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July 09, 2012

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Lifespan boost might be harder for couch potatoes—at least for now

July 9, 2012
Courtesy of Cell Press
and World Science staff

Cut­ting back sharply on food has been found to ex­tend the life­span of eve­ry an­i­mal spe­cies tested to date. Re­search sug­gests the ef­fect works in hu­mans as well.

But a new study in­di­cates that play­ing at hun­ger games alone won’t turn on any foun­tain of youth. In­creased phys­i­cal ac­ti­vity must be part of the equa­t­ion, at least judg­ing by work with fruit flies, sci­en­tists say. 

On the brighter side for couch pota­toes, the same re­search al­so hints at a hor­mone that may point to ways to one day achieve long­er life­spans with­out the seem­ingly ever-harsher self-dis­ci­pline re­quire­ments.

One rea­son the phys­i­cal ac­ti­vity re­quire­ment might not have been no­ticed be­fore, sci­en­tists said, is that flies au­to­mat­ic­ally tend to be­come more ac­tive when their food is re­strict­ed. But block this ex­tra ac­ti­vity, and the life­span ben­e­fits from the “calo­rie re­stric­tion” evap­o­rate.

The find­ings are pub­lished in the July 3 is­sue of the re­search jour­nal Cell Me­tab­o­lism.

Pankaj Ka­pahi of the Buck In­sti­tute for Re­search on Ag­ing in No­va­to, Calif., with col­leagues at Har­vard Med­i­cal School and oth­er in­sti­tu­tions, found that in flies, di­e­tary re­stric­tion causes both en­hanced fat me­tab­o­lism in the mus­cle and in­creased phys­i­cal ac­ti­vity.

Past an­i­mal stud­ies have found that cut­ting back on calo­ries by some 40 per­cent raises life­spans by as much as 40 per­cent. Sci­en­tists cau­tion that di­ets must re­main bal­anced un­der this sce­nar­i­o, and that tip­ping over the line in­to starva­t­ion won’t help an­ybody.

Ka­pahi and col­leagues cut yeast, the ma­jor source of pro­tein for fruit flies, from the in­sects’ di­ets, then con­ducted var­i­ous bio­chem­i­cal tests. They found that the in­creased ac­ti­vity was due to a shift in me­tab­o­lism in which flies in­creased both fat forma­t­ion and break­down. Block­ing fat forma­t­ion in mus­cle negated the life­span-ex­tending ef­fects, as did re­strict­ing move­ment, they said.

“Ours is the first study to sug­gest that for di­e­tary re­stric­tion to en­hance life­span, you need in­creased fat turno­ver in the mus­cle and an as­so­ci­at­ed in­crease in phys­i­cal ac­ti­vity. Fur­ther­more, it al­so sug­gests that di­e­tary changes may en­hance mo­tiva­t­ion to ex­er­cise and help de­rive max­i­mal ben­e­fits of ex­er­cise,” said Ka­pahi.

The re­search­ers al­so found that overproduction of a hor­mone called AKH—the fly equiv­a­lent of the hor­mone glu­ca­gon in hu­mans—en­hanced flies’ fat me­tab­o­lism, boosted their ac­ti­vity, and ex­tended their life­span even though their di­et was un­re­strict­ed.

“Our da­ta sug­gest that di­e­tary re­stric­tion may in­duce changes in mus­cle si­m­i­lar to those ob­served un­der en­dur­ance ex­er­cise and that mo­le­cules like AKH that en­hance fat break­down could serve as po­ten­tial di­e­tary re­stric­tion mimet­ics,” or drugs that mim­ic the ef­fect of slash­ing calo­ries, the re­search­ers wrote. “This in­di­cates that med­i­cal in­ter­ven­tions that en­hance fat me­tab­o­lism in mus­cle might have the po­ten­tial to pro­long life.”

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Cutting back sharply on food has been found to extend the lifespan of every animal species tested to date. Research suggests the effect works in humans as well. But a new study indicates that playing at hunger games alone won’t turn on any fountain of youth. Increased physical activity must be part of the equation, at least judging by fruit flies, scientists say. On the brighter side for couch potatoes, the same research also hinted at a hormone that may point to ways to one day achieve longer lifespans without the seemingly ever-tougher self-discipline requirements. One reason the physical activity requirement might not have been noticed before, scientists said, is that flies automatically tend to become more active when their food is restricted. But block this extra activity, and the lifespan benefits from the “calorie restriction” evaporate. The findings are published in the July 3 issue of the research journal Cell Metabolism. Pankaj Kapahi of the Buck Institute for Research on Aging in Novato, Calif., with colleagues at Harvard Medical School and other institutions, found that in flies, dietary restriction causes both enhanced fat metabolism in the muscle and increased physical activity. Past animal studies have found that cutting back on calories by some 40 percent raises lifespans by about the same amount. Scientists caution that diets must remain balanced under this scenario, and that tipping over the line into starvation won’t help anybody. Kapahi and colleagues cut yeast, the major source of protein for fruit flies, from the insects’ diets, then conducted various biochemical tests. They found that the increased activity was due to a shift in metabolism so that flies increased both fat formation and breakdown. Blocking fat formation in muscle negated the lifespan-extending effects, as did restricting movement, they said. “Ours is the first study to suggest that for dietary restriction to enhance lifespan, you need increased fat turnover in the muscle and an associated increase in physical activity. Furthermore, it also suggests that dietary changes may enhance motivation to exercise and help derive maximal benefits of exercise,” said Kapahi. The researchers also found that overproduction of a hormone called AKH—the fly equivalent of the hormone glucagon in humans—enhanced flies’ fat metabolism, boosted their activity, and extended their lifespan even though their diet was unrestricted. “Our data suggest that dietary restriction may induce changes in muscle similar to those observed under endurance exercise and that molecules like AKH that enhance fat breakdown could serve as potential dietary restriction mimetics,” or drugs that mimic the effect of slashing calories, the researchers wrote. “This indicates that medical interventions that enhance fat metabolism in muscle might have the potential to prolong life.