Observed high fat oxidation rates (over 1 gram per minute) in individuals on very low-carbohydrate diets are likely artifacts of gas exchange measurement, as demonstrated by a significant reduction (3-4 fold) in fat oxidation within three days of dietary change.

“there's an artifact in the uh uh metabolic heart um the metabolic heart measures uh gas exchange and and then through the equations it it it kind of says okay this got to be or this person must be burning fat or burning carbohydrates right um uh but it was calibrated the the equations are calibrated on high carb diets presumably yeah and so the thing is like as you exercise no matter what fuel you're using you you keep increasing oxygen consumption right but if you don't have much carbohydrates you're not going to produce much CO2 so that's going to uh tweak you know uh um um Mis or mis mislead that uh um stom metric equation because the uh the algorithm is going to think that oh W he's using a lot of oxygen and not producing enough CO2 so he's got to be burning a lot of fat”