How to activate your lazy fat? - The role of physical fitness in changing endocrine function of fat tissue in humans

Obesity is a major modifiable risk factor for cardiovascular and metabolic
diseases, and is strongly associated with morbidity and mortality. Large
epidemiological studies demonstrated that obese individuals with a higher
physical fitness or physical activity levels are more likely to have a
metabolic and cardiovascular healthy phenotype.1-3 However, these beneficial
effects of fitness and training cannot be simply explained by a reduction in
the amount of fat tissue.
Recently, it has been suggested that exercise training may alter the adipose
tissue endocrine function, whilst also acute exercise impacts upon adipose
tissue endocrine function. Adipose tissue has the capacity to secrete bioactive
proteins (adipokines) that may play a crucial role in the pathogenesis of the
metabolic syndrome. Obesity is associated with alterations in the secretions of
adipokines.4, 5 Therefore, the first aim of this project is to compare
endocrine function between obese/non-obese fit and unfit people under resting
conditions and immediately after a bout of exercise.
Previous studies found that the measure of the quantity of fat (fat percentage,
body mass index, waist-hip-ratio) is related to metabolic and cardiovascular
risk. However, little is known whether fat endocrine function is related to
metabolic (i.e. insulin resistance) and cardiovascular risk in obesity.
Therefore, the second aim is to explore the potential presence of a correlation
between endocrine function, metabolic and cardiovascular function.

1a. Compare fat endocrine function in obese fit versus obese unfit people under
resting conditions and immediately after exercise.
1b. Compare fat endocrine function in non-obese fit versus non-obese unfit
people under resting conditions and immediately after exercise.
2. Explore the correlation between endocrine function, metabolic function and
cardiovascular risk in obese/non-obese fit/unfit people

Single-centre cross-sectional study

Fat endocrine function. Performance of a subcutaneous fat biopsy is not
associated with an important health risk. The procedure may cause some
discomfort for the subject when taking the biopsy. However, local anaesthesia
will be applied and subjects will be informed about the procedure.
Metabolic function. For this procedure, we will take a venous blood sample to
examine glucose and insulin. This is associated with a 5% chance of developing
a hemorrhage, which will not result in functional limitation and will resolve
within 2 weeks. This venous puncture will also be used to draw blood to assess
circulating markers for endocrine and cardiovascular function.
Cardiovascular function. We will adopt non-invasive echo-Doppler to examine
endothelial function in the brachial artery and intima media thickness in the
carotid artery. This procedure is not associated with potential health risks.
Cycling test and acute exercise intervention. Performance of exercise in
healthy individuals or in those with an increased cardiovascular risk is not
associated with an important health risk. Nonetheless, we will ensure close
supervision of the subject according to our standard operating procedures to
perform exercise testing.
Patient benefit. Subjects will not gain a direct health benefit.