How are FT4 and weight loss related?

The relationship between FT4 (free thyroxine) and weight loss is physiologically well-established: FT4 is a thyroid hormone that regulates basal metabolic rate. In hyperthyroidism (elevated FT4), energy expenditure increases, often leading to unintentional weight loss. Conversely, hypothyroidism (low FT4) is associated with weight gain. However, the effect is individually variable and modulated by diet, activity, and genetics. The provided context contains no specific information on FT4 or thyroid function – the articles cover abdominal pain, allergy testing, and DNA tests for nutrition/longevity. Therefore, the evidence for this specific question is rated as 'unclear'. Important: A single FT4 value without TSH and clinical assessment is insufficient to diagnose thyroid disease. Self-tests for thyroid hormones should not be used alone to guide diet or medication decisions. If a thyroid disorder is suspected, a medical consultation is essential.