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.

Adaptability and compliance of the obese patient to restrictive gastric surgery in the short term.

BACKGROUND: Low compliance, as well as recurrent vomiting, are often pointed out as the main causes of both postoperative technical complications and poor weight loss. METHODS: 50 patients were examined. All underwent preoperative psychological assessment through an intensive clinical interview. Between October 1999 and January 2000, all the patients underwent vertical banded gastroplasty (VBG). Excess weight loss (EWL) was followed, and the number of vomiting episodes was recorded at 1, 3 and 6 months after surgery. RESULTS: 3 different groups of patients could be distinguished: 1) those with no vomiting and good weight loss; 2) those with sporadic vomiting and fairly good weight loss; and 3) those with frequent vomiting and poorer weight loss. However, this last group of patients was not homogeneous and should be divided into 2 subgroups: 1) patients who lose weight, while vomiting; 2) patients who do not lose weight, while vomiting. CONCLUSIONS: The experience of vomiting is a crucial cross-roads. The influence of psychosocial factors was noticed in all patients. The absence of psychosocial stressors, together with realistic expectations and a strong motivation to change, should be considered as reliable and replicable predictors of success. However, even those patients with accentuated psychological difficulties were able to succeed in coping with them, and achieved a good weight outcome, with good effects on the psychic side. Therefore, the evidence of psychological disorders cannot be taken as an absolute criterion of selection/exclusion of candidates for the operation. Accurate presurgical education and postoperative psychological support are likely to increase the patient's compliance and the percentage of successful cases.

Effect of significant intermediate-term weight loss on serum leptin levels and body composition in severely obese subjects.

BACKGROUND: Leptin, produced by adipose tissue, signals body fat content to the hypothalamus. Serum leptin levels (SLL), elevated in obese humans, decrease with weight loss. This study investigated the reduction of SLL and fat mass following restrictive bariatric surgery. METHODS: Obese subjects (body mass index [BMI] >35 kg/m2, n=154) undergoing gastric banding (weight-reduced subjects) were investigated for SLL and body composition before surgery and for 2 years after. Overweight subjects matched for fat mass and gender (fat mass-matched overweight controls, n=194) and subjects who had never been obese (normal weight controls, n=158) were studied for comparison. RESULTS: SLL were highest in weight-reduced subjects and decreased with weight loss (P <0.001), remaining elevated compared with normal weight controls (P <0.001) but lower than fat mass-matched overweight controls (women: P <0.04). At 2 years, SLL normalized for fat mass (allowing comparison between various levels of adiposity) were lower in weight-reduced subjects compared with fat mass-matched overweight controls (women: P =0.003), yet were similar for weight-reduced subjects at 2 years compared with normal weight controls despite 14 kg greater fat mass. Relative lean mass of extremities in weight-reduced subjects increased with weight loss (P <0.001). CONCLUSION: SLL decreased after considerable weight loss more than could be accounted for by fat mass or BMI reduction alone. This disproportionate decrease in SLL might point to a mechanism that evolved as adaptation to starvation during times of famine. Thus, post-obese subjects may be at risk of weight-regain due to disproportionately low SLL and increased appetite via the leptin-melanocortin pathway.

Unreported sauna use in anorexia nervosa: evidence from the world-wide-web.

weight loss methods employed in anorexia nervosa (AN) are vomiting, laxatives, diuretics, enemas, suppositories, ipecac, weight loss medications and inadequate insulin in diabetics. Some methods result in weight loss from fluid depletion and not a reduction in body fat. Sauna use causes rapid fluid loss, but has not been reported in the medical literature as a weight loss strategy used in AN. We found reports of sauna use in AN on the world-wide-web are rare. We hypothesize that the warming caused by the use of sauna, may result in physical improvement in AN and thereby reduce its acceptability as a weight loss strategy.

Intentional weight loss and death in overweight and obese U.S. adults 35 years of age and older.

BACKGROUND: Although weight loss improves risk factors for cardiovascular and metabolic disease, it is unclear whether intentional weight loss reduces mortality rates. OBJECTIVE: To examine the relationships among intention to lose weight, weight loss, and all-cause mortality. DESIGN: Prospective cohort study using a probability sample of the U.S. population. SETTING: Interviewer-administered survey. PARTICIPANTS: 6391 overweight and obese persons (body mass index > or = 25 kg/m2) who were at least 35 years of age. MEASUREMENTS: Intention to lose weight and weight change during the past year were assessed by self-report in 1989. Vital status was followed for 9 years. Hazard rate ratios (HRRs) were adjusted for age, sex, ethnicity, education, smoking, health status, health care utilization, and initial body mass index. RESULTS: Compared with persons not trying to lose weight and reporting no weight change, those reporting intentional weight loss had a 24% lower mortality rate (HRR, 0.76 [95% CI, 0.60 to 0.97]) and those with unintentional weight loss had a 31% higher mortality rate (HRR, 1.31 [CI, 1.01 to 1.70]). However, mortality rates were lower in persons who reported trying to lose weight than those in not trying to lose weight, independent of actual weight change. Compared with persons not trying to lose weight and reporting no weight change, persons trying to lose weight had the following HRRs: no weight change, 0.80 (CI, 0.65 to 0.99); gained weight, 0.94 (CI, 0.65 to 1.37); and lost weight, 0.76 (CI, 0.60 to 0.97). CONCLUSIONS: Attempted weight loss is associated with lower all-cause mortality, independent of weight change. Self-reported intentional weight loss is associated with lower mortality rates, and weight loss is associated with higher mortality rates only if it is unintentional.

Heterosis and recombination effects on pig reproductive traits.

The objective was to estimate breed, heterosis, and recombination effects on pig reproductive traits in two different four-breed composite populations. Breeds included Yorkshire, Landrace, Large White, and Chester White in Exp. 1 and Duroc, Hampshire, Pietrain, and Spot in Exp. 2. Data were recorded on purebred pigs, two-breed cross pigs, and pigs from generations F1 through F6, where F1 pigs were the first generation of a four-breed cross. Litter traits were considered a trait of the gilt. There were 868 first parity litters in Exp. 1 and 865 in Exp. 2. Direct heterosis significantly increased sow weight at 110 d of gestation and litter weight at 14 and 28 d (weaning) in both experiments. Direct heterosis significantly increased number of nipples, weight at puberty, lactation weight loss, litter size, and litter birth weight in Exp. 2. Gestation length in Exp. 1 and age at puberty in Exp. 1 and Exp. 2 were significantly decreased by direct heterosis. Maternal heterosis significantly increased age at puberty in Exp. 2 and decreased sow weight at 110 d of gestation in Exp. 1. Recombination significantly increased sow weight at 110 d of gestation and tended to increase total number born and litter birth weight in Exp. 1. Recombination significantly decreased age at puberty in Exp. 2. Litter heterosis significantly increased number of pigs at 14 and 28 d; litter weights at birth, 14, and 28 d; and tended to increase lactation weight loss in Exp. 1. Litter heterosis decreased litter size in Exp. 2. Maternal heterosis and recombination effects had a sampling correlation of -0.97 in Exp. 1 and -0.91 in Exp. 2 for number of fully formed pigs. Therefore, maternal heterosis and recombination effects were summed, and their net effect was tested. This net effect tended to increase number of nipples, lactation weight loss, and litter birth weight and significantly increased number of fully formed pigs in Exp. 1. Direct, maternal, and litter heterosis and recombination effects significantly influenced reproductive traits.

Weight Loss-associated changes in acute effects of nateglinide on insulin secretion after glucose loading: results of glucose loading on 2 consecutive days.

AIM: The aim of this study was to investigate the influence of changes in insulin resistance and early insulin secretion on the insulin secretagogic effects of nateglinide. METHODS: Oral glucose tolerance testing (OGTT, 75 g) was performed in obese patients before and after weight loss on 2 consecutive days (first day OGTT without nateglinide, second day OGTT with nateglinide), to compare any weight loss associated changes in the nateglinide-induced insulin response to glucose loading. RESULTS: Reductions in visceral fat, liver fat, skeletal muscle fat and homeostasis model assessment (HOMA)-R due to weight loss were associated with increased Delta insulin 30 min/Delta glucose 30 min (DeltaI30/DeltaG30), and reduced area under the curve (AUC) for plasma glucose as seen in OGTT results. Results from OGTT showed that nateglinide administration was associated with reductions in plasma glucose AUC, both before and after weight loss. Before weight loss, although there was a significant elevation of DeltaI30/DeltaG30 associated with nateglinide treatment, no major change in the insulin-secreting dynamics after glucose loading was observed. After weight loss, nateglinide administration produced a significant increase in DeltaI30/DeltaG30, with insulin secretion peaking more quickly. CONCLUSION: Insulin response to nateglinide after glucose loading varied greatly in conjunction with weight loss. This may be accounted for not only by the enhancement of early insulin response to nateglinide associated with the improvement of early insulin response with weight loss but also by the reduced visceral fat, which in turn led to reduced levels of free fatty acids in portal blood and hepatic triglycerides, as well as increased hepatic insulin clearance.

The relationship between number of medications and weight loss or impaired balance in older adults.

OBJECTIVES: To examine the relationship between cumulative medication exposure and risk of two common manifestations of adverse drug effects: weight loss and impaired balance. DESIGN: Cross-sectional and longitudinal cohort. SETTING: Urban Connecticut community. PARTICIPANTS: Eight hundred eighty-five community-dwelling residents aged 72 and older. MEASUREMENTS: weight loss (> or =10 pounds) and balance, a composite of four balance measures. RESULTS: Participants took a mean+/-standard deviation of 2.2+/-1.9 medications (range 0-15). After adjustment for age, depressive symptoms, cognitive impairment, vision and hearing impairments, number of chronic diseases, and number of hospitalizations in the previous year, the adjusted odds ratio (OR) for weight loss was 1.48 (95% confidence interval (CI)=0.85-2.59) for those taking one to two medications, 1.96 (95% CI=1.08-3.54) for three to four medications, and 2.78 (95% CI=1.38-5.60) for five or more medications. For impaired balance, adjusted ORs were 1.44 (95% CI=0.94-2.19), 1.72 (95% CI=1.09-2.71), and 1.80 (95% CI=1.02-3.19), respectively. CONCLUSION: A greater number of medications were associated with increased risk of adverse drug outcomes, after extensive adjustment for chronic illness. Clinicians should consider the adverse effects of total drug use and not merely the benefits or risks of individual medications for specific diseases.