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Old 08-25-21, 07:18 PM  
adawn
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Lightbulb So it turns out my library had the Science periodical after all

Checked out Science magazine from my local library today. There's a little intro article by Rhoads & Anderson on p. 738 and then the report on p. 808.

Quote:
Originally Posted by Vintage VFer View Post
The whole "metabolism" thing seems very retro to me. It was a big buzzword to sell diet books way back when.
While I agree metabolism was/is a marketing buzzword, it also has a scientific definition. I think most people (such as myself) have only a basic understanding of the word "metabolism" and a lot of it is probably unfortunately influenced by its use as a buzzword to market supplements, workouts, diets, etc. But metabolism is a thing that can be defined and measured by the scientific community.

The Rhoads & Anderson intro article opens with a definition of metabolism:

"Metabolism is not just about energy--how the body handles nutrient fuel and converts it to useable energetic currency. Metabolism also encompasses synthesis, modification, and exchange of the building blocks for all aspects of cellular function and acts as a sensor and regulator of cellular activities, in which individual moieties within metabolic pathways influence cellular responses." (Bonus points if, unlike me, you didn't have to google the definition for "moieties".)

As the NYT article explained, "All of the research centers involved in the project were studying metabolic rates with a method considered the gold standard—doubly labeled water [DLW]. It involves measuring calories burned by tracking the amount of carbon dioxide a person exhales during daily activities."

But back to Science magazine. They mention that the study involved more than 6400 men and women from 29 countries from around the world.

They point out that there are important implications for young people as far as far as diet and exercise recommendations and drug dosing since adolescents are in their own distinct metabolic phase which is different than that of infants and adults.

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Originally Posted by Demeris View Post
I'm deeply curious what those 'other factors' are.
As for accounting for differences between individuals, between men and women and so forth, "energy expenditure was adjusted to fat-free mass to account for differences in body size" (Rhoads & Anderson). Apparently once you account for fat-free mass, there is no longer a lower level of total energy expenditure (I assume total energy expenditure as measured by the DLW method).

They mention, "contributions from physical activity and tissue-specific metabolic rates, both of which change over the human life span, must be accounted for if computational model are to fit the observed data."

Apparently Pontzer's study had a wide variety of body composition among the 6400+ people.

"It is abundantly clear that one size does not fit all. By adjusting for fat-free mass, this study peels some of this variance away to reveal intrinsic shifts in metabolism that are matched to life phase." (So the study peels away "some" of the variance.) But they're basically focused on the excitement of finding 4 distinct life phases regarding metabolism.

There is a suggestion that "metabolism may be a driver in aging biology" and that the metabolic decline after age 60 may "reflect a change in tissue-specific metabolism, the energy expended on maintenance." All of this is important apparently when it comes to disease models, researching the causes behind age-associated diseases and disorders, and so forth.

Ok, so if I haven't bored you enough, it's on the actual Pontzer, et al. article/report later on in the magazine which is actually relatively short.

64% of the 6,421 individuals age 8 to 95 were female.

They "investigated the effects of age, body composition, and sex on total expenditure."

Total expenditure="total daily energy expenditure" measured by the DLW method.

Basal expenditure=Baseline energy needed to do basic things like breathing, etc.

There's this explanation that perhaps will be of value to people who understand such things (I'm going to leave out the figures they cite since you can't see the graphs or whatever without the article):

"We found that both total and basal expenditure increased with fat-free mass in a power-law manner, requiring us to adjust for body size to isolate potential effects of age, sex, and other factors. Because of the power-law relation with size, the ratio of energy expenditure/mass does not adequately control for body size because the ratio trends lower for larger individuals. Instead we used regression analysis to control for body size...." and it goes on and on getting even more technical for awhile. Lots about regression analysis and that sort of stuff.

Then it describe the 4 life phases that the NYT article summarized nicely.

Here's a bit that was of interest (again, I'm not including the figure(s) or prior scientific articles cited):

"Adult expenditures [adult=age 20 to 60], adjusted for body size and composition, are remarkably stable, even during pregnancy and postpartum. Declining metabolic rates in older adults could increase the risk of weight gain. However, neither fat mass nor percentage increased in this period, which is consistent with the hypothesis that energy intake is coupled to expenditure."

There's a little more stuff but I don't quite comprehend it all to be honest and I can't exactly quote 100% of the article.
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Old 08-25-21, 08:01 PM  
Leonana
 
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So, our body uses less energy for maintenance after age 60, which explains the slower metabolism. Well good to know now that I'm 61, lol. Whoever said aging is not for the faint of heart, knew what they were talking about.

I haven't noticed much difference now that I'm 61 from when I was in my 40's and 50's. I gained weight at age 41 after I had my daughter. But my guess is it will slow down more as I age. I was almost two sizes bigger after pregnancy, then lost one size after I started exercising and changing my eating in my early 50's. Over the years I go up and down. I think I'm back to being one size bigger, and I'm okay with that.

I have read that menopause does not change total amount of weight, but distribution. As in more weight around the middle, and less in the hips and thighs. That has been true for me.
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