Thermodynamics of weight loss diets.

BACKGROUND: It is commonly held that "a calorie is a calorie", i.e. that diets of equal caloric content will result in identical weight change independent of macronutrient composition, and appeal is frequently made to the laws of thermodynamics. We have previously shown that thermodynamics does not support such a view and that diets of different macronutrient content may be expected to induce different changes in body mass. Low carbohydrate diets in particular have claimed a "metabolic advantage" meaning more weight loss than in isocaloric diets of higher carbohydrate content. In this review, for pedagogic clarity, we reframe the theoretical discussion to directly link thermodynamic inefficiency to weight change. The problem in outline: Is metabolic advantage theoretically possible? If so, what biochemical mechanisms might plausibly explain it? Finally, what experimental evidence exists to determine whether it does or does not occur? RESULTS: Reduced thermodynamic efficiency will result in increased weight loss. The laws of thermodynamics are silent on the existence of variable thermodynamic efficiency in metabolic processes. Therefore such variability is permitted and can be related to differences in weight lost. The existence of variable efficiency and metabolic advantage is therefore an empiric question rather than a theoretical one, confirmed by many experimental isocaloric studies, pending a properly performed meta-analysis. Mechanisms are as yet unknown, but plausible mechanisms at the metabolic level are proposed. CONCLUSIONS: Variable thermodynamic efficiency due to dietary manipulation is permitted by physical laws, is supported by much experimental data, and may be reasonably explained by plausible mechanisms.

The effects of intentional weight loss as a latent variable problem.

Although obesity is associated with increased mortality rate and short-term weight loss improves risk factors for mortality, it has not been convincingly shown that weight loss among obese people results in reduced mortality rate. When considering the human literature, it has been pointed out that weight loss is often a sign of illness and that investigators therefore need to separate intentional from unintentional weight loss. It has generally been assumed that among people who state that they do not intend to lose weight, weight change subsequently observed is unintentional. Among such people, weight loss has been consistently associated with increased mortality rate. Complementarily, it has generally been assumed that among people who state that they do intend to lose weight, weight change subsequently observed is intentional. In these people who are intending to lose weight, some studies show apparent benefits of weight loss, some are neutral, and some show deleterious effects. The overall conclusion that some reviewers have drawn from this literature is that intentional weight loss (IWL) is at best not beneficial and may even be harmful with respect to mortality rate.We believe that this conclusion is drawn by inappropriately conflating weight loss (or more generally weight change) among people intending to lose weight with IWL (or change). Herein, under certain assumptions, we: (1) show that the association between mortality rate and weight loss among people intending to lose weight and between mortality rate and IWL are two different things; (2) show that the association between IWL and mortality rate is an inherently unobservable entity; (3) derive a method for estimating the plausible range of true effect of IWL on mortality rate if one is willing to make a number of restrictive, but perhaps reasonable assumptions; and (4) illustrate the method by application to a data set involving middle-age onset calorie restriction in mice. Copyright (c) 2005 John Wiley & Sons, Ltd.

Surgical treatment of morbid obesity by adjustable gastric band: the case for a conservative strategy in the case of failure - a 9-year series.

BACKGROUND: Lapaparoscopic adjustable gastric banding (LAGB) has become a widespread method to treat morbid obesity. Long-term complications and failures require a strategy for reoperation. METHODS: 1,180 patients have been operated on from April 1995 to December 2003. 151 had reoperation for complications (12.7%) excluding access-port problems: slippage (105), erosion (22), intolerance (24). 67 patients (5.6%) had their band removed; only 5 had a switch to another procedure. Esophageal dilatation and insufficient excess weight loss (<25%) after 5 years (13.7%) should also be addressed. Two situations are described: 1) Band in place: anterior slip, dilatation, isolated insufficient weight loss. 2) Band to be removed: posterior slip, severe anterior slip (acute, with necrosis or perforation), erosion, intolerance. Four options are recognized: 1) Conservation (adjustment management) or surgical correction (anterior slip). 2) Placement of a new band: for failure of the device, accidental removal (slippage in difficult conditions), and erosion after a delay. 3) RYGBP or BPD in selected cases only. 4) Other procedures. CONCLUSION: 1) A new band can be placed if there has been a technical problem. 2) Weight control is possible, including in the case of esophageal dilatation. Reoperation for insufficient weight loss without a technical problem is not an option. Failures of VBG cannot be fairly compared with Lap-Band (R) failures because of adjustability. 3) Reoperation is not often demanded. For failure after LAGB, the future should involve less invasive bariatric procedures and nonsurgical approaches.

Postpartum weight loss and infant feeding.

BACKGROUND: Women are often advised that lactation accelerates loss of the excess weight gained during pregnancy, but the evidence underlying this advice is sparse and conflicting. To help fill this gap, we assessed differences in the rate of postpartum weight loss in the first 9 months postpartum according to method of infant feeding. METHODS: Two hundred thirty-six women attending two public health clinics in Montreal were weighed in one to four routine infant immunization visits up to the 9th postpartum month. After each weighing, we administered a telephone questionnaire assessing the method of infant feeding (predominantly breast-feeding, mixed-feeding, or predominantly bottle-feeding) and potential confounders. Data were analyzed using unbalanced multivariate repeated measures linear regression. RESULTS: Infant feeding was not associated with statistically significant differences in the rate of weight loss. Gestational weight gain, postpartum smoking, and maternal birthplace were important predictors of postpartum weight change. CONCLUSION: Although our results cannot exclude an effect of more exclusive or more prolonged breast-feeding, breast-feeding as commonly practiced does not appear to influence the rate of postpartum weight loss. This information should be useful in counseling new or prospective mothers and in avoiding unrealistic expectations.

Neuropeptide Y in obese women during treatment with adrenergic modulation drugs.

BACKGROUND: The aim of the study is the assessment whether weight loss treatment with adrenergic modulation drugs modifies neuropeptide Y (NPY) plasma concentration in obese women. MATERIAL AND METHODS: 13 obese women (BMI 38.3 +/- 4.4) were tested before and subsequently 10 and 20 days after weight loss treatment. The treatment consisted of a very low caloric diet of 400 kcal (1670 kJ) daily combined with ephedrine with caffeine (E + C) or ephedrine with caffeine and yohimbine (E + C + Y) administered for 10 days using the cross-over method. The patients underwent physical examination, including heart rate and blood pressure measurements, spectral heart rate variability (HRV) at rest and after 3 minute handgrip and a 15 minute cycloergometer exercise at 75 W. All the above mentioned tests were carried out thrice in each patient. In 13 obese patients and in 6 control women plasma NPY concentrations were determined by a specific radioimmunoassay using rabbit anti-NPY antiserum and a standard synthetic porcine NPY (Peninsula Lab.). RESULTS: Plasma NPY concentrations were significantly lower in the obese persons compared with the control group. During weight loss treatment with adrenergic modulation drugs no changes in plasma NPY were found at rest and after physical exercise. Also no differences in HRV indices were observed. CONCLUSIONS: 1. Low plasma NPY concentration observed in obesity may be a contraregulatory factor that could prevent further weight increase. 2. Weight reduction treatment did not affect plasma NPY concentration and cardiovascular response to physical exercise. 3. The doses of adrenergic modulation drugs used in our study did not induce any serious side effects, and were so low that no change of plasma NPY concentration and cardiovascular responses were observed at rest.

Lesser curvature Roux-en-Y gastric bypass as an alternative procedure to failed vertical banded gastroplasty: surgical technique and short-term results.

PURPOSE: The incidence of revisional surgery for failed vertical banded gastroplasty has increased markedly over the last years. Conversion to gastric bypass is considered as a good alternative with satisfactory long term weight loss without further revisional surgery. Nevertheless, significant morbidity and mortality is still associated with this procedure. New technical aspects make it safer and more effective. The aim of the work is to expose a surgical bypass technique to attempt to reduce morbidity. PATIENTS AND METHODS: Thirty patients have undergone conversions from failed vertical banded gastroplasty to a lesser curvature Roux-en-Y Gastric Bypass. Surgical technique is described in detail and early complications and initial weight loss were analyzed (mean follow-up: 12 months). RESULTS: The key points of the operation were the small vertical pouch, the complete transection of the distal bypassed stomach, the interposition of a jejunal limb between the two gastric shares and the latero-lateral gastrojejunal anastomosis without proximal ring interposition. For the entire series, we noticed one major complication, an acute pancreatitis causing anastomotic fistula and four mild complications, one bleeding on the excluded stomach, one bronchopneumonia, one pleural effusion and one wound dehiscence. The percentage of excess weight loss attained 56.1% at one year follow-up. CONCLUSIONS: There have been tremendous improvements in the safety of gastric bypass over the years. One year follow-up indicates that our surgical bypass procedure is secure with a low complication rate.

Pork quality, processing, and sensory characteristics of dry-cured hams as influenced by Duroc crossing and sex.

This study was designed to evaluate Duroc (DU) crossing for Carso dry-cured ham production. One hundred fifty-four pigs (81 females and 73 castrates) of four different genotypes, pure Landrace pigs (LAN), offspring of LAN females crossed with Large White (LW) males (LWxLAN), offspring of LAN females crossed with DU males (DUxLAN), and offspring of LWxLAN females crossed with DU males (DUx[LWxLAN]), were chosen in the weight range of 105 to 120 kg (112.7 +/- 0.4 kg). Raw material quality was evaluated for ham fatness (intra- and intermuscular and subcutaneous) and meat quality (pH, color, water-holding capacity) of longissimus dorsi, biceps femoris, and semimembranosus muscles. Ham weight losses were recorded at different stages of processing. The biceps femoris and semimembranosus muscles were analyzed for chemical composition before (lipid, moisture, total nitrogen, nonprotein nitrogen) and after (moisture, salt, total nitrogen, nonprotein nitrogen) processing. Chemical and sensory analyses were performed on 96 dry hams (12 castrates and 12 females per genotype). Biceps femoris and semimembranosus muscles were evaluated for color, saltiness, aroma, and texture. Pigs of the four genotypes had similar ham fatness as estimated by subcutaneous fat thickness. Duroc crosses exhibited higher intramuscular fat content, marbling, and intermuscular fat. Crossing with DU resulted in lower weight losses during ham processing. Castrates were fatter and had more intra- and intermuscular fat and lower ham processing weight losses than females. A strong negative relationship between ham fatness and ham processing losses was observed. Chemical and sensory traits of dry ham muscles were little affected by DU crossing. Lower salt content of biceps femoris was found in DU crosses. Dry hams from female pigs had higher total and nonprotein nitrogen, but drier, firmer texture and higher resistance to cutting force compared to dry hams from castrated pigs. Crossing with DU demonstrated some disadvantages (more intermuscular fat, more slice visible fat) and advantages (lower weight loss and salt intake) for the quality of dry-cured ham.

Laparoscopic adjustable gastric banding: a prospective comparison of two commonly used bands.

BACKGROUND: Surgery for morbid obesity has increased since the introduction of the adjustable gastric bands (AGB), which can be placed laparoscopically. There are two AGB in wide use: the Swedish Adjustable Gastric Band (SAGB, Obtech), and the Lap-Band (Inamed Health). We present the results of a comparative study between the 2 AGB. METHODS: 101 patients with a minimal follow-up of 6 months were included. 49 patients received a Swedish Adjustable Gastric Band (SAGB), and the remaining 52 received the Lap-Band (LB). Postoperative weight loss and complications were compared at set intervals of 3 months in the first postoperative year, and 6 months in the years following. RESULTS: Mean follow-up was 9.9 months for the SAGB and 7.2 months for the LB. All but 5 procedures were performed laparoscopically. Mean operating-time was 102 minutes for the SAGB and 86 minutes for the LB. No significant difference in complications was noted between the 2 AGB. 1 SAGB was repositioned and 2 were removed, compared to 2 repositions and 2 removals of the LB. We excluded 5 patients with leakage of a SAGB due to technical failure. Mean preoperative weight kg/BMI of the SAGB patients was 133/45.3; in the LB patients 138/46.4. Mean weight loss at 6 months was 28 kg with the SAGB and 30 kg with the LB, and mean weight loss at 1 year 36 kg and 38 kg respectively. After 2 years, weight loss was 46 kg and 42 kg respectively. CONCLUSION: There was no significant difference in postoperative weight loss and complications between the SAGB and the LB.