Homeostasis is the term given to the large number of mechanisms that exists within an organism, in this case the human body, to ensure that it survives. Homeostatic mechanisms operate in an adverse environment with the aim of bringing a particular function back to normality and as a result ensuring that the organism as a whole is performing optimally and therefore has its best chances of survival.
Homeostatic mechanisms as a principal have evolved over a long period of time. As far as Homo sapiens are concerned our earliest ancestors can be traced back several millions of years and all of the carefully controlled processes within our body have evolved over that time, making very small adjustments. So that what exists today is a reflection of the fine tuning that is an integral part of the evolutionary process.
With regards to obesity, the deposition of adipose tissue, both subcutaneously and viscerally, is a failsafe mechanism that ensures an alternative energy source, when the primary energy source i.e. glucose is in short supply or unavailable such as in times of enforced fasting or starvation. This of course used to happen almost certainly with considerable regularity in primitive man who was a hunter-gatherer.
This defence mechanism in western societies is no longer required because there are very few circumstances where the human body is now forced to endure a period of significant fasting or starvation. However, the mechanism still exists and explains why the body continues to deposit fat as a storage facility, despite it being surplus to requirement.
Carrying around excessive amounts of adipose tissue has clearly been shown to position the individual organism at a disadvantage on many fronts, in particular its ability to move quickly (which would be an advantage when hunting a prey) or to be able to deal with certain diseases, as evidence by the fact the incidence of these diseases, such as the common cancers, are more prevalent in individuals who are suffering from obesity.
This leads on to the concept of the biological optimum weight (BOW) and is that weight that is achieved when the normal homeostatic mechanisms are allowed to operate, in particular to bring the body back to the position where it has its best chances of survival.
A good example of a homeostatic mechanism is the way insulin controls our blood sugar within very carefully defined parameters. It does this to ensure that any excess glucose that is taken in beyond our usual requirements is not wasted - it is converted to fatty acids and then stored as adipose tissue. It also ensures that it does not drop below a certain level because certain cells i.e. those of the central nervous system, have an obligatory requirement for glucose as far as their energy needs are concerned.
Another important homeostatic mechanism is of course the body’s ability to utilise fatty acids as an alternative energy source. And intermittent fasting is simply utilising this homeostatic mechanism in the management of obesity. It is in effect denying the body its primary energy source and thereby forcing it to use its secondary energy source and it derives this substrate from stored body fat. It has no alternative and it will happen simply by the individual allowing it to happen.