Cells can't use glucose and fatty acids simultaneously. What regulates this is how much glucose is in the bloodstream. What regulates that is how much carbohydrates we eat. Incidentally, this is also how we regulate fat accumulation. Cutting carbs will allow fat to be released from fat cells and will allow cells to use fatty acids for fuel. It's easy to see how we can disrupt these functions by eating carbs.

However, women here on the forum have said they feel better when they eat a bit more carbs. Whether it's around their workout or not I don't know. I don't advise to do this but if you do, go with things like berries instead of grains for example.

If you're like me and simply refuse to eat carbs, then I'd go with J-Lo's advice about coconut oil. Unlike J-Lo, I don't know about it from personal experience but based on what I read about it lately including what she just wrote here, I'd have to agree with her on the effect of coconut oil. If all else fails, there's always the option to eat a bit more animal fat like lard, suet and tallow to name a few. I prefer cured bacon myself.

About the argument to eat more carbs. It's simple, if you eat carbs, you'll use glucose for fuel. If you eat fat, you'll use fat for fuel. But which fat do I use up, you ask? Any fat, including the one in your fat cells. I mean, it's not like you can grow lean by using glucose for fuel since there isn't any in your fat cells to be used up. Unless, of course, you eat some. Then it's back to square one. That's the gist of it.