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  • Writer's pictureJess Elliott, MA, CSCS, TSAC-F, XPS

10 Possible Causes of Sudden Weight Gain - Part 2

Updated: Oct 29, 2023

A man weighing himself on a glass scale.

And we’re back for Part 2 of 10 Possible Causes of Sudden Weight Gain!

Here's a quick recap of causes 1-5:

1. Less Total Sleep than Normal

2. Caffeine Intake

3. Low Hydration Levels

4. Higher Salt Intake

5. Higher Carb Days

If you'd like to review the previous post, you can check it out here. No need for a long introduction, let’s dive in!


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6. Overloading the Body

Whether you’re picking up a new activity (pickleball anyone??) or hitting the gym, any new stimuli will overload the body. Why is this? In short, you’re asking the body to perform in ways that it is unaccustomed to. Perhaps you are moving in different directions than your typical day-to-day life (laterally, diagonally, backwards), incorporating different speeds in your training (faster or slower), increasing your range of motion (active or passive flexibility), adding more resistance (heavier weights), or increasing volume (more days/week, more sets and/or reps). Any of the above could overload the body.

Here’s a quick example. Let’s say two friends decide to try a new HIIT (high intensity interval training) class together. Friend A (regularly lifts weights) experiences minor but noticeable muscle soreness 24 hours after the class, and Friend B can barely move due to high levels of inflammation/muscle soreness. What’s the difference? The new stimulus (aka the HIIT class, while new to both, overloaded Friend B’s body to a greater degree than Friend A. More soreness = more inflammation = more “sudden weight gain.”

Please note: even if you’ve been lifting weights regularly, new movements can cause minor muscle soreness because you’re still introducing new stimuli to the body. And if you’re brand new to weight training or returning after a hiatus, you are going to experience more muscle soreness than someone who is lifting regularly.

How can you avoid excessive soreness? If you’re brand new to an activity and don’t want to hobble around for 24-72 hours post-stimulus, minimize the dose. Instead of 3-4 sets of each exercise, perform 2. Instead of 15 repetitions, start with 10. Skiing for the first time in a couple of years? Consider starting with a half-day on the mountain (especially if you weren’t an avid skier prior to taking time off). Another strategy would be to wear compression garments. If you’re bringing leg day back to your schedule, wear leggings as opposed to shorts. Light compression has been shown to reduce levels of perceived muscle soreness in athletes.

Key takeaways: any novel stimulus is likely to overload the body. Overload leads to inflammation at the cellular level, and this is what causes temporary weight gain. It could take 3-7 days for your weight to return to normal (depending on levels of inflammation and recovery post-overload). Stay hydrated and get plenty of sleep to help facilitate recovery.


7. Rest and Recovery

Rest and recovery - what’s the difference? I’m not going to use scientific definitions here; rather, I’m going to explain each as it relates to temporary weight gain.

Rest - taking dedicated time off from physical activity. In this instance, you are hitting the pause button on your regular exercise or training schedule. It could be a single rest day or a week. In this situation, the sudden decrease in physical activity results in a lower daily energy expenditure. Furthermore, if you eat normally (the same as your training days), the sudden decrease in expenditure while consuming the same amount of energy can lead to a temporary shift in the scales. Whether you’re taking a single rest day or a week off, your weight will normalize in a few days once it adapts to the sudden change in pace or returns to normal activity levels. The body seeks balance.

Note: in this situation, the rest period is relatively short. If you shift from marathon training (running 40+ miles/week) and then enter an active rest period for 2 months, you need to adjust your energy intake. If you continue eating like you’re running 40+ miles per week while resting for 2 months, you’re going to gain weight. Remember food is fuel (delicious fuel), and you need to adjust your energy intake to match your energy expenditure to maintain your weight.

Recovery - taking time off from physical activity IN ORDER to physically recover. You may be recovering from a race or a hard gym sesh. Regardless of the reason, your body is attempting to return to baseline (or establish a new baseline) and this requires fuel.

Let’s say you ran a half marathon this morning. Whether you hit a PR or not, you gave it your all. After crossing the finish line, you head home and refuel with a balanced meal featuring protein, carbs, and fats. The next day you wake up, weigh yourself, and stare in confusion when the scale is heavier than usual. WTF?! Despite burning more calories than usual, your weight went up! Why? The body is in recovery mode. Even if you’re not physically sore from inflammation, your body is pulling glycogen and water into the muscle cells to aid in the recovery process. And in the example of a half marathon, you're using large muscle groups (legs and glutes). So, there are a lot of muscle cells that need some recovery love aka refueling.

Note: For every 1g of glycogen (stored carbohydrate), there’s an additional 3g (at least) of water bound to it. If you combine this glycogen + water storage with inflammation, and factor in the size of the muscle groups impacted, it’s easy to see why your weight on the scale skyrocketed overnight.


8. Sunburn

This is simply the other side of the physical recovery coin. We tend to think that physical recovery only refers to exercise; however, sunburn is inflammation of the skin rather than muscle cells. Your body needs fuel to repair the damage, so nourish your cells and ignore the scale for a few days. Expect the inflammation and weight gain, and trust that it’s temporary.

…Unless you decide to eat 5 pizzas/day to “nourish your cells” while your body repairs. That’s no longer temporary weight gain.


9. Menstrual Cycle

Hello to all my fellow humans with uteruses!! This should come as no surprise. Hormones, while necessary and beneficial, have annoying side effects. And those of us with menstrual cycles get a monthly (-ish) reminder of the good, bad, and ugly.

What’s interesting is that no cycle is the same. While it’s obvious that no two bodies are identical; it’s important to note that one body can respond differently each cycle. The weight gain might be non-existent in April and 3 lbs in May. It could start 1 day before your period begins, and it could start 3 days before your period the next time. There might be a cycle where there’s no change on the scale. It’s annoying because we like predictability. Just remember, it’s not you; it’s your body and hormones fluctuating.


10. Too Much Accumulation

While it’s common to hear or think “you’re not exercising enough,” it’s rare to hear that you’re doing too much - unless you’re a competitive athlete.

The truth is: you CAN have too much of a good thing.

Even if you love crushing it at the gym or getting in a daily ride or run, you need to pay attention to your body. If you start accumulating more stress than your body can handle, your stress hormones shift out of balance, and as a result, your weight on the scale creeps up.

The solution? Take a day or two to rest.

For a low-tech way to assess your daily cumulative stress, take your resting heart rate (RHR) first thing every morning. I recommend doing this while laying in bed. Find your radial or carotid pulse points and count your heart rate over 60 seconds. If you start to see your RHR increase several days in a row, your body’s cumulative stress might be adding up.

Keep in mind, the body doesn’t differentiate between stressors. Whether it’s relationship troubles, midterms or finals, illness, exercise, lack of sleep, or deadlines at work, the body’s stress response activates. Don’t zoom in to one specific stressor; look at your cumulative stress response. If you lose sight of the forest by focusing on a few trees, the whole thing could go up in flames - aka you burnout. Track your stress and incorporate regular periods of rest (and actually rest - sleep, hydrate, eat well).



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