Despite concerns about the consequences of obesity, correcting calorie imbalances presents challenges few countries are prepared to meet.
When our then-editor at the University of California Press, Stan Holwitz, suggested that we write a book about calories, we said yes right away. Consumption of too few or too many calories is an important -- arguably the most important -- cause of public health nutrition problems in the world today. Problems with calories affect billions of people in rich as well as poor countries. Consuming too few calories leads to malnutrition (undernutrition), which makes people more susceptible to infectious disease. The result is stunted growth, misery, and premature death in children and adults. More than a billion people, most of them in poor countries, go hungry for lack of food.
At the same time, just as many people in the world are consuming more calories than they need and becoming overweight and obese. The numbers of obese people are rising rapidly, even in the poorest countries. Obesity is now so common that the populations of some poor countries contain nearly equal numbers of people who are undernourished and overnourished. Obesity raises risks for any number of chronic diseases, most notably type 2 diabetes.
The health consequences of too many or too few calories threaten to overwhelm the resources of individuals, families, and health care systems. Countries can ill afford the costs of health care for obesity-related chronic or infectious diseases or to have large segments of their populations unable to work or function adequately. Some analysts even suggest that the health burdens of obesity alone may shorten overall life expectancy within the next few years .
Despite widespread concerns about the health and economic consequences of obesity on the one hand and undernutrition on the other, correcting calorie imbalances presents social and economic challenges that few countries are prepared to meet. Calories, therefore, affect societies in ways that are political as well as personal.
Calories, of course, derive from food. But calories are a convenient way to say a great deal about food, nutrition, and health. For this reason, and because calories are so poorly understood, we thought it would be useful to research and write about calories in all of their dimensions -- personal, scientific, and political. And because we are both consummate "foodies" who derive enormous pleasure from eating, we liked the idea of using calories as a way to think about these aspects of food.
Let's be clear from the beginning: This is not a diet book with a breakthrough scheme for losing weight and keeping it off. Instead, we try to provide an appreciation for what you are up against if you want to control your body weight in today's "toxic," obesity-promoting -- or as we like to call it, "eat more" -- food marketing environment . We intend this book to give you the information you need to interpret food labels, diet claims, and your own reactions to this food environment. Knowledge, we argue, is not enough to counter the biological urge to eat or the subtleties of food marketing. But it is a powerful first step in developing weight-management strategies that work for your particular body, lifestyle, and food preferences.
We need to explain that both of us are or were professors in human nutrition departments, Marion Nestle at New York University and Malden Nesheim at Cornell. Our collaboration grew out of a previous project that culminated in a book about the pet food industry . In working on that project, we discovered that we enjoyed researching and writing together and shared similar views of the strengths and limitations of nutrition science and its implications for dietary advice. In this book, the word we refers to the two of us and to our joint opinion.
That these points and much else about calories are not obvious constitutes a major rationale for writing this book. In our experience, people are so confused about calories that we have come to think of them as the C-word. Nobody wants to talk about them. They are poorly understood, and understandably so. You cannot see, taste, or smell them. The only way you can tell whether you are getting enough or too many is to observe their effects on your belt size or your weight on a scale. Most people have some vague idea that calories have something to do with putting on weight, but little intuitive grasp of the number in foods or what they do in the body. This, however, does not stop diet gurus, food advertisers, or government agencies from using the word all the time.
To pick our favorite example: In the 2004 film Super Size Me! (Marion's screen debut), a camera crew asks people at random on the street to define calorie. You watch respondents struggling to say something that makes sense. The film records some of the more amusing attempts, but its director, Morgan Spurlock, tells us that his crew could not find even one person who could come up with a reasonable definition.
Public confusion about calories is widespread, has been studied extensively, and is entirely understandable. Calories are tangible when measured in food or in the body, but such measurements can be done only in laboratories using equipment or techniques that are not available to the average person. The very definition of calories is nonintuitive. They are a measure of the energy in food and in the body, but "energy" is conceptually abstract. To get a feel for calories, you have to know how they are measured and what they do, neither of which comes up much in day-to-day life.
Even talking about calories is difficult. For starters, calorie counts are given in no less than five different units -- calories, Calories, kilocalories, Joules, and kilojoules (along with their abbreviations cal, Cal, kcal, J, and kJ). Which unit you use depends on whether you are a chemist, a nutritionist, or someone just looking at a food label and whether you live in the United States or someplace else. The bewildering terminology is the result of history and geography, and not even scientists have an easy time with it.
Excerpted from Marion Nestle and Malden Nesheim's Why Calories Count: From Science to Politics (University of California Press)
 Olshansky SJ, et al. A potential decline in life expectancy in the United States in the 21st century. NEJM 2005;352:1138-45.
 Brownell K, Horgon KB. Food Fight: The Inside Story of the Food Industry, America's Obesity Crisis, and What We Can Do about It. New York: McGraw-Hill, 2004.
 Nestle M, Nesheim MC. Feed Your Pet Right. New York: Free Press/Simon and Schuster, 2010.