Your thyroid gland is like your body’s thermostat for metabolism. It produces hormones (T3 and T4) that determine how quickly your body converts food into energy.

Underactive thyroid (hypothyroidism): Slows metabolism, leading to weight gain, fluid retention, fatigue, constipation, and cold intolerance. Even mild hypothyroidism can make weight loss frustratingly slow.
Overactive thyroid (hyperthyroidism): Speeds metabolism, often causing weight loss, anxiety, rapid heartbeat, and muscle breakdown.

Why it matters for weight:
Low thyroid function reduces calorie burn at rest and during activity.
It can also cause water retention, masking fat loss on the scale.
Optimising thyroid function through medication, iodine and selenium intake, and stress reduction can restore energy, improve exercise tolerance, and make weight management more responsive.