Is Scale Weight Really Accurate?

Has this happened to you?  You step on your bathroom scale on Monday morning after a rough weekend of eating and/or drinking to find that your weight has increased by more than a few pounds. Sound familiar? If so, it may be due to more than just additional calories.

A person’s total body weight can fluctuate by as much as ten pounds – up or down — over the course of just a few days. This is why scale weight is so tricky.

It’s important to know that you’re probably not gaining or losing “pure” weight here. It takes approximately 3500 calories consumed to truly gain a pound of weight (note, this is not perfect math). In order to actually gain five pounds of pure weight over a weekend, you would have to take in a surplus of almost 18,000 calories, which is highly unlikely, unless you are Olympic swimmer Michael Phelps!

What is most likely happening is this: your body is retaining more water than usual.

Here are the ways that water retention can happen, along with some other culprits that contribute to fluctuating scale weight:

The Culprits

  • Too Many Carbs: Taking in more calories in the form of carbohydrates can lead to higher water retention. After carbohydrates are processed in your body, they are stored in the muscle (as glycogen) and liver (as glucose). For every gram of stored carbohydrate, your body stores an additional 3 grams of water.
  • Too Much Sodium.  Elevated sodium levels in the body equates to increased water retention. According to, “Salt does not cause your body to gain or lose fat. In fact, salt has no calories. High consumption of salt only results in temporary weight gain as it causes your body to retain water. Conversely, low consumption of salt can result in temporary weight loss as it causes your body to expel water.”
  • “Time of the Month” Ladies, you know what I mean. Where you are in your cycle can affect water retention. You most likely see this in the form of bloating and weight gain each month. Take solace in knowing that this is normal and temporary.
  • Dehydration. Don’t get into a habit weighing yourself post workout, because you can lose 1-2kg of body weight or more from sweat following an intense exercise session, obviously effecting the accuracy of your weight reading.
  • The Scale!  A typical scale is simply not accurate. If you step on five different scales you will see five different numbers, and the variability can range between 1-5 pounds. More importantly, bathroom scales cannot differentiate between lean muscle, body fat and water (or bone, connective tissue, etc).

At Koko, we manage this with a proprietary body composition measurement tool called Koko FitCheck. FitCheck uses precision technology to calculate and track the body’s lean muscle level and “enhanced” body mass index  – an important marker of progress and metabolism. With regular readings, our members focus on getting leaner, not just lighter.

Even without access to precision measurement tools, like FitCheck, there are ways you can better understand and manage healthy body composition beyond scale weight alone:

  • Measure your waist to hip ratio.  This can be done by taking a measurement around your waist at the navel and then again around the hips. Divide waist into hips. Keep track over time of these two measurements. A good goal is to have this ratio <0.80 for women, and <0.90 for men. There is strong evidence that shows a ratio above 1.0 increases your chance for cardiovascular disease.
  • Watch the way your clothes fit.  Even if the scale weight stays the same, if you are dropping pant or dress sizes, you know that your body is getting leaner, which is the goal.

If you must use a scale, the best time to use it is the morning after you visit the bathroom and before you eat or drink anything. Don’t let the number make or break your day. Weigh yourself naked and remember that it’s not a single reading that is important – it’s the trend over time. Your weight is just one more tool in your health and fitness tool-box. Determining your percentage of body fat, lean muscle levels and waist to hip ratio can give you a fuller picture into how your body is changing – for the better.

Michael Wood, CSCS
Chief Fitness Officer, Koko FitClub

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About Michael Wood, Chief Fitness Officer
Michael Wood, CSCS, is Chief Fitness Officer at Koko FitClub, driving the development of integrated strength and cardio training and nutrition programs for Koko members nationwide. A nationally acclaimed fitness expert, Michael has conducted research as a Senior Exercise Physiologist at the Nutrition, Exercise Physiology and Sarcopenia Laboratory at the Research Center on Aging at Tufts University, and has lectured at Boston University and the University of Connecticut. He has been named Boston Magazine’s “Best of Boston” Personal Trainer, and made the Men’s Journal “Dream Team” list of the nine best trainers in the U.S. Michael and his family live in North Attleboro, MA.

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