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

 Overview: This article is a review of the literature to date comparing the old school “energy-balance” model (calories in vs. calories out) of weight gain/loss to a more metabolically model, the “carbohydrate-insulin” model which takes into account the effects of insulin and other hormones which are moderated by the types of calories consumed.

 Key Points: 

For over a century, obesity has been viewed as solely a problem of excess caloric intake vs. caloric expenditure…the “energy-balance” model.  

In this model, intake of highly processed, hyperpalatable foods is considered as the main driver of a positive energy balance and ultimately accumulation of body fat.  

Surprisingly, the authors cite evidence that there is little evidence hyperpalatability actually drives overconsumption. 

The carbohydrate-insulin model (CIM) looks beyond mere caloric intake to also account for the effects of processed foods with their high glycemic loads to drive excess fat accumulation primarily via the actions of insulin.  

 “Glycemic Load” or GL, (Total Carbohydrate Content multiplied by the Glycemic Index) takes into account not only the amount of carbs in a particular food, but also the speed with which those carbs actually raise blood sugar levels. 

High-GL foods include processed grains such as wheat and rice, potato products, and sugary foods will raise blood sugar levels rapidly increasing insulin production and forcing glucose storage into liver, muscle, and fat tissues.  

Low-Moderate GL foods, which include most fresh whole fruits, whole grains, legumes, nuts, and non starchy vegetables, tend to break down more slowly and invoke more moderated insulin responses.  

Conversely, fats and proteins which by definition have zero carbohydrates will have “little to no direct impact on blood glucose levels”. 

The authors state that modern diets, particularly in the era of “low-fat” popularity, to have particularly high glycemic loads both from an increase in the total amount of carbohydrate consumption and the shift to more tasty, refined carbohydrates.

 The net effect is that high GL meals force insulin secretion setting off a chain of events:

·         High insulin drives rapid uptake/storage of glucose as fat.

·         Over 2-3 hours glucose levels fall rapidly often to levels below that of a full fasting state.

·        ·The brain perceives lower glucose levels as a need for more fuel and stimulates cravings for more high GL foods setting the stage for a vicious cycle.

 Although numerous challenges have been put forth to challenge the validity of  the upstart Carbohydrate-Insulin Model (and consequently support the long established Energy Balance Model) the authors address these challenges in a clear, concise manner and offer this paper as a step forward.    

Author’s Conclusions: “If the CIM is substantially correct, then the strategy to produce a negative energy balance through conscious control of food amount and physical activity level is likely to fail for many people. Restricting energy intake when consuming a high-GL diet would neither lessen the predisposition to fat storage nor diminish hunger during dieting. (emphasis ours) 

Reviewer's Comments: Most of our readership will quickly realize this paper is a formal statement of the clash between the antiquated but long established Energy Balance Model, and the newer, more elegant “low carb” school of thought (Carbohydrate-Insulin Model) which has been growing and refining itself since the 1970’s. 

Old paradigms don’t generally die quietly, but die they must. We now have a much better understanding of how and why weight loss programs which simply exhort our patients to “eat less, exercise more” so often fail at the human level.

Reviewer:  Mark R. Payne DC 

Reference: David S Ludwig, Louis J Aronne, Arne Astrup, Rafael de Cabo, Lewis C Cantley, Mark I Friedman, Steven B Heymsfield, James D Johnson, Janet C King, Ronald M Krauss. The carbohydrate-insulin model: a physiological perspective on the obesity pandemic The American Journal of Clinical Nutrition, 13 September 2021

 Link To Full Text: https://academic.oup.com/ajcn/advance-article/doi/10.1093/ajcn/nqab270/6369073