What’s the recommended daily sugar intake (in grams and calories)? Does it differ by adult/children, female/male, weight/height/BMI, ethnicity, and also weight loss goals?
These are great questions.
You ask first what is the daily recommendation for sugar. I do not recommend ANY daily sugar intake. It is simply not necessary to eat sugar. You will get all the sugar you need to fuel your body through natural foods such as fruits and vegetables. If you are asking what are the daily requirements for carbohydrates, this will depend on what type of food plan you wish to follow (see below). I would recommend a lower carb, moderate protein and moderate to higher fat diet.
How to best limit your sugar intake really depends on if you are a food addict. If you are not addicted to sugar, you may find that you can gradually reduce your intake until you have reached the amount that you are comfortable eating. However, if you are addicted to food, or have an emotional dependence on it, and want to stop eating sugar completely, I would suggest cold turkey. A gradual reduction only prolongs the withdrawal period and will make it harder to stay quit. A quick stop, and you will find that in three to four weeks, you will no longer crave sugar.
Many people do experience withdrawal symptoms from a sugar detox. These are irritability, fogginess, lethargy, cravings, restlessness, insomnia, dizziness.
The Atkins diet is just one example of a low carb diet. It is perhaps the best known because it is the first low carb diet that caused a media sensation in the 1970s and 80s. Against popular medical advice that stated that we should cut fats and proteins, Atkins advocated a diet rich with proteins and fats and very few carbs.
There are now many other popular low carb diets available – many are very similar to Atkins. There are the Paleo diets (Caveman diets) that emphasize primarily proteins, fats and vegetables. There is the Glycemic index diet that does not limit carb content but does recommend complex carbs over simple carbs. There are the higher fat diets, that recommend low carb, moderate protein and high fats. All of these would benefit a food addict. I would recommend that you find the one which suits you the most.
Here are some useful links explaining Nutrition: