the mice got fatter without a positive energy balance.
There was a lot of good feedback from the post about 5% calorie restriction, but it has left people wondering, how could this happen?
Truthfully, I have no clue. But since First Amendment Rights apply in the blogosphere, I am free to speculate. However, for anyone with proper training in nutrition and or energy balance, this may seem like shouting fire in a crowded auditorium, so please forgo this post.
Divide and conquer.
Energy balance MUST AND WILL BE MAINTAINED.
For starters, lean mass (muscle) was lost, which might be indirectly caused by the reduction in food intake. Muscle is the major contributor to energy expenditure. If food intake declines, and muscle is lost in order to reduce energy expenditure, energy balance could be in fact maintained. The only strange part of that conclusion is that it states that muscle was lost in order to reduce energy expenditure. Why would muscle do this? Perhaps it is due to a novel variation of the “use it or lose it” principle. “Use it or lose it” refers to the decline in skeletal muscle that occurs during extended periods of disuse (think of someone’s arm after it spent 2 months in a cast).
When calorie intake is reduced, leptin levels decline rapidly signaling “starvation” mode to the brain. This causes a large reduction in energy expenditure in order to preserve energy stores. Previously, the decline in energy expenditure would have been predicted to occur by decreased physical activity. And reduced physical activity could cause muscle loss due to the “use it or lose it” principle. BUT physical activity was unchanged. Therefore, it is possible that the decline in metabolic rate was manifested by processes other than physical activity in muscle tissue. This means that “use it or lose it” could apply to functions (“using it”) that occur while we are resting. Clearly, this is a marked deviation from the energy balance dogma. And it has kept me up at nights.
What processes could these be? None were measured or even suggested by the authors of the study, but I suppose some possibilities could be reduced activity of sodium potassium ion channels or possibly reduced futile cycling. This is interesting, indeed. More research is severely warranted.
So muscle was lost in order to balance the reduced food intake. OK, so where did the energy come from to build fat mass? This may have already been explained… if metabolic rate was reduced down to match food intake, energy balance would be maintained. If metabolic rate was reduced even further, it would produce a relative energy surplus. Perhaps this is precisely what occurred. Thus, muscle was lost in order to balance the reduced food intake, and metabolic rate declined in order to create a relative positive energy balance selectively to the fat tissue. Why would something like this occur? It is very strange, to be sure, but may have had something to do with the stress of the feeding regimen. The body thinks it is starving, so preserving fat mass becomes a priority. Maybe the systems that work to preserve fat mass during starvation are the same as those that build fat mass during energy surplus.
For now, trying to explain these findings without defying the laws of energy balance caused gray hairs to appear in my beard. I’ll try to figure out the why later.
The mice got fatter without a positive energy balance. Can this happen to us? Does it matter? These results suggest that fat tissue has a propensity to grow regardless of energy balance. In the abovementioned study, the trigger may have been the hormonal response to a stressful feeding regimen. Type I diabetics are usually very thin but develop fat deposits in their insulin injection sites; thus, in type I diabetics, the trigger is insulin. In both situations, fat mass grew because of the hormonal milieu, not an energy surplus.