Factors Affecting Energy Metabolism: Neuroendocrine FactorsMonday, June 18, 2018
Continuing with citations from my article in Obesity Reviews on an aeteological framework for assessing obesity, we continue discussing factors that can affect metabolic rate:
Across the entire age continuum, a wide range of neuroendocrine factors can not only affect metabolic rate, but also substrate partitioning and utilization, which may directly or indirectly contribute to weight gain. The latter point is of particular significance as low rates of fat oxidation are associated with an increased risk of weight gain.
A wide range of neuroendocrine hormones and biomarkers can affect energy metabolism; sympathetic nervous system activity and thyroid function are two major factors directly influencing resting energy expenditure.
Sympathetic nervous activity is also a major determinant of post‐prandial thermogenesis and the thermogenic response to a glucose load has been shown to be significantly lower in obese [sic] individuals, a finding that persists even with substantial weight loss.
Specific examples of endocrine hormones that affect energy metabolism and substrate partitioning include cortisol, growth hormone (GH) and testosterone.
Catabolism associated with hypercortisolism or Cushing’s syndrome can reduce energy requirements and increase the deposition of truncal fat.
Discontinuation of GH treatment at the end of childhood growth in individuals with GH deficiency markedly increases fat mass and decreases metabolic rate, whereas GH treatment in GH‐deficient adults has beneficial effects on protein metabolism, energy expenditure and thyroid metabolism.
Testosterone deficiency can also result in abnormal energy partitioning, which adversely alters anabolism and reduces metabolic rate.
It is important to note that a careful history and physical examination should precede any endocrine testing for these disorders, as testing should be reserved for patients with an above‐normal pretest probability for one of these conditions.
Commentary: as pointed out in the last paragraph, while all of the above are important considerations, each one is quite rare, which is why it is important to use clinical judgement in recognising these factors, rather than simply ordering a battery of endocrine tests on every patient.