Hello Docs,
I believe I saw either austin or jordan post or retweet a study about aging and weight loss/metabolism in older adults not being any different for younger individuals. I can’t seem to find it on either instagram or twitter, if anyone remembers this can you point me in the right direction.
Thanks in advance!
All I’m seeing is the abstract, and it’s a little above my head.
This is the key part:
“Total expenditure increased with fat-free mass in a power-law manner, with four distinct life stages. Fat-free mass-adjusted expenditure accelerates rapidly in neonates to ~50% above adult values at ~1 year; declines slowly to adult levels by ~20 years; remains stable in adulthood (20 to 60 years), even during pregnancy; then declines in older adults.”
Jordan, can you (or others) dumb the above down a bit and explain what it means?
Tl;dr- Metabolic rate doesn’t really change from ~20-60, thus weight gain during this period is not due to a “slow” or “slowing” metabolism.
Got it, thanks
From my understanding:
After birth the caloric expenditure of a baby increases. This is beyond increases in bodyweight and activity. 1 kg of lean baby mass burns more energy than 1 kg of adult lean mass, and this difference reaches its maximum at age 1. The gap then gradually closes to normal at the age of 20. From 20 to 60, there’s no meaningful difference.
Question to the Dr - What would cause a decline in metabolism in older adults as stated in the study?
We don’t really know, but it may be a reduction in the relatively expensive organ mass, reduced metabolic activity in general, an unknown mechanism, or a combination of all three.
Why would organs reduce in size/weight past roughly age 60?
And on the “reduced metabolic activity in general”: isn’t that the result that the study showed? How could that result also be the cause? I’m a little confused about the logic on this one.
It’s not known for sure just yet, but the major organs that contribute to 60-70% of resting energy expenditure all decrease in mass with age, save for the heart. There is also reduced function of these organs in general and again, the specific reason is unknown.
And on the “reduced metabolic activity in general”: isn’t that the result that the study showed? How could that result also be the cause? I’m a little confused about the logic on this one.
Not necessarily. If the organ mass was preserved in the sample (it wasn’t measured directly or indirectly in this study) and energy expenditure was corrected for body composition, AND the REE was still decreased, this could be a cause. However, it wasn’t measured and so this cannot be teased out.
Jordan, thanks. I don’t want to belabor this too much, so forgive me.
What I don’t quite understand is: previous poster Abrar asked, “What would cause a decline in metabolism in older adults as stated in the study”, and your response was “reduction in the relatively expensive organ mass, reduced metabolic activity in general, an unknown mechanism, or a combination of all three”
I gotcha on the reduction in organ mass, which you explained. On the unknown mechanism thing: sure, it’s understandable that we don’t know everything yet.
But how can “reduced metabolic activity in general” be a cause of a “decline in metabolism”. Are they not the same thing? Reduced metabolic activity = decline in metabolism, in my mind. How can one be the cause of the other?
Again, not trying to be pedantic, apologies if it sounds that way. Just not understanding the logic on this particular one.
Metabolic activity of a specific tissue =/= body-wide metabolic rate. Body-wide metabolic rate =/= total daily energy expenditure.
Reduced metabolic activity by specific tissues independent of mass is a reduction in metabolic rate ONLY IF it is sustained and nothing else changes. This would therein change energy expenditure, again, if nothing else changes.
If the question is, why does metabolic rate reduce in older individuals, then the cause (or one of the causes) could be a reduction in tissue-specific metabolic activity independent of a reduction in tissue size, which could have an additional one or a number of underlying reasons, e.g. reduced function due to reduced demands from aging, reduced blood flow and subsequent function, etc… Right now, that doesn’t look like the case, but it could be, and if it is the case, we don’t know why.
Hopefully this makes more sense.
Ok, yeah, that makes more sense. You were referring to a possible reduction in metabolism of individual organs or specific tissues (regardless of whether the mass of those organs/tissues changed), which would cause an overall reduction in metabolism of the person as a whole. Thanks for the elaboration.