Primer Energy homeostasis and body weight

That body weight is regulated has been evident to physiologists for many years. When access to food is restricted, animals increase their desire for food and indulge heartily when food reappears. To conserve energy during caloric restriction, appetite is regulated and the overall metabolic rate declines. Conversely, to resist obesity, forced overfeeding suppresses appetite and increases metabolic rate. As tiny surgical or chemical lesions within the hypothalamus in the brain can produce obesity or leanness by disrupting the link between appetite and metabolic rate, it had been surmised that the hypothalamus has a key integrative role in energy balance, as it does in many other homeostatic processes. Physiological control of energy balance, although reasonably effective, is obviously imperfect, as judged by the prevalence of obesity in the modern world.