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Miriam E. Nelson, Ph.D Responds:
Miriam E. Nelson, PhD, of Tufts University and the best-selling author of the Strong Women book series, responds: No, and yes. No, because a pound of fat weighs the same as a pound of muscle—1 pound. Yes, because a pound of fat takes up more space in the body than a pound of muscle does.
Muscle cells are denser than fat cells because they contain proteins and water. Fat cells are made up primarily of oils and are less dense, and therefore take up more space to weigh a pound. Consider how water and oil separate in salad dressing—the less-dense liquid (the oil) floats to the top, while the denser liquid sinks to the bottom (the water).
If a lean, muscular person is 5 foot 6 inches and weighs 150 pounds, she may appear thin, trim, and physically smaller than someone with less muscle and more body fat, who would appear bulkier or larger. Having less fat and more muscle not only makes you appear leaner because your body weight is taking up less space, it actually helps you stay leaner. Comparatively, muscles (and other lean tissues such as organs) use more energy to function than fat does—in other words, it burns more calories. The same lean 150-pound woman can eat a bit more than the 150-pound woman with less muscle mass can and still maintain her weight, because the leaner person likely has a faster metabolism.
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Miriam E. Nelson
Ph.D
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