Weight Fluctuation and Why You Shouldn’t Worry

I’m about to tell you a really interesting story…

Yesterday I weighed in at 170.5 lbs around 8:00am. My body fat percentage was at 7.5% using a bioelectrical impedance machine (Tanita scale – measures the water in your body to determine muscle/body fat). I was pumped since I was down 3.1% from February when my back pain was insurmountable.

Today I decided to test how accurate these things were. After eating a big dinner last night (pasta – more carbohydrates increase your glycogen stores which allows your body to hold more water), a big breakfast (three Grilled Potato Breakfast Burritos from Taco Bell – more carbs), and drinking as much water as I could, I managed to weigh-in at 184 lbs at 12:00pm today. By 4:00pm, I was back down to 177, less than what I weighed this morning. In the meantime, I had a coffee (diuretic) and urinated four times from my bloat earlier. I also pooped – TMI, I know. This goes to show how much weight can fluctuate throughout the day.

The scale I used has been discontinued, but the replacement is valued at $3,449.99. Bioelectrical impedance is said to vary by up to 9% (for percent body fat, not weight). That’s a lot of money to pay for inaccuracy. If you decide to weigh yourself regularly, make sure you are using the same scale. It doesn’t matter if it is a $10 one from Wal-Mart or a $3,449.99 one. Just make sure you’re not comparing one scale against another. If you scroll down to the bottom of this study you can get an idea of some of the factors that affect your body fat percentage reading.

There’s clearly a variance. The main reason for this is because body fat percentage is solely a prediction when using the bioelectrical impedance scale. It calculates a number without knowing the specific biometric data it needs to in order to accurately depict body fat. Water is the main factor that can mess with these numbers. Do I necessarily think the my body weight was off on any of these readings? No. I trust that the $3,449.99 scale was giving me an accurate measure. I felt bloated, chugged water, and had to urinate extremely bad by the time I took my 12:00pm reading. However, the difference in my Total Body Water (TBW) from my 9:00am reading to my 12:00pm reading only indicated that I had gained two pounds of water mass, when I had certainly chugged over a half gallon. All of the weight gain during this time was a direct result of water consumption (6.5 lbs). It also determined my body fat percentage was higher at 12:00pm, even though muscle retains more water than fat. I would have initially predicted a lower number for body fat percentage with an increased water intake.

What factors contribute to this fluctuation? After studying up on this a little bit, here’s what I found:

  1. Salt – If you have a salty diet, chances are you’re retaining a lot more water that’s providing extra weight. Since it’s extremely important to stay hydrated and not so important to consume salt, I think you know the solution. Eliminate the salty foods if you’re trying to look thin on date night.
  2. Carbs – Like I mentioned before, carbohydrates will allow you’re body to store more water. I thought this was interesting, because I used to “carb-load” before track meets. This likely weighed me down during the short-burst sprints I ran, since they relied less on glycogen stores and more on my creatine-phosphate system. It also makes sense why a low-carb, ketogenic diet would garner a lot of weight loss in the beginning. If you take out the carbs, you retain less water.
  3. Menstrual Cycles – Ladies! Did you know you retain more water at different periods during your menstrual cycle? Best to weigh in at the same point each month and perhaps avoid daily weigh-ins as your cycle may affect this.
  4. Constipation – This is something I’m typically on the opposite end of, but make sure you’re pooping on the regular. Eat some high-fiber foods and drink water continuously throughout the day. For other tips to avoid constipation, I stumbled on this.
  5. Hydration – Well duh! Everything I have mentioned to this point has something to do with water. Keep drinking it. Even if it means you weigh an extra pound, your body will feel so much better when hydrated.

So what’s my point? Stop weighing yourself everyday!! People are obsessed with weighing themselves and the way the numbers look on the scale. I never understood why. People will probably say it’s because I’ve never had to lose weight, which is partially true, but aren’t you the only one who sees your number? It’s more important to focus on how you feel and physical appearance.Use weight as information – think about how your clothes are fitting. If there’s a difference and the fit looks better, then you are doing things right. Take your measurements every so often so you can see if your chest or waist circumference is changing. Remember, changes if your body happen with exercise and nutrition. Don’t forget all those weight-loss tips and tricks – this article actually does a fairly nice job at throwing many of those tips in one place. Make sure you follow the same protocol when weighing in or testing body fat percentage. Try to do it in the morning after fasting overnight and keep that consistent. Shawn Stevenson runs a podcast called The Model Health Show which I encourage you to listen to if you want weight-loss strategies with the science to back them up. If you’re curious to hear my thoughts on diet, nutrition tips, and more, check out some of my earlier posts!


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I really wish I had taken pictures of how I looked during this process. I’ll try my best to do this again with photos! Thanks for reading.


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