In the workout itself, yes, intheory. But studies have shown that over a 24h period, ingesting carbs pre-workout actually lead to a greater overall energy expenditure.
But it goes deeper than that.
When you are doing a “lifting” workout, fat will never be the primary fuel source (unless you are ona keto diet, in which case ketones can take over as the main fuel source). So who cares if ingesting carbs pre-workout decreases fat oxidation by a few grams??? It will not lead a signficant change in fat loss AT ALL.
Furthermore, the benefits of having the carbs pre-workout FAR outweight the potential drawbacks (if there were any).
Having carbs pre-workout decrease cortisol production. The main role of cortisol during a training session is to mobilized stored glycogen to use for fuel. If you already have glucose in your blood stream while training you don’t need to mobilize as much, thus your cortisol release is lower.
Pre-workout carbs increase mTOR activation from training. mTOR is the trigger that initiates protein synthesis, the more you activate it, the more protein synthesis you get. This obviously make it easier to build muscle.
Pre-workout carbs preserve muscle glycogen. From an energy standpoint it will give you more fuel for your workout, allowing you to training harder and longer with less negative drawbacks, but if you keep your intramuscular glycogen stores high you will be more anabolic due to cell swelling that trigger pressure receptors on the muscle tissue, initiating protein synthesis and decrease protein breakdown.
4.Consuming carbs along with protein pre-workout will allow you to more easily send those nutrients inside the muscle you are training, during the session. Making it easier to repair and rebuild that muscle.
If you want to miss out all of that to burn MAYBE 10g of fat more in the session (and over 24h it won’t even be higher), be my guess. But IMHO that’s just dumb.