No. Carbs are sugars. Fats are comprised mainly of lipids. Some fats can contain sugar-like structures, but most are fairly linear hydrocarbon chains.(whereas sugars are based on carbon rings) Naturally occuring fats usually have phosphate and/or protein accessory groups attached to the lipids.
Also no. Iron oxide(rust) is different from ferritin(iron-storage protein) or haeme(iron-containing oxygen transport protein) or any other iron-containing molecule, or even elemental iron. There are many sources of iron our body can utilize, but we use different processes to obtain that iron depending on what form it is in. Some forms can be metabolized more or less efficiently than others, and some can produce toxic byproducts when metabolized(or can be toxic in their raw form)
Insulin is insulin. It’s a compound with a very specific formulation and structure. Regardless whether it is naturally occurring or synthetic, it is always exactly the same. That said, there may be a difference between injecting insulin and having a natural insulin response, despite the insulin itself being identical in both cases; there may be other processes at work during a natural insulin response which are unrelated to insulin but assist with the process. But that doesn’t mean synthetic insulin is bad. It doesn’t mean anything regarding synthetic insulin at all.
It’s not so much about the intestines as it is about the flora living in them and the enzymes floating around in there, but okay. Some processed foods can be harder to digest, for sure. But the same can be said for many unprocessed foods. Ever tried eating raw meat? Raw potatoes? Grass? I think a can of spam would definitely be easier to digest than any of those unprocessed foods. “Synthetic” or “natural” has nothing to do with it, though. Nothing is inherently good or bad just because it was made by nature or by humans. There are good and bad things under both categories, but what gives them those qualities has nothing to do with where they came from.