Although glucose is vital to your health as an important source of energy for your body and your brain's main source of fuel, too much glucose in your blood can lead to serious health problems.
When you feel tired after eating a heavy meal, what you consumed was probably high glycemic. High glycemic foods produce a quick rise and quick dip in your glucose levels in the 2-3 hours after you eat. In contrast, low glycemic foods help to sustain energy longer, with a gradual rise and fall in your glucose levels.