The Study
Extrathyroidal conversion of thyroxine to 3,5,3'-triiodothyronine (T3) and 3,3',5'-triiodothyronine (rT3) and its contribution to total triiodothyronines production rates in fed and food restricted piglets.
This study watched what happened to piglets' body chemicals when they didn't eat for a while. It saw that some chemicals went down and others went up, but it didn't make the piglets fast on purpose or control everything else. So we can say fasting is linked to these changes, but we can't say it caused them.
Analysis score
Maximum 72 for a cohort study.
Where the score came from
When piglets don't eat, their bodies make less of the active thyroid hormone (T3) and more of a backup version (rT3) to save energy.
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 58 / 100
Quality score
Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.
Key takeaways
Summary
Based on the study abstract and findings.
- 1This suggests a biological switch to conserve energy during starvation — less active hormone, more inactive form — which may help prevent muscle and energy loss.
- 2Fed piglets: 70% of T3 came from outside the thyroid; during fasting, that rose to 83%.
- 3Thyroid made 30% of T3 when fed, but only 17% when starved.
- 4rT3 production shifted from 92.8% to 97.1% from outside the thyroid.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Zentralblatt fur Veterinarmedizin. Reihe A
Year
1986
Authors
G. Nowak, A. Ślebodziński
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 6–8 week old piglets that have eaten, most of the active thyroid hormone T3 and nearly all of the inactive hormone rT3 are made outside the thyroid gland by converting T4 through a specific enzymatic process.
In 6–8 week old piglets, food restriction lowers levels of thyroxine and triiodothyronine in the blood, raises reverse T3 levels, and reduces how quickly the body produces and clears these hormones, resulting in decreased thyroid hormone activity during energy deficit.
In 6–8 week old piglets, reducing food intake changes the source of triiodothyronine so that a larger percentage comes from conversion in peripheral tissues and a smaller percentage comes directly from the thyroid gland, even though the total amount of hormone produced decreases.
In 6–8 week old piglets, reducing food intake lowers the amount of triiodothyronine (T3) and reverse T3 secreted by the thyroid gland, indicating reduced thyroid hormone production during energy deficit.
When 6–8 week old piglets are not fed, their levels of active thyroid hormone (T3) decrease, and this reduction helps conserve energy and protein.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.