Fat or water? What do we lose?

May 22, 2007 10:58 AM

There's been talk recently about people who lose weight not actually losing fat, but losing water. What's going on?

Whenever I lose weight, some killjoy always comes along and says, "Ha! You haven't actually lost weight. It was all water." So the questions are:

1) What actually goes on when we diet? How much of what we lose is water, and how much actual fat?

2) Where does the water come from? How can we do without it? Does our body just start storing less water?

3) How does one actually lose fat, as opposed to water? How does one stop the fat returning?

posted by humblepigeon to health (11 comments total)

Usually this is in reference to initial losses. When you first start a diet, you might lose 5 lbs in a week, which is much faster than the caloric decrease should merit. The difference is water loss, and you can't keep that up for subsequent weeks.
posted by smackfu at 11:07 AM on May 22, 2007

1) That amount varies based on tons of factors. Most notably: How many calories are you taking in, and how much water are you drinking? Your body is pretty smart and regulates itself. If you're drinking too much water, you might lose water first, then fat. It really depends.

2) Water weight will always be lost to an extent, due to sweat. Your body has an ideal range of how much water it needs to have, and over time, people who work out a lot learn about how much fluid to replace. Replace too much and you're just over-watering yourself and will lose that again first.

3) Don't overhydrate when you work out. Burn more calories than you take in. There's no more science to it than that - it's really that simple. Burn more calories than you take in. Period. No amount of fad dieting will change this simple fact. Burn more calories than you take in.
posted by twiggy at 11:07 AM on May 22, 2007

The storage form of glucose in muscles and the liver is glycogen which also holds water. If you limit your calories, and in particular go low carb, you'll use up a lot of your glycogen which releases its bound water to be excreted, thus dropping your weight fast than you're dropping fat. Once you top off your glycogen stores by eating a lot of carbs, the water will return and your weight will go back up. I don't think this accounts for all the water-weight loss, though, because glycogen stores are maybe 1 pound total and carry another 2-3 pounds of water with it.
posted by Durin's Bane at 11:24 AM on May 22, 2007

Your initial weight loss (some percentage) is glucose (or glycogen). Basically sugar thats been stored in your liver (mainly) and around your body in your muscles. When you burning calories (eating less/exercising more/both), you body thinks you're starving and uses the sugars first. It's easier and more available.

The thing about sugars is that you can't just store them in your cells as sugar crystals. You have to store them in solution -- aka with water. So when you gain/lose that sugar you gain/lose the water that goes along with it. Hooray!

Now, if you keep going on with that weight loss (continued negative caloric balance), your body starts tapping into your fat stores. Fat is harder to get at (this is pretty non-scientific language here), but has 3x more energy than glucose.

So that's the deal behind losing water weight. That's why Atkins works so well initially. No carbs = no sugar, so you immediately lose all that sugar and water. Best of luck!
posted by ruwan at 11:25 AM on May 22, 2007

.... or what Durin's Bane said.
posted by ruwan at 11:25 AM on May 22, 2007

Any combination of diet and/or exercise that results in weight loss will cause you to lose all of the following three substances.

1) Fat
2) Muscle tissue
3) Glycogen (a carbohydrate) bound up with water that is normally stored in your muscles and liver. When people talk about "losing water", they're talking about this.

Here's some more detail about glycogen:

The other thing to keep in mind when you're using the bathroom scale is that when you first start limiting your calories, your body is going to start burning through its glycogen stores. Glycogen is basically a fuel stored in your body. It stores sugars together with water and locks them up in the tissues and organs of your body like an energy battery, ready for you to use at a future time.

There's water locked in with those calories. That water weighs a lot. So when you start restricting your calories, the first thing your body burns is this extra storage of energy, this extra glycogen. And the glycogen causes you, as it's burned, to shed water. You might look at the scale and think, gee, I lost 5 lbs, but you really lost no body fat whatsoever. It was just water, because your body released glycogen. What usually happens to people when their glycogen store has reached zero is they get really hungry, they think they're in a starvation panic, and then they overeat. Their glycogen stores fill right back up, they gain the 5 lbs back, and usually they overate to such an extent that they store another half a pound of body fat or so. Now they're half a pound heavier than when they began and they lost no body fat whatsoever. It was just a game of glycogen and water storage they saw reflected on the bathroom scale.

Any kind of diet and exercise program will cause you to lose some glycogen, muscle tissue and fat. However, the proportion can vary depending on your weight loss strategy.

Cutting carbohydrates (Atkins, South Beach, etc.) will result in relatively high glycogen loss in the first few weeks, along with some fat and some muscle.

Drastic calorie reduction, especially without exercise, will cause you to lose a lot of glycogen and muscle tissue.

Excessive cardio can also reduce muscle significantly. Many long-distance runners at the peak of training can look quite gaunt.

Moderate calorie reduction, moderate cardio or interval work, and moderate weigh training are probably the most healthful combination for most people. You will still lose some glycogen and muscle, but a larger proportion of the loss will be fat.

There is probably no way not to lose some muscle when you lose weight. This is why competitive bodybuilders never try to lose weight (fat) and gain muscle at the same time. They go through bulking cycles, where they eat, sleep and train a lot, and slimming cycles, where they reduce their calories to lose fat, then gain back the lost muscle the next cycle, etc.

(On preview: Durin's Bane and ruwan got there first, but what the hell, I'll post).
posted by maudlin at 11:28 AM on May 22, 2007 [2 favorites]

On preview: Durin's Bane and ruwan got there first, but what the hell, I'll post

No, thanks for your reply. Sometimes it helps to have many explanations of the same thing. Thanks to the others too.

I have some bathroom scales that measure body fat via electrical contacts. Is a better plan for me to diet/workout and take notice of only the fat percentage figure?
posted by humblepigeon at 11:36 AM on May 22, 2007

Those bathroom scales are notoriously inaccurate. Your best bet, IMO, is to get a tape measure and watch your waist size (and other measurements, if you like).
posted by mendel at 11:51 AM on May 22, 2007

Each molecule of glycogen is linked with 4 times its weight in water so water loss is inevitable when you're burning fat but drinking enough water and eating enough fruit and veg (which are mostly water) will ensure you get the water back.

If your diet is very low in carbs however your body will shed even more water due to sodium depletion - your body regulates its mineral balance the best it can no matter what you eat.

If you've lost more than around 1-2lbs in a week then most of it wasnt fat.
To burn 1lb of fat you need to create a calorie deficit of 3500 calories. (around 500 calories per day) for example if you reduce your calories by 500 and increase your workout by 500 calories then you will lose around 2lbs per week of body fat. If your weight loss is greater than your calorie deficit suggests then you've just lost water and will regain the weight.

Contrary to what others have said it is not possible to overhydrate (well technically it is put in a healthy individual that would involve drinking around 2 gallons of water per day for an extended period of time) any excess water is excreted, most water retention is cause by excess sodium in your diet, if you're concerned about water retention then reduce your salt intake and have a banana (high in potassium - also regulates body fluids)
posted by missmagenta at 12:50 PM on May 22, 2007

It all depends on calories. Burn more than you take in, your body will have to use reserves of energy--first, glycogen (chains of sugar for short term storage). Your body will also start to break down lipids (fat) to restore these supplies, etc to keep your blood sugar at an optimal level (your brain can only use glucose as the main source of energy). Water is constantly being used to break bonds and is also being formed in other bond-breaking.

Basically, the weight/fat solution is very simple: go ahead and drink water, it's good for you! But: burn more calories than you take in.

Simple
posted by uncballzer at 3:11 PM on May 22, 2007

"Contrary to what others have said it is not possible to overhydrate'

WRONG.
hyponatremia
posted by vronsky at 11:07 PM on May 22, 2007