Why Does Weight Fluctuate Throughout the Day?

For as long as I can remember, I’ve had a love/hate relationship with the scale. Some mornings things looked great, other mornings not so much. I was always curious as to how weight could fluctuate so much, not only from day to day but also morning to night. We’ve all heard that it takes 3,500 calories to gain a pound (which is only 500 extra calories a day – that can sneak up on you!), but even when I was certain I wasn’t taking on that many calories in a 24-hour period, things were still moving erratically (ok, erratically may be a strong choice of words – but you know what I mean). So what gives?

Turns out, there are several factors that can artificially inflate your weight. Let’s check out the culprits.


When you consume more salt than what’s normal (for you), your body tries to normalize itself by holding on to more water. Conversely, the opposite effect happens if you consume less salt, your body lets go of the excess water. Now I say “more” or “less” than normal because if you decide to increase/decrease your salt intake permanently – your body will adjust to this new amount using the hormone aldosterone, meaning less salt is not a permanent weight loss solution (although a good choice for other reasons).

Carb Consumption

When your body doesn’t use all of the glucose from carbohydrates, it turns to glycogen and is stored. For every gram of glycogen that is stored, so are three grams of water. This is often why people see immediate weight loss when they switch to a low carb diet. However, its deceiving because they aren’t losing fat, just water weight.

Strength Training

Here at aSweatLife, we love lifting heavy shit. According to Kelly Hogan, MS, RD, CDN, clinical nutrition coordinator at the Dubin Breast Center at Mount Sinai Hospital, “Resistance training or even trying a new workout can result in fluid retention if the muscles are worked hard,” says Hogan. ”Part of the body’s response when repairing microscopic tears in muscle is fluid retention.”  In order to rebuild the muscle fibers, your muscles retain water to help speed up the process in the cells.

Cycle (for my ladies, dudes not effected)

You’re most likely familiar with this one, but just cover it – water is retained when hormones fluctuate. Enough said.


Turns out, water weight seems to be the cause of most day-to-day weight fluctuations. Try not to let it stress you out. A few pounds up or down in a day really has nothing to do with an increase and/or decrease in body fat. The scale can hold you accountable, however tracking your measurements is a better way to track your progress.

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About Rachel Mitz

The self-diagnosed work-out-a-holic, Rachel Mitz can be found all around Chicago, staying fit when she isn't crunching numbers as a director of corporate finance for a commercial real estate company. Chicago area bred and University of Illinois alum, Rachel works hard and plays hard so her daily workouts are her chance to connect with her mind and body. Rachel keeps it exciting by creating up a lineup of both fun and challenging morning workouts from personal training sessions, to boot camps, to spin classes or runs along the lake front (she just completed her first marathon in October). For fun, you can find Rachel trying new restaurants, traveling, volunteering with her favorite middle schoolers at San Miguel or enjoying a glass of red wine and fro-yo.

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