MedicalResearch.com Interview with: Professor Nuala Byrne PhD Head of School | Health Sciences Faculty of Health University of Tasmania  MedicalResearch.com: What is the background for this study? Response: Calorie restriction (or cutting back on the energy we are eating) triggers powerful compensatory responses by our body’s metabolism - we might think of it as a “Famine Reaction”. Our body weight is regulated by a series of nervous system and hormone networks that act together to make sure we have enough energy to sustain life. When we eat more energy than our body needs to meet our daily metabolic requirements (positive energy balance), we are designed to store that excess energy; and we are very good at storing. We store this energy in the fat cells (adipocytes) as an emergency reserve for when we hit hard-times when food availability is scarce. The problem in today’s society is that most of us have a constant availability of energy-dense food; making it more common to be in energy excess. When we have less calories being consumed than what we need to fuel all the body’s metabolic processes (negative energy balance), we convert the stored fat into usable energy, and consequently lose weight. While our body does sense the positive energy balance, it is designed to be more sensitive to gauging when we are in a negative energy balance. Our body senses the change in energy intake and the decreasing fat stores, and brings out the artillery to defend our energy stores - this is the Famine Reaction. Our body is constantly changing our physiology in response to challenges to the status quo; the body works constantly to keep the oxygen concentration in the blood at an optimal level, to keep a constant and optimal body temperature, and a constant and optimal amount of sugar in the blood. Our body’s regulatory systems also work hard to defend our energy stores if it senses we are continually in negative energy-balance (i.e., dieting). One major metabolic compensatory as part of the “Famine Reaction” is a decrease in the body’s resting metabolic rate (energy expended while at rest to maintain the basic functioning of our major organs). Given that resting metabolic rate is determined largely by body size and composition, it is expected to decrease with weight loss. However, during dieting, resting metabolic rate has been reported to decrease to a greater extent than that expected from changes in body composition, a phenomenon termed ‘adaptive thermogenesis’. This leads to markedly reduced efficiency of weight loss. (more…)