There are no significant side effects that you will experience by going on a three day diet. The three day weight loss plan consist of healthy foods items that will give you plenty of energy, so there is nothing much to worry about. But you need to keep in mind that miracles do not happen when it comes to weight and you will not lose much weight over three days. But you will become healthy and your body will become cleaner if you opt for a three day diet plan. Other than that there is nothing great about this type of diet.