Metabolism is essentially the speed at which the body processes energy and distributes it. The faster a metabolism, the more "fuel," in the form of food calories, one needs to maintain a healthy weight and keep each organ network running smoothly; slower metabolisms require less fuel. The thyroid is a primary manager of the metabolism engine. Excess T3 and T4 hormones cause all the cells to work harder, raising the metabolism, while lower-than-normal T3 and T4 production slows down the entire body.

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