LEP and metabolic syndrome: In addition, in healthy young men, the less favorable body compositions (or higher fat and lower muscle mass, with higher leptin concentration) are shown to be correlated with insulin resistance and FT3 levels in normal thyroid function (73) and in healthy middle-aged men and women with normal thyroid function, TSH, FT3, and FT3/FT4 are positively correlated with BMI, waist circumference and components of metabolic syndrome (such as TG, SBP, DBP, and FPG), and negatively correlated with FT4 (74).