What Causes 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.
First off, if we look at the situation logically, it takes roughly 3500 extra calories beyond one’s TDEE (total daily energy expenditure) to equal a pound of stored fat. Therefore, to gain two pounds of fat overnight, one must eat and 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 weight.
Common Causes of Water Retention
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.” – SFGate.com
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.
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.
A Woman’s Menstrual Cycle
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.
Weight Training Exercise
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 and by the next morning, this fluid has been flushed out.
Never weigh yourself after your workout as this is not a way to accurately track your progress.
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.
How to Avoid Water Retention
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.
The number one why 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 Get Frustrated and Quit!
Now that you understand the reason for weight fluctuation, don’t allow it to cause frustration or cause you to give up. It’s not an indication that your diet 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.
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