Why do some obese peo­ple have‘health­ier’fat tis­sue than oth­ers?

Sunday Trust - - NEWS HEALTH - Source: www.sci­encedaily.com

One lit­tle un­der­stood para­dox in the study of obe­sity is that over­weight peo­ple who break down fat at a high rate are less healthy than peers who store their fat more ef­fec­tively. That’s be­cause when fat breaks down, many of the fatty acids re­leased from the adi­pose tis­sue (body fat) can take up res­i­dence else­where. Too much of this and fat can ac­cu­mu­late to harm­ful lev­els in other tis­sues and or­gans, which can fuel in­sulin re­sis­tance, a hall­mark of type 2 di­a­betes and heart dis­ease.

A pair of stud­ies from the Univer­sity of Michi­gan iden­ti­fies key char­ac­ter­is­tics in fat tis­sue that may al­low some obese adults to store their body fat more healthily and sug­gests that aer­o­bic ex­er­cise may lead to health­ier fat stor­age, said prin­ci­pal in­ves­ti­ga­tor Jef­frey Horowitz, pro­fes­sor of move­ment sci­ence at the U-M School of Ki­ne­si­ol­ogy.

Most obese peo­ple de­velop in­sulin re­sis­tance, which can lead to type 2 di­a­betes and other chronic dis­eases. How­ever, Horowitz and his team found that about onethird of the 30 obese adults in their study did not de­velop in­sulin re­sis­tance.

This begged the ques­tion: What pro­tected these peo­ple?

Adi­pose tis­sue sam­ples re­vealed that the health­ier group broke down fat at slower rates, and they had fewer pro­teins in­volved in fat break­down and more in­volved in fat­stor­ing. They also had fewer fi­brotic cells in the adi­pose tis­sue, which al­lows tis­sue to be more flex­i­ble, and lower ac­ti­va­tion of cer­tain in­flam­ma­tory path­ways.

“It sounds coun­ter­in­tu­itive, but if we can bet­ter un­der­stand how to store fat more ef­fec­tively, and why some peo­ple are bet­ter at this than oth­ers, per­haps we can de­sign ther­a­pies and pre­ven­tions that will im­prove some of these obe­sity-re­lated meta­bolic con­di­tions,” Horowitz said.

In the sec­ond study, re­searchers col­lected fat tis­sue af­ter a ses­sion of aer­o­bic ex­er­cise from two groups of over­weight peo­ple: one group ex­er­cised reg­u­larly, and the other group didn’t. For both groups, just one ses­sion of ex­er­cise trig­gered sig­nals that led to the growth of new blood ves­sels in fat tis­sue.

Re­searchers also found in­di­ca­tions that the reg­u­lar ex­er­cis­ers had more blood ves­sels in their fat tis­sue than non-ex­er­cis­ers.

That’s im­por­tant be­cause the health of most tis­sues hinges, in large part, on blood flow and nu­tri­ents, Horowitz said. When we gain weight, our fat cells ex­pand, but if blood flow to fat tis­sue doesn’t in­crease in par­al­lel, it could be­come un­healthy or even necrotic.

Horowitz stressed that the two stud­ies are rel­e­vant mainly to obese peo­ple at risk for meta­bolic dis­ease. How­ever, there’s a take­away here for ev­ery­one.

“We be­lieve that the reg­u­lar ex­er­cise we do now may cre­ate a health­ier fat-storing en­vi­ron­ment for those times when we do overeat and gain weight,” Horowitz said.

Taken to­gether, the stud­ies also sup­port the no­tion that clin­i­cians must re­de­fine their view of fat, said Horowitz.

“Adi­pose tis­sue is scorned be­cause most peo­ple see it as caus­ing dis­ease and obe­sity, but in gen­eral adi­pose tis­sue doesn’t cause peo­ple to gain weight and be­come obese, it’s just where we store our ex­tra en­ergy when we do overeat,” Horowitz said. “Our stud­ies aren’t sug­gest­ing it is healthy to be obese or to overeat -- but when we do overeat, it is im­por­tant to have a safe place to store that ex­tra en­ergy.

“When peo­ple gain the same amount of body fat, those with adap­ta­tions to their fat tis­sue that can more health­fully ac­com­mo­date the ex­tra fat may be pro­tected from de­vel­op­ing in­sulin re­sis­tance and obe­sity-re­lated dis­eases. We have iden­ti­fied some of these adap­ta­tions.”

Doug Van Pelt, a for­mer doc­toral stu­dent in the Horowitz lab, con­ducted this work as part of his dis­ser­ta­tion. Van Pelt is cur­rently a post­doc­toral fel­low at the Univer­sity of Ken­tucky’s Col­lege of Health Sci­ences.

The two stud­ies are: “Fac­tors reg­u­lat­ing sub­cu­ta­neous adi­pose tis­sue stor­age, fi­bro­sis, and in­flam­ma­tion may un­der­lie low fatty acid mo­bi­liza­tion in in­sulin-sen­si­tive obese adults” and “Aer­o­bic ex­er­cise el­e­vates mark­ers of an­gio­gen­e­sis and macrophage IL6 gene ex­pres­sion in the sub­cu­ta­neous adi­pose tis­sue of over­weight to obese adults.”

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