The Role of Energy Expenditure in the Regulation of Energy Balance

Abstract

Throughout evolution, humans and animals have evolved redundant mechanisms promoting accumulation of fat (minimal energy expenditure and maximal food intake) during periods of feast to survive periods of famine. With the recent abrupt change in environmental conditions in which high fat food is constantly available and in which there is little need for physical activity (the current “pathoenvironment” or “toxic environment”), obesity has reached epidemic proportions in both industrialized countries and in urbanized populations around the world. Obesity results from a chronic imbalance between energy intake and energy expenditure. Hyperphagia, a low metabolic rate, low rates of fat oxidation, and an impaired sympathetic nervous activity characterize animal models of obesity. Similar metabolic factors have been found to characterize humans susceptible to weight gain. Despite the discovery of leptin more than 8 years ago and an unprecedented expansion of research efforts, our knowledge about the molecular mechanisms underlying obesity remains rudimentary. The cloning of genes corresponding to several mouse monogenic obesity syndromes and the subsequent characterization of the pathways involved have however shed some light, mostly on the regulation of food intake but much less on energy metabolism. This chapter will first state the premises of the regulation of energy balance, then review the variability of physiological mechanisms underlying the variability in energy balance, and finally summarize some of the important recent discoveries of the molecular mechanisms of energy expenditure.

Low capacity to oxidize fat and body weight

“…The search provided 27 reviews, commentaries, or opinion papers mentioning the low fat oxidation hypothesis . The search also provided 42 original studies including 13 cross‐sectional studies reporting on 18 comparisons of the 24‐h RQ in OP and OR (Table ) and 17 original cross‐sectional studies reporting on 22 comparisons of the fasting RQ in OP and OR (Table ).…”