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Why exactly do humans lose subcutaneous fat tissue with age? It appears that we either lose fat cell volume or we might actually be losing the number of fat cells with age.

One hypothesis is that as the vascular system weakens with age, the fat cells on the perimeter of the body shrink and die because they don't have enough blood flow to sustain them. The problem with this hypothesis is that subcutaneous fat loss is very gradual and starts during young adulthood and continues. It also happens in very fit individuals too.

Another hypothesis I read before was that subcutaneous fat is loss because of a drop in estrogen levels after menopause. This hypothesis doesn't explain why men lose subcutaneous fat with age. Also, women start to lose fat on their hands and upper cheeks long before menopause starts.

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    $\begingroup$ Another thing to mention is that not all mammals have this issue. Whales retain their subcutaneous fat well into old age. $\endgroup$ – user45506 Aug 21 '18 at 9:09
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Short answer
We do not loose fat (cells) as we age; on the contrary - we tend to gain fat by about 1 or 2% per decade. The place where it gets stored does change; instead of going into subcutaneous regions, it gets stored around the abdomen. A sex hormone imbalance might be the cause of this gain in visceral fat.

Background
What a coincidence! I just finished an article in the Sci Am May issue of this year (2018) on exactly this topic, literally just minutes ago.

In young folks, fat tends to accumulate under the skin, while in older folks this tends to shift to accumulation of fat around the abdominal viscera (the internal organs). Bottom line: we don't loose fat overall, we just store it elsewhere. What's more, as we age we store more fat as our base metabolic rates drop.

Why this happens is no known, but there are some interesting findings:

  • Sex hormones are involved; women in menopause (estrogen levels drop) gain more visceral and belly fat and loose it around the hips (they go from pear to apple);
  • However, a drop in estrogen is not the cause, as certain ailments lead to belly fat in young women with plenty of estrogen;
  • Androgen-using females (transgenders) gain more visceral fat.

These findings together have lead to the idea that a sex hormone imbalance might be the cause. However, some findings counter this idea:

  • Afro-Americans have less visceral fat, while Asians have more;
  • Blocking FSH results in less visceral fat, which may have other mechanisms of actions than estrogen.

Reference
- Wallis, Sci Am May issue 2018

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  • $\begingroup$ Children have low estrogen and very little central abdominal fat (usually). $\endgroup$ – user45506 Aug 21 '18 at 17:42
  • $\begingroup$ The question I'd ask, though, is whether the accumulation of fat is actually due to age, or whether it's a side effect of sedentary, inactive lifestyles increasing with age. E.g. this guy doesn't seem to have a lot of subcutaneous or visceral fat: adn.com/sports/2018/07/23/… $\endgroup$ – jamesqf Aug 21 '18 at 18:34

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