Reflexions on energy balance.

Calorimetry is the basis of the science of nutrition, a statement I iirst saw as the title of a paper by the chief of the department of medicine at the Mayo Foundation (Wilder, 1959). Our science began when Lavoisier put a guinea pig into a calorimeter, measured the amount of ice melted and showed that this was quantitatively related to the amount of fixed air or carbon dioxide given off by the animal. Measurement of the respiratory exchanges (indirect calorimetry) has always been technically much easier than measurement of heat loss. Systematic study of energy exchanges in man began in I 866 in Munich where Pettenkofer and Voit had constructed a respiration chamber suitable for man. This they were able to do through the patronage of King Maximillian I1 of Bavaria. Pettenkofer was a colourful personality who had been appointed professor of dietetic chemistry in 1847 at Munich, where later he founded the first Institute of Hygiene. It was there most of the fathers of nutrition came for postgraduate study under Voit, his distinguished assistant and successor. The American W. 0. Atwater, after studying at Munich returned home and with the help of an engineer, Rosa, built the first calorimeter for human subjects. Rubner, another of Voit’s pupils, played a major part in determining the energy value of human foods. When in 1906 Graham Lusk, also a pupil of Voit, wrote the first edition of The Science ofNutrition (Lusk, 1906) he was able to set out the principles of the energy exchanges in man, and these appear substantially unchanged today in undergraduate textbooks of physiology and nutrition. I am grateful to my Oxford tutor, Dr Kenneth Franklin, that he told me to read Lusk’s book during a long vacation. Thanks to the initiative of Bill Darby, the American Nutrition Foundation has reprinted Lusk’s book. I suggest that you recommend it to those of your students who have the capacity to read. In the first half of the 20th century the interest of nutritionists was diverted from the study of energy by the discovery of vitamins. It was revived in World War I1 by food shortages and problems of rationing in the combatant countries and by the appalling starvation in many prisons and concentration camps. Ancel Keys and his colleagues at the University of Minnesota in 1950 published The Biology of Human Starvation, which not only describes their famous experiments on partial starvation, but also contains a full review of the literature and of contemporary thinking on the subject. The end of World War I1 did not see the end of rationing in the United Kingdom. Indeed bread was rationed for the first time in 1946. This was because so many ships had been sunk that not enough remained to carry across the Atlantic the foods and goods needed to rehabilitate the health of the people and of the