Your pot belly is trying to kill you

I have two words for you: rat lipsuction.

One of the common features of aging throughout the Class Mammalia is the accumulation of body fat in specific deposits — specifically, the growth of visceral (or abdominal fat). We do it, monkeys do it, dogs do it, and rodents do it. Visceral fat (VF) has been implicated in a variety of age-related disorders, including metabolic syndrome and chronic inflammation, both of which have in turn been linked to frailty.

If VF produces a factor or factors that limits lifespan (either by promoting the aforementioned conditions or by another mechanism), then removing it should make those factors go away and concomitantly lengthen lifespan. (I suppose the alternative would be a parabiosis experiment in which a rat with lots of VF shared a blood supply with a rat with little VF, though (a) the results would be difficult to interpret due to myriad confounding factors; (b) I’m not sure what one would do if the fat rat died while the thin rat was still alive; and (c) the entire exercise would be a horrifying abomination.) Muzumdar et al. have collected just that sort of data: They removed the VF from rats consuming an ad libitum chow diet, and showed that the rats aged almost as successfully as calorie-restricted (CR) rats (which, by the way, never accumulate VF):

Visceral adipose tissue modulates mammalian longevity

Caloric restriction (CR) can delay many age-related diseases and extend lifespan, while an increase in adiposity is associated with enhanced disease risk and accelerated aging. Among the various fat depots, the accrual of visceral fat (VF) is a common feature of aging, and has been shown to be the most detrimental on metabolic syndrome of aging in humans. We have previously demonstrated that surgical removal of VF in rats improves insulin action; thus, we set out to determine if VF removal affects longevity. We prospectively studied lifespan in three groups of rats: ad libitum-fed (AL-fed), CR (Fed 60% of AL) and a group of AL-fed rats with selective removal of VF at 5 months of age (VF-removed rats). We demonstrate that compared to AL-fed rats, VF-removed rats had a significant increase in mean (p < 0.001) and maximum lifespan (p < 0.04) and significant reduction in the incidence of severe renal disease (p < 0.01). CR rats demonstrated the greatest mean and maximum lifespan (p < 0.001) and the lowest rate of death as compared to AL-fed rats (0.13). Taken together, these observations provide the most direct evidence to date that a reduction in fat mass, specifically VF, may be one of the possible underlying mechanisms of the anti-aging effect of CR.

The authors argue (a bit too strongly, in my opinion) that their experiment demonstrates that prevention of VF accumulation is a major mechanism of the lifespan extension due to CR. A skeptic could easily argue that it works the other way: VF represents a really large storehouse of energy, and its removal could force the rat to deplete other fat reserves and enter a state that mimics CR. The parabiosis experiment that I parenthetically described above (or some less repellent and [not entirely incidentally] more scientifically valuable version thereof, e.g., one in which candidate factors secreted by VF were introduced back into lipectomized rats) would go a long way toward bolstering the authors’ interpretation.

Regardless, it’s a good reminder not to skip yoga and jogging this weekend.

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5 comments

  1. Do note that visceral fat is rather deeper in than the fat typically
    removed via liposuction, which in and of itself doesn’t do nearly as
    much (better on cholesterol, yes; better on insulin sensitivity or
    inflammation markers, no (see PubMed IDs 18264836 and 18220642,
    for instance)). Rutgers unfortunately doesn’t have a subscription
    to Aging Cell, so I can’t check things out in more detail on this
    article. Interesting, though.

  2. Allen’s point is a valid one — the rats were, technically speaking, lipectomized by removal of visceral fat in a surgical procedure that bears no resemblance to liposuction.

    The teaser line of the post is just poetic license.

  3. Very interesting! So how do you reduce VF other than surgery and CR, given that you are already doing moderate exercise and maintaining ( with some effort and discipline ) a “normal” weight?

  4. I have seen in the news over here in england today that new research from Harvard suggest`s we can all have larger curvier bottoms as this helps to guard against diabetes….
    Has anyone heard anymore about this?

  5. All:

    Chris wrote:
    The authors argue (a bit too strongly, in my opinion) that their experiment demonstrates that prevention of VF accumulation is a major mechanism of the lifespan extension due to CR.

    They certainly argued too forcefully, for a much more important reason: the standard one, that they didn’t actually show any life extension. A colony of normal, well-cared-for, genetically healthy lab rats should have a tenth-decile survivorship in the 1000-1100 day range. While Barzilai’s group don’t give the hard numbers, it’s clear that none of their rats lived particularly long:
    the longest-lived individual in each cohort died ~age 931 (controls), 1050 (VF-removed), and 1085 (CR) days, with a considerable curve-squaring in CR. Moreover, there was no effect on cancer mortality: while the F344 rat is highly vulnerable to nephropathy, reduced cancer risk is the hallmark pathological finding in CR.

    I think a pretty reasonable interpretation is that they just overfed their controls, and corrected some of that obesity by surgery and more by normal feeding.

    A skeptic could easily argue that it works the other way: VF represents a really large storehouse of energy, and its removal could force the rat to deplete other fat reserves and enter a state that mimics CR.
    I don’t think that flies, for the simple reason that the intervention was early, and body weights were actually nonsignificantly higher in the VF-removed animals. It would’ve been nice if they’d reported food intake, however.

    Jim: the answer is negative energy imbalance: more exercise, or fewer Calories.

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