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Hepatic de novo lipogenesis (DNL) is markedly stimulated in humans by low-fat diets enriched in simple sugars. However, the dietary responsiveness of the key enzyme controlling DNL in human adipose tissue, fatty acid synthase (FAS), is uncertain.Adipose tissue mRNA for FAS is increased in lean and obese subjects when hepatic DNL is elevated by a eucaloric, low-fat, high-sugar diet.Twelve lean and seven obese volunteers were given two eucaloric diets (10% vs. 30% fat; 75% vs. 55% carbohydrate; sugar/starch 60/40) each for 2 weeks by a random-order cross-over design. FAS mRNA in abdominal and gluteal adipose tissues was compared to hepatic DNL measured in serum by isotopic and nonisotopic methods. Adipose tissue mRNA for tumor necrosis factor-alpha and IL-6, which are inflammatory cytokines that modulate DNL, was also assayed.The low-fat high-sugar diet induced a 4-fold increase in maximum hepatic DNL (P.001) but only a 1.3-fold increase in adipose tissue FAS mRNA (P=.029) and no change in cytokine mRNA. There was a borderline significant positive correlation between changes in FAS mRNA and hepatic DNL (P=.039). Compared to lean subjects, obese subjects had lower levels of FAS mRNA and higher levels of cytokine mRNA (P.001).The results suggest that key elements of human adipose tissue DNL are less responsive to dietary carbohydrate than is hepatic DNL and may be regulated by diet-independent factors. Irrespective of diet, there is reduced expression of the FAS gene and increased expression of cytokine genes in adipose tissues of obese subjects.

Jules Hirsch was born in New York City and died at age 88 after a long illness. He was considered notorious leader in the study of human metabolism mainly in the area of lipids and obesity. His research at The Rockefeller University helps establish the mechanism of obesity and lipids metabolism. Hirsch joined Rockefeller´s faculty in 1954 and remained there for the rest of his career. Hirsch´s research helped to support the idea of dynamic interactions among diet, physical activity, general metabolism and obesity. At that time most scientific considered adipose tissue to be biologically inert such as a passive insulator in which the body reserved energy in the form of triglycerides. Hirsch had a natural characteristic of showing a nice smile and greeting for everyone he worked with at the university. Another important contribution was there relationship between diet and cardiovascular ailments as well as metabolism disturbance.Jules Hirsch nació en la ciudad de Nueva York y murió en Julio 23 de 2015, a la edad de 88 años. Es considerado como un notable y eminente líder en el estudio del metabolismo; particularmente centró su interés en la obesidad ocasionada por un acumulo excesivo de grasa por exceso de alimento y falta de actividad física. Hirsch ingresó a la facultad como profesor en la Universidad Rockefeller en 1954 y permaneció por el resto de su carrera como investigador clínico hasta su jubilación como emérito. Los estudios de Hirsch apoyaron la idea de que existía una interrelación entre la dieta, la actividad física, el metabolismo y la obesidad. En ese tiempo la mayor parte de los científicos pensaba que el tejido adiposo era simplemente una reserva inerte en donde se almacenaba la grasa en forma de triglicéridos para proporcionar energía al organismo. Una de las características personales de Hirsch era una agradable sonrisa y el buen trato a todas las personas que trabajaban en la universidad. Hirsh también advirtió, y esta es otra contribución importante, que la obesidad, la falta de actividad física y el exceso de lípidos contribuyen al desarrollo de trastornos metabólicos y enfermedad cardiovascular.

In 1956, the JCI published an article by Vincent Dole on a method for titrating plasma fatty acids that uncovered the importance of fatty acids as a substrate for glucose metabolism. When asked to prepare a historical perspective on this very popular paper, I paid Dole a visit and we reminisced. His answer to my question of how he came to do this work on plasma fatty acids was: "Well, one thing leads to another." Let me remind the reader of what "things" were like in 1956 and how they might have related to Dole's important contribution.

BACKGROUND Weight gain and loss increases and decreases energy expenditure, respectively, out of proportion to changes in metabolic mass. OBJECTIVE We hypothesized that changes in energy expenditure associated with weight gain or loss were due in part to changes in catecholamine release, thyroid hormones, carbohydrate utilization, or a combination thereof. METHODS Urinary catecholamine excretion, serum thyroid hormone concentrations, and results of 3-h oral-glucose-tolerance tests were examined in obese and never-obese subjects at their usual weights, during weight loss or gain, and at stable weights 10-20% below or 10% above usual. RESULTS Urinary norepinephrine excretion decreased significantly during and after weight loss and increased during and after weight gain. Serum concentrations of reverse triiodothyronine increased significantly during and after weight loss, whereas serum concentrations of triiodothyronine increased significantly (by approximately 0%) during and after weight gain. Serum insulin and glucose concentrations during the oral-glucose-tolerance test increased significantly after weight gain in obese subjects. The percentage change in urinary norepinephrine excretion and in serum concentrations of triiodothyronine were significantly correlated with percentage changes in energy expenditure and with each other. CONCLUSIONS Changes in body weight were associated with changes in catecholamine excretion and thyroid hormones, which might-by virtue of the effects on energy expenditure-have favored a return to usual body weight. Weight gain induced more apparent insulin resistance in the obese than the never-obese subjects, suggesting a threshold effect of total body fat on this phenomenon.

Objective: Body fatness is partly under hypothalamic control with effector limbs, which include the endocrine system and the autonomic nervous system (ANS). In previous studies we have shown, in both obese and never-obese subjects, that weight increase leads to increased sympathetic and decreased parasympathetic activity, whereas weight decrease leads to decreased sympathetic and increased parasympathetic activity. We now report on the involvement of such ANS mechanisms in the action of anti-obesity drugs, independent of change in weight. Research Methods and Procedures: Normal weight males (ages 22 to 38 years) were fed a solid food diet, carefully measured to maintain body weight, for at least 2 weeks, as inpatients at the Rockefeller University General Clinical Research Center. In a single-blind, placebo/drug/placebo design, eight subjects received dexfenfluramine, seven phentermine (PHE), and seven sibutramine (SIB). ANS measures of parasympathetic and sympathetic activity included: determination of amount of parasympathetic control (PC) and sympathetic control (SC) of heart period (interbeat interval), using sequential pharmacological blockade by intravenous administration of atropine and esmolol. These autonomic controls of heart period are used to estimate the overall level of parasympathetic and sympathetic activities. Norepinephrine, dopamine, and epinephrine levels in 24-hour urine collections were measured and also resting metabolic rate (RMR). Results: Sufficient food intake maintained constant body weight in all groups. PHE and SIB produced significant increases in SC but no change in PC or in RMR. In contrast, dexfenfluramine produced marked decreases in SC, PC, and RMR. For all three drugs, the effects on urine catecholamines directly paralleled changes in cardiac measures of SC. Discussion: ANS responses to PHE and SIB were anticipated. The large, and unanticipated, response to dexfenfluramine suggests further study to determine whether there could be any relation of these ANS changes to the adverse cardiovascular effects of treatment with dexfenfluramine.

We previously reported that a eucaloric, low fat, liquid formula diet enriched in simple carbohydrate markedly increased the synthesis of fatty acids in lean volunteers. To examine the diet sensitivity of obese subjects, 7 obese and 12 lean volunteers were given two eucaloric low fat solid food diets enriched in simple sugars for 2 weeks each in a random-order, cross-over design (10% fat, 75% carbohydrate vs. 30% fat, 55% carbohydrate, ratio of sugar to starch 60:40). The fatty acid compositions of both diets were matched to the composition of each subject's adipose tissue and fatty acid synthesis measured by the method of linoleate dilution in plasma VLDL triglyceride. In all subjects, the maximum % de novo synthesized fatty acids in VLDL triglyceride 3–9 h after the last meal was higher on the 10% versus the 30% fat diet. There was no significant difference between the dietary effects on lean (43 ± 13 vs. 12 ± 13%) and obese (37 ± 15 vs. 6 ± 6%) subjects, despite 2-fold elevated levels of insulin and reduced glucagon levels in the obese. Similar results were obtained for de novo palmitate synthesis in VLDL triglyceride measured by mass isotopomer distribution analysis after infusion of [13C]acetate. On the 10% fat diet, plasma triglycerides (fasting and 24 h) were increased and correlated with fatty acid synthesis. Triglycerides were higher when fatty acid synthesis was constantly elevated rather than having diurnal variation. Thus, eucaloric, solid food diets which are very low in fat and high in simple sugars markedly stimulate fatty acid synthesis from carbohydrate, and plasma triglycerides increase in proportion to the amount of fatty acid synthesis. However, this dietary effect is not related to body mass index, insulin, or glucagon levels.—Hudgins, L. C., M. K. Hellerstein, C. E. Seidman, R. A. Neese, J. D. Tremaroli, and J. Hirsch. Relationship between carbohydrate-induced hypertriglyceridemia and fatty acid synthesis in lean and obese subjects. J. Lipid Res. 2000. 41: 595–604.

Using new nonisotopic and isotopic methods, we showed previously that fatty acid synthesis was markedly stimulated in weight-stable normal volunteers by a very-low-fat formula diet with 10% of energy as fat and 75% as short glucose polymers. In this study, we determined whether fatty acid synthesis was equally stimulated by a very-low-fat solid diet made with foods consumed typically. Four normal volunteers consumed the same very-low-fat formula diet for 25 d and then an isoenergetic solid food diet with 10% of energy as fat and 75% as starch, simple sugars, and fiber for 25 d. To measure fatty acid synthesis, the fatty acid compositions of the diets were matched to the composition of each subject's adipose tissue and compared with the composition of VLDL-triacylglycerol. In all subjects, the large increases in newly formed palmitate and decreases in linoleate in VLDL-triacylglycerol were quickly reversed by the solid food diet, and the fraction of de novo synthesized fatty acids in fasting VLDL-triacylglycerol decreased from 30-54% to 0-1%. In a second group of subjects, the stimulation of fatty acid synthesis by the formula diet with 75% glucose polymers was similarly reduced by a formula diet with amounts of fat, starch, and sugar chosen to mimic those of the solid food diet, but persisted after the addition of fiber or a diet with 75% sugar. In conclusion, an increase in fatty acid synthesis and palmitaterich, linoleate-poor VLDL-triacylglycerol induced by very-low-fat, high-sugar diets may be reduced by the substitution of dietary starch for sugar with potentially beneficial effects on cardiovascular health.

Five genes have been identified, each capable of causing obesity in mice and each with a human homologue. One of them codes for a signal expressed by adipose tissue, and another for the signal's brain receptor. The rest reveal brain pathways probably downstream from the receptor. Together, the genes offer glimpses of an intricate system that defends adipose stores--and in some persons maintains an unhealthful set-point.

Inpatient metabolic studies of human subjects were performed to obtain data on important nutritional issues. It was shown that wide variations in the ratio of carbohydrate to fat do not alter total 24-h energy need. Studies of the fatty acid composition of plasma low-density lipoproteins during low-fat feeding indicated that there can be considerable lipogenesis from carbohydrate in humans during isoenergetic feeding. The energy cost of this conversion must be small or be counterbalanced by other changes in energy metabolism because measured energy need was unaltered by fat-to-carbohydrate ratios. Energy need was, however, markedly varied by changes in body weight. Subjects at their usual body weights who had experimentally induced increases in body weight became inefficient and required a higher energy intake for weight maintenance. The reverse occurred with a reduction in body weight. The set point at which energy storage is defended is clearly different in obese persons.

Circulating concentrations of leptin are closely correlated with body fat mass, and may thus constitute an afferent limb of a system regulating body fatness, with efferent limbs that affect energy expenditure and food intake. We studied 50 subjects (27 males, 23 premenopausal females; 31 never-obese, 19 obese) at usual body weight during active weight loss or weight gain and during the maintenance of body weights 10% above usual (Wt 110%) and 10% and/or 20% below usual body weight (Wt 210% and Wt 220%) to test the hypotheses that the dynamic process of weight change and the maintenance of an altered body weight are associated with significant changes in circulating concentrations of leptin and/or the relationship between fat mass and leptin, and such changes in the plasma concentration of leptin are related to changes in energy expenditure at altered body weight. Subjects were admitted to the Rockefeller University Hospital, and energy metabolism (24-h energy expenditure, resting energy expenditure, thermic effect of feeding, and nonresting energy expenditure) and circulating concentrations of leptin and insulin were examined at various weight plateaus (usual body weight, 10% above usual body weight, 10% below usual body weight, and 20% below usual body weight). Plasma leptin was also measured in some subjects during dynamic periods of weight gain or loss. Though both plasma leptin concentrations and fat mass were significantly correlated with resting energy expenditure, only the correlation of fat mass and energy expenditure remained significant in a multiple stepwise linear regression analysis. Neither absolute nor relative changes in plasma leptin between weight plateaus were significantly correlated with any of the observed changes in energy expenditure. Plasma leptin concentrations were significantly lower during weight loss than during weight maintenance at the same body composition. Plasma leptin concentrations, normalized to fat mass, were significantly lower during the maintenance of a reduced body weight in females and higher during the maintenance of an elevated body weight in males than in the same subjects at usual body weight. At all weight plateaus, plasma leptin concentrations normalized to fat mass were significantly higher in females than in males, but gender was not a significant covariate of the relationship between leptin and energy expenditure. Postabsorptive serum concentrations of insulin was a significant covariate of plasma leptin concentration in males, but not females, at Wt initial and Wt 110%. Although plasma leptin is significantly reduced during dynamic weight loss compared with static weight maintenance at the same body weight, the lack of correlation between changes in plasma leptin and changes in energy expenditure between weight plateaus suggests that leptin is not the primary signal that mediates the changes of energy expenditure that accompany the maintenance of an altered body weight in humans. (J Clin Endocrinol Metab 82: 3647‐3654, 1997)

Autonomic nervous system (ANS) activity in age-matched, weight-stable, free-living, ad libitum-fed, obese (OB) and never-obese (NO) young men (body mass index means [SD], 38.5 [3.9] and 22.0 [1.7], respectively) was evaluated by sequential blockade of cardiac autonomic innervation with weight-adjusted doses of parasympathetic (atropine) and sympathetic (esmolol) blockers so as to produce maximal effects on heart rate. Change in heart period (interbeat interval) from baseline, induced by atropine, defined parasympathetic control (PC), and the subsequent change, after esmolol administration, defined sympathetic control (SC). The heart period, after PC and SC blockade, defined intrinsic heart period (I). In the OB group, baseline heart period and PC were lower, and SC and I were higher, than in the NO group. The results in the OB, relative to the NO subjects, are similar to those reported in a previous study of NO subjects who had undergone a 10% weight gain by overfeeding. These findings suggest that the ANS of individuals with obesity is chronically altered in a way that would tend to oppose their excessive adiposity, and that these autonomic changes are more likely to be responses to other forces that induce obesity, rather than being primary agents in the production of the disease.

PURPOSE Fatty acid composition of adipose tissue is an indicator of the long-term ingestion pattern of several specific fatty acids. There is good correlation of antecedent diet with the essential fatty acids, and there is reflection of the diet with the fatty acids that can be synthesized. The relationship between the fatty acid levels and lymph node status and clinical outcome was examined. METHODS At the time of diagnostic surgery, 161 women with clinical stage T1NO breast cancer had subcutaneous adipose tissue (breast and abdominal) aspirated. The concentrations of 35 fatty acids, seven summed classes, and six fatty acid groups were measured by capillary gas chromatography. Lymph node status was determined with axillary dissection, and patients were followed-up (mean, 7.3 years) for clinical outcome. RESULTS There was no significant association of any adipose tissue fatty acids with overall survival, although few (16 of 161 women) died of breast cancer. However, the odds of having positive lymph nodes (57 of 161 women) were significantly higher for women with a greater adipose tissue proportion of oleic acid (odds ratio [OR], 7.56; 95% confidence interval [CI], 1.78 to 32.1) or total saturated acids (OR, 8.43; 95% CI, 1.48 to 40.0) and significantly lower with a higher proportion of trans fatty acids (OR, 0.24; 95% CI, 0.07 to 0.77), as assessed by multivariate logistic regression. CONCLUSION These data support previous research with dietary questionnaire methodology, suggesting that specific dietary fatty acids may be associated with breast cancer promotion. Further research with long-term clinical follow-up is necessary to investigate these observations in large, diverse populations before dietary recommendations can be envisioned.

A new experimental approach was used to determine whether a eucaloric, low fat, high carbohydrate diet increases fatty acid synthesis. Normally volunteers consumed low fat liquid formula diets (10% of calories as fat and 75% as glucose polymers, n = 7) or high fat diets (40% of calories as fat and 45% as glucose polymers, n = 3) for 25 d. The fatty acid composition of each diet was matched to the composition of each subject's adipose tissue and compared with the composition of VLDL triglyceride. By day 10, VLDL triglyceride was markedly enriched in palmitate and deficient in linoleate in all subjects on the low fat diet. Newly synthesized fatty acids accounted for 44 +/- 10% of the VLDL triglyceride. Mass isotopomer distribution analysis of palmitate labeled with intravenously infused 13C-acetate confirmed that increased palmitate synthesis was the likely cause for the accumulation of triglyceride palmitate and "dilution" of linoleate. In contrast, there was minimal fatty acid synthesis on the high diet. Thus, the dietary substitution of carbohydrate for fat stimulated fatty acid synthesis and the plasma accumulation of palmitate-enriched, linoleate-deficient triglyceride. Such changes could have adverse effects on the cardiovascular system.

We compared three independent techniques for measurement of total energy expenditure (TEE) in human subjects: 1) weight-maintaining energy intake (dietTEE), 2) 24-h chamber calorimetry (chamberTEE), and 3) differential elimination rates 2H2O and H(2)18O (isotopeTEE). Twenty-three healthy adult in-patients [19 never obese (NO), 2 obese (OB), and 2 formerly-obese (RO); 9 female, 14 malel] ingested a liquid formula diet (40% of calories as fat, 45% carbohydrate, 15% protein), the volume of which was adjusted until body weight was stable for at least 14 days. Body composition was then determined by hydrodensitometry, isotope dilution, and dual photon beam absorptiometry (DXA). The thermic effect of feeding (TEF) and resting energy expenditure [REE; measured before arising (dietREE) and after arising (chamberREE)] were determined by indirect calorimetry. Non-resting energy expenditure (NREE) was calculated as NREE = TEE - (REE + TEF). Subjects then gained or lost 10% of their body weight and were restudied as described above. All measures of TEE were significantly correlated (dietTEE vs. chamberTEE r2 = 0.75; dietTEE vs. isotopeTEE r2 = 0.88; isotopeTEE vs. chamberTEE r2 = 0.73; P < 0.0001). ChamberTEE (mean +/- SE = 2,107 +/- 64 kcal/day) was approximately 20% lower than either dietTEE (2,536 +/- 94 kcal/day, P < 0.0001) or isotopeTEE (2,564 +/- 83 kcal/day, P < 0.0001). When data were normalized to metabolic mass, weight gain of 10% was associated with significant increases in dietTEE (P < 0.005) and isotopeTEE (P < 0.05) but not chamberTEE; weight loss of 10% was associated with significant reductions in dietTEE (P < 0.005) and isotopeTEE (P < 0.05) but not chamberTEE. We conclude that measures of energy expenditure obtained in a highly controlled environment by caloric titration (dietTEE) or differential excretion rates of 2H2O and H(2)18O (isotopeTEE) are not significantly different and that measurements of TEE obtained in a respiratory chamber (chamberTEE) are significantly lower than dietTEE or isotopeTEE, probably largely due to limitations on physical activity in the chamber.

Studies in both animals and humans indicate that the autonomic nervous system (ANS) responds to changes in systemic energy balance. In the present study, ANS response to weight change was examined by sequential blockade of cardiac autonomic innervation with parasympathetic (atropine) and sympathetic (esmolol) blockers. Change in heart period (interbeat interval) from baseline after atropine defined the amount of parasympathetic control (PC), and the subsequent change after esmolol defined the amount of sympathetic control (SC). In nonobese subjects, weight gain to 10% above initial body weight resulted in a decrease in PC and an increase in SC, and conversely, weight loss to 10% below initial weight resulted in an increase in PC and a decrease in SC. In obese subjects, weight loss resulted in the same pattern of changes in PC and SC. The major changes were in the parasympathetic arm of the ANS. These findings support the hypothesis that the ANS acts to oppose weight change.

It has been hypothesized that obesity is an abnormally high setting of a regulatory system controlling the level of fat storage in adipose tissue (1). The regulation is achieved by the operation of many elements and is determined by genetic variation and environmental factors. The autonomic nervous system (ANS), with both sympathetic and parasympathetic controls (SC and PC, respectively), is believed to play a particularly important role. SC has been intensively studied in obesity; in fact one theory of obesity causation is the Mona Lisa Hypothesis, an acronym for “most obesities known are low in sympathetic activity” (2). A widely used technique for evaluating SC in humans and in experimental animals is dependent on the turnover rate of norepinephrine as measured by the decline in plasma norepinephrine specific radioactivity after injection of tritiated norepinephrine (3). In experimental animals, direct measure of turnover in heart muscle has been a valuable tool. The most direct method for measuring SC is microneurography, using an electrode in the peroneal nerve (4). PC is also likely to be a player in fat storage, as suggested by the profound effect of vagotomy in ameliorating the effects of ventromedial hypothalamic lesioning. Some vagal effects may be related to insulin release, but there are likely other more direct relations of PC to fat storage, such as the marked bradycardia—probably not insulin related—occurring with weight reduction. Variations in heart rate, in particular, the waxing and waning of heart rate with respiration, or so-called sinus arrhythmia, is an effect of PC and thus has been used to estimate the degree of PC. In 1981, a research group at the Harvard–Massachusetts Institute of Technology Division of Health Sciences and Technology and the Massachusetts General Hospital published findings on formal spectral analyses of heart rate fluctuations to evaluate PC and SC (5). Modern electronic and computer technology enable rapid analysis of the “power” of various fluctuating or periodic inputs to heart rate at frequencies from 0 to 0.5 Hz (0 to 30 cycles/min). High-frequency peaks at 0.4 Hz are the result of sinus arrhythmia. Because sinus arrhythmia can be completely alleviated by atropine, a muscarinic parasympathetic blocker, its measure is believed to be a “pure” measure of the parasympathetic input to heart rate variability at the frequency of respiration. Lower frequency peaks were found to be a mixture of SC and PC, and another input from the renin–angiotensin system was also identified. The equipment to perform such analyses is now readily available and has often been used to evaluate SC and PC in humans, both obese and non-obese, under a variety of conditions. In this issue of Obesity Research, Nagai et al. (6) make use of this method to evaluate the relationship of ANS activity to the development of obesity in Japanese school children. We have studied spectral analyses of heart-rate variability in human subjects (7), hoping that this relatively simple and noninvasive method would give reliable measures of SC and PC in human subjects as levels of fat storage are modified by feeding low or high calorie diets. For the reasons given below, we have found that the method has several shortcomings, and a more complex approach using pharmacological blockade becomes necessary for accurate assessment of ANS (8). The beat-to-beat interval (RR) in milliseconds is shown in the Nagai et al. study (6) of autonomic activity in obese and non-obese Japanese children. They illustrate the variation of heart rate in the “time domain,” and the same figure shows how these data can be reanalyzed in the “frequency domain,” indicating the influence or power of inputs at various frequencies. Peaks at 0.3 Hz in the children were attributable to respiration and used to measure PC, and the lower frequencies were ascribed to SC. Our approach to the evaluation of the ANS is shown in Figure 1. Heart rate variability in the time domain as was obtained with the Japanese children is shown in Figure 1A. A periodic function derived from the beat-to-beat variation in RR by spectral analysis is shown in Figure 1B as a series of regular undulations, cycling at the same rate as respiration. As shown in Figure 1C, when heart rate changes under 1 Nonstandard abbreviations: ANS, autonomic nervous system; SC, sympathetic control; PC, parasympathetic control; RR, beat-to-beat interval.

The year 2010 marked the centennial of the Rockefeller University Hospital, one of the great philanthropic achievements of 20th-century science. For 100 years, the Hospital played a central role in the development and growth of medical science by enabling physician-scientists to make intensive study of human biology and disease. With ingenuity and devotion, they greatly enriched clinical medicine as well as basic biological science. This account emphasizes the founding and first half-century of the Hospital as it became a germinal center for clinical investigation. The second half of the century saw rapid change in medicine and health care with vexing problems, many yet unsolved. This history should serve as a call to arms for maintaining the linkage of science and medicine, supporting patient-oriented research as a basic discipline of medicine.

After three decades of physiological research, the precise nature of the genetic lesion in Zucker fatty (fa/fa) rats remains unknown. Several methods have been used to identify preobese rats to detect the earliest phenotypic effects of the fa mutation. Most of these methods have used phenotypic characteristics that are not reliable until the second week of life, when increased adiposity is already evident. We have used a restriction fragment length polymorphism (RFLP) for a human genomic DNA probe (VC85) that is tightly linked to the fa locus on rat chromosome 5 to genotype the F2 progeny of a Zucker (13M) x Brown Norway (BN) fa/+ F1 intercross. Sixty-four rats, comprising five litters, were killed at 5-6 wk of age. DNA was isolated either from tail at age 4-7 days (36 rats) or from organs at the time of death (28 rats). Adiposity was scored using inguinal fat pad weight as a percentage of body weight. RFLP analysis was > 99% accurate in identifying obese (fa/fa) rats. This molecular genetic method can be used to genotype fatty rats from an appropriate genetic cross at any age, even prenatally. Moreover, this method can distinguish heterozygous from homozygous littermates, enabling an analysis of gene dosage effects.

Changes in autonomic function were studied during experimentally induced weight changes in seven subjects. A spectral analysis of heart rate variability (HRV) was used to evaluate autonomic activity during weight change. With a 10% increase in body weight above the usual or starting weight, there was a decline in parasympathetic power accompanied by a rise in mean heart rate. Heart rate declined during weight reduction, but the power of HRV did not change significantly. Because heart rate power at the frequency of respiratory rate can be affected by respiratory rate, three additional subjects were tested at a constant respiratory rate. Weight increases in this group also led to a decline in the power of HRV at a frequency attributable to the parasympathetic nervous system. Such a parasympathetic effect of weight increase may be one mechanism for the arrhythmias and other cardiac alterations that accompany obesity.

Adipose-tissue fatty acid composition was studied in nine patients requiring long-term total parenteral nutrition (TPN). The patients received 17 +/- 8% of total energy as soybean-oil emulsion (Intralipid) and 66 +/- 8% as glucose. Despite low intake of 9c-16:1, 11c-18:1, and 13c-18:1, adipose-tissue concentrations of these monounsaturated fatty acids were higher in the TPN patients than in free-living control subjects (P less than 0.05) and inversely correlated with the percent energy from fat (r = -0.56, P = 0.11; r = -0.64, P = 0.06; r = -0.81, P = 0.008, respectively). This suggests that these fatty acids accumulated from endogenous synthesis from carbohydrate and thus may be markers of the percent fat in the diet. The essential fatty acids, 18:2 and 18:3n-3, positively correlated with the percent energy from fat (r = 0.79, P = 0.01; r = 0.80, P = 0.01, respectively). Linear-regression analysis suggests that normal adipose-tissue stores of 18:2 and 18:3n-3 are maintained when intravenous soybean-oil emulsion provides 11-20% and 4-12%, respectively, of total energy.

Formerly or reduced-obese (RO) subjects exhibit diminished systemic energy requirements for weight maintenance. Based on studies in animals and humans, there is reason to believe that the autonomic nervous system (ANS) plays an important role in coordinate regulation of energy metabolism and may be altered in the RO state. We have, therefore, investigated aspects of autonomic physiology in obese (OB), RO, and never obese (NO) subjects subjected to insulin-mediated hypoglycemia and incremental intravenous infusions of epinephrine. Total catecholamine secretion during insulin-induced hypoglycemia was significantly lower in the RO. The RO showed increased sensitivity to in vivo lipolytic and cardiovascular effects of endogenous and infused catecholamines. In these studies, OB subjects responded more like the NO subjects than did the RO. The RO display characteristic changes in autonomic status that may play a role in their enhanced energy efficiency.

The relationships between the adipose tissue concentrations of 19 geometric and positional fatty acid isomers and 10 cardiovascular disease risk factors were determined in 76 free-living adult males. The percentages for trans isomers (total x ± SO 4.14 ± 0.97%) and cis isomers (total.\: ± SO 2.91 ± 0.34%) in adipose tissue generally agreed with dietary estimates based on the consumption of hydrogenated oils. A major ex­ ception was the percentage of II c-18: I. which was twofold higher in adipose tissue. The total level orratty acid isomers in adipose tissue or a factor (derived by factor analysis) that was represen­ tative of isomers ofdietary origin was not significantly correlated with the cardiovascular risk factors. Only three trans isomers (l1i-18: I. 12(-18: I. and 5(-14: I ) and three cis isomers ( II c-18: I. 13c-18: I. and 7c-16: I) were weakly correlated either positively or negatively with age. body mass index. plasma and lipoprotein cholesterol. and/or blood pressure (P 0.231 l. Am J Clin NlIir 1991 :53:474-82.

Background After weight loss, total energy expenditure -- in particular, energy expenditure at low levels of physical activity -- is lower than predicted by actual changes in body weight and composition. An important clinical issue is whether this reduction, which predisposes to weight regain, persists over time. Objective We aimed to determine whether this disproportionate reduction in energy expenditure persists in persons who have maintained a body-weight reduction of > or =10% for >1 y. Design Seven trios of sex- and weight-matched subjects were studied in an in-patient setting while receiving a weight-maintaining liquid formula diet of identical composition. Each trio consisted of a subject at usual weight (Wt(initial)), a subject maintaining a weight reduction of > or =10% after recent (5-8 wk) completion of weight loss (Wt(loss-recent)), and a subject who had maintained a documented reduction in body weight of >10% for >1 y (Wt(loss-sustained)). Twenty-four-hour total energy expenditure (TEE) was assessed by precise titration of fed calories of a liquid formula diet necessary to maintain body weight. Resting energy expenditure (REE) and the thermic effect of feeding (TEF) were measured by indirect calorimetry. Nonresting energy expenditure (NREE) was calculated as NREE = TEE - (REE +TEF). Results TEE, NREE, and (to a lesser extent) REE were significantly lower in the Wt(loss-sustained) and Wt(loss-recent) groups than in the Wt(initial) group. Differences from the Wt(initial) group in energy expenditure were qualitatively and quantitatively similar after recent and sustained weight loss. Conclusion Declines in energy expenditure favoring the regain of lost weight persist well beyond the period of dynamic weight loss.

When fragments of rat or human adipose tissue, or isolated adipocytes, are incubated with [14C]glucose in vitro, [14C]diacylglycerol accumulates rapidly: it comprises 20-50% of newly synthesized (14C-labeled) acylglycerols, compared to less than 1% diacylglycerol accumulated in the bulk lipid store in vivo. The experiments reported in this study were performed to test the possibility that agents that influence the rate of lipolysis might differentially affect the accumulation of di- and triacylglycerol in human adipose tissue, and perhaps account for the discrepancy between the early labeling and the later accumulation of diacyglycerol. Fragments of gluteal subcutaneous adipose tissue obtained from obese men and women were incubated with isoproterenol, epinephrine plus yohimbine, adenosine deaminase, or dibutyryl 3‘,5‘-cyclic adenosine monophosphate to stimulate lipolysis. Tissue fragments were also incubated with clonidine, adenosine, or insulin to inhibit lipolysis. No agent had any effect on the rate of accumulation of newly synthesized triacylglycerol. The effects of these agents on the rate of lipolysis were negatively correlated with their effects on accumulation of newly synthesized diacylglycerol. Newly synthesized diacylglycerol may be preferentially hydrolyzed by hormone sensitive lipase. This increased susceptibility to lipolytic stimulation, compared to newly synthesized triacylglycerol, may account for the minute accumulation of diacylglycerol in adipose tissue in vivo.

The anatomic distribution of fat is related to the risk for obesity-associated morbidity. Among individuals with equal degrees of relative adiposity, those with an upper-body preponderance of fat distribution (android) have higher rates of diabetes, stroke, ischemic heart disease, and early death than those with preferential deposition of adipose tissue in lower portions of the body (hips, thighs, buttocks; gynecoid. There are well-documented anatomic site-related differences in the relative activities of the adrenergic receptors ( β 1 → lipolysis; α 2 → antilipolysis) that control lipolysis. We assessed modifications of the status of α 2 - and β 1 -adrenergic receptor and subreceptor function in small fragments of adipose tissue obtained by needle biopsy from the gluteal and abdominal subcutaneous regions of five android, seven gynecoid, and six uniformly obese women during a period of weight maintenance (4 weeks) (T1), and after 15% weight loss on an 840 kcal/d diet (T2). Measurements of body shape and adipocyte size were made and related to changes in the metabolism of these adipocytes. The waist-to-hip ratio (WHR) was used to define these three types of regional distribution of fat in these obese subjects: android = WHR >0.86; gynecoid = WHR ≤ 0.76; uniform = WHR > 0.76 ≤ 0.86. WHR was not significantly altered by weight loss in any of the three groups. Although significant effects of time and/or anatomic site on in vitro responses to isoproterenol, norepinephrine, clonidine, forskolin, and dibutyryl cAMP were found, these did not correlate with intra-individual changes in anthropometry or adipocyte size. Thus, the mobilization of lipid from specific subcutaneous anatomic sites during long-term restriction of caloric intake does not appear to be related to alterations in the functional status of the adrenergic receptor or subreceptor mechanisms studied. The precise mechanisms by which the body regulates fat mobilization under these circumstances remain unknown.

The effect of adrenergic agents on protein phosphorylation in human adipocytes was examined. Freshly isolated human fat cells were incubated with 32PO4 in order to label intracellular ATP, then treated with a variety of adrenergic and other pharmacologic agents. Treatment with the β-adrenergic agonist isoproterenol led to a significant increase in phosphate content of at least five protein bands (Mr 52, 53, 63, 67, 84 kDa). The increase in phosphate content of at least five partially inhibited by the α-2 agonist clonidine. Epinephrine, a combined α and β agonist, was less effective at increasing phosphate content of the proteins than was isoproterenol. Neither insulin nor the α-1 agonist phenylephrine had any discernible effect on the pattern of protein phosphorylation. The 84 kDa phosphorylated peptide band appears to contain hormone-sensitive lipase, a key enzyme in the lipolytic pathway which is activated by phosphorylation. These results are somewhat different than previously reported results for rat adipocytes, and represent the first report of overall pattern and adrenergic modulation of protein phosphorylation in human adipocytes.

Who would not rejoice to find a magic bullet that we could fire into obese people to make them permanently slim and healthy? In the United States about a third of adults are obese—that is, have a body mass index (weight(kg)/height(m)2)) above 27.1 The diagnosis can be made with reasonable accuracy by anyone. Obese people appear “chunky” and usually have some abdominal protuberance with or without unsightly thighs. Tens of billions of dollars are spent on diets, pills, spas, or special foods and advice on behavioural change. Any scientific discovery that deals with food intake or obesity quickly becomes a “hot item” for the media. The best seller list usually contains a book giving recommendations for a new diet or mixture of diet and behaviour that assures successful weight control. Medical authorities, particularly public health officials, warn the public of the rising prevalence and hazards of obesity. A recent editorial in the New England Journal of Medicine documented the failures of current treatment and questioned the benefits of weight loss while reminding us of the strong correlation of obesity with disorders such as hypertension and diabetes.2 Since current treatment so often fails, only a magic bullet would allow us to perform an experiment to determine the full benefit of weight loss. Are we on the brink of finding a drug which will solve the problem? ### Summary points

EXPERIENCES WITH CHEMOTHERAPY FOR CANCER HAVE led to an enrichment in knowledge of the molecular basis for neoplastic disease; in turn, advances in molecular genetics have opened new approaches to cancer chemotherapy. This year marks the 60th anniversary of the first report of a trial of cancer chemotherapy, an event closely related to the development of chemical poisons for use in warfare. Clinical investigators were able to derive some good for mankind from the agony and pain resulting from chemical agents created primarily to destroy humans.

The study of appetitive behavior in relation to obesity is now being enriched by molecular-genetic findings in experimental animals with genetic obesity and associated "feeding disorders". The opinion is expressed that the mutual enrichment of the disciplines of behavior and molecular biology will place the study of human ingestive behavior on a firm scientific base.

A colleague once showed me a letter from the new financial manager of a distinguished academic hospital, warning all alumni that giving special assistance to fellow physicians or their families, so...

Maintenance of reduced or elevated body weight results in respective decreases or increases in energy expended in physical activity, defined as 24-h energy expenditure excluding resting energy expenditure and the thermic effect of feeding, beyond those attributable to weight change. We examined skeletal muscle work efficiency by graded cycle ergometry and, in some subjects, rates of gastrocnemius muscle ATP flux during exercise by magnetic resonance spectroscopy (MRS), in 30 subjects (15 males, 15 females) at initial weight and 10% below initial weight and in 8 subjects (7 males, 1 female) at initial weight and 10% above initial weight to determine whether changes in skeletal muscle work efficiency at altered body weight were correlated with changes in the energy expended in physical activity. At reduced weight, muscle work efficiency was increased in both cycle ergometry [mean (SD) change = +26.5 (26.7)%, P < 0.001] and MRS [ATP flux change = -15.2 (23.2)%, P = 0.044] studies. Weight gain resulted in decreased muscle work efficiency by ergometry [mean (SD) change = -17.8 (20.5)%, P = 0.043]. Changes in muscle efficiency at altered body weight accounted for 35% of the change in daily energy expended in physical activity.