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Drastic diet may extend human life, study finds

Nov. 15, 2007
Special to World Science  

Eating little may help people live longer, a study has found, of­fer­ing sup­port for an idea that has tan­ta­lized sci­en­tists for dec­ades.

Re­search­ers have long known that cut­ting an­i­mals’ food supply to near-starva­t­ion lev­els gives them—for rea­sons still un­clear—long­er lives and health­i­er old age. Stud­ies have found that in hu­mans, too, sharply re­duced eat­ing is as­so­ci­at­ed with health­i­er ag­ing, as long as nu­tri­tion­al ba­lance is main­tained. 

Less food on the plate could mean a longer life, researchers say. (Courtesy pdphoto.org) 


But wheth­er this prac­tice could ac­tu­ally length­en our lives has re­mained un­cer­tain. 

Some sci­en­tists have ar­gued that it’s doubt­ful, be­cause hu­mans al­ready live un­usu­ally long. Only one small past study in hu­mans of­fered weak ev­i­dence that peo­ple eat­ing less lived long­er, ac­cord­ing to its au­thors, who were al­so in­volved in the new re­search.

The new study is the first to probe the claim by com­par­ing hu­man popula­t­ions, wrote the Amer­i­can and Jap­a­nese sci­en­tists in a re­port on their find­ings.

More­o­ver, they added, it’s “the first study that has shown ex­tend­ed av­er­age and max­i­mum life span in a hu­man popula­t­ion that is po­ten­tially due to” re­duced eat­ing. The prac­tice is known as ca­lor­ic re­stric­tion.

The re­search­ers stud­ied res­i­dents of the Jap­a­nese is­land of Ok­i­nawa, known through much of the last cent­ury both for ex­cep­tion­ally long-lived in­hab­i­tants and for very spare, though bal­anced di­et­s. The in­vest­i­gat­ors said they found ev­i­dence that the two things are at least par­tially re­lat­ed.

Al­though that con­clu­sion might seem ob­vi­ous to some—given the past re­search—the sci­en­tists wrote that to reach it, they had to ac­count for some fac­tors that had ham­pered sys­tem­at­ic anal­y­sis. For one, Oki­na­wan di­ets have changed, be­com­ing richer since about the end of the 1960s. Al­so, it was­n’t clear how to best as­sess his­tor­i­cal di­e­tary in­take and com­pare it to that of oth­er popula­t­ions.

The find­ings, by Brad­ley Will­cox of the Pa­cif­ic Health Re­search In­sti­tute and John A. Burns School of Med­i­cine in Hon­o­lu­lu and col­leagues, ap­pear in the No­vem­ber is­sue of the re­search jour­nal An­nals of the New York Acad­e­my of Sci­ences.

An­i­mal tests have found that the ex­treme di­et­ing of ca­lor­ic re­stric­tion en­tails cut­ting some 40 per­cent of calo­ries to get the strongest life-extending ef­fects. An­i­mals placed on such reg­i­mens live up to 40 per­cent long­er than nor­mal, as long as the di­et re­mains nu­tri­tionally bal­anced. (Some sci­en­tists pro­pose—a­gain based mostly on an­i­mal test­s—that tak­ing a sub­stance called res­ver­a­trol may rep­li­ca­te ca­lor­ic re­stric­tion’s ben­e­fits, with­out the un­pleas­ant­ness.)

Will­cox and col­leagues found that at least from the mid-20th cen­tu­ry through the 1960s, the Oki­na­wan di­et was about 11 per­cent short of what would nor­mally be rec­om­mended to main­tain body weight. As of 1995, the av­er­age Oki­na­wan lived about five years long­er than the av­er­age Amer­i­can, and about 18 months more than the av­er­age Jap­a­nese. 

The is­landers’ spar­tan di­ets may have been a leg­a­cy of “pe­ri­odic crop fail­ures that oc­curred in Oki­na­wa in the early 20th cen­tu­ry and a long his­to­ry of mar­gin­al food sup­ply,” the re­search­ers wrote.

The study had some weak­nesses, they added; for in­stance, it could­n’t rule out that Oki­na­wans lived long­er be­cause of the types of nu­tri­ents they ate, rath­er than the amount. None­the­less, the “ten­ta­tive” find­ings fit with a broad ar­ray of an­i­mal stud­ies, and point to a need for still more re­search, Will­cox and col­leagues wrote.


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Eating very little may prolong the normal human lifespan, according to a new study that offers support for an idea that has tantalized scientists for decades. Researchers have long known that cutting animals’ food supply to a near-starvation level gives them—for reasons still unclear—a longer life and healthier old age. Studies have found that in humans, too, sharply reduced eating is associated with healthier aging. But whether this practice could actually lengthen our lives has remained uncertain. Some scientists have argued that it’s doubtful, because humans already live unusually long. Only one small past study in humans offered weak evidence that people eating less lived longer, according to its authors, who were also involved in the new research. The new study is the first to investigate the claim by comparing populations, wrote the American and Japanese scientists in a report on their findings. Moreover, they added, it’s “the first study that has shown extended average and maximum life span in a human population that is potentially due to” reduced eating. The practice is also known as caloric restriction. The researchers studied residents of the Japanese island of Okinawa—traditionally known both for exceptionally long-lived inhabitants and for very spare, though balanced diets—and found evidence that the two things are at least partially related. Although that idea might seem obvious to some—given the past research—the researchers noted that to reach the conclusion, they had to account for some factors that had hampered systematic analysis of the issue. For one, Okinawan diets have changed, becoming richer since about the end of the 1960s. Also, it wasn’t clear how to best assess historical dietary intake and compare it to that of other populations. The findings, by Bradley Willcox of the Pacific Health Research Institute and John A. Burns School of Medicine in Honolulu and colleagues, appear in the November issue of the research journal Annals of the New York Academy of Sciences. Animal tests have found that the extreme dieting of caloric restriction entails cutting some 40 percent of calories to get the strongest life-extending effects. Animals placed on such regimens live up to 40 percent longer than normal, as long as the diet remains nutritionally balanced. (Some scientists have proposed—again based mostly on animal tests—that taking a substance called resveratrol may replicate caloric restriction’s benefits without the unpleasantness.) Willcox and colleagues found that at least from the mid-20th century through the 1960s, the Okinawan diet was about 11 percent short of what would normally be recommended to maintain body weight. As of 1995, the average Okinawan lived about five years longer than the average American, and about 18 months more than the average Japanese. The islanders’ spartan diets may have been a legacy of “periodic crop failures that occurred in Okinawa in the early 20th century and a long history of marginal food supply,” the researchers wrote. Today’s Okinawans eat considerably more than they did a few decades ago, they noted. The study had some weaknesses, they added; for instance, it couldn’t rule out that Okinawans lived longer because of the types of nutrients they ate, rather than the amount. Nonetheless, the “tentative” findings fit with a broad array of animal studies, and point to a need for still more research, Willcox and colleagues wrote.