The Claim
In healthy, young women without obesity, five days of moderate energy restriction (55% reduction) is associated with a 6.5% decrease in total triiodothyronine (TT3), a 10.5% increase in reverse triiodothyronine (rT3), a 2.0% decrease in thyroid-stimulating hormone (TSH), and a 7.0% increase in free thyroxine (fT4), indicating a coordinated peripheral and central adaptation to reduce metabolic rate without altering lean body mass or resting energy expenditure.
What the research says
Supports is higher
Support is ahead, but a single strong opposing study can change this.
These are independent scores, not a percentage. Higher-grade studies count more, so a single strong opposing study can outweigh several weaker ones.
In healthy young women without obesity, a five-day diet reducing calorie intake by 55% lowers total triiodothyronine and thyroid-stimulating hormone while increasing reverse triiodothyronine and free thyroxine, reflecting a coordinated adjustment in thyroid hormone metabolism that reduces metabolic rate without changing lean body mass or resting energy expenditure.
See the scientific wording
In healthy, young women without obesity, five days of moderate energy restriction (55% reduction) is associated with a 6.5% decrease in total triiodothyronine (TT3), a 10.5% increase in reverse triiodothyronine (rT3), a 2.0% decrease in thyroid-stimulating hormone (TSH), and a 7.0% increase in free thyroxine (fT4), suggesting a coordinated peripheral and central adaptation to reduce metabolic rate without altering lean body mass or resting energy expenditure.
When calorie intake drops sharply, the brain reduces its signal to the thyroid gland, and tissues switch how they process thyroid hormones: less active hormone is made, and more inactive hormone is created, slowing down metabolism without losing muscle.
What the research says
1 studyStudy: Thyroid Axis Adaptations to Moderate Short-term Energy Restriction in Healthy, Young Women.
When healthy young women cut their calories in half for five days, their bodies responded by lowering the active thyroid hormone and raising the inactive one, while slightly reducing the brain’s signal to the thyroid — all of which slow down metabolism to save energy, without losing muscle.
Score breakdown, mechanism chain, raw evidence, ideal studies needed & 1 supporting studies
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.