Fat free oil substitute for frying/sautéing and curries

Debating health is off topic here, but I think I can answer some of your question. Since you mentioned Chow Mein. I would start by saying that technically speaking you can NOT cook Chow Mein without oil. Chow directly translates to "fried" and Mein translates to "noodle". As frying (even stir/wok/pan frying in this case) by definition requires oil...

Now, can you cook noodles and sauce without oil? Sure, but it'd make a slightly different dish. You could boil the noodles for example, grill or steam the meat/vegetables and then mix it all together with sauce. You could still probably make a good dish this way. You won't get a typical chow mein though.

Chow mein aside, you could probably take a really good non stick or seasoned pan/wok and simply cook the meat/vegetables with a bit of water/broth. You'd essentially be lightly steaming it.

Though as an alternate suggestion, I would instead start with looking for dishes that utilised other cooking techniques, boiling, braising, steaming, grilling as examples. Also, can you use a, very, very small amount of oil? With the right pan a little bit goes a long way.

If you're eating meat/nuts/other things you'll get fat anyway though, some oils suitable for cooking are pretty good for you. I'd also, suggest talking to a doctor/nutritionist about how much oils are okay and which oils are okay. Not all fats are equal and humans need some fat to survive.

The fat is essential for the flavor many dishes. Curries were mentioned, and they are a prime example of a dish that would taste horrible without any fat (butter, oil, coconut products ... all are rich in fat, on a smaller scale even some of the spices are!) since the flavor from the spices would not well distribute into the sauce without fat.

If you want to REDUCE the amount of fat in a mixed-vegetable sauced dish and still get a better texture than just boiling the vegetables, oven roasting (marinated in some of the sauce for example!) is often a great alternative.

Substitutes that act like fat taste/texture wise but do not have the nutritional properties have been tried in the food industry - and failed, see Olestra (which was/is such a substitute, which turned out to have no calories indeed but unpleasant and unhealthy side effects).

Fat imparts (what most people consider good) flavor and will take a high temperature. So it is great for cooking (frying).

Even if you take flavor out the equation there is no fat substitute for frying (that I am aware of). It would be great if there was a synthetic fat that the body did not treat as fat. It is one thing to get your body not to break it down as calories. It is another thing to not have it clog veins and arteries.

With technique you can reduce the amount of fat used to fry.

You can saute vegetables with just wine (or another liquid) in a good non-stick pan. I like a fat free bitter orange marinade. Not the same flavors but your taste buds adjust over time.

Not in your question but for salad dressing balsamic vinegar and a squeeze of lime.

There are many dishes where there is just plain no good non-fried alternative. You need to adjust your diet.

For saucy curries, a masala based on onion and perhaps some tomato can be prepared with little to no oil. I have been able to cut way back on coconut cream and other fatty ingredients in this way.

https://greatcurryrecipes.net/2011/06/24/curry-base-sauce/

Is a good all around base for anything from Dhansak to Thai