What percentage of energy comes from carbs?

45-65% of ones total calorie intake with teh emphasis on complex carbohydrates.

100 grams per day is presumed to be the smallest amount needed to maintain adequate blood glucose levels.

Recommended dietary allowance 130 g/day

When less than 50 grams per day is consumed, tissue proteins and fats are used for energy fuel.

taken from Human Anatomy and physiology book.