Is the calorie concept a real solution to the obesity epidemic? — TEI-tagged view

Salvador CamachopersName, Andreas RuppelpersName (2017date). “Is the calorie concept a real solution to the obesity epidemic?.” Global Health Actiontitle·j.

Object of study — the calorie-imbalance concept as the stated cause of obesityterm·dom

Research question — whether a hormonal frame can overcome the weaknesses of the calorie concept and guide public healthterm·key against obesityterm·dom

Contribution — a revised concept of the causes of obesityterm·dom centred on insulin-driven hormonal imbalanceterm·dom from diet compositionterm

Full text — tagged

Is the calorie concept a real solution to the obesityterm·dom epidemic?

Abstract Background: The obesityterm·dom epidemic has been growing steadily across the whole world, and so far not a single country has been able to reverse it. The cause of obesityterm·dom is stated by the World Health Organization as an energy imbalance between calories consumed and calories expended. However, growing evidence suggests that the calorie imbalanceterm·key concept may not be sufficient to manage and reverse the obesityterm·dom epidemic.

Objective: To discuss the use of the calorie imbalanceterm·key concept and its elements as a tool for weight management as well as its possible negative consequences and implications for public healthterm·key, with the aim to point toward the need of an updated concept for causes of obesityterm·dom. This update should guide public healthterm·key interventions more efficiently to limit obesityterm·dom by preventing weight gain or promoting weight loss.

Methods: This is a literature reviewsterm·mth based on a semi-structured approach to determine the material to be examined.

Results: After revisiting general facts about fat generation and accumulation, we propose an updated concept for the causes of obesityterm·dom including diet compositionterm and hormonal regulation of fat metabolism.

Conclusions: We discuss how this updated concept could benefit the overall efficiency of strategies against obesityterm·dom, and hypothesize how potential resistance to adopting this new view could be lowered.

KEYWORDS: Obesityterm·dom, calorie imbalanceterm·key, obesityterm·dom cause, hormonal imbalanceterm·dom, insulinterm·key, public healthterm·key Background The World Health Organization (WHO) defines obesityterm·dom as an ‘abnormal or excessive fat accumulation that may impair health’, and states that ‘the fundamental cause of obesityterm·dom and overweight is an energy imbalance between calories consumed and calories expended’ (n.b. Food energy is commonly expressed as ‘kilocalories [kcal]’ [ 1 ]. However, the common use is to name them just ‘calories [cal]’. In this article kcal and cal will be used interchangeably). This concept is deeply rooted in public opinion as the core reason for overweight and obesityterm·dom. Most public healthterm·key strategies aiming to tackle obesityterm·dom are based on this concept, i.e. they aim to decrease caloric consumption, to increase calories expended or ideally a combination of both. However, the concept of energy balanceterm·dom or imbalance may be incomplete (n.b. Because the relevant energy unit is calories, energy balanceterm·dom, calorie balanceterm·dom, calorie imbalanceterm·key and energy imbalance will be used interchangeably). It may even be argued that this concept could be one of the reasons why public healthterm·key strategies have been so unsuccessful in reversing the obesityterm·dom epidemic [ 2 ]. The energy balanceterm·dom will be referred to as ‘concept 1term·dom’ in this article.

An alternative, although not exclusive, conceptual frame links obesityterm·dom to the insulin-dependent regulation of fat generation and takes note of the different metabolic pathways to degrade macronutrients, i.e. carbohydrates (CHO), fat and proteins. This article revisits causes for obesityterm·dom in the light of the latter frame and its concepts, e.g. glycemic indexterm, and will discuss how this frame can overcome some of the weaknesses of concept 1term·dom, with the aim to more efficiently guide public healthterm·key interventions to limit obesityterm·dom by either preventing weight gain or promoting weight loss. This can be seen as a hormonal-balance conceptterm·dom, and it will here be referred to as concept 2term·dom. Strengths and weaknesses of both concepts will be discussed.

Methods This is a narrative literature reviewterm·mth covering evidence about obesityterm·dom, its causes, control efforts and public healthterm·key strategies. There are several approaches to study the causes of obesityterm·dom, and this diversity provokes limitations. Therefore, this reviewterm·mth does not claim to analyze the literature comprehensively, nor can we fully exclude potential risks of drawing conclusions on a possibly less-than-perfect basis. However, the chosen approach appears adequate to integrate complex interactions that apparently determine obesityterm·dom [ 3 ].

Calorie imbalanceterm·key as the suggested cause for obesityterm·dom Concept 1term·dom has its roots in two laws of thermodynamics, i.e. the first lawterm known as the ‘conservation lawterm’ and the second law also known as the ‘dissipation law’. The first lawterm states that in a closed system in thermal equilibrium, the form of energy may change but the total is always conserved [ 4 ]. This has been interpreted as a caloric balance, i.e. ‘calories in should equal calories out’. Therefore, if you gain weight you are either eating too much or moving too little, and in order to lose weight you would have to ‘eat less and/or move more’. Despite its apparently straightforward logic, this concept is not complete and the second law also needs to be considered. This states that ‘in any irreversible process, the entropy must increase and balance is not expected’ [ 4 ]. That means that for digestive processes where food turns into bolus, but bolus cannot be converted back into food, some of the input energy is irreversibly lost during the metabolic process and results in thermogenesis.

Concept 1term·dom to avoid or reduce overweight and obesityterm·dom Because concept 1term·dom assumes that a positive energy balanceterm·dom results in fat mass, individuals aiming to prevent weight gain should avoid a positive balance. Of the same tenor, individuals aiming to lose weight should look for a negative balance. Dietary guidelines commonly suggest the calories deficit needs to be in the range of 500–750 kcal per day for an adult to lose weight [ 5 ]. This value is based on the ‘3500 kcal rule’, also known as the ‘Wishnofsky rule’ [ 6 ], which is still used as the basis for some guidelines, publications and nutrition textbooks [ 7 ], despite its inaccuracy and very limited effectiveness [ 8 ]. The recommended deficit tacitly assumes ‘that a calorie is a calorie’ independently of its source [ 4 ], hence ignoring the second rule of thermodynamics. When the different values of catabolism-induced thermogenesis are considered for each macronutrient [ 9 ], ‘a calorie is a calorie’ may no longer hold true, but probably many among the common population and even some nutrition professionals ignore this [ 7 , 10 ]. By consequence, inaccurate assessments and recommendations for weight management may result.

Thus, concept 1term·dom may lead to the misperception that total calorie intake is more important than the source of the calories and nutrient balance. Therefore, an individual trying to lose weight may become vulnerable to malnutrition when focusing only on calories. For example, restricting energy intake to 2000 kcal per day [ 5 ], if the resulting diet consists only of industrialized food (n.b. Products made from processed substances, extracted or refined from whole foods… [They are] very durable, palatable, and ready to consume… [They] are typically energy-dense, have a high glycemic load, are low in dietary fibers, micronutrients, and phytochemicals, and are high in unhealthy types of dietary fat, free sugars, and sodium’ [ 116 ]. Industrialized food or ultraprocessed food will be used interchangeably), may result in an overload of nutrients correlated with development of obesityterm·dom and a lack of essential nutrients and micronutrients known to act against obesityterm·dom [ 11 ]. Without discriminating the sources of calories, reducing the calorie intake usually results in a short phase of rapid weight loss, although the loss is not necessarily one of accumulated fat, but rather of fat-free mass [ 12 ]. Given that the main problem in obesityterm·dom is, however, accumulated fat, losing any mass other than fat may be unproductive and not desirable.

Assuming that to respect a negative calorie balanceterm·dom could indeed be useful for individuals to lose weight, food information on energy intake and tools to measure the energy expense should be available, and they are. However, in reality it appears quite difficult for an individual to achieve this balance, because a constant error of only 175 kcal per day would have a considerable impact of up to 3 kg lost or gained within a year [ 13 , 14 ]. The available ways to measure caloric intake and expenditure cannot overcome this margin of error, as will be discussed in the following sub-sections.

Energy intake and front label information Front labels on food are meant to inform consumers’ choices, including those who may wish to count their calorie intake. However, some industrialized foods have shown differences between the content of energy claimed on their front label and analyses by a third-party, e.g. a health organization [ 15 , 16 ]. Similarly, the caloric content of the dishes in a restaurant menu may be underestimated by either the individuals or the supplier [ 17 , 18 ]. However, it seems more problematic that this information may not be understood correctly, if individuals do not have a certain minimal knowledge of nutrition [ 19 , 20 ]. In addition, when one self-assesses energy intake, under- and over-reporting consumption may occur [ 21 ]. Several technological devices have been developed to assist assessment of energy intake to reduce these biases, e.g. chewing count devices, wrist moving devices, or special digital photographic cameras for food. However, these devices may not yield sufficiently valid data [ 22 – 25 ]. Therefore, measurements of the energy balanceterm·dom may not meet the aforementioned narrow margin of error of 175 kcal per day.

Physical activity and energy expenditure within concept 1term·dom There are also barriers to assessing physical activity. The first one is the lack of standardized definitions of its levels, i.e. moderate, intermediate or vigorous intensity. Every level implies a different energy expenditure that also depends on other factors such as duration, body size and age. Hence, it is difficult to agree on which kind of physical activity should be recommended for effective weight control [ 26 ]. Whereas some studies and guidelines recommend vigorous physical activity [ 27 , 28 ], other evidence suggests that low-intensity activities such as walking, yoga, meditation and stretching are equally effective in reducing weight [ 28 – 30 ]. Second, energy expenditure might be assessed through technological tools aiming to enhance accuracy, such as pedometers and accelerometers, which measure walked distances and estimate the energy expenditure based on the weight, age and height of an individual. These measurements, however, have already an error of about 100 kcal/day [ 13 ]. Finally, despite the common belief that physical activity could equilibrate an energy imbalance, this is in reality difficult to achieve. For example, adults who eat a sandwich containing around 290 kcal should have to walk for around 90 minutes or almost 5 kilometers [ 31 ].

The energy expended in non-exercise activities that are part of neither the basal expenditure nor the digestive process is known as ‘non-exercise activity thermogenesis’ or NEATterm·dom [ 32 ] and also plays a role in the energy balanceterm·dom. These activities include ‘energy expenditure of occupation, leisure, sitting, standing, walking, talking, toe-tapping, playing guitar, dancing, and shopping’ [ 32 ], among others. The multitude of elements involved in NEATterm·dom and their variability make it even more challenging to assess them than physical activity, and hence, for them to be considered in the energy balanceterm·dom.

Despite the consensus of the health benefits of physical activity [ 33 – 35 ], independently from its suggested reduction of fat mass [ 36 ], there is controversy about whether sedentary behavior is directly involved in obesityterm·dom development or not [ 37 ]. The relation between obesityterm·dom and lack of physical activity seems not to be strong [ 38 , 39 ], and physical activity appears not necessarily to be a useful tool to ‘increase energy expenditure’ [ 40 – 45 ]. Nevertheless sedentary behaviors and reduction of physical work in jobs have been consistently stated as major factors for the development of obesityterm·dom in modern societies [ 46 ].

Possible consequences of using concept 1term·dom Ethical considerations on obesityterm·dom and overweight ‘Eat less, move more’ appears as the most feasible solution to overweight and obesityterm·dom and both possibilities seem to be within people’s reach [ 47 ]. The solution gives the impression of being so simple and straightforward that presumably all that are needed are willingness and self-control. Failing to revert obesityterm·dom or overweight may be interpreted as lack of character, as one study has shown [ 48 ]. Concept 1term·dom, thus, may lead to blame and even stigmatize people with these conditions, e.g. punishments such as imposing a special tax on people with overweight and obesityterm·dom using airplanes are already being discussed in both academia and mass media [ 49 , 50 ]. However, it may be ethically doubtful to attribute full responsibility to people with obesityterm·dom and overweight, when individuals do not have full control over their food availability or accessibility [ 51 , 52 ]. In addition, it is thought that people may become obese through different pathways that possibly are independent of caloric balance, e.g. brain mediation of body fat mass, diminution of muscle mass and strength, as well as gut microbiota [ 53 – 55 ]. Therefore, it would be more ethical to use a ‘cause of obesityterm·dom’ concept that does not transfer total responsibility to the individual.

Public healthterm·key strategies based on concept 1term·dom Most anti-obesity programs are based on concept 1term·dom or focus at least on one of its elements [ 56 , 57 ]. Possibly as a result, within certain populations, the bigger the average BMI the higher is the prevalence of dieters or exercisers [ 58 ]. However, the obesityterm·dom epidemic continues to grow worldwide, and under the current trends, the chance to reverse it is virtually zero [ 59 ]. If apparently people and governments do what they are supposed to do to tackle the epidemic, but only isolated and not sustained results are achieved [ 60 , 61 ], it may be possible that the symptoms are being treated instead of the roots [ 62 ].

The use of concept 1term·dom may have certain advantages, e.g. it is easy to understand, it has a straightforward logic, it creates awareness on food consumption and it can reinforce discipline. However, the disadvantages of the concept may outperform its advantages under the current global circumstances. Continuing to base strategies solely on concept 1term·dom may, therefore, not only be ineffective in terms of public healthterm·key, but also be an inefficient use of resources.

Food industryterm·key and obesityterm·dom The participation of the food industryterm·key to reverse the obesityterm·dom epidemic would be crucial [ 63 , 64 ], because it plays a major role in people’s choices and perceptions of food through its products and its marketing [ 65 ]. For example, the food industryterm·key communicates characteristics of its products through front label information, influencing consumption decisions [ 65 ]. However, most of the companies that dominate the global food market seem to focus only on meeting specific growth targets [ 66 ], overlooking the impact of their strategies on people’s health and weight, because the calories can be balanced anyway.

Subsidies from government to agricultural production are commonly based on the economic incentive of the volume of pruchase by the food industryterm·key, turning out certain raw materials such as sugar cane, cornand palm oil, cheap for the farmers to produce and sell to the food industryterm·key. Although such subsidized agricultural production is not a problem by itself, these materials are turned into harmful ingredients once they are ultra-processed by the industry [ 67 ], e.g. refined sugar, corn syrup and hydrogenated fats, all of which have proven to be closely related to obesityterm·dom and to development of obesity-related chronic diseases [ 67 – 70 ]. Under concept 1term·dom, the effect of these foods on people’s health may be overlooked because individuals would self-regulate only their calorie balanceterm·dom.

Thus, the food industryterm·key has a share of responsibility within the obesityterm·dom epidemic that may not be evident, because concept 1term·dom transfers the responsibility of regulation to the individuals. By placing prime importance on the calorie balanceterm·dom, therefore, the food industryterm·key would always have a way out for not participating actively in a common frontline to tackle the obesityterm·dom epidemic, which our concept 2term·dom may avoid. The next section will propose an approach which differs from the calorie concept and might lead to more efficient actions aiming to tackle overweight and obesityterm·dom.

An alternative approach to causes for obesityterm·dom Different classes of food influence differently the energy balanceterm·dom. For example, if an individual follows a 2000 kcal diet with 55% of the total kcal from CHO, 30% from fat and 15% of protein, and if thermogenesis is taken into account, the remaining energy would be 1825 kcal and not 2000 kcal. That is because the body would use approximately 175 kcal out of those 2000 kcal only for catabolizing the macronutrients [ 4 ]. The energy needed for catabolism differs for every kind of macronutrient during the digestion process [ 9 ].

Therefore, it may be also possible that diet compositionterm affects the whole digestive process and, hence, fat production and accumulation [ 53 , 71 ]. Given that obesityterm·dom is an ‘abnormal or excessive fat accumulation that may impair health’ [ 1 ], it would appear appropriate to focus on the details of fat production and accumulation. This view may strengthen the strategies aiming to reverse the obesityterm·dom epidemic.

Lipogenesisterm·dom The production of fat is called lipogenesisterm·dom. The body uses fat in different ways, but mostly as fuel [ 72 ]. Lipogenesisterm·dom is commonly balanced with fat usage. Obesityterm·dom is not a rapidly developing condition, but develops only if more fat is being produced than used – hence stored – continuously [ 73 ].

Potentially, all the macronutrients could be used by the body to produce fat. However, proteins are normally converted into amino-acids or peptides, and only exceptionally into fat [ 74 , 75 ]. Protein intake may also play an indirect role in lipogenesisterm·dom through different hormonally controlled digestive processes [ 76 ]. Thus, it is normally considered that lipid production and storage mostly originate either from direct intake of fat, or from a process known as de novo lipogenesisterm·dom, which is the transformation of CHO into fat [ 77 ].

Fat metabolism Fat is normally ingested in the form of triglycerides (TG). Fat needs to be oxidized into free fatty acids (FFA) to be used as energy [ 78 , 79 ]. This can happen through two different pathways, either directly from fat in food or from fat in adipose tissue. Insulinterm·key plays a key role to determine which pathway dominates [ 80 ]. That means that when insulinterm·key is high due to food intake, the breakdown of fat from adipose tissue stops and fat storage starts [ 73 , 81 ]. Conversely, when the insulinterm·key level is low, e.g. during a fasting state, the body makes use of the adipose tissue to generate energy [ 79 ]. Thus, energy production is regulated between fat storage in the presence of food and fat degradation when fasting.

CHO metabolism Digestible CHO are degraded to their simplest form, i.e. monosaccharides, mainly glucose. That is why such CHO are also called glycemic. Non-digestible CHO, namely fibers, are non-glycemic. Therefore, CHO can be classified according to whether or not they lead to raised glucose levels in the blood. How fast a glycemic CHO leads to a raised glucose concentration in blood is measured by its glycemic indexterm (GI). CHO that are rapidly degraded and hence quickly raise the blood sugar level have a high GI, whereas the slowly degraded ones have a low GI.

Whenever a macronutrient is consumed, there may be an insulinterm·key response. However, the highest and longest secretion of insulinterm·key is stimulated by CHO with a high GI. Such CHO are common constituents of ultra-processed products. Insulinterm·key is a key to gear the metabolic processing of high GI carbohydrates into glucose (for immediate energy) or to build up fat reserves (for future energy needs). The latter pathway may be favored by some monosaccharides, e.g. fructose [ 82 ]. In both cases, a high and prolonged release of insulinterm·key normally takes place which relates to fat production and accumulation [ 83 ]. Whether CHO with high GI are consumed as liquid, e.g. sugary drinks, or solids, e.g. sugary cakes, seems to provoke a different insulinterm·key response, hence, different lipogenesisterm·dom reactions. The liquid forms of CHO appear to be the most obesogenic form of high-GI carbohydrates [ 84 , 85 ]. The responses of insulinterm·key to food intake may be also influenced by genetic characteristics [ 86 ], suggesting that certain populations could be more vulnerable to overweight and obesityterm·dom depending on their food availability [ 86 ].

Negative cycle: insulin-overweight Insulinterm·key plays a role in the process of lipogenesisterm·dom and subsequent fat storage. This is also a self-regulated system of energy utilization. A problem may occur, however, if the system loses its self-regulation capacity, e.g. by a constant stimulation and consequent high presence of insulinterm·key due to the diet compositionterm, and not necessarily by its overall caloric content. This disturbance of self-regulation may result in ‘more fat in and less fat out’. Additionally, a constantly high presence of insulinterm·key is known to provoke insulinterm·key and leptin resistanceterm·dom. Insulinterm·key resistance turns into a higher risk of developing diabetes type II, as several studies have shown [ 74 , 87 – 93 ], whereas leptin resistanceterm·dom may impede the body from using the stored fat as a source of energy [ 94 ].

We hypothesize that food composition could push an individual into a negative cycle: Under a constantly high presence of insulinterm·key, the body may increase its capacity for fat production and storage. As a result, the body grows bigger, and this leads to higher energy demands. If the body constantly stores fat but does not use it as a source for energy, it would not only grow bigger but also become constantly hungry. This would possibly cause a repeated intake of the diet that is at the origin of the imbalance, thus making the body even bigger and hungrier and so on. In this situation, ‘laziness’ and ‘gluttony’, i.e. concept 1term·dom, would actually be the symptoms of obesityterm·dom and overweight, whereas the cause would include a hormonal imbalanceterm·dom, i.e. concept 2term·dom. This represents a situation that can be aggravated for populations with genetic predisposition to lipogenesisterm·dom and fat storage, i.e. high insulinterm·key responses [ 86 ].

An insight into the insulinterm·key reaction provoked by different diet compositionsterm with the same caloric content is shown in Figure 1 . The graph was generated using data from the simulator of glucose and insulinterm·key levels in the human body, developed by the Illinois Institute of Technology [ 95 ]. This simulator works based on a mathematical model considering the physiological, metabolic and chemical reactions of the human body upon carbohydrate intake [ 96 ]. The depicted differences in insulinterm·key levels provoked by different diet compositionsterm are apparently considerable.

Differences in levels of blood glucose (top) and blood insulinterm·key (bottom) in the human body as provoked by diets with identical caloric content, but different compositions of macronutrients. Notes: Diets were assumed in this model calculation as follows, Diet A (blue) : 1670 kcal per day of energy content (7000 kjoules) with a composition of 53% CHO, i.e. 218 grams of CHO; 22% protein; and 25% fat. The CHO content is divided among three equal intakes during the day, i.e. 72.6 g for breakfast, 72.6 g for lunch and 72.6 g for dinner. Diet B (orange) : same composition as diet A but adding two snacks, i.e. one apple between breakfast and lunch (34 g of CHO) and one banana between lunch and dinner (30 g of CHO). Diet C (green) : the same energy content as in other diets, 1670 kcal per day (7000 kjoules), but with a composition of 38% CHO, i.e. 156 grams of CHO; 32% protein; and 30% fat. The CHO content is again divided into three equal intakes during the day, i.e. 52 g in breakfast, 52 g in lunch and 52 g in dinner. All diets were modeled for a non-diabetic adult of 60 kg of body weight using the web-based simulator of glucose and insulinterm·key levels in the human body ‘Glucosim’ developed by the Illinois Institute of Technology [ 95 ].

It is worth noting the insulinterm·key reaction provoked by fruit consumption ( Figure 1 ). This reaction may be considerably overestimated by the simulator because it does not differentiate between types of CHO. However, fructose as found in fruits may not be comparable in terms of either quality or quantity in reality to that found in industrial products [ 97 ]. There is indeed an actual controversy about the role of fruits in overweight and obesityterm·dom, due to their fructose content and its role in fat production [ 98 ]. While some researchers have provided evidence on successful weight loss diets when removing fruits, fruit juices and other sources of fructose [ 99 ], others have argued that whole fruits do not cause overweight because their flavonoid and polyphenol content regulates sugar absorption [ 100 ]. Nonetheless, regarding the controversy, there is an apparent consensus in that the industrialized form of fructose (commonly sucrose mixed with high-fructose corn syrup) is the one mostly linked to obesityterm·dom [ 82 , 97 , 101 , 102 ].

Macro-level studies may also support the latter assumption. For instance Riera-Chrichton and colleagues [ 103 ] analyzed population data from the USA between 1974 and 2006 and from 164 countries between 2001 and 2010. They determined that the strongest association between a specific type of macronutrients and development of obesityterm·dom was with CHO, although they did not clearly distinguish what kind of CHO and, hence, the association is too broad given the different types of CHO. Similarly, Austin and colleagues [ 93 ] analyzed population data from the U.S.A between 1971 and 2006 and found that the increase in obesityterm·dom prevalence was closely related to a higher consumption of CHO, again without any distinction of the types of CHO. Other studies and meta-analyses have found similar results [ 61 , 104 , 105 ]. Processed foodterm·dom apparently induces continuous insulin productionterm in the human body, possibly due not only to large amounts of highly glycemic ingredients but also to the resulting diet compositionterm, in terms of macronutrients, from consuming these products [ 76 , 83 , 106 – 108 ].

In summary, macronutrients influence fat production and accumulation either by a direct response provoked solely by intake, e.g. of CHO, or by hormonal regulation of the digestive processes, e.g. of protein and fat. A detrimental diet compositionterm may produce a hormonal imbalanceterm·dom that could turn into a negative loop where individuals accumulate fat, but are not properly nourished which makes them constantly hungry, causing them to eat more from that diet compositionterm. The resulting trap is reinforced by the modern food availability. Diet compositionterm, thus, possibly has a larger influence on obesityterm·dom and overweight than the calorie balanceterm·dom.

A proposed revision of causes for obesityterm·dom We propose to revise the current concept of causes for obesityterm·dom. Instead of placing prime importance on the energy balanceterm·dom, i.e. concept 1term·dom, we suggest to emphasize the effect of food on the metabolism. The guiding principle should be: ‘Overweight and obesityterm·dom are determined by a hormonal imbalanceterm·dom characterized by a constant and sustained secretion of insulinterm·key, which results from particular dietary compositions. These are closely linked to modern food habits.’ In contrast to concept 1term·dom, this revision accounts better for recent insights into biochemical and hormonal pathways, is consistent with epidemiological and behavioral evidence, and may allow for more adequate concepts and actions in public healthterm·key to reverse the obesityterm·dom epidemic.

In regards of public healthterm·key strategies, the revised concept 2term·dom would associate the problem predominantly with an imbalance of hormonal processes that are biologically common to all humans, and which normally control a balanced insulinterm·key action on fat metabolism. As a result, leading public organisms may focus on tasks and solutions to reduce food-induced insulinterm·key overproduction that could be adopted and applied in contexts of their respective influence [ 109 ]. Targeting actions toward insulin-related metabolic processes could also lead to more homogeneous evidence to tackle obesityterm·dom and overweight. This may also increase efficiency within the actions to reverse the obesityterm·dom epidemic by building on a reliable ground [ 110 ]. Because the costs of obesityterm·dom, including actions against it, are estimated at 2 trillion USD per year on the global gross domestic product (GDP) [ 111 ], even a small improvement in efficiency of actions could have a huge impact on savings.

Regarding ethics and stigma, the understanding of concept 2term·dom may distribute responsibilities among the stakeholders, as opposed to concept 1term·dom where corrective and preventive actions are attributed solely to the individual’s will. However, the individual dietary composition depends greatly on the availability and accessibility of food. These, in turn, are the result of regulations, economic incentives and food security, among other factors [ 112 ] that are out of individuals’ reach. For example, under concept 1term·dom, the minimal responsibility of government would be to ensure food availability and accessibility regardless of its composition, and provide knowledge about concept 1term·dom. Hence, the individual would have the option to self-achieve her or his calorie balanceterm·dom. Under the same scenario, the minimal responsibility of the food industryterm·key may be to support availability, accessibility and calorie balanceterm·dom knowledge. By contrast, under concept 2term·dom, a government’s minimal responsibility would be to ensure the availability and accessibility of such food that does not create havoc in the hormonal regulation of digestive processes along with knowledge of how a diet’s composition may affect individuals’ health. The food industryterm·key’s minimal responsibility would be to support the availability and accessibility of that non-harmful food, as well as supporting the knowledge about diet compositionterm. Under this scenario, it would be difficult for the food industryterm·key and government to provide food that is marked as harmful by the knowledge that they also provide.

It is clear that consumers would always share in the responsibility about their food intake, but under concept 2term·dom, this responsibility may not remain exclusively with them. Clear areas of responsibilities may be drawn and stakeholders could be even made accountable for them. Hence, the revised concept may help to reduce, although not to eliminate, the negative connotations of an individual’s responsibility and the resulting stigmatization.

Guided by our proposed change of perspective, industry may start developing better products by paying attention to specific characteristics of industrial products, i.e. ingredients involved in hormonal imbalanceterm·dom. Moreover, the food industryterm·key may change its current defensive approach toward a more participative one. This could mean a significant and positive impact against the obesityterm·dom epidemic. In addition, because all macronutrients have a role in insulinterm·key regulation, the proposed revision of the obesityterm·dom concept may also have the advantage of not pointing to a single food and thus blaming a single item. This revision might even avoid a possible backfire in obesityterm·dom prevalence caused by the control strategies, as may have happened when fat was stigmatized as the overweight promoter [ 88 , 113 , 114 ].

The proposed revision may have some disadvantages too. For example, people may find it harder to understand concept 2term·dom rather than concept 1term·dom. Hence, educating people in concept 2term·dom may be challenging. Another possible disadvantage is that because most of the current policies and supportive environment, e.g. front labels, mobile applications, textbooks, and Internet articles, are predominantly based on calories, concept 2term·dom may lack initial support. Thus, an individual following concept 2term·dom could have the impression of following a mistaken concept. However, it is possible that the advantages of adopting concept 2term·dom may outperform its disadvantages in the long run.

Leading to change In advocating for this revised view on causes of obesityterm·dom, resistance within institutions and their networks is to be expected. Revisiting the causes of obesityterm·dom may also be interpreted as a withdrawal of the original concept, because concept 1term·dom is broader than concept 2term·dom. However, restating the obesityterm·dom problem as a hormonal imbalanceterm·dom is not necessarily in conflict with concept 1term·dom. There is an overlapping area that can be used to integrate the proposed change of perspective with the prevailing concepts of causes for obesityterm·dom. In fact, the foods most closely related to concept 2term·dom, i.e. simple CHO, are also commonly discouraged by concept 1term·dom, although for different reasons. Lucan and DiNicolantonio [ 55 ] analyzed certain areas of compatibility between what they call ‘calorie-focused thinking’ and ‘more-nuanced thinking’, namely concept 1term·dom and concept 2term·dom. They found certain overlaps as illustrated in Table 1 , particularly in encouraging vegetables and discouraging sugary drinks.

Overlaps between calorie-focused thinking and more-nuanced thinking from Lucan and DiNicolantonio [ 55 ]. Reprinted with permission.

The encouragement to base diets on non-industrialized food, whole plants and certain lean meats, all of which do not overstimulate insulin productionterm, is also compatible with concept 2term·dom. Most of the non-obesogenic diets, such as the Mediterranean diet, Paleolithic diet or low-glycemic diet, are, therefore, compatible with concept 2term·dom. Katz and Meller compiled an extensive reviewterm·mth on this [ 115 ] and their findings are shown in Table 2 . This could also mean that most of the foregoing obesityterm·dom research framed as concept 1term·dom would still be relevant after reframing the information into concept 2term·dom. Therefore, the resistance to change could be minimized.

Compatibility between diets (adapted from [ 115 ]). Reprinted with permission.

Conclusion We have discussed that the use of calories as energy units and concept 1term·dom may be relevant to some areas of public healthterm·key, but this concept has apparently not provided an efficient framework against the obesityterm·dom epidemic. It may even foster stigma, produce negative consequences to unrelated third parties and prevent tackling strategies from being efficient.

Given the big impact of obesityterm·dom on global GDP, it is a necessity to look for strategies that may increase the cost-efficiency of actions. By revisiting the causes for obesityterm·dom, especially those stated by the leading health organisms, this article makes the case to view obesityterm·dom as a consequence of disturbing the auto-regulation of hormones related to fat production and accumulation by diet compositionterm, in particular that produced by industrialized processed foodterm·dom. Among other advantages, this proposed concept may offer an opportunity for the food industryterm·key to play a more responsible role in controlling overweight. If we really want to succeed in tackling the obesityterm·dom epidemic, we must stop treating its symptoms, and start treating its causes instead.

Acknowledgments SC is thankful to Prof. Christiane Schwieren from the Alfred-Weber Institute (Chair of Behavioral Economics) for academic support. He is also thankful to the German Academic Exchange Services (DAAD) and the Mexican National Council of Science and Technology (CONACYT) for a doctoral scholarship. The authors acknowledge the financial support for publication provided by the Deutsche Forschungsgemeinschaft and Ruprecht-Karls-Universität Heidelberg within the funding program Open Access Publishing as well as of the Institute of Public Healthterm·key of the Ruprecht-Karls-Universität Heidelberg.

Responsible Editor Stig Wall, Umeå University, Sweden Funding Statement SC receives a scholarship from the German Academic Exchange Services (DAAD) and the Mexican National Council of Science and Technology (CONACYT). A grant from the Deutsche Forschungsgemeinschaft and Institute of Public Healthterm·key of the Ruprecht-Karls-Universität Heidelberg was received for open access publishing.

Author contributions SC conceived the article and prepared the first draft. AR revised and contributed to the production of the subsequent drafts. Both authors contributed to the drafting of the final version. Both authors have read and approved the final manuscript.

Availability of data and material The data analysis from Figure 1 is publicly available online at the ‘Tableau Public’ repository: https://public.tableau.com/views/Insulinandglucosemodels/Dashboard1?:embed=y:display_count=yes .

Disclosure statement No potential conflict of interest was reported by the authors.

Ethics and consent None.

Paper context The calorie balanceterm·dom as the cause of obesityterm·dom is more complex than an intake–expense relation. By revisiting general facts about fat generation and accumulation, we propose to update the perceived causes of obesityterm·dom including diet compositionterm and recent insights into biochemical and hormonal pathways. The disadvantages of the currently stated cause of obesityterm·dom may outbalance its advantages. A revision of this cause may promote more efficient actions in public healthterm·key to reverse the obesityterm·dom epidemic.

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