by | Aug 22, 2023 | 0 comments

Beyond Fat: The Science Behind Temporary Scale Fluctuations

One of my most popular blog posts is the one called “Should You Weigh Yourself? (And How to Measure Progress Without the Scale).” I understand why this is popular – depending on the survey, around 49% of US adults have tried to lose weight in the last 12 months.  And the scale – for better or for worse – is a tool that is easily accessible and purports to measure progress.  Like I said in the previously mentioned post, it does measure progress, especially for those who have a large amount of weight to lose – if you have 100 lbs. to lose, and the scale goes down 50 lbs. in a year, you’ve made great progress.

But if you’re weighing yourself daily, the story is not so simple.  For this post, I’m going to put aside my strong conviction that fat loss is more important than weight loss, and that someone can make incredible progress for their health and how they look by increasing muscle mass and decreasing fat simultaneously, resulting in no net weight loss on the scale (but significant body fat loss).  For this post, we’re just talking about why the scale goes up and down for seemingly inexplicable reasons overnight.

I know you’re familiar with the scenario … you start a new health plan, and you have a really healthy day.  You weigh yourself the next day, and the scale goes down 0.2 lbs. … you were secretly hoping for 20, but you’ll take it.  You have another really healthy day, and then what happens … the scale goes up 0.3 lbs. the next morning, so after two healthy days, you’re actually up 0.1 lbs.!  You say to yourself, “This doesn’t work – I tried so hard and I gained weight,” so you give up and go back to how you were before.  When you read this scenario, I know you see the flaws in it, but when it’s our own real life, we so often don’t see the flaws!

Beyond Fat: The Science Behind Temporary Scale Fluctuations

You see, fat loss happens microscopically – a small fraction of a pound of fat loss per day is an excellent result, and when repeated over days and weeks and months, and years … it adds up to big results.  But why in the world would the scale drop 2 lbs. one day and jump 3 lbs. the next, if we can only lose a fraction of a pound of fat each day?  I’m about to explain.

First, let’s make it really simple.  Assuming you’re weighing yourself naked, there are only a few components of body weight:

  • Bone: this doesn’t change overnight, and we really hope it doesn’t change much at all in our adult life.
  • Organs, connective tissue, nails, and hair: doesn’t change overnight.
  • Lean body mass: this is your muscle, and while we hope it grows over time, no one gains several pounds of muscle overnight.
  • Fat: this is what we think is changing overnight, but as I said above, it changes very
  • Water: here’s the big one!!! Water weight fluctuates dramatically based on the 15 factors I’ll mention below.  How would it change so much if you’re drinking approximately the same amount each day?  I’ll tell you below!

The truth is, our body weight can be influenced by a multitude of factors that have nothing to do with actual fat loss or gain. Before you get discouraged or overjoyed by the scale, let’s dive into the science behind some common reasons why your weight might temporarily fluctuate.

15 reasons for scale fluctuations that are not fat gain or loss:

  1. Hydration: The body’s water balance can play tricks on the scale. When you’re adequately hydrated, your body’s tissues are full of water, which might lead to a temporary weight increase. Conversely, dehydration can make the scale drop temporarily, though it’s important to remember that these shifts are mainly related to fluid levels, not fat changes.This is a huge reason why I tell my clients to never weigh themselves the morning after a plane flight. Airplane cabins are notorious for their low humidity levels, which can lead to dehydration during long flights. Dehydration can cause a temporary reduction in body weight as your body loses water. This might result in a lower number on the scale.  On the flip side, flying for extended periods can lead to fluid retention, particularly in the extremities like fingers and ankles. This is often caused by prolonged sitting and reduced circulation during the flight. The puffiness is a result of fluid accumulation, and it might indeed lead to a temporary increase in weight. Understanding that both dehydration and fluid retention can occur during flights can help you make sense of the apparent contradiction. While these fluctuations are real, it’s important to remember that they primarily reflect changes in fluid balance, not actual fat gain or loss, so it’s basically useless to weigh yourself after a flight.Beyond Fat: The Science Behind Temporary Scale Fluctuations
  2. Inflammation: I talk a lot with clients about foods that cause inflammation (here are a few times I’ve talked about it on the blog!) Inflammation is a natural response to damage that causes fluid retention to aid in healing and leads to a rise in the number on the scale. This can actually be a great way to tell which foods are inflammatory for you! There are several (like fried food, added sugar, ultra-processed foods, alcohol, gluten, and dairy) that cause inflammation for almost everyone, but food sensitivities or intolerances can also cause inflammation that can be reflected by a brief uptick on the scale! It surprises some to hear that I currently weigh myself every day (but I had to get over the emotional attachment I had to the scale, which I describe in this post,  in order to do so!).  The reason I do this is so I can tell how my body is handling inflammation.  If I’ve had super tough workouts (see below!), or I’ve eaten something that doesn’t agree with my sensitive system, I can see the scale go up a few pounds, and that information is incredibly valuable to me as I stay aware of what works best for my body!  To me, it’s just like a flashing indicator on a car – it alerts me of what my body wants so I can take the best care of it possible.
  3. Muscle Recovery from Workouts: Strength workouts cause micro-tears in your muscles, which helps them develop strength as they grow back together. This process requires water and can contribute to temporary weight fluctuations that have nothing to do with fat gain.
  4. Sodium Intake: High-sodium meals can lead to water retention, making the scale tick upward. Each cell maintains a careful balance of electrolytes (do you remember the sodium-potassium pump from high school biology?), and a higher sodium diet draws fluid into the extracellular spaces to balance out concentration, which leads to temporary “puffiness” and water retention.
  5. Hormonal Fluctuations: Hormones, especially for women, can cause significant water retention during certain times of the menstrual cycle. In particular, during the luteal phase (before menstruation), when progesterone is rising, water retention can occur. These temporary weight increases are unrelated to fat gain.
  6. Medications: Some medications can influence water retention, leading to weight fluctuations. Some common medications that can lead to water retention include hormonal medications like birth control, steroids, antidepressants, calcium channel blockers, beta blockers, thiazolidinediones, and more. Always consult your doctor if you’re concerned about the impact of medication on your weight.Beyond Fat: The Science Behind Temporary Scale Fluctuations
  7. Sweating from Exercise: Post-exercise sweating can lead to a drop in weight due to fluid loss, but remember, you’ll rehydrate, and the number will go back up.
  8. Humidity: High humidity can affect how much water your body retains, potentially leading to short-term weight changes.
  9. Coffee: The diuretic effect of caffeine can lead to temporary fluid loss, reflecting on the scale. Remember to rehydrate!
  10. Alcohol: Like caffeine, alcohol is dehydrating, causing a temporary decrease in weight due to fluid loss.
  11. Stress: Stress triggers the release of cortisol, a hormone linked to fluid retention. Elevated stress levels might result in temporary weight fluctuations.
  12. Carbohydrate Intake: Carbohydrates are stored in the body as glycogen, which retains water. A high-carb meal can cause temporary weight gain due to glycogen and water binding.
  13. Sickness: Illness or infection can lead to inflammation and fluid retention, contributing to a higher scale reading. Focus on recovery, and the scale will stabilize.
  14. Digestion / Constipation: Digestive processes can cause temporary weight fluctuations, especially if you’re constipated. Just think about it (even if it’s gross) … the average adult consumes 3-5 lbs. of food per day. If that’s not coming out the other end, it’s still in you!  If you stand on the scale with a bag of broccoli in your hand, the scale reflects the weight of the broccoli as well.  If you stand on the scale with a bag of broccoli in your digestive tract, even though that is not causing fat gain, it reflects on the scale!  As your digestion normalizes, so will the scale.
  15. Sleep Interruptions: Poor sleep can affect hormone levels and fluid balance, potentially leading to short-term weight changes. Prioritize consistent sleep patterns for accurate readings. Want tips on how?  See these posts.

Beyond Fat: The Science Behind Temporary Scale Fluctuations

What to do about scale fluctuations

First, remember: the scale is just one tool among many to track your progress. Don’t let temporary fluctuations derail your journey. Instead, focus on holistic measures like how your clothes fit, energy levels, and overall well-being. Keep in mind that sustainable changes take time and that weight fluctuations are a normal part of the process. Trust the process, stay consistent with your healthy habits, and the long-term results will speak for themselves.

Second, if you are weighing yourself regularly, and the scale goes up (or down) overnight by more than a fraction of a pound, keep this list handy.  Can you identify which factors are contributing to the temporary change?  Maybe you ate really healthily yesterday, but you did a tough workout (causing muscles to hold onto water), you ate rice with salt as part of dinner (sodium and carbs cause water retention!), and you didn’t sleep well (but you’re going to prioritize my tips for how to improve sleep naturally tonight!).  Doesn’t it feel better to know what is causing the uptick, rather than just feeling frustrated?

By understanding the various factors that contribute to temporary changes on the scale, you can free yourself from unnecessary stress and anxiety. Embrace a holistic approach to health and wellness, recognizing that your worth is not defined by a number on a scale.

Now it’s your turn!  Do any of these reasons surprise you?  Do you understand now why trends are more important than daily weighs?

Want to hear about this topic in audio format? → Check out the podcast episode here!


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Megan Lyons Headshot

Hi! I'm Megan Lyons,

the voice behind The Lyons’ Share. I love all things health, wellness, and fitness-related, and I hope to share some of my passion with you. Thanks for stopping by!
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