Hilary McClure wrote:
>What I've read is that adult humans (and other precocial mammals) do not
>have any BAT. If that's true it would seem to make this whole discussion
>irrelevant. Altricial mammals such as mice keep their BAT into
>adulthood, but precocial mammals only have BAT in infancy. Does Blumberg
>disagree?
>
>
I think this is a very important point. Oliva just posted something
according to which "little" BAT exists in adults. I've also seen
sources that indicate that it decreases with age. Here is another
relevant remark, from http://www.nature.com/ng/wilma/v15n3.862408548.html.
"*This pathway has been implicated in the regulation of body
temperature, body composition and glucose metabolism^2 . However,
UCP1-containing brown adipose tissue is unlikely to be involved in
weight regulation in adult large-size animals and humans living in a
thermoneutral environment (one where an animal does not have to increase
oxygen consumption or energy expenditure to lose or gain heat to
maintain body temperature), as there is little brown adipose tissue
present^3 ."
I infer from this that BAT may be a "use it or lose it" tissue. I.e.,
if we live in a thermoneutral environment, as most of us do, we
gradually lose the BAT that we had as children. Possibly if we did not
live in a thermoneutral environment (if we were Inuit, maybe), we would
retain more BAT into adulthood.
Thinking out loud, maybe this is the cause of adult-onset obesity -- a
very common phenomenon. We all know kids and teenagers who eat heroic
amounts of crap but never gain weight. Some of us may have been like
that ourselves at one time. Then it all changes -- maybe at age 18, or
20, or 25, or 35. Without any overt change in diet, we begin to get
fat, and it gets harder and harder to lose weight. Maybe what we are
witnessing is the gradual erosion of our capacity for DIT, caused by the
disappearance of BAT.
If this is correct, then the high-fat low-protein experiment is
pointless for those devoid (or nearly so) of BAT.
Todd Moody
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