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Article 6.
Scientific American
How the Brain Understands Food and
Appetite [Excerpt]
David Linden

Editor's Note: The following is an excerpt from a chapter in the book
Compass of Pleasure: How Our Brains Make Fatty Foods, Orgasm,
Exercise, Marijuana, Generosity, Vodka, Learning, and Gambling
Feel So Good by David Linden. Copyright (c) 2001 by David Linden.

July 2, 2011 -- In studies where the food intake and energy
expenditure of subjects are carefully monitored over a period of
weeks to months (which tends to average out day-to-day fluctuations)
a remarkable balance between calories consumed and calories burned
was observed. When various mammals, from mice to monkeys, are
either overfed or starved for a few weeks, their weight soon returns to
normal levels when free access to food is resumed. Crucially, our
mammalian bodies seem to be able to regulate feeding based on the
amount of energy available in the food we consume, not just on the
volume of that food. One example of many: When groups of rats
were fed nutrient solutions of varying concentrations, they adjusted
the volume consumed to achieve a constant inflow of calories. It's a
lot like the thermostat in your house: When its thermometer registers
a drop in temperature, it sends a signal to the heater to warm the
house until the desired set point is reached.
These observations suggest that the brain must receive signals from
the body that indicate its weight and that the brain makes use of the
signals to modulate appetite and energy expenditure in order to

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