I've noticed that same effect. Certain foods are worse than others (I stopped eating canned tuna). I know that this phenomenon is quite common for many people when they eat asparagus, and it has to do with an enzyme defficiency (but is not a health concern in those people). I would gather smelling other foods would be something similar, but with a different enzyme.

My long shot guess: Since enzymes are produced by the pancreas, and since it also has to produce insulin, stressing your pancreas with a heavy Sugar diet could cause this. I believe leaky gut leads to insulin spikes after eating, so it stands to reason that even a person with a normol diet but who has leaky gut could have a strained pancreas.

For now I'd suggest keeping a mental note of what foods make this happen. This might be difficult because it might not even be a particular food - it might be a combination. My own personal opinion is that most digestive disorders are caused by an unknown food allergy , and this allergy is commonly Gluten. Try cutting it outo for a couple of weeks and see what happens.