A Serious Challenge to the 2012 Low-carbohydrate "Metabolic Advantage" Study

Warning: this post will be a bit more wonkish than usual, because I need to get detailed to make my points.  To read a summary, skip to the end.

In 2012, David Ludwig's group published an interesting RCT that suggested a substantial "metabolic advantage" resulting from a high-protein, very-low-carbohydrate diet (VLC) (1).  In other words, this diet led to a higher energy expenditure relative to a normal-protein, low-fat diet (LF) over a one month period (a low-glycemic-load, normal-protein diet was in the middle and not significantly different from the other two).  Resting energy expenditure (REE) was slightly but significantly higher on the VLC diet, and total energy expenditure (TEE) was elevated by a whopping 300+ kcal/day!  I covered the study at the time, describing it as "fascinating" and "groundbreaking", and calling for the study to be replicated so we can be more confident in its unexpected result (2).

This finding has been used by Ludwig, Gary Taubes, and others to support the carbohydrate-insulin hypothesis of obesity, although there is no evidence that the effect was mediated by insulin, and also no evidence that it was mediated by reduced carbohydrate rather than increased protein (3).

Since I published that post, my confidence in the finding-- and particularly the common interpretation of it that reducing carbohydrate intake to a very low level increases REE and TEE-- has gradually been eroding.  This is partially because other studies have generally reported that the carbohydrate:fat ratio of the diet has little or no effect on REE, TEE, or fat storage (4, 5, 6, 7, 8, 9, 10).

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