poop it all out again.

There are a number of reasons that you can become constipated, including a diet low in fibre, a sedentary lifestyle, a change in your routine, eating a lot of dairy products, as well as dehydration.

Even when things are moving well though, food still (temporarily) adds weight to your body. Generally speaking, it takes about six to eight hours for your food to get digested, and about 36 hours to get expelled, which can be longer if you’re constipated.

You just sweated out a bunch of water

If you’ve ever weighed yourself before and after a workout, there’s often a difference of a few pounds due to all of the water you’ve sweated out. The average person will lose between 0.8 to 1.4 litres of water weight during an hour-long workout, which equates to about one to three pounds of water weight. For a highly trained athlete, they can lose up to twice that amount.

This loss is all water weight, which means that you will need to replace the fluid that you’ve lost, or else risk getting dehydrated.

You’re dehydrated

When you’re dehydrated, your body has lost water weight, leading to a decrease on the scale. As tempting as it is to consider this real weight loss, this is not due to losing fat. To recover from dehydration, you’ll need to drink water regularly, which will bring your weight back to normal.