Ask a Dietitian: Why Does My Weight Fluctuate So Much?

Hi Jess, I’ve noticed my weight can fluctuate a lot throughout the day and week. Is this kind of fluctuation normal? 

Why Does Our Weight Fluctuate So Much?

Whenever you step on the scales, it can stir up a whirlwind of emotions. You might see a two-pound weight gain one day, only to find a one-pound loss the next. It’s frustrating how the numbers keep changing all the time - especially if you're looking to lose weight.

Here’s the reassuring part. Small fluctuations are completely normal. If you’re curious about the reasons behind these weight changes, here are a few factors that contribute.

Water retention

Put simply, this is when your body holds onto extra fluid, resulting in temporary weight gain or fluctuations. One of the main factors contributing to this is excess sodium intake. Consuming a highly salty meal disrupts the fluid balance in your body because sodium binds to water and encourages your body to retain or hold onto it.

In addition, hormonal variations that occur during the menstrual cycle can lead to temporary water retention and bloating. Research has shown that fluid retention tends to reach its highest point on the first day of menstrual flow.

Carbohydrate intake

If you're a fan of pasta, you know that carbs provide energy. However, for every gram of stored carbohydrates, we need 2–3 grams of water to store that fuel. As these carbohydrates are burned off, the water associated with them is lost, which is why any weight gain is only temporary.

Fluid balance

When we work out, our bodies release water through sweat. This can lead to a temporary decrease in weight. However, once we rehydrate by drinking water or other fluids, our weight will return to its previous level. 


When we're stressed, our bodies release cortisol, which is often referred to as the stress hormone. High levels of cortisol can affect digestion, fluid retention, hunger and metabolism. For example, research looking into stress and eating behaviors has shown that chronic stress can influence our food preferences, and increase our desire for highly enjoyable and indulgent foods. 


It's completely normal for your weight to fluctuate, and there are several factors that influence these changes. While it's important to be mindful of day-to-day fluctuations and not solely focus on the number on the scale, if you observe a significant change, it's a good idea to consult your doctor for advice.

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