35 0 Am J C/ i n Nui r l992;55:35 -5. Printed in USA. © 1992 American Society for Clinical Nutrition Energy intake required to maintain body weight is not affected by wide variation in diet composition13 Rudolph L Leibel, Jules Hirsch, Burton E Appel, and Gregg C Checani ABSTRACT Diets rich in fat may promote obesity by lead- ing to a greater deposition of adipose-tissue triglycerides than do isoenergetic diets with less fat. This possibility was examined by a retrospective analysis of the energy needs of 16 human subjects (1 3 adults, 3 children) fed liquid diets ofprecisely known composition with widely varied fat content, for 15-56 d (33 ± 2 d, i ± SE). Subjects lived in a metabolic ward and received fluid formulas with different fat and carbohydrate content, physical activity was kept constant, and precise data were available on energy intake and daily body weight. Isoenergetic formulas con- tamed various percentages ofcarbohydrate as cerelose (low, 15% ; intermediate, 40% or 45%; high, 75%, 80%, or 85%), a constant 15% of energy as protein (as milk protein), and the balance of energy as fat (as corn oil). Even with extreme changes in the fat- carbohydrate ratio (fat energy varied from 0% to 70% of total intake), there was no detectable evidence ofsignitlcant variation in energy need as a function of percentage fat intake. Am J C liii N uir l992;55:350-5. KEY WORDS Obesity, dietary fat, dietary carbohydrate, diet composition, energy requirements Introduction Sixty years ago, LH Newburgh and his colleagues examined the possibility that so-called endogenous obesity might be the result of special me abolic factors unrelated to energy intake or physical activity (I). They found no evidence for such purely endogenous obesity and also demonstrated that the long-term effect of any diet on body weight is related only to the total energy content of the diet. Other features of the diet such as carbohydrate or fat content did not, in the long run, have con- sequential effects on body weight. In recent years the adverse effects of high-fat diets on health have been emphasized, and the possibility that a high-fat intake may be accompanied by some special in vivo economy of energy metabolism has led to speculation on the role ofdiet composition in the production of obesity. Various investigators have reported a positi e correlation between body fat and the percentage of fat in isoenergetic diets fed to rodents (2 , 3) and humans (4, 5) and a lack of ffect of di tary fat on respiratory quotient (RQ) in human subjects studied for 9 or 24 h after the feeding of fat (6, 7). Additionally, 24-h energy balance in a respiratory chamber is reported to be due almost exclusively to differences in fat balance and unrelated to carbohydrate or protein balance (8). ne group of investigators con luded that “fat intake may play a role in obesity that is independent of energy intake” (4). The ultimate test of the validity of such a proposition is the long-term effect on metabolic efficiency of perturbations of diet composition. Usi g the technique of caloric titr metry (9), in which a formula diet ofspecified composition is fed over a period ofweeks under circumstances ofcontrolled physica activity, we examined the effect on metabolic efficiency (as reflected by changes in body weight) ofextreme changes in the composition ofotherwise isoenergetic diets. This technique was made possible by the careful collection ofdata on the effects offormula feeding, in studies done over many years by EH Ahrens and his colleagues at the Hospital of the Rockefeller University ( 10, 1 1). Subjects and methods The records of all subjects studied by the Lipid Laboratory ofthe Rockefeller University Hospital between 1955 and 1965 who were fed liquid-formula diets ofvarious carbohydrate (CHO) and fat composition were reviewed. Th se diets were prepared in the research kitchen of the Rockefeller University Hospital. Protein (20.9 Id/g), which represented a constant 15% of energy, was derived from milk protein. Fat (37.7 kJ/g) was from corn oil. CHO (16.7 kJ/g) was supplied as cerelose, a hydrated form of glucose. Coefficients of digestibility were used to determine the final available energy value ofthe constituents ofthe formula (12): protein, 0.92; fat, 0.95; and carbohydrate, 0.98. Data re- garding bomb ca orimetry of these formulas are not available. B om b calo rim etry performed on eight batches ofsimilar formula prepared in the research kitchen of the Rockefeller University Hospital between April 1988 and July 1990 had a coefficient of variation for Id/g of 1.9%. Such formula shows a ±0.2% cor- respondence between bomb calorimetric and calculated energy content. In studies designed to examine the effects of dietary lipid type and quantity on lipoprotein metabolism, the per- centage of CHO in the diet was systematically altered by iso- I From the Laboratory of Human Behavior and Metabolism and the Pew Center ofNutritional Excellence, Rockefeller University, New York. 2 Supported in part by grants D K 30583 and RROO 102 from the Na- tional Institutes of H ealth. 3 Address reprint requests to RL Leibel, Laboratory of Human Be- havior and Metabolism, Rockefeller University, 1230 York Avenue, New York, NY 10021. Received October 25, 1990. Accepted for publication March 6, 1991. a t U n i v o f C o l o r a d o H l t h S c i C t r D e i s o M e m L i b o n S e p t e m b e r 2 9 , 2 0 0 7 w w w . a j c n . o r g D o w n l o a d e d f r o m
