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We measured the effects of iopanoic acid on thyroid hormone metabolism in obese men during severe calorie restriction to study the nutrition regulation of thyroid hormone metabolism. Eight morbidly obese men received a weight-maintenance diet followed by 6 wk of 600 kcal/d. During underfeeding, patients received iopanoic acid or placebo for 2-wk periods in a double-blind crossover fashion. Underfeeding alone (UF) produced a 28.3% decline in the serum triiodothyronine (T3) concentration, and iopanoic acid plus underfeeding (IOP) produced a 49.5% decline in T3 concentration from baseline. Serum reverse T3 concentrations increased 289% during IOP compared with UF alone (p less than 0.001). Serum TSH concentration was unchanged by underfeeding but increased twofold during IOP treatment. Thyroid hormone kinetics demonstrated a decrease in T3 production during IOP compared with UF. These findings suggest that calorie restriction regulates T3 production by modulating only type I 5'-deiodinase activity.

The effects of repeated administration of different macronutrient loads on spontaneous food intake and body weight of male Sprague-Dawley rats were studied. For 6 wk, eight groups of five rats each received two daily intragastric loads, 3.5 h apart, consisting of isocaloric amounts of one of the following: albumin, sucrose, cornstarch, corn oil, a mixture of the preceding four loads, butter, medium-chain triglyceride, or a noncaloric load of water. Spontaneous intakes of rat chow were measured 3.5 and 24 h after the first daily load. All the macronutrient loads depressed subsequent 3.5-h intakes more than the water load (P less than 0.01), and protein loads depressed 3.5-h intakes the most (P less than 0.01). The macronutrient loads also depressed 24-h intakes more than water loads (P less than 0.01) but did not differ among themselves. The mixture load depressed 3.5- and 24-h food intakes by an amount comparable with the average effects of its component loads. Neither body weight nor body fat as measured by the Lee index differed among the groups after 6 wk. The results indicate that fairly accurate long-term regulation of spontaneous energy intake occurs regardless of the type of macronutrient in the load.

This study examined changes in body fat distribution in 68 women who lost an average of 12.3 kg from an initial weight of 103.6 kg. Weight reduction was accompanied by a small but statistically significant reduction of 1.2% in the waist-to-hip ratio, suggestive of a reduction in upper-body obesity. Subjects with greater upper-body obesity tended to achieve greater reductions in the waist-to-hip ratio. Changes in five circumference measures were highly correlated with losses of fat and showed that subjects with lower-body obesity tended to lose large amounts of fat from both their upper and lower fat depots while subjects with upper-body obesity lost fat primarily from their upper depots. Women with lower-body obesity tended to lose more total body fat than did women with upper body obesity (r = -0.26, p less than 0.04).

A universal eating monitor has been developed that permits covert continuous weighing of a subject's plate or other food reservoir by means of a concealed electronic balance. By coupling the device with a digital computer, it is possible to record precisely the amount consumed every 3 s throughout a single-course meal consisting of a relatively homogeneous mixture of foods. The monitor have been used to compare total intake, meal duration, initial rate of intake, and deceleration of intake in human subjects ingesting either a solid or liquid version of the same food after 3 or 6 h without food. It was found that the liquid form was eaten faster than the solid form, but that total amounts consumed in each form were not significantly different. These results suggest that when the rate of consumption is controlled by the physical consistency of the food, the amount eaten is not determined by the rate of consumption alone. Further studied are necessary to determine the relative roles of visual cues and interoceptive signals on quantity eaten.

INTRODUCTION AND SCOPE 371 DEFINITIONS 373 PHENOMENA TO BE EXPLAINED 375 THEORIES 386 TESTS OF THE THEORIES BY NUTRIENT ADMINISTRATION 392 MECHANISMS 402 CONCLUSIONS 405

During 1977 and 1978, 17 obese but otherwise healthy adult Americans died suddenly of ventricular arrhythmias during or shortly after completing rapid, massive weight reduction induced by very low-calorie diets consisting largely of collagen hydrolysates for 2 to 8 months. A reexamination of the data on these victims has disclosed a significant positive correlation (r = 0.824) between their prediet body mass index and their duration of survival on the very low-calorie diets. Since body mass index reflects degree of fatness, this observation indicates that the ability to defer the lethal effects of severe caloric restriction was a function of the proportion of body fat before dieting. During caloric reduction, the ratio of nitrogen loss to weight loss is inversely related to body fat content; accordingly, we suggest that the fattest dieters survived the longest because they were better able to conserve body (and myocardial) protein. Also, obese people have an enlarged lean body mass which may afford additional protection.

This study validated further the bioelectrical impedance analysis (BIA) method for body composition estimation. At four laboratories densitometrically-determined lean body mass (LBMd) was compared with BIA in 1567 adults (1069 men, 498 women) aged 17-62 y and with 3-56% body fat. Equations for predicting LBMd from resistance measured by BIA, height, weight, and age were obtained for the men and women. Application of each equation to the data from the other labs yielded small reductions in R values and small increases in SEEs. Some regression coefficients differed among labs but these differences were eliminated after adjustment for differences among labs in the subjects' body fatness. All data were pooled to derive fatness-specific equations for predicting LBMd: the resulting R values ranged from 0.907 to 0.952 with SEEs of 1.97-3.03 kg. These results confirm the validity of BIA and indicate that the precision of predicting LBM from impedance can be enhanced by sex- and fatness-specific equations.

The background information is reviewed regarding the American Society for Clinical Nutrition task force consensus statement on calories. Prevention or treatment of obesity necessarily involves manipulation of energy intake and output. The most important public health disorders to which obesity contributes are cardiovascular disease, diabetes mellitus, gallbladder disease, psychosocial disability, and musculoskeletal disorders. Other conditions associated with obesity include renal disease, liver disorders, ventilatory defects, venous stasis and thromboembolisms, gout, cerebrovascular disease, and (in women) endometrial and possible breast cancer. Obese persons are open to greater risk from surgery, anesthesia, and accidents, and they have a high rate of employee absenteeism. Statistics regarding relative body weight and longevity are examined.

An inventory control model is used to describe the regulation of depot fat and contribution made to the satiation process by putative feedback signals. In the two bin inventory control system, adipose tissue is viewed as a large storage reservoir which is periodically refilled by means of adjustments made in meal consumption. The gastrointestinal tract is viewed as a smaller bin which triggers renewed food ingestion when it becomes partially emptied. However, reduction in the contents of the adipose tissue bin below a critical level (reorder point quantity) generates a signal to the brain that appropriately modulates meal size and intermeal interval. Because this model evolved to cope with worst case situations, a strong bias for storage in time of plenty is inherent in the system. This fact helps to account for the high prevalence of obesity in energy-rich societies, where, in contrast to the situation that obtains in primitive societies, the energy cost of obtaining food is minimal.

It has been suggested that sufficient fiber in the diet will tend to prevent excessive food intake and depot fat accumulation by decreasing the caloric density of the diet, stowing rate of food ingestion, increasing the effort involved in eating, promoting intestinal satiety, and interfering slightly with efficiency of energy absorption. The increase in the prevalence of obesity in Western countries since 1900 has taken place concurrently with marked changes in the nature of the diet. Per capita intake of dietary fiber associated with starchy foods has greatly decreased, but intake of fiber associated with fruits and green vegetables has increased. Thus, although the type of fiber in the diet has changed, the total quantity may not have diminished considerably. Studies of the effect of caloric dilution with cellulose and other metabolically inert bulking agents have disclosed little or no inhibitory effect on the spontaneous energy intake of nonobese laboratory animals and human subjects. Nevertheless, there is evidence that obese rats and humans may defend their excess weight against nutritive dilution with less tenacity than their nonobese counterparts. The hypothesis that dietary fiber can protect against obesity therefore deserves further testing since an increase in the fiber content of the diet may tend to prevent overeating and excessive weight gain even if it does not reduce spontaneous energy intake in nonobese organisms.

This study 1) further validated the relationship between total body electrical conductivity (TOBEC) and densitometrically determined lean body mass (LBMd) and 2) compared with existing body composition techniques (densitometry, total body water, total body potassium, and anthropometry) two new electrical methods for the estimation of LBM: TOBEC, a uniform current induction method, and bioelectrical impedance analysis (BIA), a localized current injection method. In a sample of 75 male and female subjects ranging from 4.9 to 54.9% body fat the correlation between LBMd and LBM predicted from TOBEC by use of a previously developed regression equation was extremely strong (r = 0.962), thus confirming the validity of the TOBEC method. LBM predicted from BIA by use of prediction equations provided with the instrument also correlated with LBMd (r = 0.912) but overestimated LBM compared with LBMd in obese subjects. However, no such systematic error was apparent when new prediction equations derived from this heterogeneous sample of subjects were applied. Thus the TOBEC and BIA methods, which are based on the differing electrical properties of lean tissue and fat and which are convenient, rapid, and safe, correlate well with more cumbersome human body composition techniques.

Five different procedures were used to estimate composition of weight loss by six obese individuals maintained on low-calorie regimens: 1) energy-nitrogen (E-N) balance; 2) total body water-nitrogen balance (TBW-N); 3) total body water (TBW); 4) total body potassium (TBK); and 5) an anthropometric method. Quantity of weight lost by obese subjects during comparison periods lasting 25–40 days ranged from 7.9 to 17.1 kg. Expressed as percent of aggregate weight loss, collective fat loss was 47.6 by E-N balance; 46.3 by TBW-N balance; 51.7 by TBK; 50.9 by anthrometry; and 33 by TBW. The E-N balance method yielded a tight cluster of individual means, whereas the other procedures gave a wide scatter of means. For short-term studies, the E-N balance procedure, although tedious and difficult, should yield results less variable than those generated by any of the other methods examined.

The effects of starvation, an 800-kcal mixed diet and an 800-kcal ketogenic (low carbohydrate-high fat) diet on the composition of weight lost were determined in each of six obese subjects during three 10-day periods. The energy-nitrogen balance method was used to quantify the three measurable components of weight loss; protein, fat, and water. On the 800-kcal ketogenic diet, subjects lost (mean +/- SE) 466.6 +/-51.3 g/day; on the isocaloric mixed diet, which provided carbohydrate and fat in conventional proportions, they lost 277.9+/- 32.1 g/day. Composition of weight lost (percentage) during the ketogenic diet was water 61.2, fat 35.0, protein 3.8. During the mixed diet, composition of loss was water 37.1, fat 59.5, protein 3.4...

The study was designed to determine whether overfeeding rats with a diet containing medium-chain triglyceride (MCT) as the major fat source (45% of calories) would impede the expected gain in weight and body fat as compared to rats overfed with isocaloric amounts of diet containing long-chain triglyceride (LCT). For 6 wk rats were fed either MCT diet or LCT diet twice daily via a gastrostomy tube. MCT-fed rats gained 20% less weight (P less than 0.001) and possessed fat depots weighing 23% less (p less than 0.001) than LCT)-fed rats. Mean adipocyte size was smaller (p less than 0.005) in MCT- than in LCT-fed rats. Weights of carcass protein and water were similar for both groups as were concentrations of serum insulin and levels of physical activity. The decreased deposition of fat in the MCT-fed rats may have resulted from obligatory oxidation of MCT-derived fatty acids in the liver after being transported there via the portal vein, leaving almost no MCT derivatives for incorporation into body fat. MCT may have potential for dietary prevention of human obesity.

A new method for the estimation of body composition in human subjects is described which entails the measurement of total body electrical conductivity. The method is based on the principle that the electrical conductivity of lean tissue is far greater than that of fat. Comparative studies in 19 adults of widely varying fatness have demonstrated excellent correlations between the total electrical conductivity of the subjects and both their total body water (r = 0.87) and total body potassium (r = 0.86). This noninvasive method, which is safe, simple, rapid, and convenient, should prove useful in the nutritional assessment of individuals and populations.

Although the association between body weight and blood pressure is irrefutable, body fat mass and blood pressure level may not necessarily be directly related. To clarify the relative contribution of fat mass to blood pressure level, we analyzed data on 399 adults consecutively entering a weight control program. Although most subjects were notably overweight (mean ideal body weight 177%), the population represented a wide spectrum of body weights and blood pressure levels. Study parameters included body fat mass (by total body water, 40K, and Steinkamp formula), lean body mass, body build (chest to height ratio), fat cell number and size from bilateral buttock biopsy specimens, upper fat pattern by arm to thigh circumference ratio, and central fat pattern by subscapular to triceps skinfold ratio. Our results concurred with previously noted correlations between obesity and blood pressure (as mean arterial pressure): weight (r = 0.44), percentage of body fat (r = 0.19), and absolute fat mass (r = 0.38; all p less than 0.01); however, lean body mass, age, and body build correlated highly with both fat mass and mean arterial pressure, thereby confounding this relationship. Multivariate analysis was performed to evaluate the relative contribution of fat mass to mean arterial pressure in the presence of these and other potentially confounding variables. Lean body mass, age, body build, and an upper body fat pattern were found to contribute significantly to the variation in mean arterial pressure (p less than 0.01). In their presence, percentage of body fat, absolute fat mass, central fat pattern, fat cell characteristics, and age of onset of obesity did not significantly improve the predictability of mean arterial pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose tissue, the logical target component in weight reduction regimens, was measured in five obese subjects during weight reduction, and in four normal weight controls. The two compartment model of Ljunggren, consisting of adipose tissue (AT) and adipose tissue-free mass (AFM), was further developed by finding experimental values for total water, extracellular water (ECW), lipid, and cell solids in 16 biopsied subjects. The AFM was estimated from body potassium content (40K counting) by use of an age/sex specific constant for the K content in the fat free body. Five obese subjects maintained for 46 days on regimens averaging 800 kcal/day had initial AT from 48% to 60% of body weight compared with AT 27% to 46% in four normal controls. Weight reductions averaged 17.4 kg (12% of initial weight), with approximately equal reductions in adipose tissue, adipose-free mass, and water. Initial fluid compartment ratios in the obese were unusually high (ECW:ICW in AFM was 0.74 +/- 0.23 [S.D.] compared with 0.42 +/- 0.05 in normals); these values returned toward normal (to 0.59 +/- 0.06) with weight reduction. The fact that it was possible to disclose a hitherto unappreciated abnormality of hydration in the adipose-free mass of obese subjects and its change toward normal with weight reduction, suggests that the adipose:adipose-free model may have a special utility when body composition measurements are used to monitor the effects of weight reduction regimens on various body constituents.

Fat patterning was studied in a sample of 76 obese women before and after weight reduction by principal components analysis. Circumferences were selected as variables rather than skinfolds because circumferences correlated more highly with body composition determined either by total body water or total body potassium. A separate sample of 136 males and females, measured once, was employed to validate the results. The validation sample yielded similar findings. Two significant components were found, the first contrasting upper and lower fatness and the second trunk and extremity fatness. Waist circumference was the best predictor of upper-body fat patterning. For the lower body, thigh circumference loaded more highly than did the iliac crest circumference. Arm circumference did not contribute significantly to upper-lower fat patterning.

The spontaneous food intake of six normal-weight male volunteers was measured for 24 days while the subjects were inpatients on a metabolic unit. They were fed a palatable diet of conventional foods and were kept unaware that their food intake was being measured. On days 7-18 the caloric content of their diet was covertly reduced by 25% by substituting aspartame-sweetened analogues for all menu items containing sucrose. Subjects did not alter their food intake for 3 days. Then between days 4-6 on the aspartame diet, they increased their intake to compensate for 40% of the missing calories. Food intake stabilized at 85% of baseline and remained the same for the rest of the 12-day dilution period. Subjects did not show a shift in either sweetened or unsweetened food choices while their diet was being diluted. In adjusting for the missing calories, they simply ate more of their customary diet. The replacement of sucrose by aspartame tended to curb the weight gain observed on the baseline diet.

Four-pi whole body counting for the 1.46 meV photon of 40K has apparent advantages over single-crystal or two-pi counters in efficiency and in subject geometry independence. However, our studies of obese populations have disclosed a systematic undermeasurement of 40K, suggesting that nonhomogeneous K distribution results in systematic undercounting of 40K. In the current study 42K, emitting a 1.52 meV photon, was used in 109 volunteers ranging from 50 to 181 kg, and multiregression covariance analysis was applied to develop correction formulas based on anthropometrics. These corrections quantitatively account for the unappreciated loss of 40K and 42K photons in annular adipose tissue that surrounds the lean body, in which most K+ is concentrated. The correction ranges from 1 to 28% and is a linear (although different) function of weight in both sexes. Thus corrected, body potassium measurements, taken in conjunction with exchangeable sodium and water measurements, provide estimates for whole body osmolality that match measured serum values. Such a quantitative accounting for previously "lost" cation in 58 subjects provides independent evidence for the appropriateness and accuracy of the correction. With this correction, body potassium was recalculated in the 1,492 adult members of a previously reported group of 3,083 subjects.

SummaryAdministration of glucagon intravenously to 7 normal subjects resulted in prompt abolition of gastric hunger contractions on each of 16 occasions. This was associated with decrease in the experience of hunger and coincided with a rise in blood glucose levels and an increased peripheral capillary-venous glucose difference. Fall in blood glucose levels with decreasing capillary-venous differences was associated with a return of hunger contractions and intensification of the experience of hunger in 14 of the 16 occasions. Such a pattern may be a component of the normal satiety mechanism.

NUTRITION in clinical medicine has come to have several different connotations depending on whether one is thinking of diagnosis and specific treatment or of patient management. Under the first hea...

The ingestion of a diet higher in caloric content than is required for energy needs leads to energy storage; this is accomplished by the deposition of triglycerides in adipose tissue. There is no clear evidence that the metabolic burden of excess calories is in any way hazardous to health except insofar as it leads to weight gain and eventually to obesity. Some studies show that a high caloric intake coupled with physical exertion that is sufficiently increased to maintain energy balance may be more beneficial to health than is a lower caloric intake balanced by a reduction in physical activity. Caloric intake and physical activity are so interrelated that it is impossible to gauge the effects of one independently of the other.

This comparative study, conducted on 28 boys and girls of widely varying fatness, was designed to validate a new whole-body composition method [total body electrical conductivity (TOBEC)], based on bioelectrical properties of the human body. A significant correlation [r = 0.911; standard error of the estimate (SEE) = 5.3 kg] was demonstrated between the transformed TOBEC scores (TOBEC0.5 X Ht) and lean body mass (LBM) determined by hydrodensitometry and corrected for individual variations in hydration (LBMd + W). TOBEC determinations also correlated well with 1) total body water determined by deuterium oxide dilution (r = 0.877; SEE = 4.5 liters), 2) total body potassium determined by means of a 4 pi whole-body counter (r = 0.860; SEE = 430.7 meq), 3) LBM derived from skinfold thicknesses (r = 0.850; SEE = 5.8 kg). The residuals of the regression between LBMd + W and TOBEC scores did not show any significant correlation with either the potassium or the water content of the LBM. The results indicate that TOBEC is a simple, rapid, reliable, and noninvasive technique for delineating changes in body composition that occur in children during growth.

The association of obesity and hyperlipidemia does not mean that fatness per se is the primary determinant of the lipid abnormality. To evaluate the contribution of fatness to fasting levels of serum triglycerides (TG), LDL cholesterol (LDL-C), and HDL cholesterol (HDL-C), we analyzed data on 368 caucasian adults (286 women, 82 men) consecutively entering a weight control program. Although most subjects were overweight, the population represented a wide spectrum of body weights and lipid levels. Study variables included body fat mass (by total body water), fat free mass (FFM), body build (chest to height ratio), fat cell size and number (from bilateral buttock biopsy specimens), upper-lower body fat pattern by arm to thigh circumference ratio, central-peripheral fat pattern by subcapsular to triceps skinfold ratio, waist to hip ratio, and the presence or absence of diabetes. Our results concurred with previously noted correlations of body weight with TG (r = 0.29, P less than 0.0001) and with HDL-C (r = -0.28, P less than 0.0001) at least in the larger sample of women, but there was no significant correlation with LDL-C (r = -0.06). In order to evaluate the relative contribution of the various components of body composition and fat distribution to lipid levels, stepwise regression analyses were performed on the subgroups of women and men. Among women: TG level was predicted best by FFM, upper body fat pattern, age, and diabetes (explaining 30 percent of TG variance); LDL-C level was predicted by age only (explaining 12 percent of variance); and HDL-C level was predicted by body build only (8 percent). Among men: TG level was predicted best by central and upper body fat patterns and diabetes (31 percent of variance); LDL-C and HDL-C levels were not significantly predicted by any of the 11 study variables. These results, obtained from cross-sectional analysis of a predominantly obese sample, suggest that lipid levels may be more directly related to body fat pattern, fat free mass and body build than to body fatness itself.

Serum transaminase levels were measured as part of a study on the physiologic control of food intake. Twenty-one men, 15 nonobese and six obese, were housed on a metabolic ward for 30 days where they received ad libitum a baseline diet of conventional foods containing 25 to 30 percent of total calories as sucrose for 18 days and a calorically diluted diet containing less than 10 percent sucrose for 12 days. Serum glutamic pyruvic transaminase (SGPT) and serum glutamic oxaloacetic transaminase (SGOT) levels rose significantly when subjects consumed the baseline diet and returned to their original levels on the calorically diluted aspartame-sweetened diet. Markedly abnormal transaminase levels developed in two subjects on the baseline diet and they had to be discharged from the study. Correlations between various components of the diet and enzyme changes suggested that both surplus calories and a high sucrose intake played a role in the elevation of enzyme levels. Serum triglyceride levels also showed a significant reduction when the subjects were switched from the baseline to the calorically diluted diet. In a second study designed to test systematically the role of sucrose on SGPT and SGOT levels and on serum triglyceride levels, six nonobese subjects received a carefully controlled liquid diet, relatively high in linoleic acid content, containing 50 percent of total calories as either sucrose or maltose. In comparison with the first study, sucrose had a smaller but still significant effect on the levels of both enzymes, but there was no significant effect on triglyceride levels.

The present study investigated the feasibility of a new experimental approach for studying the effect of covert nutritive dilution on the spontaneous food intake of obese individuals. Eight obese subjects were studied as inpatients on a metabolic unit for 15 days during which time they were unaware that their food intake was being monitored. A platter method of food presentation encouraged ad libitum ingestion. Caloric dilution was achieved by replacing sucrose-containing products with aspartame-sweetened analogues in an otherwise normal diet. During the base-line period the subjects spontaneously ate sufficient conventional food to maintain or even slightly increase body weight. Covert substitution of aspartame-sweetened products for their sucrose counterparts resulted in an immediate reduction in spontaneous energy intake of approximately 25%. The aspartame analogues were as well accepted as their conventional counterparts, as indicated by the equal quantity of each consumed. These preliminary results demonstrate that, in a metabolic ward setting, it is possible to maintain the spontaneous food intake of obese individuals at levels sufficient to preserve body weight and arbitrarily to decrease those levels of intake by 25% or more through covert changes in the caloric density of the diet.

O delineate the role of nutrition in the regulation of blood pressure and the pathogenesis of hypertension, the National Heart, Lung, and Blood Institute in conjunction with the National Institute on Aging and the National Institutes of Health Nutrition Coordinating Committee, sponsored a Workshop on Nutrition and Hypertension in Bethesda, Maryland, on March 12 to 14, 1984. The purpose of the workshop was to identify the research needed to strengthen the understanding of the relationships between nutrition, blood pressure regulation, and hypertension. This research is important for two reasons: first, there is still an enormous amount of knowledge to be gained about the pathogenesis of hypertension, and any insights that can be derived about nutritional influences are highly desirable. Second, because the majority of patients with elevated blood pressure fall in the borderline and mild hypertensive categories, there is a need to support research on nonpharmacological strategies for management of these patients, in particular, nutritional interventions. The format of the workshop consisted of two major activities: position papers on selected dietary nutrients that may influence blood pressure and working group sessions devoted to the specification of research objectives. In addition to touching on an overview of hypertension and nutrition research methods, the position papers expounded on the roles of sodium and other electrolytes; caloric intake and obesity; dietary proteins, amino acids, carbohydrates, alcohol, and trace metals; and dietary fats and prostaglandins. Nutritional considerations of special populations, including the young and the elderly

Six morbidly obese subjects were maintained in a metabolic ward for 64 days on liquid diets providing 600 to 800 kcal/day. Three received protein at a level of 1.5 g/kg desirable weight per day. The other three were given an identical diet in which half the protein was replaced by carbohydrate. Because there were no significant differences in either mean protein or mean fat losses between the two groups, the data on all six subjects were combined. Over the 64 days, the mean weight loss (±SEM) ofthe subjects per 1000 kcal deficit was 174.3 ± 25.5 g. The composition of this weight loss was 36.0% water, 58.9% fat, and 5.1% protein. Although the rate of fat loss was relatively constant throughout the study, wide interindividual variations in cumulative protein (nitrogen)deficit were observed. Total nitrogen losses per subject ranged from 90.5 to 278.7 g. Cumulative nitrogen loss during the first 16 days tended to correlate negatively with initial mean fat cell size and positively with initial lean body mass. Most notable was the strong negative correlation between the size of the decrease in serum triiodothyronine over the 64-day study and the magnitude of the concurrent cumulative N deficit. During severe caloric restriction, one's ability to decrease circulating serum triiodothyronine levels may be critical to achievement of an adaptational decrease in body protein loss. Am J C/in Nuir l984;40:6l1-622.