Thyroid axis adaptations to moderate short-term energy restriction in healthy, young women.
Level 2 - randomized trial
Controlled crossover clinical trial in healthy volunteers (NCT02858336)
PubMed 40265345 · doi:10.1093/ejendo/lvaf083
What was done
Nineteen healthy, non-obese women aged 23.36 ± 2.08 years without thyroid disease completed two 5-day diet protocols during the early follicular phases of successive menstrual cycles: a neutral energy availability diet (NEA, ±0%) and a deficient energy availability diet (DEA, -55%). Blood was sampled every 10 minutes between 8 AM and 4 PM and analyzed for TSH, GH, and cortisol every 30 minutes, total T3 (TT3), reverse T3 (rT3), and total T4 (TT4) hourly, and free T3, free T4, and TBG at baseline and study completion. Liquid chromatography-tandem mass spectrometry assessed all thyroid hormones except TSH and TBG.
What was found
DEA produced a small reduction in body weight (1.1 ± 0.21 kg, P < .001) and BMI (0.4 ± 0.08 kg/m2, P < .001) with unchanged fat mass. Compared to NEA, DEA led to significant declines in TT3 (ls mean ± SEM: 89.15 ± 2.89 vs 95.55 ± 2.89 ng/dL, P < .0001) and TSH (0.92 ± 0.07 vs 1.03 ± 0.07 µIU/mL, P < .0001). Conversely, DEA increased TT4 (6.26 ± 0.25 vs 6.06 ± 0.25 µg/dL, P = .005), fT4 (1.83 ± 0.07 vs 1.71 ± 0.07 ng/dL, P = .0052), and rT3 (12.04 ± 0.56 vs 9.02 ± 0.56 ng/dL, P < .0001). No significant changes were seen in TBG, GH, or cortisol.
Why it matters
These findings show that both central down-regulation of the thyroid axis and peripheral shifting toward inactive reverse T3 occur rapidly within five days of moderate energy restriction in healthy, lean young women.
Limits
The sample size is small (n = 19) and restricted to young, healthy, lean females, limiting generalizability to men, older individuals, or people with obesity. The abstract does not report whether diet order was randomized, omits free T3 quantitative values, and only evaluates short-term 5-day restriction.
Cited by
- supports Prolonged carbohydrate and caloric restriction can impair thyroid function, leading to symptoms such as cold intolerance and hair shedding.