Eating a sugary cupcake or doughnut may temporarily spike your blood sugar levels making you feel happy and satisfied but as soon as they return to normal you are left feeling all the more irritable.
Fast food is packed with refined carbohydrates which cause your blood sugar levels to fluctuate rapidly. If your sugar levels dip to a very low level, it can cause anxiety, confusion and fatigue. With high content of sugar and fats, you tend to eat too fast and too much to satisfy your cravings. This can inculcate an impatient behaviour while dealing with other things. Fast foods and processed foods may be laden with artificial flavourings and preservatives like sodium benzoate that tends to increase hyperactivity.