Still Life with Loaves of Bread

The Carbohydrate Insulin Model, and Debates, Endure

A furious debate rages on. Are we meant to get half of our food energy from carbs? So naturally, this was a key theme of debates about dietary guidelines due soon from the USDA and HHS. But a quieter debate persists in the background. This is an ongoing discussion about the merits of the carbohydrate insulin model of energy balance. Can carbohydrates influence the energy that our bodies burn or store in a way that is important for treating or preventing obesity?

A new and very careful meta-analysis in the Journal of Nutrition suggests that this may be true.

29 Controlled Feeding Studies

David Ludwig and colleagues analyzed data from 29 controlled feeding studies. The duration of these studies varied from as little as one day to as much as 140 days. For this analysis, the researchers drew a line between studies of more or less than 2.5 weeks. Thus, they found that the duration did make a difference. In the shorter studies, subjects burned less energy on lower carb diets – about 15 fewer calories per day. But in the longer studies, they found subjects burning 50 calories per day more on lower carb diets.

The authors say that their results bolster the validity of the carbohydrate insulin model:

“This finding supports a prediction of the carbohydrate-insulin model and suggests a mechanism whereby dietary carbohydrate reduction could aid in the prevention and treatment of obesity.”

Debate Persists

This was a persuasive and rigorous analysis. The authors invited and acknowledged review and comments from a vocal skeptic of the model, Kevin Hall. We’ve witnessed any number of energetic disagreements between Ludwig and Hall on this subject. On Twitter, Hall still finds issues with the model, but also makes a small concession:

“Maybe long term low carb diets do increase expenditure, but the existing data aren’t compelling. The likely exaggerated long-term effect size in this study amounted to only ~135 kcal/d. If there’s a real effect, it’s probably even smaller than that. Still interesting though!”

We’ll take this as progress – a tiny bit of incremental clarity. But it is surely not the end of the ongoing debate about the importance of carbs in obesity. Where controlled feeding studies end, the messy world of real life takes over.

Click here for the new paper and here for more on the debate about carbs in the process of developing 2020 Dietary Guidelines for Americans. For perspective on the variability of results from low carb diets, click here.

Still Life with Loaves of Bread, painting by Ilya Mashkov / WikiArt

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December 17, 2020

One Response to “The Carbohydrate Insulin Model, and Debates, Endure”

  1. December 17, 2020 at 1:45 pm, David Brown said:

    The debate regarding carbs should have been settled years ago. Excerpt: (June 5, 1965) “Primary hyperglyceridemia is currently differentiated into the “fat-induced,” the “carbohydrate-induced,” and the “mixed” forms, according to the manner in which the patient’s plasma triglyceride level changes with varying proportions of fats and carbohydrates in the diet.”

    Excerpt: (Nov. 21,1964) Sixteen adults with metabolic syndrome…The results show that dietary and plasma saturated fat are not related, and that increasing dietary carbohydrate across a range of intakes promotes incremental increases in plasma palmitoleic acid, a biomarker consistently associated with adverse health outcomes.