Issues and Misconceptions About Obesity

Energy is a concept of universal importance. In relation to body weight regulation, one is so used to consider energy intake, energy expenditure, and energy balance that one forgets that energy is an abstract notion without physiological equivalent. The body's regulatory functions may strive to maintain carbohydrate (CHO), protein and/or fat balances, but not energy balance. The body ignores that 1 g of fat contains more than twice the energy present in 1 g of carbohydrate, an element of information needed to determine the energy balance. In applying this knowledge to consider body weight regulation, one introduces a biologically irrelevant fact. One may learn to be in awe at the body's ability to maintain approximate energy balances over extended periods of an individual's life, as a consequence of the organism's ability to maintain substrate balances, but attempts to understand this as the result of a regulatory process directed at the energy balance itself are doomed to be frustrated. Not surprisingly, failure to be aware of the inappropriate use of the energy and energy balance concepts in considering body weight regulation and obesity has spawned numerous misconceptions (1). The intent of this article is to provide direct access to the considerations that pertain to particular notions commonly cited in the context of obesity. Their presentation under separate headings should be helpful, in particular to individuals not necessarily immersed in obesity research who want to understand the meaning of specific terms and concepts. 1. Problems in applying the energy balance concept The energy balance equation is often invoked to frame issues relating to body weight regulation and obesity. The equation states that Energy Balance = Energy Intake — Energy Expenditure which appears to support the statement that obesity is due to a “positive energy balance,” i.e., that energy intake is exceeding energy expenditure. Unfortunately, this seemingly obvious pronouncement sets up several misconceptions (1). First, this view confuses past and present, obscuring the fact that obese individuals, like lean subjects, tend to reach a state of approximate energy balance, with similar short-term fluctuations in the energy balance. Thus, one fails to recognize that the really important difference between lean and obese individuals is the degree of adiposity at which, on average, their energy intake tends to adjust itself to their energy expenditure. This varies widely between individuals, in a manner influenced by genetic as well as by environmental conditions. Thus obesity is brought about by a failure of the interactions between body composition and food intake regulation to restrain eating when the body's energy stores are more than adequate for health (Table 1). 2. Problems with the metabolic efficiency concept Weight gains or losses generally do not exceed 1 or 2 kg per year during long periods of an individual's life (2), reflecting an error of only 1–2% in the adjustment of food intake to energy expenditure. This corresponds to an average daily difference between energy intake and expenditure in the order of 25–50 kcal. Thus even minor differences between energy intake and expenditure appear to be able, in their cumulative long-term effect, to cause or to prevent the progressive development of obesity. The second misconception promoted by notions based on the energy balance equation is that obesity could therefore be due to unusually low metabolic rates. This impression has been enhanced because rates of energy expenditures per kg body weight or per kg fat-free mass (FFM) appear to be lower in obese than in lean subjects, which is a simple artefact due to a positive intercept in the correlations between energy expenditure and body weight or FFM. Nevertheless it has led to speculations about higher “metabolic efficiency” in obesity, as a way to account for a higher than normal proportion of energy retention. Such a notion, sometimes tossed around without proper definition of “metabolic efficiency” (3), should long ago have been dispelled by the realization that total energy expenditure is raised in obesity, due to the increase in lean body mass associated with weight gain and the greater costs associated with moving a heavier body. The utter confusion introduced by the energy efficiency concept becomes apparent when one realizes that the large daily variations in food consumption that occur when food is freely available, cause energy balance to be positive on some days and negative on others. Thus, during period of weight stability, metabolic efficiency would oscillate between positive and negative values over the short term, whereas it is essentially equal to zero over extended periods. 3. The misleading emphasis on the importance of low resting metabolic rates Arguments about the potential long-term impact on body weights of differences in resting energy expenditure, or of small diet– or physical activity-induced increases in energy expenditure, hinge on the assumption that such differences would not be offset by adjustments in energy intake. This is a totally unwarranted assumption, as there is no evidence indicating that average energy intakes in subjects eating at their own discretion are “clamped” at some particular level (4). Several facts speak against the notion that minor differences in metabolic efficiency or in resting energy expenditure may be important for body weight regulation. (i) Stature, which is positively correlated with resting and with total energy expenditures, has no impact on adiposity (5). (ii) There is no correlation between % body fat and deviations from predicted (or “normal”) basal energy expenditure (Figure 1) (6). Adiposity and basal energy expenditure (BEE). (a) % Body fat contents of 433 women whose ages, anthropometric data, and BEE are listed in the dietary reference intake (DRI) database (45), plotted against the deviation (expressed in terms of %) from their predicted (i.e., “normal”) daily BEE (as kcal/day) calculated using the multiple regression equation in (45). % Body fat contents were predicted from their BMI, using the equation correlating BMI and measurements of body fat by bio-impedance in the National Health and Nutrition Examination Survey (NHANES) III data (45). (b) % Body fat contents of 335 men whose ages, anthropometric data, and BEE are listed in the DRI database (45), plotted against the deviation (expressed in terms of %) from their predicted (i.e., “normal”) daily BEE (as kcal/day) calculated using the multiple regression equation in (45). % Body fat contents were predicted from using the equation correlating BMI and measurements of body fat by bio-impedance in the NHANES III data (45). It is generally considered that causes cannot safely be inferred from correlations, especially from cross-sectional correlations. In the case considered here, however, the crucial fact is the lack of correlation. This is much simpler to interpret, as this evidence directly and simply demonstrates that factors other than deviations from predicted resting metabolic rate are overwhelming the possible effect of such deviations in determining the degree of adiposity associated with the steady state of weight maintenance. Various arguments have been made about the potential roles of futile cycles (3) and of brown adipose tissue and uncoupling proteins (UCP) in affecting adiposity by raising energy expenditure (7). However, their impact on overall energy expenditure in man appears to be small at best. Since differences in basal energy expenditure have no statistically recognizable impact on body fat contents, speculations about the potential significance of UCP and futile cycles need to be made that long-term balance be under one should only an effect on body fat the increases in energy expenditure were by in fat up an effect similar to that of physical it is of to that food intake regulation is to the impact that and in could be to on individuals whose energy expenditures for due to differences in (5). about the importance of in resting energy expenditure which or have the effect of weight gains or weight losses during periods of or to the weight which would be in resting energy expenditure were due to in body and in the effect of food This has been considered to a of “metabolic has been to be in some are in to the that it has been to The fact that differences in resting energy expenditure have no statistically recognizable impact on adiposity 1) against the view that differences in which occur only a in or the of obesity. in the importance of and of metabolic costs Several in the so of fat a of the costs for of as well as for the of in the to adipose tissue are the for of dietary carbohydrate fat may be at some The i.e., the total of the of for the and in the metabolic in and This is higher during than during The from by the of that of fat is not much by of to or by the of and of a of fat Thus, to a commonly of dietary energy by of fat cannot are to obesity than In the is essentially because from at some in subjects a is of minor significance and not to for fat even The of the concept The concept of has been in the context of the of as or fat is It is for periods of but it has been considered in the of obesity, in attempts to understand the differences in of adiposity by individuals However, in lean as well as in whose weight is essentially the over a period of a days are of level of physical and degree of the large variations in physical food and energy balance under cause balances to from to Thus the concept is when to to recognize the of energy intake and energy expenditure on energy balance intake an increase in energy expenditure, as the effect of It is due to the need to the used for the and of the It is considered to to about of the food energy when on a In increases or in resting energy expenditure occur during periods of or energy intake, which are commonly to as The of the is often to as only but not the impact of in energy intake on the energy balance. Unfortunately, the energy balance equation that energy intake and energy expenditure roles in determining energy balance, when in fact the factors energy intakes the energy balance more than the factors determining resting energy expenditure. This important fact not by a of the energy balance in food intake regulation In of the of physiological to to the regulation of food variations in daily food intake are The of for energy intake were to average in food intake are not with variations in energy expenditure, which be metabolic functions be in of large daily deviations from energy balance. is not to a over daily food The physiological in food intake should therefore be to only a minor of the in daily food intake. This has made it to the there appears to be in this regulation. Thus, or at one may to but weight generally tends to at a Since individuals maintain body weights during long periods of their (2), and in resting energy expenditure cannot for in intake it be inferred that food intake tends to adjust itself well to energy expenditure over the long term, even large daily deviations from energy balance adjustment of intake to expenditure in be over periods of several This view is by the of with for body weight obvious than the fact that energy intake be equal to energy expenditure, weight that the substrate be on average, to the composition of the is not in body composition which in are to adjustments in food intake The made by carbohydrate and by fat to the is in the of to This is as the or It varies between the values of when is the and when of fat of the body's The of to during the of a of the is as the or body only be the average the average of the The composition of the and the average are influenced by the of the body's substrate The steady state of weight tends to for a particular body composition in a under a particular of This corresponds to a Such a view the fact that cause weight to occur for of Thus it to much than the concept of a or often invoked to weight In such a concept would to be with the in the of obesity, would have to be as the impact of It has sometimes been considered that are for but in effect this the to a weight during as well as sometimes in Such the fact that their body composition is from that which corresponds to the steady state of weight maintenance. Problems with the of the concept greater than the that a and fat a to the substrate than their in the the other a the of a a higher proportion of fat than that by the this is the differences between and under of intakes are small and influenced by daily under the cannot be with to weight gain or would no correlation between data and body weights or body weight should therefore not be to the of the The of body concept The of body weights to to their a is often as the of a to a particular body The with this concept is that it appears to that to the fat mass to a particular much as one would a It fails to that the body composition for a a steady state of weight The body that such an tend to itself when the has not because a adiposity is or but because weight tends to at the i.e., at the particular body composition which that under this of of of such concepts as and of body which appear to provide for may to be one to understand environmental and dietary factors adiposity and the of obesity. The roles by and fat in energy and provide for the of the to the body's generally of dietary energy and daily intakes in from g in small and individuals to g in The body's may be to between and the of carbohydrate and during a The body's fat commonly to much in obesity. The from to in and it is some greater than the of present in the of small in relation to and the importance of adequate of stores present a metabolic therefore to regulatory to adjust to carbohydrate adjustments of the of and by by and to large variations in carbohydrate intake be without cause the of to adjust to protein intake, as long ago by the other the body's large fat stores are by daily gains or losses and adjustment of fat to fat intake has much lower in metabolic regulation. consumption of fat has or no effect on fat which even The rate of fat varies during the on intake and physical but the of fat in a period is in effect by the difference between total energy expenditure and the energy by protein intakes numerous to prevent large deviations from and protein balances, no such functions are at to daily fat Not surprisingly, deviations from fat balance be much greater than deviations from and protein (or balances It that energy balance cannot be to be more than fat balance. The roles which and fat in the body's and in body weight regulation are therefore fact that is when only the energy balance is considered (1). the long term, in and in brought about by gains or losses in the adipose tissue mass the average rate of fat to this long-term or body composition the degree of adiposity for which the average rate of fat has with fat intake important to be made here, that fat is by so a greater of the fat mass is needed in individuals who maintain intake regulation and carbohydrate balance food consumption is periods of food and weight but only the under the is This it apparent that food intake regulation not have of energy balance as In it becomes that body composition is an important in the regulation of food intake of under of food intake would be in to adjustment of to carbohydrate intake, food intake were to be in a manner to the balance between the use of and the of dietary such considerations at a when the of specific in the been the concept of regulation of food intake, in which it is that of by the for the regulation of food intake by the it is that small in tend to However, during the and there is much between the values that under and metabolic conditions. it therefore considered that in or in substrate rates would be more or more to provide to the as such be based on some of substrate and carbohydrate and is about the and that may be there is a that could be to the the One could the notion that the rate of or in the of the body's stores could provide affecting This would account for the fact that is a days of total and well on the has to low but and The in evidence about the of carbohydrate balance in food intake regulation In one of the to this used in a to substrate balances in men eating over a negative correlation between carbohydrate and food which for of the in the energy balances and energy that factors food consumption and variations in the daily energy balance occur much at a particular has even but regulatory have the potential to long-term may be to with during the short periods in The is similar to the small gains for the would be to in the short but in to The need to between the of carbohydrate balance in food intake regulation and the of in body weight regulation of food intake in a manner to maintain carbohydrate balance to body weight stability, but only when the has been for which the composition of the on average, the in the However, in relation to body weights and the in body weights are important than the factors determining the body fat for which weight tends to are at to prevent and to physical the level at which of carbohydrate fat is in in be to between a lower of some g and an of are to be higher on than on are therefore not to over the when are but to oscillate a Since the lower the are the which are individuals and be by as measurements of in are not from which one could the of in fat this effect be in in in could be calculated the which are daily fat be to fat Thus, the which in obesity in to be made to the of this effect in a of that some of the to substrate in in led to body weight whereas in weight The the view that in small to be by gains in the increases in the of obesity the past a increase in the of obesity in the has even the the considered to have the progressive increase in obesity in such as higher dietary fat greater and physical appear to have during this However, food and in energy and and have to In factors food consumption so that higher are of between is by the and of and It be that environmental are to the which are the of the fat mass to cause fat to be with fat intake, in the the food intake the The impact of raised has been in a to the overall interactions between and fat stores in It that an increase by g in the which are would an increase in body fat of to fat to the which would to a weight gain of some kg and to an increase of about in the BMI = Weight even In on food intake be due to to a degree to and to the level of adiposity in the such to prevent weight It would appear that in a large of the over food intake is on physiological appear to have been by to prevent weight gain in of an food but the fat mass has of food intake in the and are by substrate and the however, and do not over much information from one to the are commonly to be more in energy than weight gain therefore be at in food intake from one to the In it is that even when are available, on days than the that on days individuals who appear to dietary and to the development of obesity, weight gain over the is much than one would considering the associated with the regulation of daily food intake, and the for about the food intake, but their is made by the weight that periods of evidence be in the fact that there is no correlation between adiposity and even resting and total energy expenditure are positively correlated with and of are to short and (5). of food intake to gains or losses of be to result in a of intake, to maintain to prevent the at which would be Thus, the regulatory to a potential and for food intake when with an of but only the average rate of fat the average fat intake. about the effect of on the energy balance physical the of obesity and the to increase as a of body weight is to individuals However, it has been to a to account for the fact that causes a negative energy balance in some but not in others. The is by the fact that physical causes in as it and to provide the needed to the period of physical It causes the as well as in substrate be is that in the of increases in the adipose tissue mass are often to fat to a rate with the fat The effect of dietary fat and lack of in obesity is well in Their physical used to obesity, a in Since to a steady state of weight at lower of it be inferred that fat more than This is the case even often a to the at the of as this is by an increase in fat Thus, physical the daily fat to physical increases the body's ability to use more and Thus, the of food needed to maintain balance is than the increase in energy expenditure, in weight In individuals who have a steady state the impact of physical on eating to maintain fat in to maintain energy balance. considerations in one understand sometimes negative energy balance and sometimes not In the cited the impact of is brought about by the greater by between The of this be simply by considering in terms of than in terms of In a the that consumption of between by higher between to fat dietary fat or is dietary the in weight In view of the considerations made it is not that a of obesity is in of for and eating energy intakes are positively correlated with the fat of the on a particular In fat This evidence appears to be by the often on but not fat intake, such as the It is important to between of weight intake is by a specific and long-term to or body In to the numerous that dietary to weight other individuals weight by fat intake. This to the in the case that and in the second case that is the dietary for fat Such often promoted with much have confusion in the However, seemingly be simply by that on the consumption of has the effect of the of from which to This the to even without to in Thus the to the is that the is the and of a numerous often in large in which and to an even greater to the energy body weight One that as well as and food ability to eating the to in physical and There is no to that the way in which the is in the use of and fat should not be by metabolic and differences in a greater of the fat mass is needed to a proportion of It has been that under are to be by greater weight gain This effect is to be when dietary is by of or effect affecting the the effect of on fat and should be to a on body weight regulation. this is in the the other one should not adiposity to be much influenced by genetic resting metabolic rates to be higher or lower than the average (6). The of factors The of and factors on body composition are commonly by the that to the around the of BMI However, this not recognize the impact of factors in the such it is to the factors determining the in which a i.e., the and affecting an individual's this which may be as the The importance of this is that environmental factors the the BMI of men in to be when in whereas it when in The data by and the average BMI of men in the as from in to in and to in about the equal of values higher and lower than average, environmental of the have a The is to have a more on the proportion of individuals whose BMI exceed than the variations about the to such as and Thus, and genetic factors in to adiposity and to the obesity In only the factors should be to be by for weight should this account by to strive for weight or in This could provide a of in an individual's the development of physical in and the potential for the could a in a BMI % body weight body weights were to body i.e., the weight associated with the life as from life It the use of as a of This has been by the use of the BMI, which not such In BMI is well to BMI between and and BMI obesity. However, the BMI is a abstract notion and information in terms of the BMI not as much information to individuals and as their weight to their weight the of or by much it exceed the of to that be to % data could be to one could consider about their weight to the more and % The of body weight regulation and obesity to (i) are the which to the by the large short-term variations in energy intake result in energy balances or in rates of gain or of fat over and (ii) is the state of approximate weight for such widely of adiposity This second is one of but it be in a manner with the that about weight with this be to account for the increase in the of obesity. It the of the food to effect in raising the which are it important to several misconceptions that appear to in the way of a of weight maintenance. This may in to the with which the physiological regulation of food intake and are of environmental to