What role does FT3 play in weight loss?

The role of FT3 (free triiodothyronine) in weight loss is not addressed in the provided context. Generally, FT3 is the active thyroid hormone that increases basal metabolic rate by stimulating thermogenesis and cellular oxygen consumption. Low FT3 levels are associated with a slowed metabolism and weight gain. However, evidence for a direct causal role of FT3 in weight loss is limited: many studies show associations but not clear causality. FT3 levels can be influenced by caloric restriction, illness, or medications, complicating interpretation. Measuring FT3 alone to guide a weight loss diet is not evidence-based. If thyroid dysfunction is suspected, a full hormone panel (TSH, fT4, fT3) should be evaluated by a physician. The evidence level is moderate: there are mechanistic and observational hints, but no randomized controlled trials supporting targeted FT3 manipulation for weight reduction.