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Weight fluctuations are normal. However, they can be very discouraging and emotionally taxing to dieters who step on the scale and notice they’ve gained a few pounds overnight.  

However, the average adult’s weight can fluctuate between 1-and 2 kilograms (2.2 – 4.4 pounds) over the course of a day or a few days. So, for individuals who weigh themselves frequently, once a day or once a week, this may be cause for frustration – so much so – that they turn to food for comfort or end their weight loss journey altogether. 

Though these feelings are valid, it’s important to remember that our weight doesn’t provide us with the full picture of what is going on inside our bodies.


What causes weight fluctuation?

Fluctuations in weight are normal, and in many cases, can be caused by changes in water retention. More body water translates to an increase in weight and less body water translates to a decrease in weight. This leaves body fat and muscle mass unaffected. 

Water retention and body composition test

Not only does water retention change the number we see on the scale, but it can also affect body composition testing via bioelectrical impedance analysis (BIA). BIA testing is a widely used method of assessing body composition including total body water, muscle mass (fat-free mass), fat mass, and body fat percentage.

Unfortunately, despite BIA testing being considered a great way to determine body composition, water retention can alter the results of a BIA test. Consuming water immediately before BIA testing can skew your results because it can cause an overestimation of body fat mass. On the other hand, retaining water will overestimate fat-free mass (muscle mass) and increase your outputs for extracellular water.

Much like seeing an increase in body weight, seeing an increase in body fat and body fat percentage on a BIA device can be discouraging for individuals who have been dieting and/or exercising with the goal of losing body fat.   

Frequently monitoring changes in weight, muscle mass, and body fat are useful for tracking progress and maintaining motivation. However, it is important to remember that there can be small, undesirable fluctuations throughout your journey, and that’s okay. Don’t let them cause you to abandon your health and wellness goals.  

What causes water retention? 

There are many reasons why an individual’s body weight can fluctuate and the biggest contributor is water retention. 

The human body is approximately 45-75% water. Because of this, changes in how much water our bodies are retaining can affect the number we see on the scale.   

There are many factors that influence how much water our bodies retain, including: 

  • Sodium: Sodium, also referred to as salt, is essential for normal body processes and is a compound that regulates water content. Consuming excess sodium leads to water retention, and therefore, weight gain.  
  • Exercise: Exercise can cause water loss through perspiration, which leads to immediate weight loss, especially if you are not hydrating sufficiently. On the other hand, if you consume more water than you lose, you may see a slight increase in weight.  
  • Glycogen levels: Glycogen is the body’s stored form of carbohydrates. In order to store glycogen, the body also retains water. This means that the more glycogen you have, the more water you retain, which can lead to an increase in weight. On the contrary, if you lose a significant amount of your glycogen stores, which is often the result of a low-carbohydrate diet, you will lose a lot of water, and therefore, see a lower number on the scale.
  • Menstrual cycle: It’s normal for women to see a slight weight increase due to increased water retention right before they start their period. This is because of fluctuations in certain hormones.  
  • Medications: Some medications cause your body to retain more water.
  • Dehydration.: This might seem counter-intuitive, but being dehydrated causes the body to retain more water.  
  • Meal and drink consumption.: Food and liquids are heavier than most people realize. If you eat a meal that also consists of a couple of glasses of fluids and then go weigh yourself, you are going to see an increase in weight. To avoid this, try to weigh yourself first thing in the morning before eating or drinking anything.  
  • Bathroom visits.: Normal bodily excretions (urine and feces) can weigh a couple of pounds and can cause weight to fluctuate. 

How to monitor body composition while keeping water weight in mind  


If you notice undesirable results on a specific day, don’t let this discourage you. If you’ve been exercising more and being consistent with your diet, it is likely that these test results are due to water retention. Keep being consistent with your diet and exercise routine and wait until the following week to test yourself again. You will likely see favorable results at this time.
 

In order to minimize weight fluctuations due to changes in water retention, here are some tips for obtaining the most accurate body composition test results: 

  • Test in the morning: Test in the morning after you’ve gone to the bathroom and before you’ve consumed any liquids and before you’ve engaged in any exercise. 
  • Test once a week: Test yourself once a week on the same day. For example, test yourself every Sunday or Monday morning. 
  • Meal timing: The night before you weigh yourself, try to eat your last meal around the same time. This will help minimize any digestive changes that could alter your results.
  • Exercise: Be consistent with your exercise the day before. This can mean that you always exercise the day before your test or that this will always be a rest day for you. Sticking to a specific pre-test workout routine will ensure that there are no changes in water retention due to exercise.  
  • Clothes.: Be consistent with what you wear. While this will not affect the BIA test results, it can affect your weight. 

Overall, it’s important to try and keep your testing condition the same as your first body composition test.

Conclusion

There are many reasons why your body retains extra water. This can cause fluctuations in body weight and skewed BIA test results. While this may be disappointing, it’s important to remember that weight fluctuations are normal and small setbacks will not derail your progress. Consistency will keep you on the path toward achieving your fitness and weight loss goals.   

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