"Long before it's in the papers"
October 14, 2007

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Genes for overeating?

Oct. 14, 2007
Courtesy American Psychological Association
and World Science staff

Re­search­ers say they’ve found a ge­net­ic ex­plana­t­ion for why some peo­ple crave food more than oth­ers do. Peo­ple who are driven to eat a lot may need more food than others do to get the same feel­ing of re­ward, the scientists claim.

The research, they said, found that peo­ple with ge­net­ic­ally low lev­els of a brain chem­i­cal called do­pa­mine find food to be more “re­in­forc­ing” than oth­er peo­ple do. Do­pa­mine, a neu­ro­trans­mitter—or sub­stance that transmits nerve im­puls­es—is as­so­ci­at­ed with pleas­ure. Having less of it may prompt people to work hard­er to sti­mu­late re­ward­ing feelings, such as by eat­ing, ac­cord­ing to the sci­ent­ists.

The find­ings, by in­ves­ti­ga­tors at the Un­ivers­ity at Buf­fa­lo, N.Y., ap­pear in the Oc­to­ber is­sue of re­search jour­nal Be­hav­ior­al Neu­ro­sci­ence. The lead re­searcher, Leon­ard Ep­stein, is al­so a con­sult­ant to comestibles gi­ant Kraft Foods Inc. The team stud­ied a gene var­i­ant car­ried by about half the popula­t­ion, called the Taq1 A1 al­lele. It leads to low­er do­pa­mine lev­els by pro­duc­ing lower amounts of a type of re­cep­tor, or mo­lec­u­lar ga­te­way, that al­lows do­pa­mine trans­mis­sion.

The re­search­ers stud­ied 29 obese and 45 non-o­bese adults, tak­ing DNA sam­ples and hav­ing them fill out ques­tion­naires. They al­so asked the par­ti­ci­pants to ra­te var­i­ous snack food­s—but this as­sign­ment was a sham. Ac­tu­al­ly, the in­ves­ti­ga­tors were ex­am­in­ing how much par­ti­ci­pants ate when food was freely avail­a­ble.

Par­ti­ci­pants were al­so asked to per­form a sec­ond task in which they could swiv­el be­tween two com­put­ers. Press­ing spec­i­fied keys on one earned points to eat their fa­vor­ite food; press­ing keys on the oth­er earned points to read a news­pa­per. The idea was for re­search­ers to find out how hard the par­ti­ci­pants worked to ob­tain food, ver­sus some­thing else.

Both obes­ity and low­er-dopamine gene var­i­ants pre­dicted a sig­nif­i­cantly stronger re­sponse to food’s re­in­forc­ing pow­er, and more cal­o­rie con­sump­tion, the re­search­ers found. Ep­stein differentia­tes re­in­forc­ing val­ue, de­fined by how hard some­one will work for food, from the “feel good” pleas­ure peo­ple get from food. “They of­ten go to­geth­er, but are not the same thing,” he said. 

“Food is a pow­erful re­in­forc­er that can be as re­in­forc­ing as drugs of abuse,” the scient­ists wrote. They added that the find­ings may help ex­perts iden­ti­fy peo­ple at risk for obes­ity and de­vel­op treat­ments tai­lored to them. “Be­hav­ior and bi­ol­o­gy in­ter­act and in­flu­ence each oth­er,” said Ep­stein. “The gen­o­type [ge­net­ic make­up] does not cause obes­ity; it is one of many fac­tors that may con­trib­ute to it,” in­clud­ing learn­ed habits.

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Researchers say they’ve found a genetic explanation for why some people crave food more than others do. People with genetically low levels of a brain chemical called dopamine find food to be more “reinforcing” than other people do, the scientists found. This may help explain why some individuals overeat, they added. Dopamine, a neurotransmitter—or substance that tramits nerve impulses—is associated with pleasure. People with lower dopamine may have to eat more to feel as good as others, the researchers said. The findings, by investigators at the University at Buffalo, N.Y., appear in the October issue of research journal Behavioral Neuroscience. The lead researcher, Leonard Epstein, is also a consultant to comestibles giant Kraft Foods Inc. The team studied a gene variant carried by about half the population, and linked to lower dopamine levels, called the Taq1 A1 allele. It creates this effect by producing low amounts of a type of receptor, or molecular gateway, that allows dopamine transmission. The researchers studied 29 obese 45 non-obese adults, taking DNA samples and having them fill out questionnaires. They also asked the participants to rate various snack foods—but this assignment was a sham. Actually, the investigators were examining how much participants ate when food was freely available. Participants were also asked to perform a second task in which they could swivel between two computers. Pressing specified keys on one earned points to eat their favorite food; pressing keys on the other earned points to read a newspaper. The idea was for researchers to find out how hard the participants worked to obtain food, versus something else. Both obesity and lower-dopamine gene variants predicted a significantly stronger response to food’s reinforcing power, and more calorie consumption, the researchers found. Epstein differentiates reinforcing value, defined by how hard someone will work for food, from the “feel good” pleasure people get from food, saying, “They often go together, but are not the same thing.” “Food is a powerful reinforcer that can be as reinforcing as drugs of abuse,” they wrote, adding that the findings may help experts to identify people at greater risk for obesity and to develop treatments tailored to them. “Behavior and biology interact and influence each other,” said Epstein. “The genotype [genetic makeup] does not cause obesity; it is one of many factors that may contribute to it,” including learned habits.