The answer is simple: Eat food. Mostly plants. Not too much.
When you say wheat, do you mean processed and refined flour? And by potatoes, do you mean chips and fries?
Potatoes are loaded with vitamins and minerals. Some of the starch isn't easily digestible and acts similarly to fiber (in addition to the fiber found in the skin).
The fact that they are little bombs of nutrition aside (along with sweet potatoes, yummm!), they will also keep fresh for months.
source: Most meat is corn http://www.scientificamerican.com/article.cfm?id=that-burger...
most everything we eat is from corn http://www.ecoliteracy.org/essays/we-are-what-we-eat
Don't mean to be flippant, but it kinda sounds like you lumped potatoes in with corn for the sake of it.
See Jeremy Rifkin's: Beef, if you want to read up on a fascinating piece of North American history. Nice fatty corn fed beef was (and probably still is) highly prized.
I don't doubt that carbohydrate consumption has gone up and with it, suspiciously, so too has obesity. But I can't help but think we should be looking at the package containing these newly consumed carbohydrates.
A mars bars contains 40g of carbohydrate...are people grouping that with 40g of carbohydrates yielded by potatoes and wheat?
Nothing gets me ranting like the old "everything in moderation" line.
(Those are subrreddits.)
In short: coconut oil (also palm oil) will be useful after you use it to fry, while olive oil will stop being olive oil after just some heating. In fact, do not fry anything with olive oil. Olive oil should be added to food in your plate only.