When thyroid hormone levels are low, the body's energy use slows down, leading to less fat burning, increased weight, constipation, and tiredness.

When there is too much thyroid hormone in the body, the rate at which the body uses energy increases, resulting in more frequent bowel movements, loss of body weight, and a higher body temperature.

When thyroid hormone levels are below the optimal range, the body's core metabolic processes slow down, which can result in widespread physiological dysfunction and a higher risk of death.