Factors affecting energy expenditure

Abstract

Sixteen years ago I presented a paper on this topic to this Society (Miller & Mumford, 1966) and much of the subject matter was highly controversial: some might say it still is. However, it is my contention that if controversy exists today it is largely terminological, and therefore essential to define some of the terms used, such that any debate may be scientific rather than semantic. My earlier paper began with a traditional treatment of the first law of thermodynamics (I):A Body energy = energy intake -energy expenditureA B = I -E In common with other authors at that time no units of measurement were indicated, despite the fact that it was common practice to measure intake as metabolizable energy but the other terms in gross energy; for human food the difference between gross and metabolizable energy was small (approximately 5%) but with the current fashion for high-fibre diets the error would be greater. In those days energy expenditure was conceptually made up of the basal metabolic rate (BMR) plus physical activity (A) plus specific dynamic action (SDA): (3)However, in practice, the energy costs of physical activity were measured as gross values (i.e. including BMR and SDA) and these were listed in the superb tables of Passmore & Durnin (1955) which have been widely used in time and motion studies to estimate energy expenditure. The net cost of physical activity (i.e. excluding BMR and SDA) was primarily the interest of exercise physiologists concerned with muscle metabolism, BMR that of clinicians concerned with thyroid disorders and SDA that of animal nutritionists producing fat stock. Much of this has changed and a more sensible way of looking at energy expenditure is given in Equation 4:It should be noted that work is the quantity of physical work performed on the external environment, since chemical work (e.g. the net cost of fat and protein synthesis), SDA, and even BMR will all appear as heat. Quantitatively the values for excreta and work are small, and a sedentary adult in our labour-saving society degrades almost all of his food energy to heat. If, in contrast to farm animals, he maintains weight for 50 years, his existence may be seen as a tedious degradation Energy output = excreta + work + heat

Energy Cost of Standing in a Multi-Ethnic Cohort: Are Energy-Savers a Minority or the Majority?

“…Within this zone, increasing the allocation of posture to standing rather than sitting is perhaps the most simplistic approach aimed at increasing activity levels. However, investigations of the energy cost of standing versus that of sitting have been equivocal–with reported mean increase in energy expenditure (EE) between the two postures ranging from <1 to >100% [6–8]. In addition to methodological differences, such large discrepancies in study findings may be due to the large inter-individual variability in the energy cost of posture maintenance.…”

The diversity of sex steroid action: regulation of metabolism by estrogen signaling

“…A series of complex systems regulate energy homeostasis in order to keep energy levels and body weight stable (Miller 1982). Central brain circuits receive peripheral signals indicating satiety, energy levels, and energy stores.…”

Estrogen Receptors in Glucose Homeostasis

“…This initial study was followed by numerous other studies and it is now firmly established that the CNS regulates glucose homeostasis through the hormones insulin, leptin and glucagon-like peptide (GLP)-1, as well as by glucose and fatty acids (FA). A series of complex systems regulate energy homeostasis in order to keep energy levels and body weight stable (Miller, 1982). Glucose is the vital energy source for the brain.…”