| By :
Nick Clipton
Copyright (c) 2010 Nick Clipton Now, many, if not most systems in the human body are regulated. Consider body temperature where the body strives to maintain a rather normal level (98.6 Fahrenheit in the US, I have no idea what that is in Celsius). If you are put somewhere cold, your body will make you shiver, as well as cutting off blood flow to your extremities (this is why fingers and toes get so cold) to try and keep your body heat up. Go into the heat or exercise and your body sweats and increases blood flow to the extremities to try and get rid of the excess heat so that you don't overheat. So what about body weight? After three decades of research and endless argument in the journals, it's now well established that human body weight is regulated (it might be more accurate to say that body fat percentage is regulated). Animal studies decades ago demonstrated that the animals would strive to maintain a relatively stable body weight. In humans, studies had demonstrated that metabolism would slow more than you'd predict (for the weight loss) when you dieted people. To a smaller degree, metabolism would also go up when you overfed them. As well, appetite and activity would change accordingly: activity would go down and appetite would go up when people were dieted and activity would tend to increase and appetite would go down when you overfed them. All of which tended to affect body weight/body fat. In essence, the body is more or less trying to maintain a given level of body fat, that level being called the 'setpoint'. This would be roughly equivalent to setting your thermostat higher in the winter and lower in the summer or the cruise control faster on the freeway and slower in town (where the speed limit is lower). You pick a different settling) point depending on the circumstances. So a given individual might settle at one body fat level (and maintain around that level fairly closely) if they were inactive and eating the modern American diet and settle at a different (and generally lower) body fat level if they start exercising and eating better. They would regulate just fine around those settling points (i.e. their body weight would fluctuate a little bit) but they'd have to change habits to alter the settling point very much. If you think about this within the context of human weight gain, the idea of a settling point is probably a little closer to the truth: people don't continue gaining weight indefinitely. Rather, based on their environment (and, of course genetics), they gain some amount of weight and then stay pretty stable around that new weight. Anyhow, the issue of set vs. settling points is sort of tangential to the topic of this chapter. The main idea I want you to take away from this is that within some range, the body appears to 'defend' (another way of saying 'regulate') body weight against change to some degree or another. By 'defend', I mean that it adjusts its physiology to try and maintain that set/settling point within a certain range. Towards this goal, the body can, in premise anyhow, adjust metabolic rate, appetite and a whole host of other systems up or down to try and defend against changes in body fat or body weight.
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