Diet versus exercise in "the biggest loser" weight loss competition

BACKGROUND

Obesity experts have criticized The Biggest Loser television show for its portrayal of an unrealistic intervention that raises false expectations for weight loss. However, the magnitude of the diet and exercise intervention has not been previously quantified.

DESIGN AND METHODS

Using a validated computational model of metabolism, I quantified the diet and exercise intervention by integrating data on energy expenditure, body weight and fat mass collected during The Biggest Loser competition.

RESULTS

Participant body mass index, weight, and percent body fat at baseline were 48.7 ± 10.1 kg/m(2) , 144.9 ± 39.4 kg, and 49 ± 6% (mean ± SD), respectively. During the first phase of the competition when the contestants were isolated in a boot camp environment, the average rate of weight loss was 0.4 ± 0.1 kg/d and decreased to 0.19 ± 0.1 kg/d after returning home. Total weight loss was 58.2 ± 26 kg with 81.6 ± 8.4% coming from body fat. The computer simulations closely matched these data and calculated that average energy intake decreased by 65% during the first phase to 1300 kcal/d while participating in 3.1 h/d of vigorous exercise. After returning home, energy intake increased to 1900 kcal/d and vigorous exercise decreased to 1.1 h/d. Simulation of diet alone resulted in 34 kg of weight loss with 65% coming from body fat, whereas exercise alone resulted in a loss of 27 kg with 102% from fat.

CONCLUSION

The intense diet and exercise intervention during The Biggest Loser competition were not sustainable. However, a relatively modest permanent lifestyle intervention of 20% caloric restriction and 20 min/d of vigorous exercise could maintain the massive weight loss.

Metabolism of mice and men: mathematical modeling of body weight dynamics

PURPOSE OF REVIEW

Dynamic interrelationships between food intake, energy expenditure, energy partitioning, and metabolic fuel selection underlie changes in body weight and composition. A quantitative understanding of these interrelationships is becoming increasingly important given the rise of the worldwide obesity epidemic and the widespread interest in weight management. This review describes how mathematical models offer a quantitative framework for integrating dynamic physiological and behavioral data underlying body weight dynamics in both humans and mice.

RECENT FINDINGS

Mathematical models have provided important insights regarding the drivers of the obesity epidemic, how metabolism adapts to different diets, the predicted magnitude and variability of weight change, and why mouse models have obesity phenotypes. Because mathematical models are constrained by conservation laws, they can also be used to infer physiological variables that are difficult to measure directly.

SUMMARY

Mathematical models can help improve our understanding of the dynamic energy and macronutrient imbalances that give rise to changes in body weight and composition over time. The model development process can also highlight important knowledge gaps and model simulations can help design and predict the results of key new experiments to fill those gaps.

Metabolic slowing with massive weight loss despite preservation of fat-free mass

CONTEXT

An important goal during weight loss is to maximize fat loss while preserving metabolically active fat-free mass (FFM). Massive weight loss typically results in substantial loss of FFM potentially slowing metabolic rate.

OBJECTIVE

Our objective was to determine whether a weight loss program consisting of diet restriction and vigorous exercise helped to preserve FFM and maintain resting metabolic rate (RMR).

PARTICIPANTS AND INTERVENTION

We measured body composition by dual-energy x-ray absorptiometry, RMR by indirect calorimetry, and total energy expenditure by doubly labeled water at baseline (n = 16), wk 6 (n = 11), and wk 30 (n = 16).

RESULTS

At baseline, participants were severely obese (× ± SD; body mass index 49.4 ± 9.4 kg/m(2)) with 49 ± 5% body fat. At wk 30, more than one third of initial body weight was lost (-38 ± 9%) and consisted of 17 ± 8% from FFM and 83 ± 8% from fat. RMR declined out of proportion to the decrease in body mass, demonstrating a substantial metabolic adaptation (-244 ± 231 and -504 ± 171 kcal/d at wk 6 and 30, respectively, P < 0.01). Energy expenditure attributed to physical activity increased by 10.2 ± 5.1 kcal/kg.d at wk 6 and 6.0 ± 4.1 kcal/kg.d at wk 30 (P < 0.001 vs. zero).

CONCLUSIONS

Despite relative preservation of FFM, exercise did not prevent dramatic slowing of resting metabolism out of proportion to weight loss. This metabolic adaptation may persist during weight maintenance and predispose to weight regain unless high levels of physical activity or caloric restriction are maintained.

Modeling metabolic adaptations and energy regulation in humans

Mathematical modeling of human energy regulation and body weight change has recently reached the level of sophistication required for accurate predictions. Mathematical models are beginning to provide a quantitative framework for integrating experimental data in humans and thereby help us better understand the dynamic imbalances of energy and macronutrients that give rise to changes in body weight and composition. This review provides an overview of the various approaches that have been used to model body weight dynamics and energy regulation in humans, highlights several insights that these models have provided, and suggests how mathematical models can serve as a guide for future experimental research.

Effects of 4 weight-loss diets differing in fat, protein, and carbohydrate on fat mass, lean mass, visceral adipose tissue, and hepatic fat: results from the POUNDS LOST trial

BACKGROUND

Weight loss reduces body fat and lean mass, but whether these changes are influenced by macronutrient composition of the diet is unclear.

OBJECTIVE

We determined whether energy-reduced diets that emphasize fat, protein, or carbohydrate differentially reduce total, visceral, or hepatic fat or preserve lean mass.

DESIGN

In a subset of participants in a randomized trial of 4 weight-loss diets, body fat and lean mass (n = 424; by using dual-energy X-ray absorptiometry) and abdominal and hepatic fat (n = 165; by using computed tomography) were measured after 6 mo and 2 y. Changes from baseline were compared between assigned amounts of protein (25% compared with 15%) and fat (40% compared with 20%) and across 4 carbohydrate amounts (35% through 65%).

RESULTS

At 6 mo, participants lost a mean (±SEM) of 4.2 ± 0.3 kg (12.4%) fat and 2.1 ± 0.3 kg (3.5%) lean mass (both P < 0.0001 compared with baseline values), with no differences between 25% and 15% protein (P ≥ 0.10), 40% and 20% fat (P ≥ 0.34), or 65% and 35% carbohydrate (P ≥ 0.27). Participants lost 2.3 ± 0.2 kg (13.8%) abdominal fat: 1.5 ± 0.2 kg (13.6%) subcutaneous fat and 0.9 ± 0.1 kg (16.1%) visceral fat (all P < 0.0001 compared with baseline values), with no differences between the diets (P ≥ 0.29). Women lost more visceral fat than did men relative to total-body fat loss. Participants regained ~40% of these losses by 2 y, with no differences between diets (P ≥ 0.23). Weight loss reduced hepatic fat, but there were no differences between groups (P ≥ 0.28). Dietary goals were not fully met; self-reported contrasts were closer to 2% protein, 8% fat, and 14% carbohydrate at 6 mo and 1%, 7%, and 10%, respectively, at 2 y.

CONCLUSION

Participants lost more fat than lean mass after consumption of all diets, with no differences in changes in body composition, abdominal fat, or hepatic fat between assigned macronutrient amounts. This trial was registered at clinicaltrials.gov as NCT00072995.

Measuring weight outcomes for obesity intervention strategies: the case of a sugar-sweetened beverage tax

Taxing unhealthy foods has been proposed as a means to improve diet and health by reducing calorie intake and raising funds to combat obesity, particularly sugar-sweetened beverages (SSBs). A growing number of studies have examined the effects of such food taxes, but few have estimated the weight-loss effects. Typically, a static model of 3500 calories for one pound of body weight is used, and the main objective of the study is to demonstrate its bias. To accomplish the objective, we estimate income-segmented beverage demand systems to examine the potential effects of a SSB tax. Elasticity estimates and a hypothetical 20 percent effective tax rate (or about 0.5 cent per ounce) are applied to beverage intake data from a nationally representative survey, and we find an average daily reduction of 34-47 calories among adults and 40-51 calories among children. The tax-induced energy reductions are translated into weight loss using both static and dynamic calorie-to-weight models. Results demonstrate that the static model significantly overestimates the weight loss from reduced energy intake by 63 percent in year one, 346 percent in year five, and 764 percent in year 10, which leads to unrealistic expectations for obesity intervention strategies. The tax is estimated to generate $5.8 billion a year in revenue and is found to be regressive, although it represents about 1 percent of household food and beverage spending.

Quantification of the effect of energy imbalance on bodyweight

Obesity interventions can result in weight loss, but accurate prediction of the bodyweight time course requires properly accounting for dynamic energy imbalances. In this report, we describe a mathematical modelling approach to adult human metabolism that simulates energy expenditure adaptations during weight loss. We also present a web-based simulator for prediction of weight change dynamics. We show that the bodyweight response to a change of energy intake is slow, with half times of about 1 year. Furthermore, adults with greater adiposity have a larger expected weight loss for the same change of energy intake, and to reach their steady-state weight will take longer than it would for those with less initial body fat. Using a population-averaged model, we calculated the energy-balance dynamics corresponding to the development of the US adult obesity epidemic. A small persistent average daily energy imbalance gap between intake and expenditure of about 30 kJ per day underlies the observed average weight gain. However, energy intake must have risen to keep pace with increased expenditure associated with increased weight. The average increase of energy intake needed to sustain the increased weight (the maintenance energy gap) has amounted to about 0·9 MJ per day and quantifies the public health challenge to reverse the obesity epidemic.

The global obesity pandemic: shaped by global drivers and local environments

The simultaneous increases in obesity in almost all countries seem to be driven mainly by changes in the global food system, which is producing more processed, affordable, and effectively marketed food than ever before. This passive overconsumption of energy leading to obesity is a predictable outcome of market economies predicated on consumption-based growth. The global food system drivers interact with local environmental factors to create a wide variation in obesity prevalence between populations. Within populations, the interactions between environmental and individual factors, including genetic makeup, explain variability in body size between individuals. However, even with this individual variation, the epidemic has predictable patterns in subpopulations. In low-income countries, obesity mostly affects middle-aged adults (especially women) from wealthy, urban environments; whereas in high-income countries it affects both sexes and all ages, but is disproportionately greater in disadvantaged groups. Unlike other major causes of preventable death and disability, such as tobacco use, injuries, and infectious diseases, there are no exemplar populations in which the obesity epidemic has been reversed by public health measures. This absence increases the urgency for evidence-creating policy action, with a priority on reduction of the supply-side drivers.

Estimating changes in free-living energy intake and its confidence interval

BACKGROUND

Free-living energy intake in humans is notoriously difficult to measure but is required to properly assess outpatient weight-control interventions.

OBJECTIVE

Our objective was to develop a simple methodology that uses longitudinal body weight measurements to estimate changes in energy intake and its 95% CI in individual subjects.

DESIGN

We showed how an energy balance equation with 2 parameters can be derived from any mathematical model of human metabolism. We solved the energy balance equation for changes in free-living energy intake as a function of body weight and its rate of change. We tested the predicted changes in energy intake by using weight-loss data from controlled inpatient feeding studies as well as simulated free-living data from a group of "virtual study subjects" that included realistic fluctuations in body water and day-to-day variations in energy intake.

RESULTS

Our method accurately predicted individual energy intake changes with the use of weight-loss data from controlled inpatient feeding experiments. By applying the method to our simulated free-living virtual study subjects, we showed that daily weight measurements over periods >28 d were required to obtain accurate estimates of energy intake change with a 95% CI of <300 kcal/d. These estimates were relatively insensitive to initial body composition or physical activity level.

CONCLUSIONS

Frequent measurements of body weight over extended time periods are required to precisely estimate changes in energy intake in free-living individuals. Such measurements are feasible, relatively inexpensive, and can be used to estimate diet adherence during clinical weight-management programs.

Hypertrophy-driven adipocyte death overwhelms recruitment under prolonged weight gain

Fat pads dynamically regulate energy storage capacity under energy excess and deficit. This remodeling process is not completely understood, with controversies regarding differences between fat depots and plasticity of adipose cell number. We examined changes of mouse adipose cell-size distributions in epididymal, inguinal, retroperitoneal, and mesenteric fat under both weight gain and loss. With mathematical modeling, we specifically analyzed the recruitment, growth/shrinkage, and loss of adipose cells, including the size dependence of these processes. We found a qualitatively universal adipose tissue remodeling process in all four fat depots: 1), There is continuous recruitment of new cells under weight gain; 2), the growth and shrinkage of larger cells (diameter >50 μm) is proportional to cell surface area; and 3), cell loss occurs under prolonged weight gain, with larger cells more susceptible. The mathematical model gives a predictive integrative picture of adipose tissue remodeling in obesity.

Predicting changes of body weight, body fat, energy expenditure and metabolic fuel selection in C57BL/6 mice

The mouse is an important model organism for investigating the molecular mechanisms of body weight regulation, but a quantitative understanding of mouse energy metabolism remains lacking. Therefore, we created a mathematical model of mouse energy metabolism to predict dynamic changes of body weight, body fat, energy expenditure, and metabolic fuel selection. Based on the principle of energy balance, we constructed ordinary differential equations representing the dynamics of body fat mass (FM) and fat-free mass (FFM) as a function of dietary intake and energy expenditure (EE). The EE model included the cost of tissue deposition, physical activity, diet-induced thermogenesis, and the influence of FM and FFM on metabolic rate. The model was calibrated using previously published data and validated by comparing its predictions to measurements in five groups of male C57/BL6 mice (N = 30) provided ad libitum access to either chow or high fat diets for varying time periods. The mathematical model accurately predicted the observed body weight and FM changes. Physical activity was predicted to decrease immediately upon switching from the chow to the high fat diet and the model coefficients relating EE to FM and FFM agreed with previous independent estimates. Metabolic fuel selection was predicted to depend on a complex interplay between diet composition, the degree of energy imbalance, and body composition. This is the first validated mathematical model of mouse energy metabolism and it provides a quantitative framework for investigating energy balance relationships in mouse models of obesity and diabetes.

Mechanisms of metabolic fuel selection: modeling human metabolism and body-weight change

Casual observation of any magazine rack or browsing the diet section of any bookshop provides convincing evidence that weight loss is of great interest to the U.S. population. Americans spend more than US$30 billion/year on weight-loss products, and the health cost of obesity was recently estimated to be as high as US$147 billion/year. Understanding the development of obesity and how excess weight can be lost requires knowledge of the physiological mechanisms by which the body uses food to provide fuel for metabolism and how the body copes with imbalances between fuel delivery and utilization.

Predicting metabolic adaptation, body weight change, and energy intake in humans

Complex interactions between carbohydrate, fat, and protein metabolism underlie the body's remarkable ability to adapt to a variety of diets. But any imbalances between the intake and utilization rates of these macronutrients will result in changes in body weight and composition. Here, I present the first computational model that simulates how diet perturbations result in adaptations of fuel selection and energy expenditure that predict body weight and composition changes in both obese and nonobese men and women. No model parameters were adjusted to fit these data other than the initial conditions for each subject group (e.g., initial body weight and body fat mass). The model provides the first realistic simulations of how diet perturbations result in adaptations of whole body energy expenditure, fuel selection, and various metabolic fluxes that ultimately give rise to body weight change. The validated model was used to estimate free-living energy intake during a long-term weight loss intervention, a variable that has never previously been measured accurately.

Nutritional systems biology modeling: from molecular mechanisms to physiology

The use of computational modeling and simulation has increased in many biological fields, but despite their potential these techniques are only marginally applied in nutritional sciences. Nevertheless, recent applications of modeling have been instrumental in answering important nutritional questions from the cellular up to the physiological levels. Capturing the complexity of today's important nutritional research questions poses a challenge for modeling to become truly integrative in the consideration and interpretation of experimental data at widely differing scales of space and time. In this review, we discuss a selection of available modeling approaches and applications relevant for nutrition. We then put these models into perspective by categorizing them according to their space and time domain. Through this categorization process, we identified a dearth of models that consider processes occurring between the microscopic and macroscopic scale. We propose a "middle-out" strategy to develop the required full-scale, multilevel computational models. Exhaustive and accurate phenotyping, the use of the virtual patient concept, and the development of biomarkers from "-omics" signatures are identified as key elements of a successful systems biology modeling approach in nutrition research--one that integrates physiological mechanisms and data at multiple space and time scales.

Estimating the continuous-time dynamics of energy and fat metabolism in mice

The mouse has become the most popular organism for investigating molecular mechanisms of body weight regulation. But understanding the physiological context by which a molecule exerts its effect on body weight requires knowledge of energy intake, energy expenditure, and fuel selection. Furthermore, measurements of these variables made at an isolated time point cannot explain why body weight has its present value since body weight is determined by the past history of energy and macronutrient imbalance. While food intake and body weight changes can be frequently measured over several weeks (the relevant time scale for mice), correspondingly frequent measurements of energy expenditure and fuel selection are not currently feasible. To address this issue, we developed a mathematical method based on the law of energy conservation that uses the measured time course of body weight and food intake to estimate the underlying continuous-time dynamics of energy output and net fat oxidation. We applied our methodology to male C57BL/6 mice consuming various ad libitum diets during weight gain and loss over several weeks and present the first continuous-time estimates of energy output and net fat oxidation rates underlying the observed body composition changes. We show that transient energy and fat imbalances in the first several days following a diet switch can account for a significant fraction of the total body weight change. We also discovered a time-invariant curve relating body fat and fat-free masses in male C57BL/6 mice, and the shape of this curve determines how diet, fuel selection, and body composition are interrelated.

The unrelenting obesity epidemic has resulted in intensive basic scientific investigation into the molecular mechanisms of body weight regulation—with the mouse being the organism of choice for such studies. We know that any mechanism of body weight regulation must exert its effect by influencing food intake, energy output, fuel selection, or some combination of these factors over extended time scales (∼weeks for mice). While food intake and body weight can be frequently measured in mice, current methods prohibit corresponding measurements of energy output or fuel selection on such long time scales. We address this deficiency by developing a mathematical method that quantitatively relates measurements of food intake, body weight and body fat to calculate the dynamic changes of energy output and net fat oxidation rates during the development of obesity and weight loss in male C57BL/6 mice. The mathematical model is based on the law of energy conservation, makes very few assumptions, and provides the first continuous-time estimates of energy output and fuel selection over periods lasting many weeks. Application of our methodology to various mouse models of obesity will improve our understanding of body weight regulation by placing molecular mechanisms in their whole-body physiological context.

Persistent diet-induced obesity in male C57BL/6 mice resulting from temporary obesigenic diets

BACKGROUND

Does diet-induced obesity persist after an obesigenic diet is removed? We investigated this question by providing male C57BL/6 mice with free access to two different obesigenic diets followed by a switch to chow to determine if obesity was reversible.

METHODOLOGY/PRINCIPAL FINDINGS

Male C57BL/6 mice were randomly assigned to five weight-matched groups: 1) C group that continuously received a chow diet; 2) HF group on a 60% high fat diet; 3) EN group on the high fat diet plus liquid Ensure; 4) HF-C group switched from high fat to chow after 7 weeks; 5) EN-C group switched from high fat plus Ensure to chow after 7 weeks. All food intake was ad libitum. Body weight was increased after 7 weeks on both obesigenic diets (44.6+/-0.65, 39.8+/-0.63, and 28.6+/-0.63 g for EN, HF, and C groups, respectively) and resulted in elevated concentrations of serum insulin, glucose, and leptin and lower serum triglycerides. Development of obesity in HF and EN mice was caused by increased energy intake and a relative decrease of average energy output along with decreased ambulatory activity. After the switch to chow, the HF-C and EN-C groups lost weight but subsequently maintained a state of persistent obesity in comparison to the C group (34.8+/-1.2, 34.1+/-1.2 vs. 30.8+/-0.8 g respectively; P<0.05) with a 40-50% increase of body fat. All serum hormones and metabolites returned to control levels with the exception of a trend for increased leptin. The HF-C and EN-C groups had an average energy output in line with the C group and the persistent obesity was maintained despite a non-significant increase of energy intake of less than 1 kcal/d at the end of the study.

CONCLUSION

Our results illustrate the importance of considering the history of energy imbalance in determining body weight and that a persistent elevation of body weight after removal of obesigenic diets can result from very small increases of energy intake.

A viscerally driven cachexia syndrome in patients with advanced colorectal cancer: contributions of organ and tumor mass to whole-body energy demands

BACKGROUND

Cancer cachexia-associated weight loss is poorly understood; energetically demanding tissues (eg, organ and tumor mass) and resting energy expenditure (REE) are reported to increase with advanced cancer.

OBJECTIVE

The objective was to quantify the potential contribution of increasing masses of energetically demanding tissues to REE with colorectal cancer cachexia progression.

DESIGN

A longitudinal computed tomography (CT) image review was performed to quantify organ size (liver, including metastases, and spleen) and peripheral tissues (skeletal muscle and adipose tissue) during colorectal cancer cachexia progression (n = 34). Body composition was prospectively evaluated by CT and dual-energy X-ray absorptiometry, and REE was determined by indirect calorimetry in advanced colorectal cancer patients (n = 18).

RESULTS

Eleven months from death, the liver (2.3 +/- 0.7 kg) and spleen (0.32 +/- 0.2 kg) were larger than reference values. One month from death, liver weight increased to 3.0 +/- 1.5 kg (P = 0.010), spleen showed a trend to increase (P = 0.077), and concurrent losses of muscle (4.2 kg) and fat (3.5 kg) (P < 0.05) were observed. The estimated percentage of fat-free mass (FFM) occupied by the liver increased from 4.5% to 7.0% (P < 0.001). The most rapid loss of peripheral tissues and liver and metastases gain occurred within 3 mo of death. A positive linear relation existed between liver mass and measured whole-body REE (r(2) = 0.35, P = 0.010); because liver accounted for a larger percentage of FFM, measured REE . kg FFM(-1) . d(-1) increased (r(2) = 0.35, P = 0.010).

CONCLUSIONS

Increases in mass and in the proportion of high metabolic rate tissues, including liver and tumor, represented a cumulative incremental REE of approximately 17,700 kcal during the last 3 mo of life and may contribute substantially to cachexia-associated weight loss.

Modeling weight-loss maintenance to help prevent body weight regain

BACKGROUND

Lifestyle intervention can successfully induce weight loss in obese persons, at least temporarily. However, there currently is no way to quantitatively estimate the changes of diet or physical activity required to prevent weight regain. Such a tool would be helpful for goal-setting, because obese patients and their physicians could assess at the outset of an intervention whether long-term adherence to the calculated lifestyle change is realistic.

OBJECTIVE

We aimed to calculate the expected change of steady-state body weight arising from a given change in dietary energy intake and, conversely, to calculate the modification of energy intake required to maintain a particular body-weight change.

DESIGN

We developed a mathematical model using data from 8 longitudinal weight-loss studies representing 157 subjects with initial body weights ranging from 68 to 160 kg and stable weight losses between 7 and 54 kg.

RESULTS

Model calculations closely matched the change data (R(2) = 0.83, chi(2) = 2.1, P < 0.01 for weight changes; R(2) = 0.91, chi(2) = 0.87, P < 0.0004 for energy intake changes). Our model performed significantly better than the previous models for which chi(2) values were 10-fold those of our model. The model also accurately predicted the proportion of weight change resulting from the loss of body fat (R(2) = 0.90).

CONCLUSIONS

Our model provides realistic calculations of body-weight change and of the dietary modifications required for weight-loss maintenance. Because the model was implemented by using standard spreadsheet software, it can be widely used by physicians and weight-management professionals.

Computational modeling of cancer cachexia

PURPOSE OF REVIEW

Measurements of whole-body energy expenditure, body composition, and in-vivo metabolic fluxes are required to quantitatively understand involuntary weight loss in cancer cachexia. Such studies are rare because cancer cachexia occurs near the end of life when invasive metabolic tests may be precluded. Thus, models of cancer-associated weight loss are an important tool for helping to understand this debilitating condition.

RECENT FINDINGS

A computational model of human macronutrient metabolism was recently developed that simulates the normal metabolic adaptations to semi-starvation and re-feeding. Here, this model was used to integrate data on the metabolic changes in patients with cancer cachexia. The resulting computer simulations show how the known metabolic disturbances synergize with reduced energy intake to result in a progressive loss of body weight, fat mass, and fat-free mass. The model was also used to simulate the effects of nutritional support and investigate inhibition of lipolysis versus proteolysis as potential therapeutic approaches for cancer cachexia.

SUMMARY

Computational modeling is a new tool that can integrate clinical data on the metabolic changes in cancer cachexia and provide a conceptual framework to help understand involuntary weight loss and predict the effects of potential therapies.

Dynamic coordination of macronutrient balance during infant growth: insights from a mathematical model

BACKGROUND

Complex dynamic changes in body composition, dietary intake, energy expenditure, and macronutrient oxidation occur during infant growth. Although previous investigators have focused on energy requirements for normal growth, little is known about the dynamic coordination of macronutrient balance.

OBJECTIVE

Our objective was to develop a mathematical model of the dynamic relations between diet, macronutrient oxidation, and energy expenditure during normal infant growth.

DESIGN

We developed a mathematical model that integrates longitudinal data on changes of body composition and carbon dioxide production determined with the doubly labeled water method to calculate both energy intake requirements and macronutrient oxidation rates during normal infant growth.

RESULTS

The calculated fat oxidation rate was initially <20 kcal x kg(-1) x d(-1), despite the consumption of >60 kcal x kg(-1) x d(-1) of dietary fat. This discrepancy was maintained until approximately 6 mo, after which fat intake was only slightly greater than fat oxidation. Nonfat oxidation closely followed nonfat dietary intake for the duration of the period studied. Model calculations of the energy intake requirements for normal growth were slightly lower than previous estimates. The calculations were robust to variations of body weight, body composition, and diet composition input data, but depended sensitively on variations of carbon dioxide production data.

CONCLUSIONS

Our model presents a dynamic picture of how macronutrient oxidation adapts in concert with dietary changes and energy expenditure to give rise to normal tissue deposition. The model integrates a variety of data in a self-consistent way, simulating the complex metabolic adaptations occurring during normal growth while extracting important physiologic information from the data that would otherwise be unavailable.

Allometric relationship between changes of visceral fat and total fat mass

OBJECTIVE

To elucidate the mathematical relationship between changes of visceral adipose tissue (VAT) and total body fat mass (FM) during weight loss.

DESIGN

We hypothesized that changes of VAT mass are allometrically related to changes of FM, regardless of the type of weight-loss intervention, as defined by the differential equation dVAT/dFM=k x VAT/FM, where k is a dimensionless constant. We performed a systematic search of the published literature for studies that included measurements of VAT changes via magnetic resonance imaging (MRI) or computed tomography (CT) imaging along with measurements of FM changes by dual-energy X-ray absorptiometry, hydrodensitometry, air-displacement plethysmography or whole-body MRI or CT imaging. We then examined whether or not the data could be explained by the allometric model.

RESULT

We found 37 published studies satisfying our search criteria, representing 1407 men and women of various ethnicities, degrees of adiposity and weight-loss interventions. The hypothesized allometric equation relating changes of VAT and FM accurately modeled the data for both men and women and for all methods of weight loss studied. The best-fit value for the dimensionless constant was k=1.3+/-0.1 and the resulting model had an R(2)=0.73.

CONCLUSION

This is the first report to reveal an allometric relationship between changes of VAT and FM that holds for both genders as well as a wide variety of weight-loss interventions including bariatric surgery, caloric restriction with or without exercise and exercise alone. We conclude that changes of VAT are primarily determined by FM changes as well as the initial VAT to FM ratio.

What is the required energy deficit per unit weight loss?

One of the most pervasive weight loss rules is that a cumulative energy deficit of 3500 kcal is required per pound of body weight loss, or equivalently 32.2 MJ kg(-1). Under what conditions is it appropriate to use this rule of thumb and what are the factors that determine the cumulative energy deficit required per unit weight loss? Here, I examine this question using a modification of the classic Forbes equation that predicts the composition of weight loss as a function of the initial body fat and magnitude of weight loss. The resulting model predicts that a larger cumulative energy deficit is required per unit weight loss for people with greater initial body fat-a prediction supported by published weight loss data from obese and lean subjects. This may also explain why men can lose more weight than women for a given energy deficit since women typically have more body fat than men of similar body weight. Furthermore, additional weight loss is predicted to be associated with a lower average cumulative energy deficit since a greater proportion of the weight loss is predicted to result from loss of lean body mass, which has a relatively low energy density in comparison with body fat. The rule of thumb approximately matches the predicted energy density of lost weight in obese subjects with an initial body fat above 30 kg but overestimates the cumulative energy deficit required per unit weight loss for people with lower initial body fat. International Journal of Obesity (2008) 32, 573-576; doi:10.1038/sj.ijo.0803720; published online 11 September 2007.

Body fat and fat-free mass inter-relationships: Forbes's theory revisited

A theoretical equation was developed by Forbes that quantifies the fat-free proportion of a weight change as a function of the initial body fat. However, Forbes's equation was strictly valid only for infinitesimal weight changes. Here, I extended Forbes's equation to account for the magnitude and direction of macroscopic body weight changes. The new equation was also re-expressed in terms of an alternative representation of body composition change defined by an energy partitioning parameter called the P-ratio. The predictions of the resulting equations compared favourably with data from human underfeeding and overfeeding experiments and accounted for previously unexplained trends in the data. The magnitude of the body weight change had a relatively weak effect on the predicted body composition changes and the results were very similar to Forbes's original equation for modest weight changes. However, for large weight changes, such as the massive weight losses found in patients following bariatric surgery, Forbes's original equation consistently underestimated the fat-free mass loss, as expected. The new equation that accounts for the magnitude of the weight loss provides better predictions of body composition changes in such patients.

How adaptations of substrate utilization regulate body composition

OBJECTIVE

To elucidate the mathematical relationship between longitudinal changes of body composition and the adaptations of substrate utilization required to produce those changes.

DESIGN

We developed a simple mathematical model of macronutrient balance. By using an empirical relationship describing lean body mass as a function of fat mass, we derived a mathematical expression for how substrate utilization adapts to changes of diet, energy expenditure and body fat such that energy imbalances produced the required changes of body composition.

RESULTS

The general properties of our model implied that short-term changes of dietary fat alone had little impact on either fat or non-fat oxidation rates, in agreement with indirect calorimetry data. In contrast, changes of non-fat intake caused robust adaptations of both fat and non-fat oxidation rates. Without fitting any model parameters, the predicted body composition changes and oxidation rates agreed with experimental studies of overfeeding and underfeeding when the measured food intake, energy expenditure and initial body composition were used as model inputs.

CONCLUSION

This is the first report to define the quantitative connection between longitudinal changes of body composition and the required relationship between substrate utilization, diet, energy expenditure and body fat mass. The mathematical model predictions are in good agreement with experimental data and provide the basis for future study of how changes of substrate utilization impact body composition regulation.

Computational model of in vivo human energy metabolism during semistarvation and refeeding

Changes in body weight and composition are the result of complex interactions among metabolic fluxes contributing to macronutrient balances. To better understand these interactions, a mathematical model was constructed that used the measured dietary macronutrient intake during semistarvation and refeeding as model inputs and computed whole body energy expenditure, de novo lipogenesis, and gluconeogenesis as well as turnover and oxidation of carbohydrate, fat, and protein. Published in vivo human data provided the basis for the model components that were integrated by fitting a few unknown parameters to the classic Minnesota human starvation experiment. The model simulated the measured body weight and fat mass changes during semistarvation and refeeding and predicted the unmeasured metabolic fluxes underlying the body composition changes. The resting metabolic rate matched the experimental measurements and required a model of adaptive thermogenesis. Refeeding caused an elevation of de novo lipogenesis that, along with increased fat intake, resulted in a rapid repletion and overshoot of body fat. By continuing the computer simulation with the prestarvation diet and physical activity, the original body weight and composition were eventually restored, but body fat mass was predicted to take more than one additional year to return to within 5% of its original value. The model was validated by simulating a recently published short-term caloric restriction experiment without changing the model parameters. The predicted changes in body weight, fat mass, resting metabolic rate, and nitrogen balance matched the experimental measurements, thereby providing support for the validity of the model.

Student development and ownership of ethical and professional standards

Ethics and professional conduct are vital to civil engineering undergraduate curricula. Many programs struggle to ensure that students are given an adequate exposure to and appreciation of ethical and professional conduct issues. This paper describes a two-part ethics/professionalism project used in a senior-level course taught at the University of Arkansas. Initially, students scrutinize ethical canons and standards of professional conduct published by the American Society of Civil Engineers (ASCE) and the National Society of Professional Engineers (NSPE), and prepare an essay concerning the applicability of these standards. The second part of the project builds on the first: based on the opinion(s) generated in Part 1, students are asked to develop a set of canons or standards targeted specifically to the undergraduate student, and suggest processes for implementing those standards within the department. Project objectives include: (1) exposure to nationally-recognized ethical canons and standards of professional conduct; (2) personal formulation of ethical and professional standards; (3) skill enhancement for non-technical written communications. Feedback by students prior to and after the project indicates success in meeting all objectives. The feedback also indicates that for some students, definitions and applications of ethics and professionalism are being broadened to include more than academic honesty issues.

A longitudinal investigation of speaking rate in preschool children who stutter

Both clinical and theoretical interest in stuttering as a disorder of speech motor control has led to numerous investigations of speaking rate in people who stutter. The majority of these studies, however, has been conducted with adult and school-age groups. Most studies of preschoolers have included older children. Despite the ongoing theoretical and clinical focus on speaking rate in young children who stutter and their parents, no longitudinal or cross-sectional studies have been conducted to answer questions about the possible developmental link between stuttering and the rate of speech, or about differences in rate development between preschool children who stutter and normally fluent children. This investigation compared changes in articulatory rate over a period of 2 years in subgroups of preschool-age children who stutter and normally fluent children. Within the group of stuttering children, comparisons also were made between those who exhibited persistent stuttering and those who eventually recovered without intervention. Furthermore, the study compared two metrics of articulatory rate. Spontaneous speech samples, collected longitudinally over a 2-year period, were analyzed acoustically to determine speaking rate measured in number of syllables and phones per second. Results indicated no differences among the 3 groups when articulation rate was measured in syllables per second. Using the phones per second measure, however, significant group differences were found when comparing the control group to the recovered and persistent groups.

Reversion to a previously learned foreign accent after stroke

Foreign accent syndrome occurs rarely after stroke. Most patients with this syndrome develop an aphasia characterized by a new accent. This report presents a 48-year-old man who sustained a left parietal hemorrhagic stroke resulting in right hemiparesis and the inability to speak. As spontaneous speech emerged several weeks later, he was noted to have a Broca's aphasia and a Dutch accent. Analysis of his speech demonstrated final consonant deletion, substitution of "d" for "th" sounds, vowel distortions, additional "uh" syllables added at the end of words, and errors in voicing. This speech pattern has persisted for more than 5 years after the stroke. Elicitation of additional history found that the patient was born in Holland and lived there until the age of 5 years, when he moved to the United States with his family. Before his stroke, he had no foreign accent. This report illustrates the importance of considering foreign accent syndrome during aphasia recovery and suggests several pathogenetic mechanisms that may contribute to the development of this syndrome.

Comparison of fundamental frequency and perturbation measurements among three analysis systems

The need for standardization of procedures in approaches to voice measurement has been recently emphasized. The purpose of this study was to determine the extent to which the acoustic perturbation measurements from three different analysis systems agree when standardized recording and analysis procedures are used. High-quality acoustic voice recordings from 20 patients were analyzed. The results showed that, although fundamental frequency measurements were in strong agreement among the three systems tested, frequency and amplitude perturbation measurements were not in agreement. The underlying approaches to perturbation measurement appeared to be sufficiently different to produce different results. An argument is made for a standardized set of acoustic signals representing normal, dysphonic, and synthesized voices with known characteristics to facilitate testing of new acoustic analysis systems and confirm measurement accuracy and sensitivity.

Variations across time in acoustic and electroglottographic measures of phonatory function in women with and without vocal nodules

The purpose of this investigation was to identify variations over time in phonatory function of women with and without vocal nodules using acoustic and electroglottographic measures. Subjects were 10 women with vocal nodules (mean age = 22.1, range = 19-25) and 10 women with healthy larynges (mean age = 25.0, range = 18-32). Electroglottographic and audio recordings of speech were obtained for each subject over 3 consecutive days at three target times: morning, afternoon, and evening. Estimates of fundamental frequency (Hz), jitter (msec), shimmer (dB), and signal-to-noise ratio (dB) were made from a 1000 msec midportion of the vowel /a/ produced in a carrier phrase. In addition, a closed-to-open ratio was derived from the EGG duty cycle of the same 1000 msec segment and used to estimate timing characteristics of vocal fold vibration. The results showed no significant differences between the groups regarding a pattern of change in the acoustic or the EGG measures across times throughout the day. Furthermore, the experimental group demonstrated significantly lower closed-to-open ratios than the control group. With this exception, no other statistically significant differences between the groups were found.

Temporal relations within repetitions of preschool children near the onset of stuttering: a preliminary report

The purpose of this study was to compare duration characteristics of single repetitions of single-syllable words in the speech of preschool children who stutter (N = 15) recorded near the onset of their stuttering to those of control nonstuttering children (N = 18). Disfluent episodes were identified in audio tape recordings of the subjects' conversational speech. The digitized signals were analyzed by means of the CSpeech computer software (Milenkovic, 1987). Using visual displays of the sound-pressure waveforms, as well as spectrography, the durations of the first production of the word (1st Unit), the second production (2nd Unit), the silent interval, and the total disfluency were measured. There were no statistically significant differences between the two groups on any of these segments although there was a tendency for the stutters to exhibit shorter silent intervals between repeated units. Relative measures, however, indicated that the ratio of the 2nd Unit to the total disfluency was significantly larger for the stutterers than the controls. For both groups, the ratio of the 1st to the 2nd Unit was positive, that is, the first production of the word was longer than the second. There was also a tendency for the ratio of the silent interval to total disfluency to be smaller for the stutterers. Overall, there appears to be a tendency for repetitions of very early stutterers to be faster than repetitions of nonstuttering children.

Differential strength decline in patients with osteoarthritis of the knee: revision of a hypothesis

A quadriceps-to-hamstring isometric peak torque ratio (Q/H ratio) of approximately 2.0 is considered necessary for appropriate knee biomechanics. Lower ratios may affect the function of persons with osteoarthritis (OA) and the progression of the disease. This study examined the isometric Q/H ratio in subjects with and without OA of the knee and explored the effect of age, pain, and joint enlargement on the ratio. Twenty-one pairs of subjects (OA, control) were matched on age (mean = 62.6 years; SD = 13.9), gender (F = 17, M = 4), and leg dominance (Dominant = 10, Nondominant = 11). Isometric quadriceps and hamstring peak torque, knee pain, and joint enlargement were measured. Paired t-tests demonstrated that the OA group had significantly lower quadriceps peak torque than the control group but did not have significantly lower hamstring peak torque or gravity-corrected isometric Q/H ratio. Age correlated with the ratio in subjects without OA (rho = -0.46; P = 0.03) but not in subjects with OA. Pain was not significantly correlated with the ratio in either group. Joint enlargement correlated with the ratio in the OA group (rho = -0.45; P = 0.03). The gravity-corrected isometric Q/H ratio appears to decrease with age in subjects without OA. In subjects with OA, the Q/H ratio appears not to change with disease, pain, or age. Joint enlargement may decrease the ratio and merits further study.

[Brain function and level of consciousness in fentanyl anesthesia in heart surgery]

The level of consciousness and the supply/demand ratio of oxygen in the brain was studied in anaesthetized patients undergoing open heart surgery. Anaesthesia was accomplished with intravenous fentanyl; 26 patients received 25 micrograms/kg and 24 patients received 50 micrograms/kg fentanyl. In addition only pancuronium bromide was administered for muscular relaxation; all patients were ventilated with 100% oxygen. The following measurements were made during induction and prior to cardiopulmonary bypass and in the first ten minutes of bypass: 1. EEG with the Klein EEG Analyzer. This instrument permits simultaneous analysis of frequency and amplitude while eliminating muscular artifacts. 2. Cerebral oxygen with the Niroscope. This instrument uses an infrared light beam through the brain to evaluate cerebral oxygen sufficiency. 3. Oxygen supply/demand ratio in the whole body, estimated from mixed venous oxygen saturation measured with a fiberoptic pulmonary artery catheter. Clinical unconsciousness occurred in all patients within about 30 s after the administration of fentanyl. Simultaneously the EEG showed a significant decrease in frequency and an increase in amplitude. With the Niroscope no change in oxygen supply and demand was seen in any patients. This is in contrast to previous studies with thiopental, where changes were seen. A slight increase in mixed venous oxygen saturation was observed. This indicates an increase in the total oxygen supply/demand ratio, probably due to decreased muscle metabolism induced by pancuronium bromide paralysis. From the end of induction until cardiopulmonary bypass a slight increase in cerebral electrical activity was observed; an additional increase occurred in the first ten minutes of bypass.(ABSTRACT TRUNCATED AT 250 WORDS)

Persistence of weight gain and hibernation onset in juvenile thirteen-lined ground squirrels (Spermophilus tridecemlineatus) in spite of long-term administration of naloxone

Sexual differences in body weight of juvenile thirteen-lined ground squirrels (Spermophilus tridecemlineatus) were significant (P less than 0.05) at all weeks of age except weeks 0-4, 6, 7, 9, 20 and 24. Hibernation onset between sexes did not differ significantly. Naloxone administration did not alter weight gain nor onset of hibernation when compared to saline controls.