Sweet tooth. Greedy guts. Hungry eyes. Lazy bones. We blame every part of the body for making us fat, but there's one vital organ we sometimes forget to mention: the brain.
Maybe we don't say it because it's so obvious. The brain controls all complex behaviors, and that includes planning what to get from a fast-food restaurant, or deciding when to put down your spoon and step away from the ice-cream tub.
What's interesting is that if you're obese, your brain looks different even before you start making those decisions. Not in terms of structure or volume - Homer Simpson's brain size is clearly nothing to do with his ample weight - but in terms of responses to stimuli.
In one study, researchers showed lean and obese females pictures of food and scanned their brains. When the obese women were shown high calorie foods, they showed greater activity in the orbitofrontal cortex and striatum - areas associated with anticipating reward.
(And if simple pictures can trigger excitement just think about what the real world can do, with its onslaught of food smells and snack carts and fast-food ads.)
Of course the brain's involvement doesn't end there.
In another study people were given food rather than just looking at pictures of it. This time obese participants showed less activation in the striatum. This suggests that - although certain foods inspire high hopes for reward - when consumed they actually produce less of a thrill than expected. This creates the urge to eat greater amounts, and seek out tasty calorie-packed morsels which provide a bigger hit.
In truth, it's a very new area of science - you have to be pretty brainy to work out what on earth's going on up there.
But what you definitely can't tell from these particular studies is whether obese adults are really born with fat brains that compel them to overeat. It's equally likely that heavier people learn to eat in certain ways and this is what makes them gain weight and shows up in the fMRI scan. The state of being fat could even actively change the way your mind works.
What can you do if you happen to have a fat brain?
The answer is probably to avoid the triggers that set your food neurons firing. Successful dieters show greater activity in brain areas involved in inhibiting responses - so you can always try to reprogram yourself. And if all else fails there's a sure way to lose three pounds, although I wouldn't recommend it.
Total lobotomy, anyone?
