Many people have a guilt complex about Christmas. It is a time to eat to excess. Overeaters plan to suffer later to rip away the pounds gained by Christmas. Unfortunately, future suffering from fasting and exercise won't work. Perhaps people do it to reduce the guilt while knowing that weight reduction will only be temporary.
Detox diets are really myths. They can harm your body damaging the liver. Eating a lot doesn't necessarily build up toxins anyway. One's weight is genetically determined. If you reduce what you generally eat your body will slow the metabolism making weight loss more difficult. Ironically, eating less will increase your appetite as the body feels you need to go up to your determined weight level.
The best you can hope for is to change the balance of fat and muscle while accepting that your overall weight will not change. Cut out the carbs and eat more vegetables, fruit and lean meat. The real problem today is not really food intake. It is the high consumption of soft drinks packed with sugar. Sugar is pure carbohydrate which is transformed into fat by the body. While many will not accept the fact, consuming soft drinks seems to be addictive.