Modern rhythm of life, bad ecology, wrong eating and stresses cause overweight. Calories are essential for stoking the body's furnace; they become unwanted only when an excess of them is not burned up and instead turns to fat. North Americans are in general overweight, and those excess calories in the form of stored fat total about 8,350,000,000 pounds for all the adults in the United States alone.
Recent calculations show that if these adults were to eliminate the excessive calories they have stored as fat, the slimming-down process would produce, in terms of fossil-fuel energy, 160 trillion - enough to run about 250000 automobiles for 65000 miles a year. And if all of these same adults were to maintain their ideal weights, they would consume 27 trillion fewer - each year, more than enough to supply electricity for a year to the residents of Boston, Chicago, Washington, and San Francisco combined. For many North Americans, a dinner consisting of shrimp cocktail, T-bone steak, baked potato with sour cream, tossed salad with French dressing, hot rolls and butter, and apple pie & la mode, accompanied by wine and coffee, represents a special treat. To the digestive system, however, it is intrinsically just a collection of nutrients, forty-four kinds altogether, that go into the process of growth and the replacement of dead cells. Virtually all of the nutritional elements in this meal can be found on the shelves of a supermarket and a pharmacy - such as six and a half ounces of liquid protein, half an ounce of salt, about six ounces of sugar, somewhat less than three ounces of lard, thirty ounces of mineral water, and so on. These could be purchased at a considerably lower cost than would go into purchasing the foods on the menu.
Few humans in modern societies go without food long enough to know what real hunger is like; and research indicates that humans cannot gauge accurately the difference between slight and moderate hunger, so as then to make the appropriate adjustments in the amount of food they consume. Experimental animals have been shown to respond promptly and accurately to the need for calories, but humans possess no innate mechanism for distinguishing between meals with high calories and those with low. Instead, they rely on cultural knowledge and on trial and error. In one recent experiment, humans who were given meals in which the caloric content was disguised in gruel could not distinguish between one providing 3500 calories and another providing only 200.
People eat a lot or a little for reasons that obviously do not have much to do with their awareness of the food's energy value, but those reasons are subject to at least four internal controls that regulate the body's intake of calories and thus keep the weight of most adults nearly constant.