Magnetic-field effects on the size of vortices below the surface of NbSe2 detected using low energy beta-NMR.

A low energy radioactive beam of polarized 8Li has been used to observe the vortex lattice near the surface of superconducting NbSe2. The inhomogeneous magnetic-field distribution associated with the vortex lattice was measured using depth-resolved beta-detected NMR. Below Tc, one observes the characteristic line shape for a triangular vortex lattice which depends on the magnetic penetration depth and vortex core radius. The size of the vortex core varies strongly with the magnetic field. In particular, in a low field of 10.8 mT, the core radius is much larger than the coherence length. The possible origin of these giant vortices is discussed.

beta-NMR of isolated lithium in nearly ferromagnetic palladium.

The temperature dependence of the frequency shift and spin-lattice relaxation rate of isolated, nonmagnetic (8)Li impurities implanted in a nearly ferromagnetic host (Pd) are measured by means of beta-detected nuclear magnetic resonance (beta-NMR). The shift is negative, very large, and increases monotonically with decreasing T in proportion to the bulk susceptibility of Pd for T > T* approximately 100 K. Below T*, an additional shift occurs which we attribute to the response of Pd to the defect. The relaxation rate is much slower than expected for the large shift and is linear with T below T*, showing no sign of additional relaxation mechanisms associated with the defect.

Near-surface structural phase transition of SrTiO3 studied with zero-field beta-detected nuclear spin relaxation and resonance.

We demonstrate that zero-field beta-detected nuclear quadrupole resonance and spin relaxation of low energy (8)Li can be used as a sensitive local probe of structural phase transitions near a surface. We find that the transition near the surface of a SrTiO(3) single crystal occurs at T(c) approximately 150K, i.e., approximately 45K higher than T(c)bulk, and that the tetragonal domains formed below T(c) are randomly oriented.

Depth-controlled beta-NMR of 8Li in a thin silver film.

Depth-controlled beta-NMR can be used to probe the magnetic properties of thin films and interfaces on a nanometer length scale. A 30 keV beam of highly spin-polarized 8Li+ ions was slowed down and implanted into a 50 nm film of Ag deposited on a SrTiO3 substrate. A novel high field beta-NMR spectrometer was used to observe two well resolved resonances which are attributed to Li occupying substitutional and octahedral interstitial sites in the Ag lattice. The temperature dependence of the Knight shifts and spin relaxation rates are consistent with the Korringa law for a simple metal, implying that the NMR of implanted 8Li reflects the spin suspectibility of bulk metallic silver.

Factors influencing body composition during very-low-calorie diets.

Apparent body composition changes with weight loss on very-low-calorie diet (VLCD) can depend on the method of fat-free mass estimation. In this report the implications of differences in measurement by direct versus indirect methods are examined. The nitrogen sparing and protein economy associated with ketosis is relevant and results of clinical trials with diets of varying composition are presented. The analytical findings of a multicenter, multimethod long-term VLCD study illustrate protein and metabolic conservation during VLCD. Protein losses, by total body nitrogen, over 10 wk dieting, independent of body mass index, were 4.75% of weight lost, as conservatively expected from obesity tissue reduction with no degradation of total energy expenditure. The implications of utilization of glycogen (water and potassium release) in interpretation of diet success and of body compositional change is evaluated. Evidence is presented that ultimate compositional changes with weight change may be individually specific and that body composition may be predicted from weight considerations alone.

Dependence of weight loss during very-low-calorie diets on total energy expenditure rather than on resting metabolic rate, which is associated with fat-free mass.

The assumption that total energy expended is related to resting metabolic rate (RMR) has not been validated. Intuitively, weight lost should be determined by the difference between the total energy consumed and the total energy expended. The ratio of actual daily energy usage to RMR by subjects dieting for 11 wk on a 1695-kJ (405-kcal) very-low-calorie diet (VLCD) was variable 1.9 +/- 0.3 (range 1.47-2.36). Weight loss correlated with total energy expenditure measured by 2H2 18O and not RMR, body mass index or body composition. Although RMR may be a reliable indicator of fat-free mass, there is little evidence that subjects with similar RMR will lose comparable weight or have comparable difficulty in weight maintenance.

Changes in total body nitrogen during weight reduction by very-low-calorie diets.

Body composition measurements, including total body nitrogen (TBN) by in vivo neutron activation analysis, were made on 11 female volunteers before and after an 11-wk very-low-calorie diet (VLCD) [1695 kJ (405 kcal) 6.7 g N]. Mean body mass index (BMI) changed from 32.1 to 26.2 kg/m2, corresponding to a mean weight loss of 16.2 +/- 2.4 (SD) kg. The mean loss of TBN was 125 +/- 57 g, equivalent to 781 +/- 356 g protein. The fat-free mass (FFM) component of the weight loss was calculated by two different methods as 23.5% (+/- 3% SEM) and 22.8% (+/- 2.7% SEM), respectively, thereby demonstrating the improved protein sparing of ketogenic VLCDs. FFM loss was not clearly related to BMI.

Across-the-day monitoring of mood and energy intake before, during, and after a very-low-calorie diet.

Mood, hunger, and energy intake were monitored in eight obese women before, during, and after 2 wk on a very-low-calorie diet (VLCD). Energy intake was significantly lower by approximately 30% in the week after the VLCD compared with the prediet week, both from food diaries and at a controlled ad libitum test meal. There was a gradual reduction in hunger, irritability, and urge to eat after 1 wk on the VLCD, which persisted through the postdiet week. Hunger and discontent were greatest in the evening during the first few days of the VLCD but diminished as the duration of the VLCD increased.

Long-term outcome of a self-help very-low-calorie-diet weight-loss program.

This paper presents 90-wk data on five seriously overweight subjects originally brought together for 1-2 wk in simple residential accommodation to share the experience of beginning a program of very-low-calorie dieting. All subjects have remained well below their starting weight; four of the five subjects have continued to lose weight (weight losses 33.7-66.8 kg), now weighing less than at the end of the first 26 wk previously reported (1). It is proposed that this self-help group model, incorporating a very-low-calorie diet, is valuable for the long-term management of obesity.

Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition.

Glycogen is stored in the liver, muscles, and fat cells in hydrated form (three to four parts water) associated with potassium (0.45 mmol K/g glycogen). Total body potassium (TBK) changes early in very-low-calorie diets (VLCDs) primarily reflect glycogen storage. Potassium released from glycogen can distort estimates of body composition during dieting. TBK changes due to glycogen mobilization were measured in 11 subjects after 4 d dieting with a VLCD. The influence of water-laden glycogen on weight fluctuations during the dieting process, the exaggerated regain if carbohydrate loading occurs, and the implications for weight control programs and overestimation of nitrogen losses with dieting are discussed.

Effect of diet-induced weight loss on total body bone mass.

1. Total body areal bone mineral density was measured by dual-energy X-ray absorptiometry in eight women before and 10 weeks after a very-low-calorie diet [405 kcal (1701 kJ)/day]. 2. The mean weight loss of 15.6 kg was accompanied by a statistically significant reduction in total body bone mineral density from 1.205 +/- 0.056 to 1.175 +/- 0.058 g/cm2 (mean +/- SD, P less than 0.005). 3. After cessation of the diet, weight gradually increased and by 10 months was similar to baseline values. Total body bone mineral density also increased after stopping the diet and mean values obtained 10 months after the diet did not differ significantly from initial values. Throughout the study total body bone mineral density values in all subjects were well within the range reported for normal subjects. 4. These data indicate that diet-induced weight loss is associated with rapid bone loss, subsequent weight gain being accompanied by increases in bone mass. Further studies are required to establish the clinical significance of these findings and, in particular, the skeletal distribution of bone loss.

Effect of very low calorie diet on body composition and exercise response in sedentary women.

The effect of very low calorie diet (VLCD) on fat-free mass (FFM) and physiological response to exercise is a topic of current interest. Ten moderately obese women (aged 23-57 years) received VLCD (1695 kJ.day-1) for 6 weeks. FFM, estimated by four conventional techniques, and heart rate (fc), blood lactate (la(b)), mean arterial pressure (MAP), respiratory exchange ratio (R) and rating of perceived exertion (RPE) were measured during a submaximal cycle ergometry test 1 week before, in the 2nd and 6th week, and 1 week after VLCD treatment. Strength and muscular endurance of the quadriceps and hamstrings were tested by isokinetic dynamometry. The 11.5-kg reduction in body mass was approximately 63% fat and 37% FFM. The latter was attributed largely to the loss of water associated with glycogen. Whilst exercise fc increased by 9-14 beats.min-1 (P < 0.01), there were substantial decreases (P < 0.01) in submaximal MAP (1.07-1.73 kPa), la(b) (0.75-1.00 mmol.l-1 and R (0.07-0.09) during VLCD. R and fc returned to normal levels after VLCD. Gross strength decreased (P < 0.01) by 9 and 13% at 1.05 rad.s-1 and 3.14 rad.s-1, respectively. Strength expressed relative to body mass (Nm.kg-1) increased (P < 0.01) at the lower contraction velocity, but there was no change at the faster velocity. Muscular endurance also decreased (P < 0.01) by 62 and 82% for the hamstrings and quadriceps, respectively. We concluded that the strength decrease was a natural adaptation to the reduction in body mass as the ratio of strength to FFM was maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of changes of water and electrolytes on the validity of conventional methods of measuring fat-free mass.

Fat-free mass was measured by hydrodensitometry, electrical impedance and total body potassium before and after water and electrolyte loss induced by (a) the administration of the diuretic frusemide, and (b) sweat loss. All methods of measuring fat-free mass were shown by pilot experiments to have procedural reliability. The diuretic caused a reduction in apparent fat-free mass of 2.63 kg by the impedance method, of 2.33 kg by hydrodensitometry and of 1.8 kg by total body potassium. Water and electrolyte loss from sweating caused a fat-free loss of 2.3 kg, 2.7 kg and 1.3 kg by the same three procedures. Urinary potassium accounted for about one fifth of the observed 40K fat-free mass loss. Each method was thus clearly sensitive to the induced water loss. These data suggest that in evaluating the composition of weight loss, existing methods of measuring body composition do not distinguish between water and other more critical components of fat-free mass. It is thus essential that stable hydration levels are established for any longitudinal comparison of weight loss by these methods.

Selection of appropriate exercise regimens for weight reduction during VLCD and maintenance.

Body composition, resting metabolic rate (RMR) and physical work capacity (aerobic capacity) were measured in four groups of 10 overweight women during 8 weeks of VLCD (405 kcal/day (42 g protein] followed by 8 weeks of 1500 kcal/day maintenance with two additional non dieting groups as controls. Five groups, i.e. two control groups plus three dieting groups, undertook exercise in bicycle ergometry (aerobic) or isotonic resistance or 8 week ergometry followed by 8 week resistance. Weight loss and body composition patterns were similar in diet and diet and exercise groups but efficiency of residual FFM in isotonic resistance groups improved significantly (P less than 0.05). Strength gains/kg body weight significantly improved (P less than 0.05) in the isotonic and dieting group. We conclude that exercise with VLCD is beneficial particularly isotonic resistance training, in improving muscular efficiency and RMR/lean.

Three year hospital experience with control of major obesity by VLCD in medically compromised individuals.

A very low calorie formula diet (VLCD) with physician and dietitian support was used to achieve and maintain weight loss in 408 overweight patients, referred by consultants because of concurrent health problems. The patients had failed to lose weight on conventional diets, and their obesity was considered a significant risk factor in their health. Using 330 or 405 kcal formula diets, the mean rate of weight loss in men was 1.87 kg/week and in women 1.27 kg/week. Women sustained the dieting process over longer periods, with a time to maximum weight loss of 5-72 weeks (mean 24) compared to the achievement in men of 4-40 weeks (mean 12.5). Sixteen per cent of the patients dropped out in the first 3 weeks. Of the remaining 84 per cent, weight loss to within 80-100 per cent BMI 25 (target weight) was achieved by 53 per cent men and 46 per cent women who had completed more than 5 weeks dieting. Women were more complaint than men at weight maintenance follow-up and 58 per cent of the start group were observed for more than 50 weeks (50-164), only 10 per cent experiencing weight regain of 20-70 per cent. Physician support was required to adjust medication in patients attending. Complications of obesity were remarkably improved after weight loss.

The myth of the yo-yo: consistent rate of weight loss with successive dieting by VLCD.

Four subjects in a recent trial of eight weeks dieting with the 405 kcal/day, 42 g protein formula (Cambridge diet extra), had participated 18 months previously in an 8-week trial using the 330 kcal/day Cambridge diet formula. This permitted a quantitative comparison of two similar dieting episodes, but following substantial weight loss and variable weight regain after a successful experience with a very low calorie diet. Within the reasonable bounds of comparison between outpatient dieting experiences, there was no suggestion of impairment in ability to lose weight in subsequent dieting after weight loss on a VLCD. The experience of these subjects would not support the contention that lasting metabolic debilitation had occurred that could be attributed to repeated dieting experiences with VLCD.

Restoration to normal body composition by VLCD: a comparison of post obese and lean subjects questions BMI 25 as diet limit.

Body composition was assessed in naturally lean female subjects who never had need to diet. At BMI 21-22 their body weight distribution of 75 per cent FFM and 25 per cent fat was compared with subjects who had dieted below BMI 25 by various conventional self-selected diets; subjects who had dieted to BMI 21-22 by VLCD and subjects who were dieting with VLCD but were still above BMI 25. These body composition studies support values of BMI 22-22 as a better estimate of desirable weight in women than BMI 25. At BMI 21-22 the distribution of body weight between fat and FFM of post VLCD dieters matches that of normal lean women.