Just wondering which is better fat vs carb for immediate energy (say 1-6 hrs) and if they differ in terms of thinking clearer/could perform better physically?
Not sure what you mean by ‘immediate energy (say 1-6 hrs)’ but substrate utilization (carbs or fat) are governed by intensity and influenced by duration. Generally fat metabolism occurs at lower intensities and carbs at higher intensities. As for energy density per gram, fat is far more energy rich than carbohydrate.
Carbs would be faster. They start digesting in your mouth whereas fat doesn’t start digesting until the stomach.
Glucose, the simplest carb molecule, is found in simple carb foods like table sugar. They are absorbed very fast which causes a spike in blood sugar. Many athleles use gels with glucose to have quick digestible energy. Fat can be broken down into glucose but it takes longer.
That being said, it is good to have a balance of fats, carbs, and proteins to help sustain your energy long term. The carbs will be digested first and then the protein and fat.