Low brown adipose tissue activity in endurance-trained compared with lean sedentary men

Area of Science:

• Metabolic Physiology
• Adipose Tissue Biology
• Exercise Science

Background:

• Functional brown adipose tissue (BAT) in humans can be activated by cold.
• BAT activation is explored as a strategy against obesity.
• Exercise-induced myokines like irisin and IL-6 may promote "browning" of white adipose tissue (WAT) in rodents.

Purpose of the Study:

• To investigate if endurance-trained athletes exhibit enhanced cold-stimulated BAT activity and WAT browning compared to sedentary males.
• To explore the relationship between endurance exercise and brown/beige adipocyte recruitment in humans.

Main Methods:

• Compared 12 endurance athletes and 12 lean sedentary males.
• Measured cold-induced BAT activity using [(18)F]FDG-PET-CT during 2 hours of mild cold exposure.
• Assessed skeletal muscle FNDC5 expression, plasma irisin and IL-6 levels, and WAT gene expression for browning markers.

Main Results:

• Athletes had significantly lower cold-induced BAT activity than sedentary individuals.
• No differences in gene expression for brown and beige adipocyte markers in subcutaneous WAT.
• Skeletal muscle FNDC5 mRNA was higher in athletes, but plasma irisin and IL-6 levels were similar between groups.

Conclusions:

• Chronic endurance exercise is not associated with increased brown or beige adipocyte recruitment in humans.
• Endurance training appears to be linked to reduced metabolic activity of BAT in humans.