In case anyone is interested, this thread includes a more specific set of methodological critiques made by Dr. Kevin Hall at this week's ObesityWeek conference (unfortunately does not include Dr. Ludwig's rebuttal):
https://twitter.com/YoniFreedhoff/status/1062760576869371910
Hall's research focus is on mathematical metabolism models, so his critique comes from that angle: it is possible doubly-labeled water measurements of energy expenditure may behave differently in a lower-carb environment, so the observed EE difference may not be meaningful. Ludwig actually briefly addresses this in their published paper, citing a few other studies suggesting that DLW is accurate and carb intake does not mess with isotopic measurements.
Hard to tell if this is a meaningful advance for the low-carb crowd, or just an artifact of insufficiently validated methodology.
Hall's research focus is on mathematical metabolism models, so his critique comes from that angle: it is possible doubly-labeled water measurements of energy expenditure may behave differently in a lower-carb environment, so the observed EE difference may not be meaningful. Ludwig actually briefly addresses this in their published paper, citing a few other studies suggesting that DLW is accurate and carb intake does not mess with isotopic measurements.
Hard to tell if this is a meaningful advance for the low-carb crowd, or just an artifact of insufficiently validated methodology.