The Study
Thyroid Axis Adaptations to Moderate Short-term Energy Restriction in Healthy, Young Women.
This study watched how 19 young women's body hormones changed when they ate less for 5 days. It saw that some hormones went up and others went down, but it didn't prove that eating less caused those changes — maybe something else was involved. So we can say the diet and hormone changes happened together, but not that one definitely made the other happen.
Analysis score
Maximum 90 for a randomized controlled trial.
Where the score came from
When you eat much less for a few days, your body thinks it's starving and switches to energy-saving mode — even if you don't lose fat or feel slower.
Where does this study sit?
Reviews of RCTs (Meta-analyses)
Max 100Randomized Trials
Max 90Reviews of Cohort Studies
Max 85Cohort Studies
Max 72Reviews of Case-Control Studies
Max 63Case-Control Studies
Max 58Cross-Sectional & Case Series
Max 50Expert Opinion
Max 572 / 100
Quality score
Participants are randomly assigned to treatment or control groups, minimizing bias. The gold standard for testing whether an intervention causes an effect.
Key takeaways
Summary
Based on the study abstract and findings.
- 1These changes mean your metabolism slows down automatically to save energy — not because you lost weight, but because your body is protecting itself from perceived starvation.
- 2After 5 days of eating 55% less: T3 (active thyroid hormone) dropped 6.5%, reverse T3 (inactive) rose 33%, TSH (brain signal) dropped 11%, and free T4 rose 7% — but weight, muscle, and energy use stayed the same.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
European journal of endocrinology
Year
2025
Authors
Skand Shekhar, Joselyne Tessa Tonleu, C. Okigbo, Helen Leka, Anne E Kim, Bona Purse, Katie R. Hirsch, Brian R. Stolze, John A McGrath, A. Smith‐Ryan, S. J. Soldin, Janet E Hall
Related Content
Claims (6)
When the body experiences low energy availability or extreme stress, it converts more thyroxine into reverse T3, which lowers the metabolic rate.
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.
In healthy young women, a short-term reduction in calorie intake increases reverse triiodothyronine (rT3) by about 33% without changing thyroid-binding globulin levels, reflecting a change in how the body converts thyroid hormone toward inactivation rather than activation.
In healthy young women, eating fewer calories for five days lowers thyroid-stimulating hormone levels by about 11% but does not change the daily pattern of hormone release, reflecting a direct reduction in signaling from the brain to the thyroid gland.
In healthy young women, a five-day period of reduced calorie intake does not change resting energy expenditure or lean body mass, even though thyroid hormone levels change significantly.
In healthy young women, a short period of reduced calorie intake raises the level of free thyroxine by about 7% without changing total thyroxine, showing that the distribution of the hormone between bound and unbound forms shifts without altering overall production.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.