I know if you have a fast weight loss initially on a diet, a lot of people say it's water weight. This makes sense if you believe the calorie rule (3,500 calories = 1 lb fat). I mean, if you lose 10 pounds in the first week, it's probably not because you cut 35,000 calories from your diet. lol
But WHY do we lose water weight? What if your sodium intake essentially stays the same when you're on- or off-plan? Is water weight still a factor? Why is it that going on a diet causes water loss? And how much "water" can someone actually lose?
If your sodium intake stays the same on-plan or off-plan, water weight is going to affect you less. I'm a picture of that -- I don't control my sodium intake so if I eat out or eat in, water weight doesn't affect me.
But, for a lot of people that isn't true -- if they are changing their lifestyle/diet and they are going from processed food to whole foods, then there will be a drastic drop in sodium content because it's in so many processed food items!
A week on whole foods will eliminate a lot of that previously eaten sodium in processed foods, hence the "water weight."
Okay, but what is someone doesn't change their processed food diet and is just counting calories?
Well, even then, they are going to adjust the quantities of the processed food. Maybe in the past they ate a whole bag of oreo cookies in a week. That is now eliminated. That's a lot of sodium that's left the diet. Or even just cutting down from super-size fries at McDonald's to the small size -- sodium content goes down significantly, even if the food type is relatively the same.
Through both changing of the diet and/or limiting calories, you're going to see an effect of sodium "water weight."
The other thing that happens that some people go to high protein diets because it keeps them fuller longer, which means that they might also be limited their carbs (whether it's a low carb diet or a calorie counting diet) because protein packs a bigger punch in satiety versus the high calorie carbs. When you eat a high protein diet, you lose water weight from in your body because carbs require water to be stored, while protein (if I understand correctly) do not.
Also, what can happen is that when someone starts an exercise program that's intense, they retain water, as the body "protects" itself from the intensity. Eventually, with time, the body gets used it and doesn't retain as much and it will let it go (maybe some of those whooshes that everyone mentions are a cause of that too). It's not that suddenly you peed out 1 lb of fat, but rather water that your body was retaining.
I don't know how much water someone can lose in all of this. I know I can't lose a lot of water weight in general because of what I eat and exercise. My body has already adjusted.
Carbs cause the body to retain 4 grams of water for every gram of carbs stored. The cut in carbs is what causes us to lose water weight, more than less sodium. Refined carbs are terrible things to put in our bodies. Stick with whole grains and avoid this to some extent.
Hormonal changes will cause water retention also, a woman's monthly cycle.
Exercising, specifically weight training, will cause your muscles to retain water as they rebuild themselves. Cardio will do this to an extent, as your muscles are working as well, but not as much as 'real' lifting will.
ETA: The day before my weekly weigh-ins I have my rest day from exercise. I drink lots of water and take one low dose diuretic pill before I go to bed, with a full glass of water.
There are countless factors that can affect how much water weight you carry, and how much you lose. There are so many factors, that you could probably fill half a dozen college classes with the information.
Sodium is one of the more commonly known contributers to water weight gain, but there are many others.
For example, higher-carb diets. You need more water to digest carbohydrates than proteins and fat - so if you're on a low-carb diet, you will lose proportionally more water (at first). It also explains why people who go off a low-carb diet, seem to gain more rapidly. They do - but just until they pick up the extra water they need.
I look at it thii way - my "normal" low-carbing weight is going to be a little lower than my "normal" higher-carb eating weight. So that little bit of extra water on high-carb and less water on low-carb really isn't "real" weight to count (yes it's "really" on my body, but when I'm eating more carbs I "need it" and when I'm eating lower-carb, I don't - so it's not something to worry about).
Hormones are another one of the factors (and why even on starvation calories, I still manage to gain weight every month with TOM).
When I see the TOM gain, if I've been on-plan and logging my food, I know that it will disappear in a few days. Sometimes, if I want to try to get those water pounds to disappear a little quicker, I will eat even lower carb to help speed up the water loss. But I'm not all that concerned about temporary water weight, so usually I just decide to wait it out.
Injury and illness also affect water balance. I recently found this out after a sudden and unexpected gain after a bad sunburn. I went online, and sure enough discovered (well, rediscovered what I learned in college biology class)
that the body uses water for repair and recovery.
I experienced this again about a week ago - when I drastically overworked my legs on the elliptical machine. I could barely walk, and I put on about six pounds, virtually overnight (well 2 lbs overnight for 3 consecutive days). I also had a bacterial infection in my jaw and perhaps a virus on top of it that I wasn't aware of until a couple days ago (and now am on antibiotics).
Since I also was "sidelined" and was eating off-plan, I wasn't sure how much if any of that six pound gain was "real" (fat gain) and how much was temporary water gain.
My morning weight today was 4 (FOUR) pounds lower than my morning weight yesterday (and I was peeing all night).
Losing 4 lbs in 24 hours is a pretty good indication that it was water weight (because I do not normally eat 14,000 calories per day).
Most of the time, you'll never be able to tell how much weight is "water" and how much is fat and how much is muscle (because muscle is lost with dieting too. Adequate protein intake and exercise can minimize muscle loss, but you can't prevent it, entirely).
Even though this is all (well I think) interesting information, it's not all that practical for the home dieter. It's good to know that fluctuations on the scale don't necessarily mean you're doing anything wrong, but trying to determine or control precisely how much of the weight loss is muscle, fat, and water is for the most part, pointless. You can influence it a little, but the numbers aren't as important as progress and the direction you're going.
Most of us want to lose fat and gain muscle, but water balance shouldn't be a major concern unless we're dehydrated or suffering from edema.
Explain "water weight" to me
