Adipocyte size, adipose tissue calories, and circulating adipokines, before and after diet-induced weight loss in humans.

Objective: Adipose tissue (AT) contains a bimodal population of large and small adipocytes. Changes in fat cell size (FCS) distribution and AT caloric density (kcal/g) with weight loss are unclear. We aimed to evaluate changes in FCS and AT calories in weight loss and determine associations with anthropometrics.

Materials And Methods: Healthy adults (6 men/4 women; age 33 ± 11 years; BMI 35 ± 6 kg/m) underwent DXA and subcutaneous abdominal/thigh fat biopsies, before and after 6 weeks of caloric restriction. AT calories (bomb calorimetry) and hormones (adiponectin, leptin, FGF21) were measured.

Results: Abdominal large cell diameter (LCD; Δ = -13.2 μm, p = 0.01) and nadir (Δ = -7.3 μm, p = 0.03) decreased. In repeated measures correlations (r), abdominal and thigh LCD and nadir were associated with fat mass (FM) loss (r = 0.68; r = 0.63; r = 0.66; r = 0.62, p's < 0.05, respectively) and waist circumference decrease (r = 0.70; r = 0.60, p's ≤ 0.05). Small cell percentage did not change and was not associated with FM changes. Abdominal AT calories were unchanged with weight loss. Change in leptin was associated with change in abdominal LCD (r = 0.77, p = 0.01).

Conclusions: Caloric restriction reduces adipocyte LCD and nadir. These changes are associated with FM loss. Larger fat cells should be considered as phenotypic targets for weight loss.

Clinical Trials Registration: clinicaltrials.gov identifier: NCT00687115, May 29, 2008.