Weight VS Fat

Weight versus fat: they are not the same thing

Every tissue in your body (including muscle, bodyfat, your heart, liver, spleen, kidneys, bones, etc.) weighs a given amount. We could (conceivably anyhow) take them out of your body, plop them on a scale and find out how much they weigh. Your total bodyweight is comprised of the weight of every one of those tissues. But only some percentage of your total bodyweight is bodyfat.
Researchers and techie types frequently divide the body into two (or more) components including fat mass (the sum total of the bodyfat you have on your body) and lean body mass (everything else). Without getting into unnecessarily technical details about different kinds of bodyfat,

let’s just go from there.

Let’s say that we could magically determine the weight of only your fat cells. Of course, we know your total weight by throwing you on a scale. By dividing the total amount of fat into the total bodyweight, you can determine a bodyfat percentage which represents the percentage of your total weight is fat. Lean athletes might only have 5-10% bodyfat, meaning that only 5-10% of their total weight is fat. So a 200 pound athlete with 10% bodyfat is carrying 20 lbs (200 * 0.10 = 20) of bodyfat. The remaining 180 pounds (200 total pounds - 20 pounds of fat = 180 pounds) of weight is muscle, organs, bones, water, etc. Researchers call the remaining 180 pounds lean body mass or LBM. In cases of extreme obesity, a bodyfat percentage of 40-50% or higher is not unheard of. Meaning that nearly 1/2 of that person’s total weight is fat. A 400 pound person with 50% bodyfat is carrying 200 lbs of bodyfat. The other 200 pounds is muscle, organs, bones, etc. Again, 200 pounds of LBM. Most people fall somewhere between these two extremes. An average male may carry from 18-23% bodyfat and an average female somewhere between 25-30% bodyfat. So a male at 180 lbs and 20% bodyfat is carrying 36 pounds of fat and the rest of his weight (144 lbs) is LBM. A 150 pound female at 30% bodyfat has 50 pounds of bodyfat and 100 pounds of LBM.

Why is this important?

So let’s say you start a diet, reducing some part of your daily food intake. Maybe you start exercising too. After some time period, you get on the scale and it says you’ve lost 10 lbs. That’s 10 lbs of weight. But how much of it is fat? Frankly, you have no way of knowing with just the scale (unless it’s one of those Tanita bodyfat scales, which attempt to estimate bodyfat percentage but more or less suck, by the way). You could have lost fat or muscle or just dropped a lot of water. Even a big bowel movement can cause a weight loss of a pound or two (or more, depending). A colonic that clears out your entire lower intestinal tract may cause a significant weight loss. The scale can’t tell you what you’ve lost, it can only tell you how much you have lost.
When you’re worrying about long-term changes, the real goal is fat loss (some LBM loss is occasionally acceptable). That is, cycling water weight on and off of your body (as frequently happens with certain dieting  pproaches) isn’t really moving you towards any real goal even if makes you think you are. Don’t get me wrong, it may be beneficial in the short-term (again, I’ll talk about reasons to crash diet shortly) but it doesn’t represent true fat loss.
My point in bringing up this distinction is that it’s easy to hide the true results of a diet by not making the distinction between weight loss and fat loss.

Just how quickly

So just how quickly can you lose fat (or weight for that matter)? Most mainstream diet books and authorities echo the idea that 2 lbs per week (a little less than 1 kilogram per week for the metrically inclined) is the maximum. Where did this value come from? Frankly, I have no idea. To at least some degree, it probably represents about the maximum weight/fat loss that most feel should be attempted. To understand this, I have to do a little bit of math for you. One pound of fat contains roughly 3,500 calories of energy. Therefore to lose two pounds of fat per week (this assumes that you are losing 100% fat which turns out to be a bad assumption) requires that you create a weekly deficit of 7,000 calories.
Meaning you either have to restrict your food intake or increase your energy expenditure (with exercise or drugs) by that much. Obviously, that averages out to 1,000 calories/day. You either end up having to restrict food pretty severely or have to engage in hours of exercise each day. From that perspective alone, losing faster than 2 pounds per week is considered unrealistic or unwise. At the same time, it’s not uncommon to see claims of weight losses of one pound per day or 3-5 lbs per week on some diets. In the initial stages of some diets, weight losses of 15-20 pounds are not unheard of. Are these all lies? Not exactly. Part of it has to do with the issue of weight loss and fat loss discussed above. An extremely large individual, put on a restrictive diet can probably lose significantly more than two pounds of weight per week. But it’s not all fat.
This is especially true for the myriad low-carbohydrate dieting approaches out there. Studies demonstrate a rapid weight loss of anywhere from 1-15 lbs in the first week or two of a lowcarbohydrate diet and average weight losses of 7-10 lbs in the first week are fairly standard. Most of it is simply water loss although some of it will be true tissue loss, meaning fat and muscle. After that initial rapid weight loss, true weight/fat loss slows down to more ‘normal’ levels. The same goes in reverse, by the way, when you take someone on a low-carbohydrate diet and feed them carbs again, it’s not uncommon to see weight spike by many pounds very quickly. A high salt intake can cause a rather large retention of water (especially if you’ve been on a low-salt diet) and most women will readily tell you about the rapid weight gain (from water retention) that occurs during their menstrual cycle.