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September 21, 2012

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Eating far less doesn’t extend monkey lives, study finds

Aug. 30, 2012
Courtesy of Nature
and World Science staff

Eat­ing much less than nor­mal does­n’t seem to ex­tend the life­span of rhe­sus mon­keys, , ac­cord­ing to a new stu­dy, though such a diet has been found to do so for some oth­er ani­mal spe­cies.

The 23-year study was de­signed to shed light on whe­ther re­strict­ing cal­o­rie in­take by 10–40 per­cent would pro­long life in animals closely related to humans, as it has done for ro­dents and sev­er­al oth­er spe­cies.

The new re­sults do sug­gest this “cal­o­rie re­stric­tion” may have some health ben­e­fits for mon­keys, re­search­ers said. The strict reg­i­men, which be­gan when the crea­tures were 16 to 23 years old, led to im­proved met­a­bol­ic health and func­tion, ac­cord­ing to Raf­a­el de Cabo and col­leagues of the Na­t­ional In­sti­tute on Ag­ing, who re­ported the find­ings in the Aug. 30 is­sue of the re­search jour­nal Na­ture.

Mean­while, they wrote, “our find­ings con­trast with an on­go­ing study at the Wis­con­sin Na­t­ional Pri­mate Re­search Cen­ter,” as well as “a pre­lim­i­nar­y re­port with a small num­ber of [cal­o­rie-re­strict­ed] mon­keys,” they wrote. The Wis­con­sin study re­ported im­proved sur­viv­al as­so­ci­at­ed with 30 per­cent cal­o­rie re­stric­tion in­i­ti­at­ed in adult rhe­sus mon­keys aged 7 to 14 years.

De Cabo’s study aimed to ver­i­fy wheth­er the life-prolonging ef­fects of cal­o­rie re­stric­tion ob­served in low­er or­gan­isms al­so oc­cur in mon­keys and thus, might plau­sibly trans­late to hu­man age­ing. Young mon­keys on a ca­lor­ic re­stric­tion di­et showed a trend to­wards a de­lay in age-as­so­ci­at­ed dis­ease on­set, but again, no in­crease in life­span. 

Con­sid­er­ing the dif­fer­ences be­tween their find­ings and the re­sult of si­m­i­lar stud­ies, the au­thors pro­posed that the ef­fects of ca­lor­ic re­stric­tion in long-lived an­i­mals are not straight­for­ward. They sug­gest that a va­ri­e­ty of en­vi­ron­men­tal, nu­tri­tional and ge­net­ic fac­tors may al­so af­fect how cal­o­rie re­stric­tion af­fects longe­vity.

De Cabo and col­leagues said rhe­sus mon­keys typ­ic­ally live for about 27 years in cap­ti­vity, al­though their mon­keys lived some­what long­er, in both groups that they stu­died and com­pared—one group with cal­o­rie-re­strict­ed, and one with nor­mal di­ets.

Ste­ven N. Aus­tad, a bi­ol­o­gist at the Uni­vers­ity of Tex­as Health Sci­ence Cen­ter, said a dif­fer­ence be­tween the newly pub­lished re­sults and those from the Wis­con­sin study is that the non-cal­o­rie re­strict­ed mon­keys in the Wis­con­sin study were al­lowed to eat as much as they wanted. That could have harmed their health fur­ther in com­par­i­son to the di­eting mon­keys.

The find­ings over­all raise the ques­tion wheth­er for hu­mans and their close rel­a­tives, cal­o­rie re­stric­tion is “any­thing more than the elimina­t­ion of ex­cess fat,” Aus­tad wrote in a com­men­tary in the re­search jour­nal ac­com­pa­nying the new find­ings. If that is the case, then “some­what dis­ap­point­ingly — no spec­tac­u­lar in­crease in health or longe­vity should be ex­pect­ed” from cal­o­rie re­stric­tion, or from pills de­signed to mim­ic its phys­i­o­logi ef­fects.

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Eating much less than normal doesn’t seem to extend the lifespan of rhesus monkeys, though it has been found to do so for a variety of other species, according to a new study. The 23-year study contrasts with others that have shown that restricting calorie intake by 10–40% compared to a nutritious diet can extend lifespan in rodents and several other species. However, the new results do suggest this “calorie restriction” may have some health benefits, researchers said. The strict regimen, which began when the monkeys were 16 to 23 years old, led to improved metabolic health and function, according to Rafael de Cabo and colleagues of the National Institute on Aging, who reported the findings in the Aug. 30 issue of the research journal Nature. Meanwhile, they wrote, “our findings contrast with an ongoing study at the Wisconsin National Primate Research Center,” as well as “a preliminary report with a small number of [calorie-restricted] monkeys,” they wrote. The Wisconsin study reported improved survival associated with 30% calorie restriction initiated in adult rhesus monkeys aged 7 to 14 years. The National Institute on Aging study aimed to verify whether the life-prolonging effects of calorie restriction observed in lower organisms also occur in monkeys and thus, might plausibly translate to human ageing. Young monkeys on a caloric restriction diet showed a trend towards a delay in age-associated disease onset, but again, no increase in lifespan. Considering the differences between their findings and the result of similar studies, the authors proposed that the effects of caloric restriction in long-lived animals are not straightforward. They suggest that a variety of environmental, nutritional and genetic factors may also affect how calorie restriction affects longevity. De Cabo and colleagues said rhesus monkeys typically live for about 27 years in captivity, although theirs lived somewhat longer, both with calorie-restricted and normal diets. Steven N. Austad, a biologist at the University of Texas Health Science Center, said a difference between the newly published results and those from the Wisconsin study is that the non-calorie restricted monkeys in the Wisconsin study were allowed to eat as much as they wanted. That could have harmed their health further in comparison to the dieting monkeys. The findings overall raise the question whether for humans and their close relatives, calorie restriction is “anything more than the elimination of excess fat,” Austad wrote in a commentary in the research journal accompanying the new findings. If that is the case, then “somewhat disappointingly — no spectacular increase in health or longevity should be expected” from calorie restriction, or from pills designed to mimic its physiological effects, he added.