Obese people become as addicted to food in the same way that junkies do to their drugs, according to a new study, which may explain their constant cravings.
Evidence that the obese are food 鈥渏unkies鈥� comes from brain scans of seven obese people who were fitted with electrical devices designed to fool them into thinking they are full by making their stomachs stretch.
The implanted devices, known as 鈥済astric stimulators鈥�, provide low-level electrical stimulation of the vagus nerve, which runs from the stomach to the brain. When the device is switched on, the vagus nerve stimulation causes the stomach to expand and produce peptides that send a message of 鈥渇ullness鈥� to the brain.
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鈥淲e know that if we eat, our stomach sends a signal to the brain via the vagus nerve. The ingredients of food touch the wall of the stomach and the signal goes through to the brain to say 聭eat more鈥� or 聭eat less鈥�,鈥� says Gene-Jack Wang at Brookhaven National Laboratory in Upton, New York, US.
鈥淏ut we wanted to know which area of the brain the signal goes to,鈥� Wang explains. So he and his colleagues gave participants radioactive sugar so that they could use a scanner to see which parts of the brain were active, by tracing where the sugar was metabolised in the brain.
Cocaine craving
鈥淲e know the 鈥榟unger centre鈥� of the brain is the hypothalamus, but what we observed was astonishing,鈥� Wang says.
The team found that when the gastric stimulators were turned on, the seahorse-shaped parts of the brain, called the hippocampus were activated.
鈥淸The hippocampus] is the area related to memory and the reward system. The areas lighting up were areas activated in drug addicts. It鈥檚 very similar to what triggers the craving for cocaine,鈥� he says. So despite receiving the 鈥渇ull鈥� signal, they still have the craving for more.
Magic bullet
The findings help explain why it is so difficult to retreat from obesity. 鈥淲e now know the decision to eat involves emotion and the cognitive system too. This study shows how the brain tries to manipulate the body, not the other way around,鈥� he explains.
It is difficult for an obese person to diet because they can鈥檛 suppress the craving to get their next 鈥渇ix鈥� even when physiologically, they鈥檙e getting a 鈥渇ull鈥� signal from the stomach, Wang says. Such people may continue to feel hungry, even when they have eaten an amount that would satisfy the hunger of a healthy person.
It shows that we cannot find a magic bullet for obesity, and that we must consider other areas of the brain, Wang says.
Steven Heymsfield, at Merck in Rahway, New Jersey, US, says: 鈥淚t鈥檚 entirely possible that hunger addiction overrides other signals. The addiction thing is a very compelling idea when applied to obesity.鈥�
Journal reference: Proceedings of the National Academy of Science (DOI: 10.1073/pnas.0601977103)
