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He fidgeted the weight away
The overfeeding study
The classic study from the mid-1990s ran in a metabolic ward, about as tightly controlled as research gets. Participants were overfed by roughly 1,000 calories a day for around six weeks. On average, people gained weight and fat mass, though some gained more than expected. The man who gained the least never decided to move more. His physical activity simply went up on its own.
What NEAT is
That kind of movement is called NEAT, short for non-exercise activity thermogenesis: fidgeting, tapping a foot, waving hands while talking. It cannot be switched on by deciding to do it, because purposeful movement is exercise, and consciously tapping a foot competes with whatever else the brain is doing. One natural bodybuilder, Jim Cordova, stayed very lean and would start sweating after climbing a flight of stairs or sitting down to eat.
Why NEAT matters
Of resting metabolic rate, the thermic effect of food, and NEAT, NEAT appears to be the most modifiable. In people who stay lean when they overeat, what looks like a high metabolism or a lot of exercise seems to be NEAT.
How much do people differ in NEAT?
In a 1999 study in Science, James Levine and colleagues overfed 16 volunteers by 1,000 calories a day for eight weeks. Fat gain ranged from about 0.4 kilograms to more than 4 kilograms. Changes in NEAT ranged from a drop of nearly 100 calories a day to a rise of nearly 700 calories a day, and they predicted who stored the least fat.
What in the brain drives spontaneous movement?
Orexin neurons in the hypothalamus are one candidate. Studies in rats by Catherine Kotz and colleagues found that injecting orexin A into certain brain regions increased spontaneous physical activity and raised NEAT. Orexin also helps regulate wakefulness, and its loss causes narcolepsy. The same system links alertness, appetite, and motion.
Do lean people sit differently from others?
In a 2005 Science study, James Levine and colleagues fitted people with sensors that recorded posture and movement every half second. People with obesity sat for an average of about two hours more per day than lean people. The lean group spent more time standing and walking. The difference worked out to roughly 350 calories per day.
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