Obesity and Insulin Resistance Are Inversely Associated with Serum and Adipose Tissue Carotenoid Concentrations in Adults

Background: Low tissue concentrations of carotenoids have been suggested to contribute to insulin resistance in obesity. Objectives: The objectives of the study were to 1) evaluate the relations of adipose tissue and serum carotenoids with body fat, abdominal fat distribution, muscle, adipose tissue and liver insulin resistance, and dietary intake; 2) evaluate the relations and distributions of carotenoids detected in adipose tissue and serum; and 3) compare serum carotenoids and retinol concentrations in subjects with and without obesity. Methods: Post hoc analysis of serum and adipose tissue carotenoids in individuals [n = 80; 31 men, 49 women; age (mean +/- SEM): 51.4 +/- 1.1 y] who participated in 2 separate studies conducted at the Clinical Research Facility at the Garvan Institute of Medical Research (Sydney) between 2008 and 2013. Retinol, alpha-carotene, beta-carotene, zeta-carotene, lutein, lycopene, phytoene, and phytofluene were measured using HPLC. Body composition was measured by dualenergy X-ray absorptiometry. Insulin resistance was measured by 2-step hyperinsulinemic-euglycemic clamps with deuterated glucose (n = 64), and subcutaneous and visceral abdominal volume and liver and pancreatic fat by MRI (n = 60). Periumbilical subcutaneous fat biopsy was performed and carotenoids and retinol measured in the tissue (n = 16). Results: We found that zeta-carotene, phytoene, and phytofluene were stored in considerable amounts in adipose tissue (25% of adipose tissue carotenoids). Carotenoid concentrations in adipose tissue and serum correlated significantly, but they followed different distributions: zeta-carotene was 3-fold higher in adipose tissue compared with serum, while lutein and lycopene made up 20% and 21% of serum carotenoids compared with 2% and 12% of adipose tissue carotenoids, respectively. Liver (P = 0.028) and adipose tissue (P = 0.023), but not muscle (P = 0.16), insulin resistance correlated inversely with many of the serum carotenoids. Conclusions: Multiple serum and adipose tissue carotenoids are associated with favorable metabolic traits, including insulin sensitivity in liver and adipose tissue in humans.