Testing the carbohydrate-insulin model in mice: The importance of distinguishing primary hyperinsulinemia from insulin resistance and metabolic dysfunction

The Metabolic and Endocrine Effects of a 12-Week Allulose-Rich Diet

The global rise in type 2 diabetes (T2D) and obesity necessitates innovative dietary interventions. This study investigates the effects of allulose, a rare sugar shown to reduce blood glucose, in a rat model of diet-induced obesity and T2D. Over 12 weeks, we hypothesized that allulose supplementation would improve body weight, insulin sensitivity, and glycemic control. Our results showed that allulose mitigated the adverse effects of high-fat, high-sugar diets, including reduced body weight gain and improved insulin resistance. The allulose group exhibited lower food consumption and increased levels of glucagon-like peptide-1 (GLP-1), enhancing glucose regulation and appetite control. Additionally, allulose prevented liver triglyceride accumulation and promoted mitochondrial uncoupling in adipose tissue. These findings suggest that allulose supplementation can improve metabolic health markers, making it a promising dietary component for managing obesity and T2D. Further research is needed to explore the long-term benefits and mechanisms of allulose in metabolic disease prevention and management. This study supports the potential of allulose as a safe and effective intervention for improving metabolic health in the context of dietary excess.

Carbohydrate-insulin model: does the conventional view of obesity reverse cause and effect?

Conventional obesity treatment, based on the First Law of Thermodynamics, assumes that excess body fat gain is driven by overeating, and that all calories are metabolically alike in this regard. Hence, to lose weight one must ultimately eat less and move more. However, this prescription rarely succeeds over the long term, in part because calorie restriction elicits predictable biological responses that oppose ongoing weight loss. The carbohydrate-insulin model posits the opposite causal direction: overeating doesn't drive body fat increase; instead, the process of storing excess fat drives overeating. A diet high in rapidly digestible carbohydrates raises the insulin-to-glucagon ratio, shifting energy partitioning towards storage in adipose, leaving fewer calories for metabolically active and fuel sensing tissues. Consequently, hunger increases, and metabolic rate slows in the body's attempt to conserve energy. A small shift in substrate partitioning though this mechanism could account for the slow but progressive weight gain characteristic of common forms of obesity. From this perspective, the conventional calorie-restricted, low-fat diet amounts to symptomatic treatment, failing to target the underlying predisposition towards excess fat deposition. A dietary strategy to lower insulin secretion may increase the effectiveness of long-term weight management and chronic disease prevention. This article is part of a discussion meeting issue 'Causes of obesity: theories, conjectures and evidence (Part II)'.

Testing the protein-leverage hypothesis using population surveillance data

It is hypothesized that humans exhibit 'protein leverage' (PL), whereby regulation of absolute protein intake results in the over-consumption of non-protein food on low percentage protein diets. Testing for PL using dietary surveillance data involves seeking evidence for a negative association between total energy intake and percentage energy from protein. However, it is unclear whether such an association might emerge without PL due to the structure of intake data (protein and non-protein intakes have different means and variances and covary). We derive a set of models that describe the association between the expected estimate of PL and the distributions of protein and non-protein intake. Models were validated via simulation. Patterns consistent with PL will not emerge simply because protein intake has a lower mean and/or variance than non-protein. Rather, evidence of PL is observed where protein has a lower index of dispersion (variance/mean) than non-protein intake. Reciprocally, the stronger PL is the lower the index of dispersion for protein intake becomes. Disentangling causality is ultimately beyond the power of observational data alone. However, we show that one can correct for confounders (e.g. age) in generating signals of PL, and describe independent measures that can anchor inferences around the role of PL.

Competing paradigms of obesity pathogenesis: energy balance versus carbohydrate-insulin models

The obesity pandemic continues unabated despite a persistent public health campaign to decrease energy intake (“eat less”) and increase energy expenditure (“move more”). One explanation for this failure is that the current approach, based on the notion of energy balance, has not been adequately embraced by the public. Another possibility is that this approach rests on an erroneous paradigm. A new formulation of the energy balance model (EBM), like prior versions, considers overeating (energy intake > expenditure) the primary cause of obesity, incorporating an emphasis on “complex endocrine, metabolic, and nervous system signals” that control food intake below conscious level. This model attributes rising obesity prevalence to inexpensive, convenient, energy-dense, “ultra-processed” foods high in fat and sugar. An alternative view, the carbohydrate-insulin model (CIM), proposes that hormonal responses to highly processed carbohydrates shift energy partitioning toward deposition in adipose tissue, leaving fewer calories available for the body’s metabolic needs. Thus, increasing adiposity causes overeating to compensate for the sequestered calories. Here, we highlight robust contrasts in how the EBM and CIM view obesity pathophysiology and consider deficiencies in the EBM that impede paradigm testing and refinement. Rectifying these deficiencies should assume priority, as a constructive paradigm clash is needed to resolve long-standing scientific controversies and inform the design of new models to guide prevention and treatment. Nevertheless, public health action need not await resolution of this debate, as both models target processed carbohydrates as major drivers of obesity.

The energy balance model of obesity: beyond calories in, calories out

A recent Perspective article described the "carbohydrate-insulin model (CIM)" of obesity, asserting that it "better reflects knowledge on the biology of weight control" as compared with what was described as the "dominant energy balance model (EBM)," which fails to consider "biological mechanisms that promote weight gain." Unfortunately, the Perspective conflated and confused the principle of energy balance, a law of physics that is agnostic as to obesity mechanisms, with the EBM as a theoretical model of obesity that is firmly based on biology. In doing so, the authors presented a false choice between the CIM and a caricature of the EBM that does not reflect modern obesity science. Here, we present a more accurate description of the EBM where the brain is the primary organ responsible for body weight regulation operating mainly below our conscious awareness via complex endocrine, metabolic, and nervous system signals to control food intake in response to the body's dynamic energy needs as well as environmental influences. We also describe the recent history of the CIM and show how the latest "most comprehensive formulation" abandons a formerly central feature that required fat accumulation in adipose tissue to be the primary driver of positive energy balance. As such, the new CIM can be considered a special case of the more comprehensive EBM but with a narrower focus on diets high in glycemic load as the primary factor responsible for common obesity. We review data from a wide variety of studies that address the validity of each model and demonstrate that the EBM is a more robust theory of obesity than the CIM.

The energy balance model of obesity: beyond calories in, calories out

A recent Perspective article described the "carbohydrate-insulin model (CIM)" of obesity, asserting that it "better reflects knowledge on the biology of weight control" as compared with what was described as the "dominant energy balance model (EBM)," which fails to consider "biological mechanisms that promote weight gain." Unfortunately, the Perspective conflated and confused the principle of energy balance, a law of physics that is agnostic as to obesity mechanisms, with the EBM as a theoretical model of obesity that is firmly based on biology. In doing so, the authors presented a false choice between the CIM and a caricature of the EBM that does not reflect modern obesity science. Here, we present a more accurate description of the EBM where the brain is the primary organ responsible for body weight regulation operating mainly below our conscious awareness via complex endocrine, metabolic, and nervous system signals to control food intake in response to the body's dynamic energy needs as well as environmental influences. We also describe the recent history of the CIM and show how the latest "most comprehensive formulation" abandons a formerly central feature that required fat accumulation in adipose tissue to be the primary driver of positive energy balance. As such, the new CIM can be considered a special case of the more comprehensive EBM but with a narrower focus on diets high in glycemic load as the primary factor responsible for common obesity. We review data from a wide variety of studies that address the validity of each model and demonstrate that the EBM is a more robust theory of obesity than the CIM.

The carbohydrate-insulin model: a physiological perspective on the obesity pandemic

According to a commonly held view, the obesity pandemic is caused by overconsumption of modern, highly palatable, energy-dense processed foods, exacerbated by a sedentary lifestyle. However, obesity rates remain at historic highs, despite a persistent focus on eating less and moving more, as guided by the energy balance model (EBM). This public health failure may arise from a fundamental limitation of the EBM itself. Conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms that promote weight gain. An alternative paradigm, the carbohydrate-insulin model (CIM), proposes a reversal of causal direction. According to the CIM, increasing fat deposition in the body-resulting from the hormonal responses to a high-glycemic-load diet-drives positive energy balance. The CIM provides a conceptual framework with testable hypotheses for how various modifiable factors influence energy balance and fat storage. Rigorous research is needed to compare the validity of these 2 models, which have substantially different implications for obesity management, and to generate new models that best encompass the evidence.

Intermittent fasting for obesity and related disorders: unveiling myths, facts, and presumptions

Intermittent fasting (IF) is an increasingly popular method of weight loss, as an alternative to daily caloric restriction (DCR). Several forms of IF exist, such as alternate-day fasting or time-restricted feeding regimens. Some of its proponents claim several health benefits unrelated to caloric restriction or weight loss, which rely mainly on animal models. Although several studies published in the last few years confirm that IF can be a useful and safe therapeutical option for obesity and related disorders, no superiority to conventional caloric restriction diets have emerged. There are still several questions left answered. In this Review, we discuss some of the claims, unveiling myths, facts, and presumptions about several models of IF. The focus of this article is obesity, but there is a brief discussion of the potential benefits of IF on overall human health.

On the causal relationships between hyperinsulinaemia, insulin resistance, obesity and dysglycaemia in type 2 diabetes

Hundreds of millions of people are affected by hyperinsulinaemia, insulin resistance, obesity and the dysglycaemia that mark a common progression from metabolic health to type 2 diabetes. Although the relative contribution of these features and the order in which they appear may differ between individuals, the common clustering and seemingly progressive nature of type 2 diabetes aetiology has guided research and clinical practice in this area for decades. At the same time, lively debate around the causal relationships between these features has continued, as new data from human trials and highly controlled animal studies are presented. This 'For debate' article was prompted by the review in Diabetologia by Esser, Utzschneider and Kahn ( https://doi.org/10.1007/s00125-020-05245-x ), with the purpose of reviewing established and emerging data that provide insight into the relative contributions of hyperinsulinaemia and impaired glucose-stimulated insulin secretion in progressive stages between health, obesity and diabetes. It is concluded that these beta cell defects are not mutually exclusive and that they are both important, but at different stages.

Hyperinsulinemia in Obesity, Inflammation, and Cancer

The relative insufficiency of insulin secretion and/or insulin action causes diabetes. However, obesity and type 2 diabetes mellitus can be associated with an absolute increase in circulating insulin, a state known as hyperinsulinemia. Studies are beginning to elucidate the cause-effect relationships between hyperinsulinemia and numerous consequences of metabolic dysfunctions. Here, we review recent evidence demonstrating that hyperinsulinemia may play a role in inflammation, aging and development of cancers. In this review, we will focus on the consequences and mechanisms of excess insulin production and action, placing recent findings that have challenged dogma in the context of the existing body of literature. Where relevant, we elaborate on the role of specific signal transduction components in the actions of insulin and consequences of chronic hyperinsulinemia. By discussing the involvement of hyperinsulinemia in various metabolic and other chronic diseases, we may identify more effective therapeutics or lifestyle interventions for preventing or treating obesity, diabetes and cancer. We also seek to identify pertinent questions that are ripe for future investigation.