When I’m on a diet and excercising and actually gaining weight some wiseguy always tells me (among other spurious theories) that muscle weighs more than fat, and that accounts for the gain. Today my son told me his Physiology professor told his class that the difference in weight between fat and muscle is negligible. So, if this is true, why do I see this stupid idea EVERYwhere? And does anyone know any differently or actually know how much a liter of fat weighs comparted to a liter of muscle, for example?
My Weight Watchers leader happened to say tonight that protein weighs twice as much as fat. However, I certainly wouldn’t think she’s as reliable as a physiology professor.
From here (PDF document):
From here:
Therefore, fat floats on water, muscle doesn’t. But the difference is small, nowhere near double.
Look at it this way. I work out 6 days a week. I am 6’ 190# and have a 46 inch chest and a 32 inch waist. My friend is similar (6’ 185#) and has a 36 waist and a 42 chest.
Obviously the muscle that makes up my weight MUST weigh less.
That’s specious reasoning. The two of you likely have different body fat percentages, and differences in skeletal structrure could account for some of it too, as bone is heavier than either fat or muscle. Simply measuring weight and a couple of dimensions is hardly conclusive.
Okay, so given the same volume, the muscle weighs more because it’s more dense? I don’t have a clue how to translate this into I’ve gained 4lbs since I started exercising and dieting. But, to tell you the truth these numbers don’t look too good for that dumb idea anyway. I know I LOOK smaller at the same weight, but my muscles are tighter. I think this is just another false reassurance they give to fat people to explain the unexplainable. I want to be the monkey that lost 7% of his body weight in one week with that thyroid hormone. Bring it on!
I was going to comment on QED’s answer, but that site really does say grams per centimeter. Very odd unit of measure for density. 
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They probably meant grams per mL like the other site hehe.
Whenever a person starts to weight-train, (s)he gains weight (espcially a she). Physiology instructors who claim otherwise are arrogant scientists.
Get a tape-measurer; monitor the fattiest part of your body.
Simple weight measurements are only the roughest guide to fitness.
And I would not necessarily trust a scientist over a recovering fat person; scientist routinely present assumptions and averages as facts and absoutes. Real people know that a 5’ 6" woman who wears a size ten (in the Midwest) is not fat, no matter WHAT her BMI is.
So, stay off the scale for at least six weeks; by then you will have done all the easy bulking-up, and simple weight will be a beter indicator.
Oprah’s current fitness guy says that muscle isn’t properly hydrated unless it’s being used. Therefore, when you begin exercising, your muscle gets hydrated and you gain about 2 pounds in water weight. Hmmmm…
If the above numbers are correct (and are truly both g/mL), a pound of muscle would be 11.7% smaller than a pound of fat. That would make a pretty significant difference in the shape of a body.
That’s complete bullshit. Muscles at rest contain the same amount of water as highly active muscles. Plus where is this extra weight coming from all of a sudden? From the air? Oprah’s trainer is a boob.
I think the theory (not that I necessarily believe it) is that when you excercise, the blood vessels supplying those muscles open up. Or that new capillaries develop to make better use of those muscles.
I understand it’s not your theory, but this neglects to note that only a small fraction of your circulatory system has blood in it at any one time. Arterioles continually contrict and relax, in response to local phenomena, adjusting the flow of blood through their “drainage area” (for lack of a better term). So even if angiogenesis does take place (which I belive it does), not all of the new vessels will have blood in them.