I’d mention, and I’ll come back to this in a future blog post that it’s most likely body fat levels that are being regulated, more than absolute body weight per se.
This almost suggests that any attempt to alter body weight or body fat levels is futile because of the body’s defenses (and some have interpreted the concept in exactly that fashion). This is especially true when it comes to weight/fat loss as the human body appears to defend against weight/fat loss much moreso than against weight/fat gain.
In contrast, the essential idea of a settling point is that bodyweight/body fat levels will ’settle’ at a given point based on the environment. The availability (or lack thereof) of food (and how tasty it is), the amount of activity done, all work to adjust where the body will settle.
So if you take the average human being and put them in America, with tasty inexpensive food readily available and very little activity required on a daily basis, their body weight will ’settle’ at a certain point that may be somewhat high.
Now change their diet, or enforce a large amount of exercise, presumably their body weight will settle at some lower point (regardless of set point). At least assuming that the intervention to diet/activity is maintained.
Now take that same person and put them in a third world country where massive amounts of food aren’t available and high amounts of activity have to be done daily to obtain it; bodyweight will presumably settle at the lowest level.
This would tend to occur absolutely regardless of any biological set point.
And, as usual, there is data to support both concepts. And, given recent understanding that a variety of systems regulate body weight (including homeostatic and hedonic), it seems pretty obvious to me that both set point and settling point concepts are working to regulate body weight/fat levels.
Nobody can deny that the body fights back (to relatively greater or lesser degrees) when weight/fat levels change, especially when weight/fat is lost.
At the same time it’d be asinine to think that humans are little more than automatons driven by a homeostatic drive to eat with no control over what goes into their mouth.
As well, clearly the environment plays a huge role in eating behavior. Increasing portion sizes, exposure to food advertising and a host of other factors all impact on eating behavior regardless of homeostatic systems.
An excellent synthesis of these ideas came in a 2002 paper titled “Putting behavior back into feeding behavior: a tribute to George Collier.”
Quoting from the abstract:
“The combination of these data with George’s insightful idea, has merged into a modification of the popular Set-Point Theory of the regulation of body weight. The alternative “Settling Zone” Theory suggests that whereas biology may determine a range of body weights (adiposity) that are maintained fairly constant for long periods of time, within this “zone”, the behaviors responsible for controlling energy intake and energy expenditure are influenced primarily by environmental and cognitive stimuli.”
Essentially, while the set point may be working to keep people within some range of body fat levels, even within that range individual behaviors and environment will affect where within that range folks will end up. This model manages to tie pure biology in with pure psychology which, as I noted earlier, is a false separation in the first place.
And, I’d note again, it’s becoming abundantly clear that, regardless of set points or settling points or whatever you want to call it, the prevailing environment and individual behaviors can overcome either.
For most people given the current environment (which researchers are now terming obesigenic, meaning that it generates obesity), this means maintaining a much higher bodyweight/body fat level than you’d expect based on the set point concept (note again that any homeostatic system defending against weight gain appears to be pretty weak).
I’d note also, and this is a contentious issue, that some evidence suggests that the set point can go up (apparently permanently) with the maintenance of chronic obesity. Other things such as pregnancy, puberty and a couple of others may be able to permanently move the set point up as well.
However, there are clearly subgroups of dieters and athletes who, through various behavioral means (generally involving dietary choice and activity) can clearly maintain bodyweight and bodyfat levels that are presumably below (or at least at) their biological setpoint.
Of course, contest dieters (bodybuilders, figure competitors) often work like to hell to diet down far below their set point. Fighting against hunger, metabolic slowdown, etc. these individuals clearly can and do reach the extreme lower limits of human body fat levels (roughly 3-5% for men and 7-9% for women). Few maintain that in the long-term of course and most suffer from the post-starvation hyperphagia I mentioned in Friday’s post.
Horror stories of competitors gaining weight rapidly and massively following a strict 12-16 week diet are plentiful, many people will finish their contest preparation and go on month-long food binges (with no training) afterwards. Some of this is clearly physiological, some of it is psychological and, again, there are overlaps in the system.I’ll continue with some of the physiology behind this system next time and (finally, really, I promise) move into psychological stuff after that.