Many of the so-called paradoxes of weight and energy balance disappear when the problem is properly formulated.
We cannot do any better than using the Le Magnens’s splendid research to begin. He states that regulation of body energy and regulation of body weight are not identical, and their habitual confusion in the literature is misleading. Body weight is not regulated per se. Body water content, the major component of body weight (70%), is regulated by a mechanism that is independent of energy flow. So, the energy regulation, if it even existed, is not equivalent to regulation of body weight.
Energy balance in the brain, heart, or kidney is achieved by mechanisms specific to each organ. Because brain metabolism is vital and because behavior is governed by the brain, energy intake and expenditure are primarily mechanisms to assure the safety of the brain’s energy flux or flow.
Fat stores are necessary reserves or buffers of energy that are primarily of importance to the brain. The buffers create the possibility of a constant flow of energy to the brain when muscular energy expenditures might change by as much as 300% and energy intake may vary from a feast to nothing. The brain is clearly capable of directing feeding and energy expenditure to achieve a safe flow of energy to itself. In my book, I referred to this as the selfish brain theory.
The brain’s energy demands are unrelated to body weight. The brain seeks to manage its energy supply continuously because it has small capacity to store energy. So, it must use other stores and resources in the body to maintain the constancy of its energy flow.
If energy balance is maintained at all it is in the brain, not the body. The brain’s energy supply is balanced as a necessary condition for survival. The body and its many components may be sacrificed to satisfy the brain’s requirements. Eating and moving are activities intended to obtain energy for the brain. In order for this to happen, it may be necessary that whole body energy intake and expenditure do not balance. If the brain is lacking energy it will cause you to seek food and expend energy, unless the shortage is lasting. Acute shortfalls are not anticipated to be lasting and so activity is the best strategy for the brain to obtain energy. In chronic starvation, brain energy shortfalls are anticipated to be lasting so the brain curtails activity to preserve its energy supply.
Hunger, eating and movement only have meaning in context. Hunger causes eating and food seeking movement in the context intermittent energy shortfalls. But, hunger curtails movement in the context of lasting energy shortfalls.
There will be a few more posts in this topic as I try to converge on a theory of body composition and obesity.
Le Magnen, J. (1983). Body energy balance and food intake: a neuroendocrine regulatory mechanism. Physiological Reviews.
Swinburn, B., & Ravussin, E. (n.d.). Energy balance or fat balance?” 2. American Journal of Clinical Nutrition.
Feinman, R. D., & Fine, E. J. (2004). 1475-2891-3-9. Nutrition Journal, 3(1), 9. doi:10.1186/1475-2891-3-9
Hitze, B., Hubold, C., Van Dyken, R., Schlichting, K., Lehnert, H., Entringer, S., & Peters, A. (2010). How the selfish brain organizes its supply and demand. Frontiers in Neuroenergetics, 2.