Optimizing measures of insulin-regulated lipolysis in humans.
Level 3 - non-randomized controlled study
Prospective repeated-measures cohort evaluating physiological clamp methodology and responsiveness to intervention.
PubMed 40411805 · doi:10.1152/ajpendo.00078.2025
What was done
Researchers evaluated the accuracy and reproducibility of measuring insulin suppression of lipolysis (free fatty acid palmitate IC50) using a two-step euglycemic, hyperinsulinemic clamp (EHC) combined with an intravenous [U-13C]palmitate tracer. They analyzed 46 clamp studies across 27 adult participants enrolled in two weight-loss trials (lifestyle modification or bariatric surgery). Measurements tested methodological overestimation across clamp steps, 4-month test-retest reproducibility in 10 weight-stable participants, and response of IC50 to weight loss and changes in adipocyte size.
What was found
In 40 of the 46 clamp studies, using data from both steps of the EHC overestimated FFA palmitate IC50 compared to calculations using only the initial low dose, which itself suppressed palmitate rate of appearance by >50%. In 10 weight-stable individuals evaluated across 4 months, FFA palmitate IC50 was reproducible (r = 0.70, P = 0.02). Following weight loss by either lifestyle intervention or bariatric surgery, FFA palmitate IC50 decreased, and this reduction correlated with total fat loss and changes in adipocyte size (exact correlation coefficients for weight loss not reported in the abstract).
Why it matters
Standard two-step hyperinsulinemic clamp protocols can introduce systematic errors in lipolysis sensitivity metrics if insulin suppression exceeds 50% on the first step. Refining the calculation ensures accurate quantification of adipose tissue insulin sensitivity before and after metabolic interventions.
Limits
The study is limited by a small sample size (n = 27 total, with reproducibility assessed in only 10 participants). The abstract does not provide exact numerical effect sizes or correlation statistics for the relationship between IC50 reduction, fat loss, and adipocyte size changes.
Cited by
- supports Adipose tissue is highly sensitive to insulin, such that subtle amounts of insulin dramatically blunt fat breakdown and lipolysis.