Bone mass and fat mass measurements from DEXA scans do not change when a person's fluid levels shift temporarily, such as after drinking a lot of water or sweating. In contrast, total body weight and...
Mechanism
Synthesis from 1 study
Bone and fat don’t change weight when you drink or lose water because they’re made of minerals and oils that don’t hold water. But muscles and skin do hold water, so their weight goes up or down when you’re hydrated or dehydrated. DEXA scans pick up on this difference, so they show bone and fat as...
Most probable mechanism
Bone is made mostly of hard minerals like calcium and phosphorus that don’t dissolve in water, and fat is made of oily molecules that don’t mix with water. When the body gains or loses water, these parts don’t change in amount because water doesn’t get stored in them. But other tissues like muscle and skin hold a lot of water, so their weight changes when hydration changes.
Bone tissue consists primarily of a mineralized extracellular matrix composed of calcium phosphate crystals, which are chemically inert and do not bind or release water under physiological fluid shifts.
Adipose tissue is composed predominantly of lipid droplets enclosed in cell membranes, which are hydrophobic and exclude water, preventing hydration from altering their mass.
Dual-energy X-ray absorptiometry distinguishes bone and fat mass based on differential X-ray attenuation properties of mineral and lipid components, which remain constant regardless of water content in surrounding tissues.
Evidence from Studies
Supporting (1)
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Detection of small changes in body composition by dual-energy x-ray absorptiometry.
Contradicting (0)
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