Counting Macros

What Causes Water Weight, Water Retention, and Weight Fluctuation?

I often get frantic emails from my macro dieting coaching clients that they are frustrated because they seemingly gained two pounds overnight.

I quickly assure them that drastic weight fluctuation like this is due to water retention rather than fat tissue gain.

Here’s why the increase is just water weight…

First off, if we look at the situation logically, it takes roughly 3500 extra calories beyond one’s TDEE (total daily energy expenditure) to create a pound of stored fat. Therefore, to gain two pounds of fat overnight, one must eat an additional 7000 calories beyond their TDEE.

This is a lot of food! And, is almost impossible for most people to even attempt to do. It’s even difficult to eat enough extra calories to gain just one pound overnight!

So what’s happening and what causes weight fluctuations of 1 to even 3 pounds overnight or even over a couple of days?

The main culprit is water retention and there’s a multitude of things that can cause this. One pound equals just 15.34 fluid ounces of water or 450 ml. So, if you have simply 1 liter of extra water in your system, that’s more than two pounds of extra water weight.

Common Causes of Water Weight & Water Retention

too much salt

Salt causes excess water weight

When you eat too much salt, the cells of your body must compensate by absorbing more water to balance out sodium concentrations.

“Consuming 400 milligrams of sodium, the amount in a single gram of table salt, causes your body to retain an extra 4 cups of water, which equals roughly 2 pounds.” –

When people say that “just eating fast food once makes them gain weight overnight”  this is what is happening. Fast food and processed food is high in sodium and causes weight fluctuations of 2 pounds or more when eaten.

Too much salt is the number one reason for fluid retention and if your weight fluctuates often, pay attention to how much salt you are eating and when.

How long do you retain water after eating salt? 

This usually takes a couple of days of normal sodium consumption for your body to flush excess sodium from your body through your urine or from sweating. You can speed the process up by drinking more water and by getting a good sweaty workout in.

Medication side effects can be water retention

The medication you take may also cause you to retain water. Even common drugs like ibuprofen can cause water retention, which is common for people working out or exercising to take because it helps with muscle soreness.

If you take NSAIDs (Advil, Aleve, aspirin) to help you recover from exercise, they will cause water retention and therefore, weight gain. Weigh yourself without these drugs in your system to get a more accurate measure of your progress.

For other medication, check with your doctor or pharmacist to see if water retention is a side effect of the drug in question.

How long do you retain water after taking medications? 

This usually clears up in about 24 hours after taking NSAIDs and other medications may cause water weight at first but then this symptom levels out once your body builds up a tolerance to the drug.

A Woman’s Menstrual Cycle causes her to retain water

A few days before a woman gets her period each month bloating and water retention are common due to hormonal changes.

Gaining water weight during this period is common and should be considered before getting frustrated that you aren’t losing weight or have gained weight quickly.

How long do you retain water during your period? 

This water retention lasts about a week in all. It’s probably best to avoid weigh-ins during this time of the month.

Weight training exercise water weight gain

You may be staying true to your weight loss TDEE and working out hard at the gym, but notice that after a good workout, you can be 2-3 pounds heavier than you were prior to working out. This is totally normal and shouldn’t cause concern.

When you stress your muscle tissue, the body responds by filling the tissue with fluid. This is why after you workout your muscles appear larger or “pumped up”. Unfortunately, the size is just temporary.

How long do you retain water during your period? 

Most people are safe to weigh in the next morning but if you had a really hard workout and feel sore, it may take two days for the inflammation to subside.

Never weigh yourself after your workout as this is not a way to accurately track your progress.

Refined carbs and fiber both cause water weight

Refined carbs or simple carbs like added sugar, bleached flour, and other processed foods also cause water retention by causing the kidneys to reabsorb sodium instead of flushing it out.

“Eating refined carbs can increase insulin levels in the body. Insulin increases the re-absorption of sodium in the kidneys, leading to increased fluid volume” – Authority Nutrition

Some people think that when they eat a candy bar, they automatically gain one or two pounds overnight. This is a myth. All the sugar in the candy bar is the true culprit and the weight gain is from water retention, not fat gain unless the candy bar is causing you to exceed your TDEE and this happens regularly.

High fiber diets also cause water weight since fiber absorbs water in your intestines.  Think of the way oatmeal rice swell up when left in water. This same thing happens in your gut. This is why it’s always best to weigh in after you have a bowel movement.

How to Prevent Water Weight and Water Retention

drink more water

While some water retention is unavoidable especially if you are female and/or lifting weights, we can make lifestyle changes that will greatly reduce the volume of retention or water weight fluctuations.

The number one way to cut water retention is to watch your salt intake.

This can be challenging as it seems like salt is in everything these days. Sea salt this and sea salt that. Sea salt is even marketed as being “healthy”, but, salt is salt and too much sea salt is just as bad as too much table salt (both are 40% sodium).

According to the 2015-2020 Dietary Guidelines published by the US Government, Adults should limit their sodium intake to 2300 mg (1 teaspoon) or less. Those that exercise intensely daily can consume more as long as they are also consuming plenty of potassium.  Those that don’t exercise should really consume less than 2300 mg.

Since most flexible dieters are using an app like MyFitnessPal to track food intake, they are also able to track their sodium intake. If you’re flexible dieting and notice a drastic weight fluctuation, just look at your app and I bet you that your prior day’s sodium intake was higher than normal.

The second most important way to reduce water retention is to drink more water. It may seem counterintuitive to drink more water when water is the problem, but, this is the solution.

If you think back to your science classes in high school or college, you may remember the word osmosis? This is simply the movement of solutions across a semi-permeable membrane until the concentration on both sides of the membrane is equal. When you drink more water, this causes the excess salt to diffuse out of your cells and it can then be flushed from the body by your kidneys and skin.

In a related way, working up a good sweat also helps to flush excess sodium out of the body quicker. If you splurge and eat salty foods, counteract it with some intense exercise and a lot of water.

Just don’t allow water weight gain to make you frustrated and quit!

Now that you understand the reason for water weight fluctuation, don’t allow it to cause frustration or cause you to give up. It’s not an indication that counting macros is not working but simply an indication of water retention.

Look at your lifestyle and diet for possible clues as to what’s causing it and then take the steps mentioned above to prevent it.

Rest assured that anytime you see your weight shoot up overnight or over a couple of days, this is a water weight issue, not a fat gain issue.

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Ted Kallmyer is an ISSA certified Specialist in Fitness Nutrition, is an expert macros coach, and the author of The Macro Solution. If you need personal help reaching your weight loss/fitness goals see his nutrition & macros coaching options. Follow Ted on Instagram
Last Updated: June 16, 2021


  1. kris 6 days ago

    thats the thing i think you should “give up” and hav a refeed day or cheat day because in my case its always from not eating enough, so stupid, i wish there was an easier way to get rid of it without stuffing yourself silly because it usually works.

  2. Tony 9 months ago

    Really good well-written article, and zero BS like almost every other diet / fitness article I stumble on – Bookmarked you, thanks.

    • Ted Kallmyer (Certified Macro Coach) 9 months ago

      Hi Tony, I always try to shoot it straight. Thanks for taking the time to comment.

  3. Jo

    Dear Ted,
    I just weighed myself on a new scale that measure body fat, bone mass and water levels. I’m really curious, why does the scale seem to the percentage of body fat and decrease the percentage of water after only drinking water (tap). My salt intake did not increase nor did I any food. Weighed myself in the morning. Thank you.

    • Jo

      *Meant increase body fat percentage

    • Ted Kallmyer (Certified Macro Coach)

      Hi Jo, These scales use electrical impedance which passes a small electrical current through your body. Fat cells have more water than muscle and other tissues so it changes the way the current passes and thus estimates how much fat you have. If you drink a glass of water before weighing yourself then the water in your stomach will skew the calculation. You should use the scale prior to eating and drinking and after using the bathroom in the morning. Breast tissue also causes these type of scales to estimate body fat higher so also be aware of that.

  4. Heidi

    Hi Ted this totally makes sense. Yesterday I had two chicken nuggets and two normal bites out of a filet fish sandwich lunchtime and I gained 1.5 pounds this morning, even though I went for a 25 min walk and a 5 mins jog that same evening, it’s hot so I sweat bullets, but that’s the second time I have noticed weight gain from eating chicken nuggets as opposed to my regular eating of low sodium, low carb diet .
    Am I right in my observation?

    • Ted Kallmyer (Certified Macro Coach)

      Hi Heidi, Yes, high sodium food, especially processed food will do it every time.

  5. Amy

    Just joined the program and am getting results but yesterday, I flipped bc I gained weight- sure enough I inflated my muscles, I took NSAIDS and ate too much sodium!!! I am surprised I didn’t gain more based on my trifecta of mistakes! Thanks for the article!

  6. Shauna Lankford

    I count Macro’s and love it! However, I drink plenty of water and tea during the day and 1 cup of coffee when I get up. I monitor salt because I don’t like it. The problem is I retain water all day long and urinate very little and then I go to bed and then I am up every 2 hours expelling what I was retaining during the day. Can someone help me?

    • Ted Kallmyer

      Hi Shauna, Have you talked to your doctor about this? Are you taking any medications where this could be a possible side-effect?

  7. John Lang

    An not losing weight

    • Ted Kallmyer

      Have you calculated how many calories/macros your should be eating for weight loss and eating at those levels? Diet is 85% of the process, the gym is 15%.
      Try ours here.

  8. John Lang

    I’ve been gaining weight

    • John Lang

      I’ve been working out at the gym

  9. Stacey Bartley-Smith

    Oh my goodness this whole website is the most sensible easy to understand program I have ever come across. All the questions I had have been answered and now I’m excited!