Why diets don’t work: a brief description of Adaptive Thermogenesis from the perspective of your DNA.
Your DNA doesn’t like most diets because most diets imply a significant sustained caloric deficit and the DNA interprets that as a threat against the organism (you) and causes adaptations to occur in the body’s metabolism to counteract that threat—this is the definition of adaptive thermogenesis.
During the initial stages of a significant caloric deficit, which includes fasting, there is not a significant decrease in the basal metabolic rate (BMR), which is the metabolism/burning of the energy stored as fat or glycogen, or ingested energy/food. In fact, there may even be a counter-intuitive increase in the BMR within the first few days before it begins to drop; however, by 2-3 days the BMR does fall precipitously for a host of reasons. There have been some published reports suggesting that the decrease in metabolism is long-lasting and possibly even permanent, but more recent studies have discounted those findings; however, there can be prolonged effects of a diminished BMR, and normalization of the metabolic rate (if it fully occurs) is never as rapid as the initial decrease in it.
In order to fully appreciate this, you need to think like your DNA, which has been programmed to perform automated tasks based upon over 200 million years of evolution. So, when you restrict your caloric intake, your DNA’s