Scientific American

23 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 HOUSE_OVERSIGHT_029954