Obesity Energetics: Body Weight Regulation and the Effects of Diet Composition
2017; Elsevier BV; Volume: 152; Issue: 7 Linguagem: Inglês
10.1053/j.gastro.2017.01.052
ISSN1528-0012
Autores Tópico(s)Regulation of Appetite and Obesity
ResumoWeight changes are accompanied by imbalances between calorie intake and expenditure. This fact is often misinterpreted to suggest that obesity is caused by gluttony and sloth and can be treated by simply advising people to eat less and move more. Rather various components of energy balance are dynamically interrelated and weight loss is resisted by counterbalancing physiological processes. While low-carbohydrate diets have been suggested to partially subvert these processes by increasing energy expenditure and promoting fat loss, our meta-analysis of 32 controlled feeding studies with isocaloric substitution of carbohydrate for fat found that both energy expenditure (26 kcal/d; P <.0001) and fat loss (16 g/d; P <.0001) were greater with lower fat diets. We review the components of energy balance and the mechanisms acting to resist weight loss in the context of static, settling point, and set-point models of body weight regulation, with the set-point model being most commensurate with current data. Weight changes are accompanied by imbalances between calorie intake and expenditure. This fact is often misinterpreted to suggest that obesity is caused by gluttony and sloth and can be treated by simply advising people to eat less and move more. Rather various components of energy balance are dynamically interrelated and weight loss is resisted by counterbalancing physiological processes. While low-carbohydrate diets have been suggested to partially subvert these processes by increasing energy expenditure and promoting fat loss, our meta-analysis of 32 controlled feeding studies with isocaloric substitution of carbohydrate for fat found that both energy expenditure (26 kcal/d; P <.0001) and fat loss (16 g/d; P <.0001) were greater with lower fat diets. We review the components of energy balance and the mechanisms acting to resist weight loss in the context of static, settling point, and set-point models of body weight regulation, with the set-point model being most commensurate with current data. Juen GuoView Large Image Figure ViewerDownload Hi-res image Download (PPT) Obesity is often described as a disorder of energy balance arising from consuming calories in excess to the energy expended to maintain life and perform physical work. While this energy balance concept is a useful framework for investigating obesity, it does not provide a causal explanation for why some people have obesity or what to do about it. In particular, obesity prevention is often erroneously portrayed as a simple matter of bookkeeping whereby calorie intake must be balanced by calorie expenditure.1Levine D.I. The curious history of the calorie in U.S. policy: a tradition of unfulfilled promises.Am J Prev Med. 2017; 52: 125-129Abstract Full Text Full Text PDF PubMed Scopus (4) Google Scholar Under this “calories in, calories out” model, treating obesity amounts to advising people to simply eat less and move more, thereby tipping the scales of calorie balance and resulting in steady weight loss that accumulates according to the widely known, but erroneous, 3500 kcal per pound rule.2Guth E. JAMA patient page. Healthy weight loss.JAMA. 2014; 312: 974Crossref PubMed Scopus (5) Google Scholar, 3Hall K.D. Chow C.C. Why is the 3500 kcal per pound weight loss rule wrong?.Int J Obes (Lond). 2013; 37: 1614Crossref PubMed Scopus (10) Google Scholar Therefore, failure to experience substantial weight loss implies that an individual lacks the willpower to adhere to a modest lifestyle intervention over a sufficient period of time. However, this naïve view is incorrect because it considers energy intake and expenditure to be independent parameters that can be adjusted at will and thereafter remain static without being influenced by homeostatic signals related to weight loss.3Hall K.D. Chow C.C. Why is the 3500 kcal per pound weight loss rule wrong?.Int J Obes (Lond). 2013; 37: 1614Crossref PubMed Scopus (10) Google Scholar We now understand that energy intake and expenditure are interdependent variables that are dynamically influenced by each other and body weight.4Hall K.D. Heymsfield S.B. Kemnitz J.W. et al.Energy balance and its components: implications for body weight regulation.Am J Clin Nutr. 2012; 95: 989-994Crossref PubMed Scopus (251) Google Scholar Attempts to alter energy balance through diet or exercise are countered by physiological adaptations that resist weight loss.5Ochner C.N. Tsai A.G. Kushner R.F. et al.Treating obesity seriously: when recommendations for lifestyle change confront biological adaptations.Lancet Diabetes Endocrinol. 2015; 3: 232-234Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar This review focuses on our current understanding of the components of human energy balance and the counterbalancing physiological processes that act to resist weight loss. Furthermore, we address the question of whether all diet calories are created equal regarding the effects of carbohydrate, fat, and protein on energy balance, body weight, and composition. Finally, we compare 3 conceptual models of energy balance regulation and examine the implications for human body weight dynamics and the treatment of obesity. There are 3 components of daily energy expenditure: the thermic effect of food, physical activity expenditure, and resting energy expenditure (REE) (Figure 1A). The smallest component of daily energy expenditure in humans is the thermic effect of food (also called diet induced thermogenesis or specific dynamic action), which is defined as the increase of metabolic rate observed for several hours following the ingestion of a meal.6de Jonge L. Bray G.A. The thermic effect of food and obesity: a critical review.Obes Res. 1997; 5: 622-631Crossref PubMed Google Scholar, 7Westerterp K.R. Diet induced thermogenesis.Nutr Metab (Lond). 2004; 1: 5Crossref PubMed Scopus (203) Google Scholar The thermic effect of food is believed to represent the energy cost of digestion, absorption, storage, and metabolic fate of dietary macronutrients.7Westerterp K.R. Diet induced thermogenesis.Nutr Metab (Lond). 2004; 1: 5Crossref PubMed Scopus (203) Google Scholar While the precise mechanisms underlying the thermic effect of food are not fully understood, there is a clear macronutrient hierarchy, with protein causing a greater energy expenditure increment than carbohydrate. which is greater than that of fat.7Westerterp K.R. Diet induced thermogenesis.Nutr Metab (Lond). 2004; 1: 5Crossref PubMed Scopus (203) Google Scholar For typical diet compositions, the thermic effect of food is approximated to be about 10% of energy intake (Figure 1A). REE corresponds to the energy expended when not performing physical work and is typically the largest contribution to daily energy expenditure. Contrary to popular belief, people with obesity generally have a higher absolute REE (Figure 1A).8Nelson K.M. Weinsier R.L. Long C.L. et al.Prediction of resting energy expenditure from fat-free mass and fat mass.Am J Clin Nutr. 1992; 56: 848-856Crossref PubMed Scopus (235) Google Scholar It has long been recognized that fat-free mass comprises the metabolically active tissues of the body and therefore contributes more to REE than body fat. Fat-free mass is elevated in obesity, along with body fat, resulting in increased REE compared with lean subjects (Figure 1B). Across a wide range of weights, REE is linearly related to both fat-free mass and body fat,8Nelson K.M. Weinsier R.L. Long C.L. et al.Prediction of resting energy expenditure from fat-free mass and fat mass.Am J Clin Nutr. 1992; 56: 848-856Crossref PubMed Scopus (235) Google Scholar such that the elevated REE with obesity is generally in line with what is expected for the body weight and composition. While fat-free mass, and to a lesser extent fat mass, are good predictors of REE, these variables explain only about 70% of inter-individual REE variability, such that for a given body composition the REE residual standard deviation is about 300 kcal/d.8Nelson K.M. Weinsier R.L. Long C.L. et al.Prediction of resting energy expenditure from fat-free mass and fat mass.Am J Clin Nutr. 1992; 56: 848-856Crossref PubMed Scopus (235) Google Scholar Because the organs that contribute to the fat-free mass have a wide range of metabolic rates,9Elia M. Organ and tissue contribution to metabolic rate.in: Kinney J.M. Tucker H.N. Energy metabolism: tissue determinants and cellular corollaries. Raven Press, New York1992: 61-79Google Scholar some of the residual REE variability after accounting for body fat and fat-free mass may be caused by variations in organ masses. Magnetic resonance imaging methodologies have been used to quantify organ sizes and REE prediction equations that sum the individual metabolic rates of various organs explain about 80% of the REE variability.10Gallagher D. Belmonte D. Deurenberg P. et al.Organ-tissue mass measurement allows modeling of REE and metabolically active tissue mass.Am J Physiol. 1998; 275: E249-E258PubMed Google Scholar, 11Muller M.J. Bosy-Westphal A. Kutzner D. et al.Metabolically active components of fat-free mass and resting energy expenditure in humans: recent lessons from imaging technologies.Obes Rev. 2002; 3: 113-122Crossref PubMed Scopus (150) Google Scholar Another potentially important contributor to REE involves fluxes through various energy-requiring metabolic pathways. Major macronutrient fluxes such as gluconeogenesis, de novo lipogenesis, triglyceride synthesis, and protein turnover all require energy and these flux rates can be significantly influenced by both the energy content of the diet as well as its composition.12Hall K.D. Predicting metabolic adaptation, body weight change, and energy intake in humans.Am J Physiol Endocrinol Metab. 2010; 298: E449-E466Crossref PubMed Scopus (118) Google Scholar Physical activity expenditure can be subdivided into volitional exercise and the activities of daily living, also called spontaneous physical activity or non-exercise activity thermogenesis. The energy expended in physical activities is determined by their duration and intensity in proportion to overall body weight.13Schoeller D.A. Jefford G. Determinants of the energy costs of light activities: inferences for interpreting doubly labeled water data.Int J Obes (Lond). 2002; 26: 97-101Crossref PubMed Scopus (49) Google Scholar Thus, despite typically being less physically active, people with obesity often have similar daily energy costs for physical activity as those without obesity (Figure 1A)14Westerterp K.R. Physical activity, food intake, and body weight regulation: insights from doubly labeled water studies.Nutr Rev. 2010; 68: 148-154Crossref PubMed Scopus (81) Google Scholar and physical activity energy expenditure declines with weight loss unless its quantity or intensity increases to compensate. While often considered a first-line treatment option for obesity, large amounts of exercise are required to result in a modest degree of average weight loss.15Donnelly J.E. Blair S.N. Jakicic J.M. et al.American College of Sports Medicine position stand. Appropriate physical activity intervention strategies for weight loss and prevention of weight regain for adults.Med Sci Sports Exerc. 2009; 41: 459-471Crossref PubMed Scopus (1184) Google Scholar However, exercise results in preferential loss of body fat and maintenance of fat-free mass compared with diet-induced weight loss,16Washburn R.A. Szabo A.N. Lambourne K. et al.Does the method of weight loss effect long-term changes in weight, body composition or chronic disease risk factors in overweight or obese adults? A systematic review.PLoS One. 2014; 9: e109849Crossref PubMed Scopus (20) Google Scholar, 17Weinheimer E.M. Sands L.P. Campbell W.W. A systematic review of the separate and combined effects of energy restriction and exercise on fat-free mass in middle-aged and older adults: implications for sarcopenic obesity.Nutr Rev. 2010; 68: 375-388Crossref PubMed Scopus (174) Google Scholar but exercise does not appear to prevent the slowing of metabolic rate during weight loss.18Johanssen D.L. Knuth N.D. Huizenga R. et al.Metabolic slowing with massive weight loss despite preservation of fat-free mass.J Clin Endocrinol Metab. 2012; 97: 2489-2496Crossref PubMed Scopus (101) Google Scholar Exercise interventions typically result in an average weight loss that is less than expected based on the exercise calories expended, and individual weight changes are highly variable even when exercise is supervised to ensure adherence.19Melanson E.L. Keadle S.K. Donnelly J.E. et al.Resistance to exercise-induced weight loss: compensatory behavioral adaptations.Med Sci Sports Exerc. 2013; 45: 1600-1609Crossref PubMed Scopus (64) Google Scholar A likely explanation for these observations is that the energy expended during exercise is variably compensated by changes in food intake and non-exercise physical activity behaviors.19Melanson E.L. Keadle S.K. Donnelly J.E. et al.Resistance to exercise-induced weight loss: compensatory behavioral adaptations.Med Sci Sports Exerc. 2013; 45: 1600-1609Crossref PubMed Scopus (64) Google Scholar The recently proposed “constrained energy expenditure model” provides an alternative explanation for why exercise interventions often result in minimal weight loss.20Pontzer H. Constrained total energy expenditure and the evolutionary biology of energy balance.Exerc Sport Sci Rev. 2015; 43: 110-116Crossref PubMed Scopus (45) Google Scholar According to this model, daily energy expenditure is regulated and increments in physical activity expenditure are predicted to be offset by decreases in non-physical activity expenditure (ie, the thermic effect of food or REE) resulting in minimal energy imbalance. The experimental basis of the constrained energy expenditure model in humans includes cross-sectional data demonstrating that free-living daily energy expenditure adjusted for body composition is relatively constant for a wide range of physical activity levels measured using accelerometry.21Pontzer H. Durazo-Arvizu R. Dugas L.R. et al.Constrained total energy expenditure and metabolic adaptation to physical activity in adult humans.Curr Biol. 2016; 26: 410-417Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar, 22Pontzer H. Raichlen D.A. Wood B.M. et al.Hunter-gatherer energetics and human obesity.PLoS One. 2012; 7: e40503Crossref PubMed Scopus (133) Google Scholar Furthermore, longitudinal data have found that progressive increases in the quantity and intensity of aerobic exercise training do not lead to corresponding increases in total daily energy expenditure in ad libitum-fed men and women.23Westerterp K.R. Alterations in energy balance with exercise.Am J Clin Nutr. 1998; 68: 970S-974SPubMed Google Scholar However, in contrast to the predictions of the constrained energy expenditure model, exercise training does not lead to decreased REE under conditions of weight stability24Wilmore J.H. Stanforth P.R. Hudspeth L.A. et al.Alterations in resting metabolic rate as a consequence of 20 wk of endurance training: the HERITAGE Family Study.Am J Clin Nutr. 1998; 68: 66-71Crossref PubMed Scopus (0) Google Scholar and REE adjusted for body composition is not different between people with a wide range of physical activity levels.21Pontzer H. Durazo-Arvizu R. Dugas L.R. et al.Constrained total energy expenditure and metabolic adaptation to physical activity in adult humans.Curr Biol. 2016; 26: 410-417Abstract Full Text Full Text PDF PubMed Scopus (82) Google Scholar Furthermore, exercise may actually increase the thermic effect of food.6de Jonge L. Bray G.A. The thermic effect of food and obesity: a critical review.Obes Res. 1997; 5: 622-631Crossref PubMed Google Scholar Therefore, when physical activity increases via exercise, the non-physical activity components of daily energy expenditure do not decrease as predicted by the constrained model. Finally, increments in daily energy expenditure shortly after starting an exercise program can be greater than the expected energy cost of the exercise.23Westerterp K.R. Alterations in energy balance with exercise.Am J Clin Nutr. 1998; 68: 970S-974SPubMed Google Scholar Subsequent failure to increase daily expenditure as training progresses, despite increasing exercise volume and intensity, may be because of improvements in biomechanical efficiency that decrease the energy cost of exercise.23Westerterp K.R. Alterations in energy balance with exercise.Am J Clin Nutr. 1998; 68: 970S-974SPubMed Google Scholar Reductions in energy intake lead to decreased energy expenditure to a degree that is often greater than expected based on changes in body composition or the thermic effect of food.25Rosenbaum M. Leibel R.L. Adaptive thermogenesis in humans.Int J Obes (Lond). 2010; 34: S47-S55Crossref PubMed Scopus (148) Google Scholar, 26Westerterp K.R. Metabolic adaptations to over–and underfeeding–still a matter of debate?.Eur J Clin Nutr. 2013; 67: 443-445Crossref PubMed Scopus (28) Google Scholar This phenomenon has been called adaptive thermogenesis or metabolic adaptation and it may continue for years after energy balance is reestablished at a lower weight,27Camps S.G. Verhoef S.P. Westerterp K.R. Weight loss, weight maintenance, and adaptive thermogenesis.Am J Clin Nutr. 2013; 97: 990-994Crossref PubMed Scopus (62) Google Scholar, 28Fothergill E. Guo J. Howard L. et al.Persistent metabolic adaptation 6 years after “The Biggest Loser” competition.Obesity (Silver Spring). 2016; 24: 1612-1619Crossref PubMed Scopus (173) Google Scholar, 29Rosenbaum M. Hirsch J. Gallagher D.A. et al.Long-term persistence of adaptive thermogenesis in subjects who have maintained a reduced body weight.Am J Clin Nutr. 2008; 88: 906-912Crossref PubMed Google Scholar although controversy remains regarding its persistence.30Wadden T.A. Foster G.D. Letizia K.A. et al.Long-term effects of dieting on resting metabolic rate in obese outpatients.JAMA. 1990; 264: 707-711Crossref PubMed Scopus (110) Google Scholar, 31Weinsier R.L. Nagy T.R. Hunter G.R. et al.Do adaptive changes in metabolic rate favor weight regain in weight-reduced individuals? An examination of the set-point theory.Am J Clin Nutr. 2000; 72: 1088-1094Crossref PubMed Google Scholar The mechanistic basis of metabolic adaptation is unclear, but it may be related to reduced sympathetic drive or blunted thyroid activity, possibly as a result of decreased leptin.25Rosenbaum M. Leibel R.L. Adaptive thermogenesis in humans.Int J Obes (Lond). 2010; 34: S47-S55Crossref PubMed Scopus (148) Google Scholar, 32Lecoultre V. Ravussin E. Redman L.M. The fall in leptin concentration is a major determinant of the metabolic adaptation induced by caloric restriction independently of the changes in leptin circadian rhythms.J Clin Endocrinol Metab. 2011; 96: E1512-E1516Crossref PubMed Scopus (37) Google Scholar, 33Rosenbaum M. Goldsmith R. Bloomfield D. et al.Low-dose leptin reverses skeletal muscle, autonomic, and neuroendocrine adaptations to maintenance of reduced weight.J Clin Invest. 2005; 115: 3579-3586Crossref PubMed Scopus (377) Google Scholar, 34Rosenbaum M. Murphy E.M. Heymsfield S.B. et al.Low dose leptin administration reverses effects of sustained weight-reduction on energy expenditure and circulating concentrations of thyroid hormones.J Clin Endocrinol Metab. 2002; 87: 2391-2394Crossref PubMed Scopus (0) Google Scholar, 35Rosenbaum M. Nicolson M. Hirsch J. et al.Effects of weight change on plasma leptin concentrations and energy expenditure.J Clin Endocrinol Metab. 1997; 82: 3647-3654Crossref PubMed Scopus (230) Google Scholar, 36Weinsier R.L. Hunter G.R. Zuckerman P.A. et al.Energy expenditure and free-living physical activity in black and white women: comparison before and after weight loss.Am J Clin Nutr. 2000; 71: 1138-1146Crossref PubMed Scopus (0) Google Scholar Experimental quantification of metabolic adaptation depends on calculating the residual difference between measured and expected values of energy expenditure.37Galgani J.E. Santos J.L. Insights about weight loss-induced metabolic adaptation.Obesity (Silver Spring). 2016; 24: 277-278Crossref PubMed Scopus (14) Google Scholar, 38Muller M.J. Bosy-Westphal A. Adaptive thermogenesis with weight loss in humans.Obesity (Silver Spring). 2013; 21: 218-228Crossref PubMed Scopus (57) Google Scholar However, the expected energy expenditure is typically calculated based on observed body fat and fat-free mass changes and typically ignores factors like organ sizes or altered fluxes through energy-requiring metabolic pathways. Whether such considerations can explain the observed adaptations in energy expenditure is presently unclear. Metabolic adaptation can be interpreted teleologically as the body’s response to a perceived state of starvation by decreasing the energy cost of living in an attempt to prolong life given the body’s finite energy stores. In this context, it is interesting that the robustness of metabolic adaptation does not appear to be attenuated by the quantity of stored energy such that people with obesity, who have very large energy reserves, experience decreases in energy expenditure that are similar in magnitude to those having dramatically fewer energy reserves (Figure 1C).39Leibel R.L. Rosenbaum M. Hirsch J. Changes in energy expenditure resulting from altered body weight.N Engl J Med. 1995; 332: 621-628Crossref PubMed Scopus (1301) Google Scholar In contrast to the growing consensus supporting the existence of important metabolic adaptations to underfeeding and weight loss, the adaptive response to overfeeding and weight gain is less clear.26Westerterp K.R. Metabolic adaptations to over–and underfeeding–still a matter of debate?.Eur J Clin Nutr. 2013; 67: 443-445Crossref PubMed Scopus (28) Google Scholar While some investigators have observed that overfeeding induces highly variable increases in spontaneous physical activity expenditure that may be greater than expected based on the observed weight changes,39Leibel R.L. Rosenbaum M. Hirsch J. Changes in energy expenditure resulting from altered body weight.N Engl J Med. 1995; 332: 621-628Crossref PubMed Scopus (1301) Google Scholar, 40Levine J.A. Eberhardt N.L. Jensen M.D. Role of nonexercise activity thermogenesis in resistance to fat gain in humans.Science. 1999; 283: 212-214Crossref PubMed Scopus (710) Google Scholar, 41Levine J.A. Lanningham-Foster L.M. McCrady S.K. et al.Interindividual variation in posture allocation: possible role in human obesity.Science. 2005; 307: 584-586Crossref PubMed Scopus (488) Google Scholar others have found that the increased energy expenditure associated with overfeeding is in accord with the expected increased thermic effect of food, along with increased REE and physical activity expenditure based on the observed weight gain.14Westerterp K.R. Physical activity, food intake, and body weight regulation: insights from doubly labeled water studies.Nutr Rev. 2010; 68: 148-154Crossref PubMed Scopus (81) Google Scholar, 26Westerterp K.R. Metabolic adaptations to over–and underfeeding–still a matter of debate?.Eur J Clin Nutr. 2013; 67: 443-445Crossref PubMed Scopus (28) Google Scholar The effect of energy intake changes on energy expenditure and body weight have recently been incorporated within dynamic mathematical models in both adults42Hall K.D. Sacks G. Chandramohan D. et al.Quantification of the effect of energy imbalance on bodyweight.Lancet. 2011; 378: 826-837Abstract Full Text Full Text PDF PubMed Scopus (518) Google Scholar and children43Hall K.D. Butte N.F. Swinburn B.A. et al.Dynamics of childhood growth and obesity: development and validation of a quantitative mathematical model.Lancet Diabetes Endocrinol. 2013; 1: 97-105Abstract Full Text Full Text PDF PubMed Scopus (74) Google Scholar to replace the static “calories in, calories out” model that erroneously assumed independence of energy intake and expenditure.44Hall K.D. Gortmaker S.L. Lott M. et al.From calories to weight change in children and adults: the state of the science. issue brief. Healthy Eating Research, Durham, NC2016Google Scholar Mathematical models have been used to calculate the so-called “energy gap” required to reverse obesity, which amounts to about 200–250 kcal/d for both adults and children at the population level,44Hall K.D. Gortmaker S.L. Lott M. et al.From calories to weight change in children and adults: the state of the science. issue brief. Healthy Eating Research, Durham, NC2016Google Scholar and have been used to estimate the potential effects of policy changes on overweight and obesity prevalence.45Lin B.H. Smith T.A. Lee J.Y. et al.Measuring weight outcomes for obesity intervention strategies: the case of a sugar-sweetened beverage tax.Econ Hum Biol. 2011; 9: 329-341Crossref PubMed Scopus (95) Google Scholar The energy released during carbohydrate, fat, and protein oxidation within the body can be equated to the energy derived from their combustion in a bomb calorimeter, with suitable corrections for the differing thermodynamic constraints and the end products of the reactions. In other words, “a calorie is a calorie” when macronutrients are oxidized either in the bomb calorimeter through combustion or via the intricate biochemical pathways of oxidative phosphorylation inside cells. However, thermodynamic arguments alone do not necessarily imply that “a calorie is a calorie” when it comes to the effects of diet composition on body weight or composition. Isocaloric diets differing in macronutrient composition may result in preferential partitioning of energy storage toward body fat and away from body protein. Such energy partitioning differences over the long term will alter the proportions of body fat and fat-free mass and thereby influence energy expenditure. Dietary protein in particular is known to positively influence fat-free mass during weight loss46Leidy H.J. Clifton P.M. Astrup A. et al.The role of protein in weight loss and maintenance.Am J Clin Nutr. 2015; 101: 1320S-1329SCrossref Scopus (125) Google Scholar, 47Westerterp-Plantenga M.S. Nieuwenhuizen A. Tome D. et al.Dietary protein, weight loss, and weight maintenance.Annu Rev Nutr. 2009; 29: 21-41Crossref PubMed Scopus (287) Google Scholar and weight gain.48Bray G.A. Smith S.R. de Jonge L. et al.Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial.JAMA. 2012; 307: 47-55Crossref PubMed Scopus (146) Google Scholar A recent meta-analysis found that dietary protein resulted in a small positive influence on REE during reduced-calorie, low-fat diets amounting to about 150 kcal/d.49Wycherley T.P. Moran L.J. Clifton P.M. et al.Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials.Am J Clin Nutr. 2012; 96: 1281-1298Crossref PubMed Scopus (241) Google Scholar Overfeeding with higher protein diets also led to small increases in REE and increases in daily energy expenditure,48Bray G.A. Smith S.R. de Jonge L. et al.Effect of dietary protein content on weight gain, energy expenditure, and body composition during overeating: a randomized controlled trial.JAMA. 2012; 307: 47-55Crossref PubMed Scopus (146) Google Scholar as did weight loss maintenance diets with higher protein.50Ebbeling C.B. Swain J.F. Feldman H.A. et al.Effects of dietary composition on energy expenditure during weight-loss maintenance.JAMA. 2012; 307: 2627-2634Crossref PubMed Scopus (131) Google Scholar While higher protein diets appear to offer advantages regarding energy expenditure and body composition, the relative effects of dietary carbohydrate and fat are debated. According to the popular “carbohydrate-insulin model” of obesity, diets high in carbohydrate are conjectured to be particularly fattening because of their propensity to elevate insulin secretion, thereby directing fat toward storage in adipose tissue and away from oxidation by metabolically active tissues, leading to an adaptive decrease in metabolic rate.51Hall K.D. A review of the carbohydrate-insulin model of obesity.Eur J Clin Invest. 2017; 71: 323-326Google Scholar, 52Ludwig D.S. Friedman M.I. Increasing adiposity: consequence or cause of overeating?.JAMA. 2014; 311: 2167-2168Crossref PubMed Scopus (68) Google Scholar In contrast, because dietary fat does not stimulate insulin secretion, isocaloric diets lower in carbohydrate but higher in fat reduce insulin secretion, thereby promoting fat loss from adipose tissue, making free-fatty acids available for use by metabolically active tissues. The increased fuel availability theoretically leads to increased metabolic rate with a net “metabolic advantage” of very low carbohydrate diets amounting to as much as 400–600 kcal/d of additional energy expenditure.53Fine E.J. Feinman R.D. Thermodynamics of weight loss diets.Nutr Metab (Lond). 2004; 1: 15Crossref PubMed Scopus (70) Google Scholar Such large increases in daily energy expenditure could explain why low carbohydrate diets that are unrestricted in calories typically result in greater short-term weight loss compared with reduced energy, low-fat diets.54Foster G.D. Wyatt H.R. Hill J.O. et al.A randomized trial of a low-carbohydrate diet for obesity.N Engl J Med. 2003; 348: 2082-2090Crossref PubMed Scopus (1249) Google Scholar, 55Gardner C.D. Kiazand A. Alhassan S. et al.Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women: the A to Z Weight Loss Study: a randomized trial.JAMA. 2007; 297: 969-977Crossref PubMed Scopus (608) Google Scholar, 56Samaha F.F. Iqbal N
Referência(s)