Consumption of Carbohydrates, Fat, and Protein
We adapt to our environment. Some better than others. We can up-regulate and down-regulate hormones and enzymes, change cellular structure (which changes efficiency of substrate utilization), all by changing our activity patterns (Epigenetics) and something else: what we consume (Nutragenomics).
So a logical question is “If I consume less carbohydrate and more fat (and protein) will my body adapt by becoming more efficient at utilizing that fat; will I then burn more fat? Again, if the genetics allow for it, yes! If not, not so much.
It’s important to remember here that both your brain and your muscle tissue use about 20% of your total daily energy needs respectively and for the muscle tissue that only increases when you are active. So ultimately what kind of muscle tissue you have, or can shift via training will play a role in your ability to burn fats and/or carbohydrates efficiently both at rest and during activity.
The real problem with carbohydrates seems to be the kinds of carbs we are consuming in the standard American diet. Way too much sugar and processed carbohydrates and way too few vegetables, fruits and whole grains. That however, is an entirely different post.