It is common to think that after exercise, if you make a carbohydrate intake, fat oxidation will be completely stopped (since insulin is elevated and this a priori stops the “burning” of fat), being that athletes or subjects who are in a phase of fat loss, hesitate between whether or not to eat carbohydrates post exercise, as they do not want to inhibit fat oxidation, but want to replenish muscle glycogen. This is also a concern among subjects seeking body recomposition, as they want to lose fat while improving their muscle mass, and the latter benefits from having glycogen in their stores as it will help this process.
Not to mention that whether fat is lost or not will be mainly induced by the total energy balance and not by the acute intake of a macro nutrient, it should also be remembered that it is not a mistake to think that after exercise the “burning” of fat will stop completely by ingesting carbohydrates.
As we see in the image of the Andersson-Hall et al 2018 study, despite ingesting carbohydrates post-workout, the fat oxidation rate was still very high, above pre-exercise values. In addition, 2 hours after ingesting the high-carbohydrate meal, the rate of fat oxidation was almost equal to that of the control group and the group that consumed protein.
It is evident that part of those carbohydrates will be used as a post-workout energy source, but another part will be used for other purposes and with other destinations.
And just like the compensation that occurs in other physiological examples when we talk about energy substrates used, in this context, at two hours the fat oxidation rates are practically equalized regardless of whether or not carbohydrates have been ingested post-workout.
As always, the human being tends to think in linear and acute, without understanding the globality and redundancy that human physiology almost always shows.