Thermogenesis after a mixed meal: role of leg and splanchnic tissues in men and women

To determine the relative contribution of splanchnic and leg tissues to postprandial thermogenesis, systemic and regional oxygen consumption rates were measured in nine women and eight men before and for 6 h after the consumption of a mixed meal that provided one-third of the daily energy needs. In women, the increase in splanchnic oxygen uptake accounted for 63 +/- 12% of the postprandial increase in oxygen consumption, whereas in men it accounted for 35 +/- 14% (P = not significant between women and men). Leg oxygen uptake accounted for 11 +/- 4 and 10 +/- 3% of the increase in postprandial oxygen consumption in women and men, respectively. The combined data suggest that approximately 48% of postprandial thermogenesis over 6 h occurs in splanchnic tissues, whereas 30-35% occurs in skeletal muscle. Thus the increase in oxygen consumption after a mixed meal is primarily localized to splanchnic tissues, and major reductions in postprandial thermogenesis are unlikely to be attributable solely to abnormalities of skeletal muscle metabolism.

Measurement of abdominal and visceral fat with computed tomography and dual-energy x-ray absorptiometry

These studies were undertaken to compare dual-energy x-ray absorptiometry (DXA) and computed tomography (CT) measurements of abdominal fat and to determine whether anthropometry could be combined with DXA to predict intraabdominal (visceral) fat mass in humans. Twenty-one volunteers underwent abdominal CT scans, DXA, and anthropometry. DXA- and CT-measured total abdominal fat were similar (8448 +/- 5005 and 8066 +/- 5354 mL, respectively; NS) and were highly correlated (r = 0.985, P < 0.001). The combination of anthropometry and DXA was a suboptimal predictor of CT-measured intraabdominal fat (r = 0.61, P < 0.05); however, the combination of a single CT slice (to assess the ratio of intraabdominal to total abdominal adipose tissue) and DXA-measured abdominal fat was an excellent predictor of CT-measured intraabdominal fat (r = 0.98, P < 0.001). We conclude that a single-slice CT scan (or other imaging technique) with or without DXA is required for accurate predictions of intraabdominal fat.

Technical and practical considerations involved in operations on patients weighing more than 270 kg

Care of the patient with superobesity requires special precautions and appropriate equipment. Recently, we performed bariatric procedures (modified very-long-limb Rouxen-Y gastric bypass) on patients weighing 355 kg and 377 kg. These procedures required preoperative preparation concerning safe means of transport of the patient, techniques of anesthesia and intraoperative exposure, provisions for postoperative recovery, and measures to assure patient comfort and hygiene postoperatively. In addition to specially designed bariatric procedures for the superobese, specialized equipment is needed to protect the health of the patient and the staff. All health care providers and especially acute care centers must have preconceived protocols to treat the superobese patient. In addition, specialized equipment is necessary to allow safe transport and support of these patients.

Effects of isoenergetic, low-fat diets on energy metabolism in lean and obese women

Whether changing from a high-fat diet to an isoenergetic, low-fat, high-complex-carbohydrate diet results in thermogenic benefits is controversial. Brief dietary interventions and failure to account for the potential influence of body-fat distribution on energy metabolism could have confounded the interpretation of previous studies. To address these issues, eight upper-body obese, seven lower-body obese, and eight non-obese premenopausal women underwent measurements of body composition, resting energy expenditure, overnight energy expenditure, and meal fat oxidation at the end of a weight-stabilizing, high-fat (42%) diet, and after 4 wk of an isoenergetic, low-fat (27%) diet. No change in body composition, resting energy expenditure, overnight energy expenditure, or meal fat oxidation occurred. We conclude that isoenergetic shifts from dietary fat to dietary carbohydrate within the generally recommended range have little or no effect on energy metabolism, and that body-fat distribution does not predict differences in energy expenditure.

Serum lipid responses to a eucaloric high-complex carbohydrate diet in different obesity phenotypes

OBJECTIVE

To determine whether the eucaloric substitution of complex carbohydrates for dietary fat (15% of daily energy intake) affects plasma lipid concentrations differently in upper-body obese, lower-body obese, and nonobese women.

DESIGN

We studied 23 premenopausal women before and after dietary intervention.

MATERIAL AND METHODS

After the 23 subjects achieved weight maintenance on their usual high-fat diet (43% fat, 37% carbohydrates, and 20% protein), the 7 upper-body obese, 8 lower-body obese, and 8 nonobese women consumed a eucaloric, high-complex carbohydrate, low-fat diet (27% fat, 53% carbohydrates, and 20% protein) for 4 weeks in the Clinical Research Center. Before and after the high-carbohydrate diet, body composition and plasma lipids and apoproteins were measured.

RESULTS

After the high-carbohydrate diet, fasting plasma triglyceride concentrations increased (from 1.50 +/- 0.14 mmol/L to 2.00 +/- 0.25 mmol/L; P = 0.04) in upper-body obese women but were not significantly changed in lower-body obese (1.37 +/- 0.28 mmol/L and 0.96 +/- 0.12 mmol/L) or nonobese (0.70 +/- 0.08 mmol/L and 0.73 +/- 0.08 mmol/L) women. The hypertriglyceridemia was present before the evening meal and throughout the night in upper-body obese women. Plasma cholesterol and high-density lipoprotein cholesterol were not significantly affected by the change in diet. No changes in plasma apoprotein concentrations or body composition occurred that could account for the dietary-induced hypertriglyceridemia in the women with upper-body obesity.

CONCLUSION

The hypertriglyceridemic response to a high-complex carbohydrate, low-fat diet may be obesity phenotype specific. These findings suggest that further studies of this phenomenon should be focused on this obesity phenotype and further emphasize the importance of assessing body fat distribution when treatment outcomes are determined.

Effects of estrogen on free fatty acid metabolism in humans

To determine whether estrogen directly affects effective adipose lipolysis, palmitate rate of appearances ([14C]palmitate) was measured in 15 postmenopausal women. Each volunteer was studied after > or = 2 mo of estrogen treatment and again after > or = 2 mo of estrogen deficiency. Plasma hormone concentrations were controlled and identical on the 2 study days with use of the pancreatic clamp technique, and the lipolytic response to epinephrine and epinephrine + phentolamine was assessed. Results showed that overall palmitate flux was greater (10-20%, P < 0.05) during the estrogen-deficient than during the estrogen-replete study. Adrenergic stimulation of lipolysis was not specifically influenced by estrogen treatment, and control of plasma hormone concentrations did not eliminate the difference in palmitate flux between the estrogen-deficient and estrogen-replete study days. We conclude that estrogen deficiency is associated with increased plasma free fatty acid availability and that estrogen likely has direct, albeit small, effects on adipose tissue lipolysis.

In vivo regulation of lipolysis in humans

Fatty acids are important oxidative fuel for liver, kidney, skeletal muscle, and myocardium. There has been much interest in the role of fatty acids in the pathogenesis of non-insulin-dependent diabetes because they compete with glucose for oxygen and inhibit whole body glucose disposal via the 'Randle cycle,' Control of lipolysis in adipose tissue determines systemic fatty acid supply. A wide range of hormones and other substances have been recognized as regulators of lipolysis, but insulin and catecholamines appear to be the most important. The regulation of lipolysis, in most circumstances, provides a supply of lipid fuel exceeding the rate of lipid oxidation, requiring reesterification to triglyceride of surplus circulating free fatty acids. Thus, free fatty acid supply is usually not matched to the demand for lipid oxidation, and there is no known mechanism for accurately sensing such demand. This lax regulation may be disadvantageous in conditions such as aging, stress, obesity, and diabetes, where the antilipolytic effect of insulin is impaired and lipolysis is therefore increased. In these conditions, the surfeit of fatty acid may impair glucoregulation. In addition, the excess lipolysis may induce hypertriglyceridemia (via increased very low density lipoprotein production) and thus contribute to atherogenesis. Considerable additional research is needed in order to fully understand both normal lipolytic regulation and the abnormalities of lipolysis which accompany pathological conditions.

Postprandial free fatty acid kinetics are abnormal in upper body obesity

Excess free fatty acid release (rate of appearance) is seen in overnight postabsorptive, upper body obese women and, if present postprandially, could contribute to glucose intolerance. These studies examine the antilipolytic effect of a mixed meal in upper body obese, lower body obese, and nonobese women and the contribution of meal triglyceride fatty acids to circulating free fatty acids. Eight upper body obese, 8 lower body obese, and 8 nonobese age-matched, premenopausal women were studied. Systemic oleate Ra ([3H]oleate) was measured before and after an evening meal that contained triolein labeled with [14C]triolein as the only source of fat. Premeal oleate Ra was greater in both upper body obese and lower body obese women than nonobese women. The nadir of total oleate Ra occurred 90-240 min postprandially and was less (P < 0.01) in nonobese and lower body obese women (63 +/- 10 and 87 +/- 17 mumol/min) than in upper body obese women (140 +/- 21 mumol/min). Meal oleate Ra contributed substantially to total oleate Ra. The nadir for endogenous oleate Ra in nonobese and lower body obese women was less (P < 0.01) than that observed in upper body obese women. We conclude that the antilipolytic effect of a mixed meal is reduced in upper body obese women and that meal triglyceride fatty acids contribute significantly to postprandial free fatty acid flux.

Assessment of body composition with use of dual-energy x-ray absorptiometry: evaluation and comparison with other methods

Dual-energy x-ray absorptiometry (DEXA) is a relatively new method of assessing body composition in humans. In the current study, DEXA was analyzed for accuracy and precision by using both anthropomorphic phantoms and a combination of body composition techniques in humans. Satisfactory precision for measurement of total body fat, fat-free mass, and total body bone mineral could be demonstrated in vivo and in vitro. Predictions of lean body mass in humans on the basis of DEXA, total body water, and total body potassium were significantly different. The results of multiple regression analysis suggested that a component of total body water was related to body potassium, and another component was predicted by body fat. In addition, extracellular fluid volume, as measured by the bromide space technique, was significantly associated with both fat-free mass and fat mass as measured by DEXA. These findings have implications for the interpretation of body composition data in humans.

Fatty acid kinetic responses to exercise. Effects of obesity, body fat distribution, and energy-restricted diet

Upper body obesity (UB Ob) is associated with a reduced net free fatty acid (FFA) response to epinephrine compared with nonobese (Non Ob) and lower-body obese (LB Ob) women. Because catecholamines regulate some of the metabolic responses to exercise, we hypothesized that UB Ob would have a reduced net FFA response to exercise. Plasma FFA rate of appearance (Ra) ([1-14C]palmitate) and fatty acid oxidation (indirect calorimetry) were therefore measured during 2.5 h of stationary bicycle exercise (45% VO2 peak) in 13 UB Ob, 11 LB Ob, and 8 Non Ob premenopausal women. 10 UB Ob and 8 LB Ob women were retested after an approximately 8-kg weight loss.

RESULTS

During exercise Non Ob and LB Ob women had greater increments in FFA availability (51 +/- 7 and 53 +/- 8 mmol, respectively) than UB Ob women (27 +/- 4 mmol, P < 0.05). Total exercise FFA availability and fatty acid oxidation were not different between Non Ob, LB Ob, and UB Ob women, however. Following weight loss (approximately 8 kg), the FFA response to exercise increased (P < 0.01) and remained greater (P < 0.05) in LB Ob than in UB Ob women. In conclusion, the FFA response to exercise was reduced in UB Ob women before and after weight loss, but no effects on fatty acid oxidation were apparent.

Effects of exercise and weight loss on leucine turnover in different types of obesity

These studies were performed to determine whether protein turnover during exercise and after weight loss is influenced by obesity and body fat distribution. Leucine carbon flux was measured before, during, and after 2.5 h of bicycle exercise in 10 upper body obese, 9 lower body obese, and 6 nonobese, age-matched, premenopausal women. The obese women then followed an energy-restricted diet for 16 wk, resulting in approximately 8 kg weight loss. Baseline leucine carbon flux was greater (P < 0.01) in obese women than in nonobese women but decreased in a similar fashion in response to exercise in all groups. There were no differences between upper body and lower body obese women during exercise. After weight loss, baseline leucine carbon flux decreased (P < 0.05) similarly in both groups of obese women and was further suppressed by exercise. Thus obesity phenotype has no specific effect on either baseline protein turnover or the antiproteolytic response to moderate intensity exercise or weight loss. We conclude that the previously observed defect in insulin suppression of leucine flux in upper body obese women appears related to insulin resistance and does not represent an inherent abnormality of protein metabolism.

Insulin-like growth factor-binding protein-1 response to insulin during suppression of endogenous insulin secretion

Insulin-like growth factor-binding protein-1 (IGFBP-1) is one of several related proteins that bind and modulate the actions of IGFs. The liver is the primary source of IGFBP-1, and insulin is a major regulator of hepatic IGFBP-1 production. We report five sets of investigations that further define the characteristics of hepatic IGFBP-1 response to insulin. In normal subjects, a continuous high-dose insulin infusion caused a rapid decrease in plasma IGFBP-1 concentrations, with a rate of 0.24 +/- 0.04 microgram/L.min-1 and a t1/2 of 89 +/- 4 minutes. Conversely, a 3-hour somatostatin (SRIF) infusion caused a 4.5-fold increase in plasma IGFBP-1 levels. SRIF plus low-dose insulin infusion (to inhibit break-through insulin secretion) resulted in a plateau in IGFBP-1 concentrations at 5 to 8 hours, with a t1/2 to achieve steady state of 60 to 75 minutes. Under similar conditions, a stepped increase in plasma glucose level from 5 to 9 mmol/L had no effect on the rate of IGFBP-1 increase in plasma, indicating that an acute increase in glucose concentration within a physiologic range has no independent inhibitory effect on IGFBP-1 production in the presence of a nonsuppressive insulin level. Using SRIF plus sequential graded insulin infusions, the threshold peripheral (= portal) plasma insulin concentration for IGFBP-1 suppression was between 65 and 172 pmol/L. Subjects with insulin-dependent diabetes mellitus (IDDM) showed a similar dose-response pattern, suggesting that insulin regulation of IGFBP-1 may be normal in IDDM.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential health benefits of weight loss in upper-body and lower-body obese women

Upper-body obesity (UB Ob) is more strongly associated with adverse health consequences; however, few obesity-treatment studies have examined outcome according to body-fat distribution. To examine whether diet and formal- or informal-exercise instruction causes differential changes in health and lipid profiles, ten LB Ob and nine UB Ob premenopausal women received dietary intervention (2.1 MJ-deficit/d for 16 wk) and were randomly assigned to either formal- or informal-exercise instruction. Weight loss was similar between groups (approximately 8 kg), and no change occurred in lean body mass or basal metabolic rate. Baseline cholesterol and triglycerides were greater (P < 0.01) in UB Ob than LB Ob women and decreased more (P < 0.01) in response to treatment in UB Ob women. Formal exercise instruction increased high-density-lipoprotein cholesterol (P < 0.05) especially in UB Ob women. Future studies on treatment of obesity should include consideration of regional fat distribution.

Body-composition changes in patients who gain weight while receiving megestrol acetate

PURPOSE

Randomized placebo-controlled clinical trials have now established that megestrol acetate causes appetite stimulation and weight gain in patients with anorexia and/or cachexia. There is a paucity of available data to delineate the substance of this increased weight.

PATIENTS AND METHODS

Using dual-energy x-ray absorptiometry and tritiated body water methodologies, we performed body-composition measurements in 12 patients with advanced cancer before the institution of oral megestrol acetate (800 mg/d) and at subsequent 2-month intervals.

RESULTS

Seven of the 12 patients gained weight (2.1 to 16.5 kg) and had repeat body-composition measurements performed at the time of maximum weight gain. The vast majority of the gained weight was clearly from an increase in adipose tissue, while there was a suggestion that an increase in body fluid was responsible for a minority of the weight gain.

CONCLUSION

Megestrol acetate-induced weight gain is primarily the result of an increase in body mass.

Effect of megestrol acetate on the human pituitary-adrenal axis

A few previous reports have suggested that megestrol acetate, a synthetic progestational agent frequently used as an antineoplastic drug, suppresses serum cortisol concentrations in humans. To explore this concept further, we prospectively performed several measurements of the pituitary-adrenal axis in patients receiving megestrol acetate (160 or 800 mg/day). The data from these evaluations demonstrate that megestrol acetate reversibly decreases serum cortisol concentrations in humans and that this effect seems to originate from a suppression of the pituitary-adrenal axis. Additional studies should be conducted to determine the implications of the low levels of serum cortisol.

Insulin regulation of insulin-like growth factor binding protein-1 in obese and nonobese humans

Insulin is the principal regulator of hepatic insulin-like growth factor binding protein-1 (IGFBP-1) production, mediating the rapid decrease in plasma IGFBP-1 in response to nutritional intake. In this study, we defined IGFBP-1 regulation by insulin in upper and lower body obesity, conditions associated with insulin resistance and chronic hyperinsulinemia. Overnight postabsorptive IGFBP-1 levels in obese and nonobese women showed an inverse, nonlinear relationship with plasma insulin concentrations. Maximum suppression of IGFBP-1 was seen at 70-90 pmol/L plasma insulin. Both groups of obese women had mean fasting plasma insulin concentrations above this threshold level and, consequently, markedly suppressed IGFBP-1 levels. To assess the dynamics of insulin regulated IGFBP-1, 10 obese and 8 nonobese women were studied during sequential saline infusion (0-90 min), hyperinsulinemia (insulin infusion; 90-210 min) and hypoinsulinemia (somatostatin + GH infusion; 210-330 min). Insulin infusion rapidly decreased plasma IGFBP-1 levels in nonobese subjects (60% decrease in 2 h), but had little or no further suppressive effect in obese subjects. Complete insulin withdrawal resulted in a significant rise in plasma IGFBP-1 concentrations in all subjects, but the response was blunted in obese compared to nonobese groups. In contrast to plasma IGFBP-1, IGF-I concentrations did not vary during hyper- and hypoinsulinemic infusion periods and were not significantly different between groups. Basal GH levels were significantly higher in nonobese when compared to obese women, but did not change with infusions. In conclusion, low IGFBP-1 levels in obesity are related to elevated insulin levels which are, in turn, related to body fat distribution and insulin resistance. The chronically depressed levels of IGFBP-1 may promote IGF bioactivity as well as its feedback regulation of GH secretion, thus contributing to the metabolic and mitogenic consequences of obesity. In addition, our findings imply that hepatic insulin sensitivity in terms of IGFBP-1 production is preserved despite peripheral insulin resistance in obesity.

Free fatty acid metabolism in the follicular and luteal phases of the menstrual cycle

To determine whether the hormonal changes associated with the normal menstrual cycle influence FFA metabolism, FFA turnover was measured in 12 women during both the follicular (days 4-10) and luteal (days 18-24) phases of their menstrual cycles. The luteal phase was confirmed by increased serum progesterone concentrations. Overnight postabsorptive FFA flux was similar in the follicular and luteal phases of the menstrual cycle (6.9 +/- 0.8 vs. 5.8 +/- 0.5 mumol kg-1 min-1, respectively, P = NS). In addition, the FFA response to 3 h of somatostatin-induced hypoinsulinemia was virtually identical on both study days. Finally, we compared the intraindividual variability of basal FFA flux from studies performed in different vs. the same phase of the menstrual cycle; no difference was present. We conclude that the cyclic changes in estrogen and progesterone production which occur during the normal menstrual cycle appear to have minor, if any, effects on FFA mobilization.

Research techniques for body composition assessment

Although a variety of techniques are currently available to measure body composition in human beings, each has limitations with respect to its applicability in addressing nutrition research issues. Several methods "directly" determine an individual's body fat or lean tissue mass with sufficient precision and accuracy such that the data are appropriate for making fine distinctions between individuals or within an individual over time. Such direct methods are most useful in nutritional/metabolic research that requires such distinctions. Each of these techniques will be discussed. There also exist a number of "indirect" measures of body composition. These techniques require more interpretative assumptions and are perhaps better suited to population studies, in which it is often less critical to make fine distinctions between individuals. The appropriate design and interpretation of many nutrition-related research studies depend upon the correct use of body composition data. This review will attempt to help the reader understand the principles of each of the currently available body composition techniques and its optimal use.

How valid are isotopic measurements of fatty acid oxidation?

These studies were performed 1) to compare two isotopic methods (3H2O and 14CO2 production) of measuring free fatty acid (FFA) oxidation; 2) to determine whether isotopic estimates of fatty acid oxidation during hypoinsulinemia are plausible when compared with those obtained using indirect calorimetry; and 3) to examine whether the delay between the exit of [14C]FFA from plasma and the appearance of 14CO2 in breath is accounted for solely by bicarbonate kinetics. Studies in 11 healthy volunteers revealed that [14C]- and [3H]FFA tracers provide similar estimates of FFA turnover and oxidation. Isotopic estimates of fatty acid oxidation were less than those of indirect calorimetry under basal conditions but equaled or exceeded indirect calorimetry estimates after 3 h of acute hypoinsulinemia (somatostatin induced). After stopping tracer infusions, the half-life of plasma [14C]FFA was 3.7 +/- 0.1 min. The half-life of 14CO2 decay from [14C]bicarbonate was 37 +/- 1 min, and the half-life of 14CO2 decay after discontinuation of [14C]FFA infusion was 141 +/- 10 min. Intracellular preoxidative fatty acid pools (possibly triglycerides) most probably account for the marked delay between the exit of FFA tracers from plasma and the appearance of isotopic markers of oxidation in measurable spaces. This delay can result in erroneous estimates of "FFA oxidation." We conclude that tracer measurements of FFA oxidation are invalid under most circumstances.

Stimulation of lipolysis in humans by physiological hypercortisolemia

The effect of glucocorticoids on adipose tissue lipolysis in animals and humans is controversial. To determine whether a physiological increase in plasma cortisol, similar to that observed in diabetic ketoacidosis and other stress conditions, stimulates lipolysis, palmitate kinetics were measured in seven nondiabetic volunteers on two occasions with [1-14C]palmitate as a tracer. Subjects received a 6-h infusion of either 2 micrograms.kg-1.min-1 hydrocortisone or saline in random order. On both occasions, a pancreatic clamp (0.12 micrograms.kg-1.min-1 somatostatin, 0.05 mU.kg-1.min-1 insulin, and 3 ng.kg-1.min-1 growth hormone) was used to maintain plasma hormone concentrations at desired levels. Plasma cortisol concentrations increased to approximately 970 nM during cortisol infusion. Palmitate rate of appearance (Ra) and concentration increased by approximately 60% during cortisol infusion but did not change during saline infusion. Increments in palmitate Ra and concentration over the 6-h study were significantly greater during cortisol than saline infusion when compared by area-under-the-curve analysis (152 +/- 52 vs. -48 +/- 23 mumol.kg-1 and 12.2 +/- 4.1 vs. -4.9 +/- 4.1 mmol.min-1.L-1, respectively; P less than 0.02). Plasma glucose concentrations did not change significantly during cortisol (5.0 +/- 0.3 vs. 6.1 +/- 0.6 mM, NS) or saline (4.9 +/- 0.2 vs. 4.9 +/- 0.1 mM, NS) infusion. In nondiabetic volunteers, a 6-h cortisol infusion was associated with a 60% increase in palmitate Ra that did not occur with saline infusion. Thus, physiological hypercortisolemia may contribute to the increased rates of lipolysis observed in humans during stress.

Prospective evaluation of vertical banded gastroplasty as the primary operation for morbid obesity

Our previous experience with vertical (nonbanded) gastroplasty proved disappointing because of unsatisfactory maintenance of weight loss. Vertical banded gastroplasty seemed to be an attractive alternative operation because it provided an externally reinforced (banded) stoma that would not enlarge over time. In this study, our aim was to determine prospectively the results of vertical banded gastroplasty used as a primary, weight-reducing procedure in patients with morbid obesity. Seventy consecutive patients with morbid obesity (mean weight, 139 kg), all of whom had obesity-related complications, underwent vertical banded gastroplasty and prospective follow-up. The hospital mortality was nil, and substantial morbidity occurred in 3% (two patients). Long-term achievement and maintenance of satisfactory weight loss, however, were variable. The median weight loss at 1 year after operation was 36.7 kg or 48% of excess body weight. At 3 years postoperatively, however, weight loss was only 32.4 kg or 40% of excess body weight, and only 38% of patients had achieved and maintained a weight loss of 50% or more of their preoperative excess body weight. Vertical banded gastroplasty caused major changes in eating habits, and many patients were unable to eat red meat or untoasted bread; moreover, approximately 30 to 50% of patients continued to vomit once or more per week. Despite theoretically attractive advantages as a weight-reduction operation, vertical banded gastroplasty does not seem to be the optimal procedure for most patients with morbid obesity.

Effects of body fat distribution on regional lipolysis in obesity

To determine the contribution of the major body fat depots to systemic free fatty acid (FFA) availability, palmitate ([1-14C]-palmitate) release was measured from leg (lower body) and non-leg (upper body) fat in eight upper body obese (UB Ob), six lower body obese (LB Ob), and six nonobese (Non Ob) age-matched premenopausal women in the overnight postabsorptive state. Splanchnic palmitate release was determined in 16 of these subjects.

RESULTS

total palmitate release was greater in UB Ob (P less than 0.005) than LB Ob or Non Ob women (161 +/- 16 vs. 111 +/- 9 vs. 92 +/- 9 mumol/min, respectively). Despite increased leg fat mass in obese women, leg palmitate release was similar in each group. Therefore, leg fat palmitate release was greater in Non Ob women than LB Ob (P less than 0.01) or UB Ob (P = 0.06) women (3.7 +/- 0.3 vs. 2.4 +/- 0.2 vs. 2.7 +/- 0.2 mumol.kg fat-1.min-1, respectively). Upper body fat palmitate release was less (P less than 0.01) in LB Ob than Non Ob or UB Ob women (3.0 +/- 0.4 vs. 5.0 +/- 0.3 vs. 4.9 +/- 0.4 mumol.kg fat-1.min-1, respectively). Splanchnic palmitate release accounted for 20-32% of upper body fat palmitate release in each group (P = NS between groups). Leg fat palmitate release was significantly less than upper body fat palmitate release. We conclude that the major difference in resting FFA metabolism between UB Ob and LB Ob women is the ability of the later to down-regulate upper body fat lipolysis to maintain normal FFA availability.