FROM ANCIENT GREECE TO MODERN CALORIE SCIENCE

THE HISTORY 

Although it may seem self-evident that food is essential to life, scientists did not have much real understanding about how food energy keeps bodies warm, growing, and functioning until the late 1700s. The earliest understanding of calories as energy released by the interaction of oxygen with food molecules is usually attributed to Antoine Lavoisier, who lived and died in the eighteenth century. Lavoisier's view of metabolism as an oxidation process—the “burning” of food molecules in the presence of oxygen—still holds true. We explain how this works in later chapters, but to jump-start the discussion let's begin with a quick overview of the basic concepts. The three energy-producing molecules in foods—proteins, fats, and carbohydrates—are highly structured. Creating them takes energy, some of which gets stored in their chemical bonds. Once eaten, food molecules are attacked by digestive enzymes. Enzymes break the organized structures into pieces small enough to be absorbed through the wall of the digestive tract. Enzymes disassemble complex molecules of starch, for example, into simple sugars, a process that releases small amounts of energy. During metabolism, enzymes further disassemble the absorbed sugars into even smaller pieces, releasing more energy. Other enzymes transfer some of this energy to small storage molecules. When the body needs energy, still other enzymes split the storage molecules to release it. The released energy powers the chemical reactions that create new body molecules or make muscles contract, and some of it keeps the body warm. The chemical reactions involved in these processes are “oxidation” reactions. They require oxygen, which is obtained through respiration. You breathe in oxygen. You exhale carbon dioxide as waste. Your other metabolic waste product is water, which you mostly excrete in urine. Food molecules that are completely “burned” in the body end up as carbon dioxide and water. All of these processes yield heat. Scientists now know a great deal about the chemical structure of food and each of the processes crucial to obtaining energy from food: digestion, absorption, metabolism, respiration, and excretion. We'll examine them all in subsequent chapters. But first, it's worth exploring why it took such a long time to figure out the role of food in the body.

ANCIENT IDEAS ABOUT FOOD ENERGY: HIPPOCRATES AND GALEN

Hippocrates

The most important early writings about energy and body heat are attributed to the Greek physician Hippocrates (~460–370 B.C.).Because the authorship of ancient texts is uncertain, the writings of Hippocrates are generally considered to include not only those of the physician himself but also those of his contemporaries and followers. In that sense, Hippocrates is something of a collective term. The writings, however, come across as if written by a single person, one who tried hard to make sense of his observations but sometimes jumped to conclusions that do not always make sense in modern terms. Even when his observations are right on target, he can sound much like a present-day diet guru. Here, for example, he boasts of having been the first to discover the secret of health—balancing diet and activity: “This discovery reflects glory on myself its discoverer, and is useful to those who have learnt it, but no one of my predecessors has even attempted to understand it though I judge it to be of great value in respect of everything else. It comprises prognosis before illness and diagnosis of what is the matter with the body, whether food overpowers exercise, whether exercise overpowers food, or whether the two are duly proportioned. For it is from the overpowering of one or the other that diseases arise, while from their being evenly balanced comes good health.” Hippocrates produced aphorisms, among them “Growing creatures have most innate heat, and it is for this reason that they need most food, deprived of which their body pines away.” This particular statement was singled out by the twentieth-century nutrition scientist Graham Lusk as the earliest understanding of the role of calories in the body. Hippocrates also recognized that dietary prescriptions had to be tailored to individuals: “The various ages have different needs. Moreover, there are the situations of districts, the shiftings of the winds, the changes of the seasons, and the constitution of the year.” Whether such pronouncements made sense or not, they stayed in print, repeatedly translated—and famously mistranslated—from Greek into Arabic and Latin, and back again into Greek. Five centuries later, Galen (~130–200), a Roman physician of Greek origin, translated the Hippocrates texts himself and became a devoted disciple. In prolific writings, Galen paraphrased (or plagiarized, if you prefer) Hippocrates, adding his own commentaries. He repeated much of what Hippocrates said about the digestion of common foods, their speed of passage through the body,and — apparently an issue of great concern—their propensity to produce flatulence. Hippocrates found turnips, for example, to be “heating, moistening, and disturbing to the body” but unable to “pass easily, either by stool or by urine.” Galen solved this problem by insisting that turnips be cooked; otherwise, a turnip is “difficult to concoct [digest], flatulent, and causes loss of appetite, and sometimes gnawing sensations in the stomach.” Despite what we would now consider minor—and sometimes major—errors in fact and interpretation, Galen sharply criticized anyone who disagreed with his or Hippocrates's views: “My opinion—and I swear to it by God—is that Hippocrates has made this account of his so clear and obvious that not even a child, much less anyone else, should find it obscure.” The vehemence of these opinions would be of interest only to classical scholars except for one distressing historical fact.

The writings of Hippocrates and Galen, no matter what they said, were accepted as indisputable by subsequent generations. Their ideas so dominated medical practice from the fifth century B.C. until the eighteenth century A.D. that science could make little headway. Hippocrates and Galen, for example, favored bloodletting as a treatment for many diseases. Although this practice is certain to increase calorie needs — if not cause anemia, infections, or death—it continued as routine medical treatment until well into the nineteenth century.

ORIGINS OF CALORIE SCIENCE

Fast-forward through the Middle Ages and Renaissance to the Enlightenment and the onset of the modern scientific era. To grasp how food provides energy and how the body uses it, scientists had a great deal of work to do. They first had to discover:
* oxygen and carbon dioxide
* the role of these gases in respiration
* the relationship of food components to heat
* the chemical conversions involved in digestion and metabolism
* the chemical composition of foods
These discoveries were gradually accomplished and accumulated during the seventeenth to twentieth centuries. Santorio Sanctorius of Padua gets credit for the first fumblings toward a scientific understanding of human energetics — the use of energy in and by the body. In the 1600s, perhaps suffering from some kind of obsessive-compulsive disorder, he weighed himself, everything he ate and drank, and everything he produced in urine and feces nearly every day for thirty years. From these observations and measurements, Sanctorius observed the effects on his body of the difference in weight between the foods he ate and the waste products he excreted. He attributed this difference to “insensible perspiration.” True modern understanding of human energetics begins with the revolution in scientific thinking that accompanied the political revolution in France in the late 1700s.Antoine Lavoisier, a French aristocrat, was its best-known scientific revolutionary. He constructed a device large enough to permit measurements of the heat produced by a living animal, in this case, a guinea pig. From experiments using such “whole-body” calorimeters, he concluded that animal respiration is a form of oxidative combustion, just like the burning of a candle. Both, he said, require oxygen. Both release carbon dioxide and water. These promising investigations ended prematurely. Lavoisier was arrested during the deadliest days of the French Revolution and guillotined. At about the same time in England, Adair Crawford was performing similar investigations with similar results. Although neither Lavoisier nor Crawford used the word calorie to describe animal heat, Lavoisier came close. He called his measurement device a calorimeter (calorimètre) and used terms such as calorique (caloric) and chaleur (heat) to describe his observations of animal metabolism. The first record of the use of calorie in its present sense as a measurement of body heat dates to notes taken from lectures by the French scientist Nicolas Clément in 1824. Max Rubner in Germany gets credit as the first scientist to publish the use of the term in its modern sense.
German physiologists of the mid-1800s, such as Julius Mayer, determined that living systems conform to basic laws of physics, most notably the first law of thermodynamics. This precept states that energy can be neither created nor destroyed but can only change forms. It explains how metabolism can transform food energy into heat energy, the chemical energy of biosynthesis, the electrical energy of nerve action, or the mechanical energy of muscle work. If not used for such immediate purposes, food energy can be stored in the body as fat or, to a lesser extent, glycogen, the storage form of carbohydrate in liver and muscles. According to the first law of thermodynamics, burning a food in the presence of oxygen should produce the same amount of heat as metabolism does in the body. Knowing this, scientists began to develop “bomb” calorimeters to measure the energy value of a thoroughly burned food. By the mid-1800s, they were also able to build whole-body calorimeters large enough to measure energy intake and output in larger and larger animals, eventually including sheep, horses, cows, and people.

THE MODERN ERA

W. O. Atwater Writing a book about calories required us to read a great deal of the prodigious output of Wilbur O. Atwater (1844–1907), rightfully honored as the father of modern nutrition science in the United States. Atwater studied agricultural chemistry, earned his doctorate by analyzing the chemical composition of corn, and established a food analysis laboratory at Wesleyan University.In the early 1880s he traveled to Germany, where he learned how to use large, whole-body calorimeters to perform energy balance studies in humans. On his return, Atwater continued to analyze the content of calories and nutrients in foods, based either on the amounts of heat they produced in a calorimeter or on calculations of the number of calories stored in their proteins, fats, and carbohydrates. In 1887 he summarized what was then known about food calories in a series of popular articles in Century magazine. There he explained that a gram of protein or carbohydrate yields less than half the energy of a gram of fat and that these differences—and variations in water content—account for variations in food calories. Most food energy, Atwater explained, is “used for the interior work of the body, breathing, keeping the blood in circulation, digestion, etc., but a large part of this is transformed into heat before it leaves the body.” These conclusions were new to the public, and the Century articles made Atwater the most famous scientist in America. He soon held three jobs in three different cities: professor at Wesleyan in Middletown, Connecticut; director of the U.S. Department of Agriculture (USDA) Experiment Station at Storrs, Connecticut; and director of the USDA Office of Experiment Stations in Washington, DC. In these positions he continued his research on the nutrient and calorie content of foods, the ways calories are used in the body, and the calorie needs of people of different occupations and social classes. We discuss his discoveries in each of these areas in subsequent chapters. In 1894 Atwater summarized the essence of nutritional energetics: “energy from the sun is stored in the protein and fats and carbohydrates of food, and…is transmuted into the heat that warms our bodies and into strength for our work and thought.”Three years later, in a stunning monograph of more than four hundred pages, Atwater and a colleague did what we might now call a meta-analysis of the thousands of metabolic studies that they or previous investigators had published to date. They reported their conclusions in Hippocrates-like aphorisms:

“The animal organism requires food for a twofold purpose,
(1) to furnish material for the building and repair of tissue, and
(2) to supply fuel for the production of heat and energy. In serving as fuel, food protects the material of the body from consumption.”

“The food of animals consists of the so-called nutrients—protein, fat, and carbohydrates, various mineral salts, and water.” (Vitamins were presumed to exist at the time but were not identified until after 1910.)

“Food is to the body what fuel is to the fire.”

THE POLITICS OF CALORIE HISTORY

Atwater stated repeatedly that the purpose of his experiments was to devise the most economical diets that could meet the nutritional needs of people of various ages, occupations, and social classes. As a USDA official explained in a letter introducing one of Atwater's studies, “The immediate purpose in conducting an inquiry into the food of the colored population of the Southern States was to obtain information as to the kinds, amounts, and composition of the food materials used. The ulterior purpose was to get light upon the hygienic and pecuniary economy of their diet, its deficiencies, the ways in which it might be improved, and the steps which should be taken to bring about an improvement.”We mention the USDA's goals at this point because Atwater's work has been sharply criticized for its subsequent effects on society. The science studies scholar Jessica Mudry charges that Atwater's work created an unfortunate “discourse of quantification.” In her view, measuring calories caused them to be transformed “from a unit of physical science, to a unit of human fodder, and finally, through Atwater's application, a determinant of quality.” By treating food components as things that could be calculated and measured, Atwater's work led to “the belief that science and quantification can tell us all that we need to know about food and eating.” Instead, Mudry argues, “Any rhetoric of food and eating is incomplete and inadequate if it does not take culture, geography, tradition, experience, and taste into consideration along with the nutritional composition of foods and health,” a statement with which we wholeheartedly agree. A more specific critique of Atwater's calorie investigations comes from the historian Nick Cullather. He argues that measuring calories not only takes food out of its taste and cultural traditions, but also turns food into an instrument of social control by governments. Once governments determine the number of calories needed by a population, they can quantify dietary adequacy and assume that when calories are adequate, food intake and nutritional status must also be adequate. The calorie, he says, “has never been a neutral objective measure of the contents of the dinner plate. From the first its purpose was to render food and the eating habits of populations politically legible.” Atwater had said that the purpose of determining the number of calories needed by workingmen and by the “Negro” in Alabama was to establish “scientific standards of living.” But Cullather argues that such standards could be and were used by governments and manufacturers to “contain wage levels while maintaining a healthy, contented workforce.” He also maintains that using calorie requirements as the basis for assessing a population's need for food aid is a tool for international political domination. In making such arguments, Cullather appears to view setting standards for calorie intake as a metaphor for the mixed motivations and sometimes negative consequences associated with attempts to evaluate and meet the food requirements of undernourished populations—issues we address in later chapters. Although we suspect that neither Mudry nor Cullather intended their analyses to be anti-scientific, their arguments appear that way to us. Should scientists not measure anything having to do with human physiology? Objections to the quantification of human energy requirements would also seem to apply to setting dietary standards for intake of protein, vitamins, and minerals, or to measurements of body weight, blood pressure, or blood sugar. Although the argument could be made that such tests are equally reductive in the sense that they reduce the health of a whole person to a single number, surely such numbers can be useful when put in context and interpreted appropriately. We enjoy conspiracy theories as much as anyone, but we have a hard time believing that Atwater—or Lavoisier, for that matter—investigated energy metabolism out of a desire for political domination. We view both as intensely curious and committed scientists who valued knowledge for its own sake and assumed that their work would add to human knowledge and be useful. We doubt that either gave much thought to how his work might be interpreted or used by others. The humanitarian goals of many international aid agencies necessarily require some means of quantifying human food needs, and establishing standards for calorie intake can be a useful way to do this. Mudry's and Cullather's critiques, thought-provoking as they are, do not provide meaningful alternatives. They do, however, reinforce one of the central themes of this book: calories have political dimensions.

By Marion Nestle & Malden Nesheim in "Why Calories Count" - From Science to Politics, University of California Press, USA, 2012, p. 16-26. Adapted and illustrated to be posted by Leopoldo Costa.