Factors Affecting Energy Metabolism: Genetics, Sex, and Aging

Continuing with citations from my article in Obesity Reviews on an aeteological framework for assessing obesity, we now turn to the some of the factors that can affect metabolic rate:

Genetics
Because heritable factors appear to be responsible for 45–75% of the inter‐individual variation in body mass index (BMI), the potential impact of genetic determinants of metabolic rate upon the predisposition to obesity must be considered. While numerous somatic and mitochondrial genes with potential effects on metabolic rate have been identified, their contribution to human obesity has yet to be defined Likewise, although there is preliminary evidence for intrauterine and perinatal programming of genes involved in energy metabolism, their role in human obesity remain unclear. What is apparent is that the genetic predisposition to obesity (including both energy intake and metabolism) is not explainable on the basis of a small number of common mutations exerting substantial effects on the individual tendency to weight gain. Thus, a great deal of work is still required before investigation into the multitude of genetic determinants of body weight can potentially impact clinical management. Currently, a careful clinical assessment of family history of obesity and related risk factors remains the best measure of genetic risk for obesity.

Sex
There is a clear effect of gender [sic] on metabolic requirements, whereby, for the same BMI, women consistently display lower metabolic rates (approximately 20% less) than men, largely accounted for by differences in fat‐free mass (FFM).

Aging
Aging is an important determinant of a decline in metabolic rate, with an estimated reduction of around 150 kcal per decade of adult life. Factors that result in the age‐related decline in energy requirements include changes in neuroendocrine factors (e.g. sympathetic activity, thyroid function, etc.) as well as a reduction in skeletal muscle quantity and quality (resulting from reduced physical activity, reduced protein intake and other less‐well‐understood factors).

Additional factors that can affect metabolic rate will be discussed in subsequent posts.

@DrSharma
Edmonton, AB