The Study
Adaptive thermogenesis driving catch-up fat during weight regain: a role for skeletal muscle hypothyroidism and a risk for sarcopenic obesity
This paper doesn't do any new experiments — it just reads other studies and puts together a story about why people might regain fat faster than muscle after dieting. It's like putting together puzzle pieces from other people's work to guess how things might work — but it doesn't prove anything for sure.
Analysis score
Maximum 5 for a narrative review.
Where the score came from
When you lose weight, your body slows down its energy use to save fuel. When you eat normally again, it doesn’t fully turn back on—especially in your muscles—so it stores extra calories as fat instead of rebuilding muscle.
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 51 / 100
Quality score
Systematic reviews and meta-analyses of cohort studies. They sit above a single cohort study but below a single randomized trial, because the underlying evidence is still observational.
Key takeaways
Summary
Based on the study abstract and findings.
- 1Yes—this explains why many people regain weight as fat and struggle to rebuild muscle, even when eating healthy, making weight cycling lead to more body fat and less strength over time.
- 2After weight loss, people regain 20–40% more fat than muscle.
- 3This happens because muscles make more D3 enzyme, which blocks thyroid hormone, slowing metabolism and repair.
Score breakdown, methodology, conflicts of interest, evidence analysis & raw study data
Publication
Journal
Reviews in Endocrine & Metabolic Disorders
Year
2025
Authors
Abdul G Dulloo
Related Content
Claims (7)
When the body experiences low energy availability or extreme stress, it converts more thyroxine into reverse T3, which lowers the metabolic rate.
During weight regain, increased activity of the type 3 deiodinase enzyme in skeletal muscle lowers local levels of the thyroid hormone T3, which slows muscle metabolism, reduces energy use, and enhances muscle efficiency, leading to greater fat accumulation.
After losing a large amount of weight, the body restores more fat than muscle during weight regain, with fat mass increasing 20-40% more than lean tissue in multiple human populations.
People who repeatedly lose and regain weight five or more times have a higher likelihood of developing sarcopenic obesity, a condition characterized by low muscle mass and high fat mass.
When thyroid hormone levels are low in skeletal muscle during weight regain, satellite cells fail to shift from multiplying to maturing, resulting in slower or incomplete restoration of muscle mass.
During weight regain, skeletal muscle becomes resistant to insulin without an increase in fat inside muscle cells, and this is caused by reduced thyroid hormone activity locally, which redirects glucose to be stored as fat.
Not medical advice. For informational purposes only. Always consult a qualified healthcare professional before making health decisions.