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Aims/hypothesis: Increased circulating methylarginines (MA) have been linked to the metabolic syndrome to explain endothelial dysfunction and cardiovascular disease risk. Proteins that contain MA are regulatory and release them during catabolism. We hypothesised that increased protein turnover in insulin-resistant states contributes to an increase in circulating MA. MATWERIALS AND METHODS: We performed hyperinsulinaemic, euglycaemic, and isoaminoacidaemic experiments on 49 lean, obese and elderly subjects, with measurements of the kinetics of glucose and protein metabolism. Plasma MA, i.e. asymmetrical dimethylarginine (ADMA), symmetrical dimethylarginine (SDMA), and N -monomethyl-L-arginine (NMMA), lipids and body composition were measured., Results: Insulin resistance of glucose and protein metabolism occurred in obese and elderly subjects. ADMA concentrations were 29 to 120% higher in obese and 34% higher in elderly than in lean subjects. SDMA were 34 and 20% higher in obese than in lean and than in elderly subjects, respectively. NMMA were 32% higher in obese than in lean subjects. ADMA differed by sex, being higher in men, namely by 1.75x in obese men and by 1.27x in elderly men. Postabsorptive ADMA (r=0.71), SDMA (r=0.46), and NMMA (r=0.31) correlated (all p<0.05) with rates of protein flux. All three MA correlated negatively with clamp glucose infusion rates and uptake (p<0.001). ADMA and SDMA correlated negatively with net protein synthesis and clamp amino acid infusion rates (p<0.05). All MA also correlated with adiposity indices and fasting insulin and triglycerides (p<0.05)., Conclusions/interpretation: Obesity, sex and ageing affect MA. Elevations of the three MA in obese, and of ADMA in elderly men, are related to increased protein turnover and to lesser insulin sensitivity of protein metabolism. These interrelationships might amplify insulin resistance and endothelial dysfunction.

Background: Plasma leptin in humans is subject to both long- and short-term regulation; it correlates with indexes of body fat that can only change slowly. However, short-term fasting causes large and rapid decreases., Objective: We tested the interactions between energy intake and fat loss on plasma leptin during prolonged moderate and severe energy restriction, with a view to understanding mechanisms of control., Design: Postabsorptive leptin was measured with an enzyme-linked immunosorbent assay specific for the human peptide in 21 obese women aged 41 +/- 3 y (weight: 102 +/- 4 kg; 48 +/- 1% body fat) after 1 wk of a weight-maintaining diet and then weekly for 4 wk during a total fast (group 1); a 1.9-MJ/d all-protein, very-low-energy diet (VLED) (group 2); or a low-energy, balanced-deficit diet (BDD) providing 50% of maintenance energy (group 3). In groups 1 and 2, leptin was also measured after 1 wk of refeeding with a diet equivalent to the BDD., Results: Mean leptin decreased markedly by up to 66% (P < 0.001) at week 1 of energy restriction and then gradually thereafter. The change in leptin per kilogram fat mass correlated with that in glucose concentrations [r = 0.538 (P = 0.012) at week 1 and r = 0.447 (P = 0.042) at week 4] but not with that in fat mass. During refeeding postfasting, leptin increased (P = 0.008), despite an ongoing loss of fat mass and correlated positively with changes in resting energy expenditure. At times with comparable cumulative energy restriction and fat loss between diets, the percentage change in leptin paralleled that in glucose., Conclusions: In obesity, changes in energy intake over days to weeks are a primary modulator of plasma leptin concentrations that are related to the change in glycemia and are able to override the regulatory influence of fat mass.

Objective: To determine if insulin treatment combined with a generous protein intake would normalize whole-body protein kinetics and nitrogen balance in obese subjects with Type 2 diabetes mellitus when compared to obese nondiabetic subjects: 1) during weight-maintenance and 2) after a very low energy diet (VLED)., Design: Clinical intervention study of iso- followed by hypoenergetic feedings with or without exogenous insulin., Subjects: Sixteen obese subjects with a body mass index (BMI) of 39+/-4 kg/m2, with Type 2 diabetes mellitus (three men, six women) or without (one man, six women)., Measurements: Nitrogen flux rate calculated from the urine 15N-urea enrichment by using the 60 h oral 15N-glycine method, rates of protein synthesis and breakdown calculated from nitrogen flux on days 6-8 (and 13-15 in the diabetic subjects) of isoenergetic feeding and days 24-26 of a 1.9 MJ diet., Results: With insulin therapy: 1) during isoenergetic feeding, in the hyperglycaemic diabetic subjects, nitrogen balance was significantly less than in the obese controls (-0.6+/-0.6 compared with +1.8+/-0.9 g N/d, P = 0.037) but became positive (+2.6+/-0.6 g N/d, P < 0.05); nitrogen flux decreased and net protein synthesis increased from values different from those of the obese controls to values no longer different; 2) during the VLED, plasma glucose concentrations < 7 mmol/L were achieved and maintained in all diabetic subjects. Nitrogen equilibrium observed in five out of seven obese nondiabetic and four out of nine diabetic subjects was associated with no change in nitrogen flux from the euglycaemic isoenergetic studies, but with 17% and 23% lower rates of synthesis (P < 0.05) and 7% and 15% lower rates of breakdown (NS) in nondiabetic and diabetic subjects, respectively., Conclusion: Sufficient exogenous insulin to near-normalize glycaemia improves the altered protein metabolism in hyperglycaemic diabetic subjects during isoenergetic feeding, and restores nitrogen equilibrium better than with VLED alone. Protein metabolism is more sensitive to the state of diabetes control than is generally appreciated 'clinically'.

Objective: To determine whether the kinetics of protein metabolism would differ with the prolonged use of a casein-soy 96 g protein, 1.7MJ/d very low energy diet (VLED) from those of a tryptophan- and methionine-supplemented hydrolyzed collagen VLED, in obesity., Design: Clinical intervention study of 1 week isoenergetic diet followed by 6 weeks VLED., Subjects: 6 (1M,5F) healthy obese subjects (age: 38 +/- 4 y, BMI: 33 +/- 1 kg/m2, weight: 97 +/- 7 kg)., Measurements: Whole-body nitrogen (N) flux rate (Q) from 15N abundance in urinary urea using the oral 15N-glycine method and rates of protein synthesis (S) and breakdown (B) calculated from Q; N balance; resting metabolic rate; metabolic and hormonal responses., Results: Q (per kg LBM) was maintained with both collagen and casein-soy VLED. S and B decreased (P < 0.05) at week 4 of both VLEDs with resulting decreases in net protein synthesis. At week 6, S decreased with both VLEDs, but B decreased only with casein-soy, at which time N balance was at equilibrium with casein-soy but returned to negative with collagen. Initial resting metabolic rate correlated with baseline Q and S. It decreased by 16% with the VLEDs; 25% of the decrease may derive from the decline in S., Conclusion: A 6 week casein-soy VLED with 46% of amino acids as essential does not provide a substantial advantage compared to hydrolyzed collagen with 16% of amino acids as essential. With prolonged use, it may better maintain N equilibrium by preventing further increments in protein breakdown.

Objective: To determine the changes in the plasma level of acylation stimulating protein (ASP) during a one month total fast in female subjects with marked obesity., Design: Patients with marked obesity underwent a month total fast, before, during (2 weeks), and at the end of which, a variety of relevant metabolic parameters were measured., Setting: A metabolic unit of a teaching hospital., Subjects: 10 women with marked obesity were studied and the results compared with those in 16 age-matched controls., Main Outcome Measures: Plasma ASP, lipoprotein lipids, apoB, free fatty acid, and ketone levels., Results: At baseline, fasting levels of ASP in the obese group were double that in control subjects (116 +/- 26 vs 53 +/- 30 nM P < 0.001). During the fast, ASP levels dropped progressively and were within the normal range at the end of the study (63 +/- 16 vs 53 +/- 30 nM pNS). In addition, there was a strong correlation between the plasma ASP at baseline before beginning the fast and the 4 week drop in ASP. That is, those subjects who had the highest starting ASP also had the largest 4 week drop in ASP (r2 = 0.644, P < 0.005). Of interest, as plasma ASP levels dropped, plasma free fatty acid and ketone levels rose and when all timepoints were considered, there was a significant inverse relation between plasma ASP and plasma free fatty acid (r2 = 0.295, P < 0.0002)., Conclusions: The pattern of responses during the fast is that of increasing mobilization of fatty acids from adipose tissue coincident with decreased activity of the pathway responsible for the storage of adipocyte triglyceride mass. The data are consistent, therefore, with the role proposed for ASP as a major determinant of the rate of triglyceride synthesis in human adipocytes and thus a potentially important factor in the pathophysiology of obesity.

We postulated that dietary protein utilization and body protein metabolism are altered in hyperglycemic individuals with non-insulin-dependent diabetes mellitus (NIDDM). This was tested by estimating the kinetics of protein metabolism in obese NIDDM patients in the hyperglycemic state of isoenergetic feeding and in the normoglycemic state induced by the prolonged use of a very-low-energy diet (VLED) and comparing them with results in obese nondiabetic subjects studied previously. Seven obese subjects with NIDDM (one male, six females, body mass index = 35.8 +/- 2.0 kg/m2) were given a 1.7 MJ (410 kcal) all protein (93 g/day) diet derived from hydrolyzed collagen and supplemented with tryptophan and methionine, which provides 16% of its amino acids as essential, a multivitamin and mineral supplement, and 16 mmol KCl for 42 days. During the seven-day isoenergetic diet and at weeks 4 and 6 of the VLED, amino nitrogen (N) flux rate was calculated from the urine [15N]urea enrichment by using the 60-h oral [15N]glycine method to obtain the integrated feeding-fasting metabolism. Rates of synthesis (S) and breakdown (B) were calculated from N flux. At day 7 of the isoenergetic diet, whole-body N flux, S, B, and resting metabolic rate (RMR) were 12-24% greater (P < 0.05) in the NIDDM subjects than observed in nondiabetic obese subjects. Mean plasma glucose decreased (P < 0.05) from the isoenergetic period (14.9 +/- 2.4 mM) to 7.2 +/- 1.2 mM at week 4 and 6.5 +/- 1.1 mM at week 6 of the VLED. RMR declined progressively by 25% at week 5 of the VLED. Corresponding significant (P < 0.05) decreases from isoenergetic feeding to weeks 4 and 6 of the VLED occurred in whole-body N flux (from 51 +/- 2 to 42 +/- 1 g N/day), in S (from 38 +/- 3 to 24 +/- 1 g N/day), and in B (from 39 +/- 3 to 26 +/- 1 g N/day) resulting in net losses (S-B). S-B was significantly more negative (P < 0.05) in NIDDM than in the nondiabetic obese subjects at week 4 (-1.5 +/- 0.5 vs. 0.9 +/- 0.3 g N/day) but not at week 6 (-1.3 +/- 0.4 vs. -0.9 +/- 4 g N/day). During the VLED, N balance became less negative with time but never reached equilibrium in NIDDM. Thus, abnormal protein metabolism is present in NIDDM in the isoenergetic fed state with moderate hyperglycemia and persists during a VLED that restores glycemia to near normal.

We postulated that the return to nitrogen equilibrium after 3 wk of a negative balance during a very-low-calorie diet (VLCD) providing low-quality protein in obese subjects was due to availability of endogenously originating amino acids from a "pool" that, when depleted, would result in worsening balance. This should be reflected in altered kinetics of protein metabolism with the requirement for increased breakdown to maintain synthesis constant. Seven female obese subjects [body mass index (BMI) = 34.4 +/- 1.8 kg/m2] were given a 1.7-MJ/d all-protein diet (16.8 g N) derived from hydrolyzed gelatin (supplemented with tryptophan and methionine) that provides 18% of its amino acids as essential, a multivitamin-mineral supplement, and 16 mmol KCl for 42 d. At baseline (7-d isocaloric diet), and weeks 4 and 6 of VLCD, amino nitrogen flux rate was calculated from the 15N abundance in urinary urea using the oral 15N-glycine method and rates of synthesis (S) and breakdown (B) inferred from N flux. Whole-body N flux did not change from baseline to weeks 4 and 6 (39.5 +/- 2.0 vs 37.4 +/- 2.0 vs 39.2 +/- 1.9 g N/d). By contrast, S and B decreased at weeks 4 and 6 with S decreasing more so that net protein synthesis (S-B) was less positive at week 4 than at baseline (2.2 +/- 0.2 and 0.9 +/- 0.3 g N/d; P less than 0.05) and became negative at week 6 (-0.9 +/- 0.2 g N/d; P less than 0.05). Concurrently, N equilibrium was achieved by week 4 but returned to negative balance by week 6.(ABSTRACT TRUNCATED AT 250 WORDS)

We tested whether sodium restriction would counteract the decrease in sympathetic nervous system activity usually associated with marked energy restriction. The effects of two levels of energy restriction, with different sodium intakes, on plasma norepinephrine (NE) levels while supine and in response to standing were studied. Twenty-two healthy normotensive obese female subjects (body mass index, 34 +/- 1 kg/m2; weight, 90 +/- 2 kg) followed one of three 3-week protocols: 1) total fasting with 80 mmol/day NaCl, 2) a very low energy diet (VLED) containing 1.7 MJ, 93 g protein, and 90 mmol Na/day, with an additional 60 mmol/day NaCl supplement, or 3) total fasting without NaCl (0 Na fast). At the end of the baseline isocaloric diet and of total fasts or VLED, pulse, blood pressure, and plasma NE were measured after 4 h of recumbency and 5 and 10 min after assuming the upright posture. These measurements were repeated after 1 L physiological saline was infused into the 0 Na fast subjects. Cumulative negative sodium balance was observed only in the 0 Na fasting subjects. Supine blood pressure decreased from baseline with fasting, but not with the VLED. The decreases in systolic pressure and increases in heart rate on standing observed with all diets were greatest with the 0 Na fast. Supine plasma NE (vs. baseline value) declined (P less than 0.05) with the VLED, remained unchanged with the Na supplemented fast, but increased with the 0 Na fast (P less than 0.05). The upright plasma NE values were highest in the 0 Na fast subjects, but lower after the saline infusion as well as in the subjects on the VLED. Thus, the decrease in NE due to energy restriction with normal sodium intake was counteracted by moderate sodium restriction, and levels increased with zero sodium intake. Therefore, sodium depletion can override the suppressive effect of energy restriction and, instead, increase the activity of the sympathetic nervous system, as reflected by plasma NE.

Changes in adipose tissue distribution as defined by the waist-to-hip ratio (WHR), were evaluated in 16 android, obese subjects (seven male and nine female) given a very low energy ketogenic diet of 1.72 MJ (411 kcal) for 4 weeks. Total weight loss was significantly greater for the males (11.2 +/- 2.5 kg) compared to females (8.3 +/- 0.8 kg); the relative weight loss however, was similar (9.9 vs 9.3 percent). Female and male losses in percent body fat and lean body mass were not significantly different. For both groups, significant (P less than 0.01) changes in waist and hip circumferences were observed; however, no significant changes were observed in WHR. These results indicate that in obese android male and female subjects, adipose tissue distribution as measured by WHR, does not change in response to rapid weight loss.

Chronic and acute protein-energy malnutrition impairs immune function but little is known of the effects of energy deprivation alone. Indexes of cell-mediated immunity (CMI) were therefore studied during a 6-wk very-low-energy diet (VLED) (1.7 MJ/d, weight loss 13 +/- 1 kg, means +/- SEM) in 12 nondiabetic obese [body mass index 33 +/- 1 (in kg/m2)] subjects. Significant decreases (P less than 0.05) were observed in the numbers of total leukocytes, neutrophils, lymphocytes, and monocytes from 1 to 2 wk of the VLED and onward. Only lymphocyte counts returned to baseline levels with refeeding. The proportions of other monoclonal-antibody-defined mononuclear cell populations (except a small decrease in CD4+) did not change during dieting. [3H]Thymidine uptake by mononuclear cells cultured for 96 h decreased significantly (P less than 0.05) at wk 6 in response to concanavalin A, phytohemagglutinin, and pokeweed mitogen and after only 1 wk to phorbol myristate acetate + ionomycin. Delayed-type-hypersensitivity skin-test responses did not decrease at wk 5 vs those at baseline. The VLED produced nonspecific decreases in circulating leukocyte numbers and in vitro responses to several mitogens (of different cell-subset specificity), suggesting that in susceptible individuals or if there is longer exposure to such diets, such responses could assume clinical significance.

Sustained elevations of plasma glucose and insulin concentrations follow intense (80% maximum oxygen uptake) exercise performed in the postabsorptive state. To provide insights into possible mechanisms and influence of obesity, 8 lean and 12 obese subjects [106 +/- 11% (SD) and 193 +/- 31% of reference table weight, respectively] eating previously isocaloric diets were exercised to exhaustion (7 +/- 3 min) on a cycle ergometer, then followed for 60 min of recovery. The obese subjects at rest had slightly increased plasma glucose and insulin and elevated blood glycerol concentrations. Both lean and obese subjects had little or no changes in plasma glucose or insulin during exercise, but the increases during the recovery period were greater and/or sustained longer in the obese. Such results raise the possibility of transient hepatic insulin resistance after exercise and are possibly relevant to restoration of depleted muscle glycogen. Both groups had a marked fall in plasma FFA during exercise; the reduction was sustained in the lean but not in the obese subjects. Blood glycerol increased during the recovery period to higher values in the obese than in the lean subjects. Plasma norepinephrine increased about 4-fold in both groups, returning promptly to preexercise values. In contrast, the exercise-induced increment in plasma epinephrine [values at exhaustion, 933 +/- 548 vs. 1970 +/- 787 pmol/L; P less than 0.005] was markedly attenuated in the obese subjects. Thus, the obese subjects had exercise-induced changes in glucose and inulin metabolism consistent with greater postexercise insulin resistance, despite an impaired plasma epinephrine response to intense exercise.

Eleven obese subjects (body mass index, 41.3 kg/m2) were examined to determine their metabolic and acid-base responses during two hypoenergetic diets, and the diets' influence on subsequent responses to prolonged total fasting. Subjects were first treated for 2 wk with 400-kcal/d (1.67-MJ/d) diets of either protein (13.2 g nitrogen, 23 mmol potassium) or glucose with 16 mmol potassium chloride and a multivitamin supplement. Mild acidosis developed during the protein diet as well as greater excretions of urinary ammonium and urea N, a greater degree of ketosis, and significantly better N balance (-42.7 vs -80.4 g, p less than 0.05) than during the glucose diet. The subsequent fast was associated with greater negative N balance after protein (-129 vs 83 g), mainly as urea N, but despite similar ketosis there was a greater acidosis after glucose and greater ammonium N excretion and cumulative K losses. These data support the concept of a labile N pool, depleted during a glucose diet and resulting in a decreased loss with the subsequent fast. We suggest a role for K depletion in augmenting fasting ammonium excretion.

The hormone-substrate milieu has been investigated in male fasted lean (C57BL/6-+/+) mice and mutant obese mice of the same strain (C57BL/6-obob). The lean mouse, in winter, mobilized insufficient fat (due to inadequate stores) to permit survival beyong 3 days and was unable to achieve any degree of conservation of vital protein stores. By contrast, in summer, the same animals survived 7 days and showed evidence of greater and more sustained fat mobilization and ketosis and the ability to conserve protein. The insulin, glucagon, and insulin/glucagon molar ratios changed in both groups in a direction consistent with conversion to a catabolic state, and hence were probably largely responsible for the mobilization of substrates and stimulation of gluconeogenesis and ketogenesis. The seasonal difference in response is unexplained. The obob mice, generally employed as a model for obesity, hyperglycemia, and hyperinsulinemia showed these features but also adapted to fasting in a fashion permitting prolonged survival during this state. In a fashion analogous to that known to occur in man, these animals developed fall in glycemia, rise in circulating fat-derived substrates, and marked protein conservation. Profound fall in insulinemia was associated with a fall in glucagonemia, the latter from normal levels. Thus the initial markedly "anabolic" insulin/glucagon molar ratio diminished, but nevertheless remained higher than at any time in the lean mice. Pancreatic contents of insulin showed markedly different changes with fasting in obob compared with lean mice. The ability of the obese mouse to adapt to prolonged fasting in a fashion largely analogous to that of man renders it a useful model for the study of metabolism in this state, with the potential of applicability of findings to man.

This study evaluated the effects of oral sodium bicarbonate (NaHCO3) supplementation on ammonium (NH4+) nitrogen (N) and urea N excretion and on ketone bodies during the metabolic acidosis of a very low energy protein diet. Ten healthy obese female subjects (BMI, 38.4 +/- 1.5 kg/m2;weight, 100 +/- 4 kg) were given a 1.72 MJ (412 kcal) all protein (16.8 g N) liquid formula, 16 mmol KCl and a multivitamin-mineral supplement daily for 4 weeks. In addition, the five subjects in group 1 received 60 mmol Na+ daily as sodium chloride (NaCl) for 3 weeks and as NaHCO3 during week 4. The subjects in group 2 were given 40 mmol/d NaHCO3 during the first week, 60 mmol/d during weeks 2 and 3, and 60 mmol/d NaCl during week 4. Nitrogen balance was achieved in both groups by the end of week 3. The subjects in group 1 at week 2 showed an increase in blood [H+] of 0.41 +/- 0.06 x 10(-8) mol/L and a decrease in blood bicarbonate from 26.0 +/- 0.8 to 23.8 +/- 1.2 mmol/L. The subsequent NaHCO3 curtailed NH4+ N excretion by one half, without significant change in ketone body levels or excretion. Administration of NaHCO3 from the start of the diet to the subjects in group 2 prevented both the metabolic acidosis and the increase in NH4+ N excretion and attenuated the increase in blood and urine 3-hydroxybutyrate. When NaCl replaced NaHCO3 during week 4, ammonium N excretion doubled. Urea N excretion was comparable in both groups and was unaffected by bicarbonate.(ABSTRACT TRUNCATED AT 250 WORDS)

Skeletal muscle function and standard nutritional assessment parameters were measured in six obese patients. Base-line measurements were made on a weight-maintaining diet, and further measurements after 2 wk of a 400-cal diet, followed by 2 wk of fasting and then after 2 wk of refeeding. The function of the adductor pollicis muscle was assessed by electrical stimulation of the ulnar nerve. The objective parameters of muscle function measured were: 1) force of contraction expressed as a percentage of the maximal force obtained with electrical stimulation at 10, 20, 30, 50, and 100 Hz. 2) Maximal relaxation rate expressed as percentage force loss/10 ms. 3) Endurance expressed as percentage force loss/30 s. Standard nutritional assessment parameters (serum albumin and transferrin, creatinine height index, anthropometry and total body nitrogen and potassium) were also measured. There was a significant increase in the force of contraction at 10 Hz from a base-line of 29.6 +/- 1.0% to 49.0 +/- 2.8% (mean +/- SEM) after 2 wk of a 400-cal diet (p less than 0.01). These was a significant slowing of the maximal relaxation rate from a base-line of 9.8 +/- 0.03% force loss/10 ms to 8.2 +/0 0.3% force loss/10 ms (mean +/- SEM) (p less than 0.01) after 2 wk of a 400-cal diet. After a further 2 wk of fasting these abnormalities in muscle function persisted. There was a significant increase in muscle force loss from a base-line of 3.9 +/- 0.8% force loss/30 s to 13.7 +/- 3.4% force loss/30 s (mean +/- SEM) after fasting (P less than 0.01). After 2 wk of refeeding all aspects of muscle function measured were normal. During the study the standard nutritional assessment parameters did not change significantly.

The effect of prolonged (3-5 wk) fasting on tracer-determined glucose turnover and of recycling radioactive glucose has been examined. We followed the specific activity of plasma glucose after the simultaneous administration of 1-14C-glucose and 3-3H-glucose. The rate of glucose turnover decreased during prolonged fasting. Recycling of radioactive glucose was estimated by two different techniques: (1) the appearance of 14C in positions 2 to 6 glucose was measured; (2) the difference in the slopes of specific activity decline for 1-14C-glucose and for 3-3H-glucose was calculated. The two methods of estimating the radioactive recycling gave results similar to each other. The amount of glucose recycled did not change during prolonged fasting. However, in view of the decline in glucose production during fasting, the proportion of glucose production which was represented by recycling increased. Based on weight and urinary nitrogen loss an estimate of the glucose production from amino acids and glycerol was obtained. The difference between the rate of glucose production from the contribution of amino acids and glycerol and that estimated by radioisotopic techniques was much larger than the measured rate of recycling. This finding suggests that either a large exchange of 12C with 14C occurred in some glycolytic intermediates or that a hitherto unknown source of carbon for glucose production appeared during prolonged fasting.

Hypocaloric dieting and fasting alter the contraction-relaxation characteristics of skeletal muscle and result in low frequency fatigue. We report the metabolic and structural changes in skeletal muscle in five morbidly obese female subjects who had biopsies of the gastrocnemius muscle on a base-line diet (2500 kcal/day) followed by a repeat biopsy after 2 wk of a 400-kcal/day carbohydrate diet. Hypocaloric dieting resulted in a significant increase in the intracellular muscle calcium content (p less than 0.05), which may account for the observed changes in muscle function. There were no significant changes in muscle glycogen, lactate, pyruvate, or free energy stores. There was a significant decrease in muscle enzymes [phosphofructokinase (p less than 0.05), succinate dehydrogenase (p less than 0.02)] and some muscle amino acid levels [glutamine (p less than 0.025), glycine (p less than 0.01), and alanine (p less than 0.02)], while muscle histochemistry showed type II fiber atrophy (p less than 0.025). However, these changes reflect a generalized response to hypocaloric dieting and probably do not explain the specific functional changes. Change in the muscle calcium content is probably an important mediator of the adverse functional effects of malnutrition.

The metabolic response to exercise in obese postabsorptive noninsulin-dependent diabetics was compared to that of obese nondiabetics. Exercise consisted of 45 min on a cycle ergometer at 60% maximum oxygen consumption. Six diabetic subjects were studied during oral hypoglycemic therapy and four on diet alone. The sulfonylurea therapy had no effect on the response. Glycemia was elevated at rest in both diabetic subgroups (192 +/- 24 mg/dl for diet alone, 226 +/- 36 mg/dl for sulfonylurea treatment) and a similar fall (35 and 37 mg/dl, respectively) occurred with exercise. In control subjects, glycemia was 86 +/- 4 mg/dl and did not change with exercise. In the diabetics at rest, glucose production was elevated (220 +/- 25 mg/min), whereas the metabolic clearance of glucose was suppressed. During exercise the increase in glucose utilization was similar to that in controls, but glucose production failed to increase significantly, thus accounting for the decline in plasma glucose. At rest, plasma immunoreactive insulin (IRI) was elevated to 0.90 ng/ml in the controls and decreased to 0.65 ng/ml with exercise. In the diabetics IRI was similarly elevated (0.89 ng/ml) but failed to decrease normally with exercise. Lactate, pyruvate, alanine, and free fatty acids increased similarly in diabetics and controls, whereas the increase in 3-hydroxybutyrate during recovery was less in diabetics. The sustained insulinemia, the basal overproduction of glucose, and hyperglycemia itself may all contribute to the observed differences in glucose flux during exercise in noninsulin-dependent diabetics.

Studies were undertaken to examine triglyceride turnover in obese humans on isocaloric balanced diets and during prolonged (3-5 wk) fasting. The data were related to plasma concentrations of insulin (IRI), glucagon (IRG), and free fatty acids (FFA) and to blood ketone concentrations. The triglyceride turnover rates were also related to the plasma triglyceride concentration. This relationship was the same in the obese on isocaloric balanced diets as that we have previously observed in lean humans on similar diets. The relationship between triglyceride turnover and concentration changed during prolonged fasting in a way that suggested that triglyceride removal was impaired. This viewpoint is consistent with the known effects of fasting on adipose tissue lipoprotein lipase activity. In another group of fasted obese, refed with a hypocaloric diet, the relationship returned toward normal. In addition to the impaired triglyceride removal, prolonged fasting resulted in a decrease in triglyceride production. This decrease occurred despite an increase in plasma FFA. After 3-5 wk of fasting the IRI was about 50% of the initial value, while the IRG was the same as the initial value. While triglyceride production fell during fasting, the blood ketone concentration rose. Others have seen similar changes in ketones and triglycerides in livers perfused with medium in which the ratio of insulin to glucagon fell. The rate of triglyceride production was not related to body weight. However, regardless of nutritional state, it was positively related to the basal plasma insulin levels. These data indicate that, in man as in animal preparations, insulin may regulate hepatic triglyceride production.

We investigated whether the respiratory defect in the obesity-hypoventilation syndrome might respond to dietary manipulation. The effects of hypocaloric ketogenic regimens on the ventilatory response to carbon dioxide were studied in a manner excluding changes in weight or thoracic mechanics as factors. Six obese subjects with hyporesponse (less than 1.1 1/min/mm Hg) and 12 with normal response were fasted or given a diet containing 400 kcal per day of protein. During ketosis carbon dioxide response more than doubled in those with hyporesponse (0.8 +/- 0.1 to 1.8 +/- 1/min/mm Hg, P less than 0.05) but was unchanged in those with normal response. This improvement could not be accounted for by changes in weight, pulmonary function, pH or degree of ketosis between the two groups. However, a significant positive (r = 0.70; P less than 0.001) correlation between ketone-body concentrations and carbon dioxide response was observed in subjects with hyporesponse. These results indicate that depressed sensitivity to carbon dioxide in obese patients can be increased by dietary manipulation.

Catecholamines have multiple metabolic and fluid-electrolyte as well as cardiovascular effects, and their levels in plasma respond to alterations in nutrient and sodium intakes. Plasma norepinephrine, epinephrine, and dopamine were measured in 12 obese nondiabetic subjects before and after 400 kcal/day diets of either protein or glucose, followed by total fasting, and then by hypocaloric refeeding, each for 14-day periods. Measurements were made in the supine and upright posture and during and after 6-10 min of exhaustive exercise at 80% maximal VO2. Sodium intake varied with the nutrients ingested, being markedly decreased with the 400 kcal/day diets and fasting. Norepinephrine levels were higher in fasting than base line while subjects were lying or standing and after recovery from exercise. Those of epinephrine were elevated on standing. No differences were found after the 400 kcal/day diets, with protein and glucose yielding equivalent results. In contrast, refeeding was associated with lower norepinephrine levels than all other diets while subjects were lying or standing and after recovery from exercise. Peak levels of norepinephrine and epinephrine with exercise were indistinguishable among diets. Fasting was associated with lower systolic and diastolic blood pressures and lower responses to standing and exercise than base line, whereas upright heart rate was greater and that during exercise less than base line. Significant though less extensive changes occurred with the other diets. Thus both electrolyte status and nutrient intakes interact to determine net catecholamine responses, and the former seem to override the latter.(ABSTRACT TRUNCATED AT 250 WORDS)

During a total fast in obese subjects, the daily rate of nitrogen excretion undergoes only a small further decline after 2 wk, the excretion rate being about 5 g N/day. At this time, ammonium and urea each constitute about one-half of this excretion. The purpose of this study was to consider two alternative hypotheses: first, that the near plateau in nitrogen excretion represents an irreducible minimum rate of net protein breakdown in order to supply essential organs with calories in the form of glucose; second, that protein breakdown could be further reduced by minimizing the requirement to provide nitrogen for ammonium excretion during the ketoacidosis of fasting. Because ammonium excretion is largely controlled by acid-base balance, 150 mmol of sodium bicarbonate plus 60 mmol of potassium chloride were administered daily to decrease ammonium excretion in eight obese subjects who were totally fasting for more than 14 days. Urine ammonium nitrogen fell with this treatment (from 3.8 +/- 0.4 to 2.0 +/- 0.4 g N/g creatinine). In addition, there was a smaller fall in the rate of urea excretion (from 2.5 +/- 0.2 to 2.1 +/- 0.3 g N/g creatinine) together with a fall in the blood urea nitrogen. Therefore, it appears that ammonium excretion contributes to the negative nitrogen balance of a prolonged total fast, as assessed over a 3-day period of observation, is responsible for about one-third of the net lean body mass loss.

To determine the effects of different hypocaloric diets on insulin secretion, 24-h urine C-peptide was measured in 11 obese subjects on a weight-maintaining baseline diet, and the results were compared with values obtained during 14-day periods of diets containing 400 kcal/day of only protein (n = 6) or glucose (n = 5), followed by 14 days of fasting and 14 days of refeeding on 800-1000 kcal/day. A significant positive correlation between total caloric intake and urine C-peptide excretion was found once the C-peptide excretion reached steady state after several days on each diet. Multiple regression analysis showed no contribution of body weight to urine C-peptide during the different diets. In contrast, a significant correlation was found between body weight and urine C-peptide in the fasting state. A marked and identical decrease of approximately 75% in urine C-peptide occurred over the first 5-7 days of the two 400-kcal diets, followed by a further decrease during fasting to 5% of baseline values. Refeeding was associated with a progressive increase. Plasma insulin and C-peptide followed the same trends as found for urine C-peptide, although the magnitude of change was much smaller. C-peptide clearance was not assessed because of the variation in plasma levels on eating meals. However, the same responses were found when C-peptide excretion was factored for creatinine excretion. Thus, the major determinant of urine C-peptide excretion appears to be food intake, and adaptations take 5-7 days to reach steady state.(ABSTRACT TRUNCATED AT 250 WORDS)

The alleged benefits of protein diets remain unproven, since research data on the safety and long-term utility of protein products as the principal or only source of nutrients for weight reduction programs are as yet insufficient. First, it is uncertain whether the decreases in body protein turnover occurring with these diets are consistent with normal function over long periods, though net balance of protein is obtained. Second, the main advantage to the patient is the suppression of appetite by the ketoacidosis, but it is the ketoacidosis that causes many of the untoward effects. Third, the addition of carbohydrate to a protein diet does not mitigate the benefit of the protein and prevents most of the untoward effects. Fourth, there is clearly no advantage of "predigested" proteins (which are generally poorer in quality than normal high-protein foods) except for the psychologic factor of being given "medication" for the "disease" of obesity. Fifth, there is a distinct danger of deficiencies of micronutrients developing with prolonged consumption of unsupplemented diets. Sixth, the cardiac disorders associated with death in persons taking these diets have not been shown to be coincidental rather than a direct consequence of the diets.In the present state of understanding of protein diets, they should be supervised only by specially trained physicians in rigorous multidisciplinary programs, preferably those with ongoing research. Only individuals free from contraindications should be so treated. Until compelling data proving the safety and efficacy of these diets are forthcoming, the general public should be counselled against their use.

Exogenous protein in the absence of other calories can cause protein-sparing, but the mechanisms involved are controversial. It has been postulated that low insulin and high fat-derived substrate levels are necessary and sufficient conditions for such protein-sparing. We therefore established such conditions with differing protocols of protein input to define the role of protein input in mediating the response. Three groups of obese, nondiabetic subjects received the following diets: (1) 82.5+/-1.0 g protein/day (400 cal/day) for 21 days, n = 7; (2) the same, but as a refeeding diet for 7 days after 21-28 days of total fasts, n = 7; and (3) commencing with the same input, but with daily stepwise decrements over 14 days to 19.4+/-2.2 g/day, then maintained an additional 7 days, n = 4. Diet 3 gave approximately the amount and pattern of protein lost during total fasting. The circulating hormone and substrate responses of diets 1 and 3 were comparable and resembled those of total fasts, in that plasma glucose and insulin fell and free fatty acids rose. Blood levels of alanine, pyruvate, and other glucogenic amino acids fell and blood levels of branched-chain amino acids rose transiently. Blood 3-hydroxybutyrate levels and urinary excretion were greater in diet 3 than diet 1, but less than in total fasting. Nitrogen balance in diet 1 was transiently negative, but in equilibrium from 12 to 21 days. In diet 3, it was constantly negative at -6 g/day, the values also observed at 21 days of fasting. Mean 3-methylhistidine excretion decreased by 170 mumol/day in diet 1 and 107 mumol/day in diet 3, reflecting decreased muscle protein catabolism. The refed, protein-depleted subjects, diet 2, showed an increase in plasma glucose without alteration in insulin levels. Free fatty acid and ketone body levels decreased to those of the steady state observed in diet 1. Glucogenic and branched-chain amino acids decreased transiently. Nitrogen balance became positive, and the low 3-methylhistidine excretion increased by 152 mumol/day. The differing responses of nitrogen balance could not be accounted for on the basis of levels of insulin or of fat-derived substrates. The primary determinants of the protein-sparing observed appeared to be the protein supply itself, and the magnitude of the decrease in endogenous protein catabolism. The positive balance on refeeding after prior depletion of protein stores was likely due to the exogenous supply, combined with decreased catabolism and considerably increased reutilization.