Talking about nutrition isn't a very smart idea since people don't like to hear about it, especially when it doesn't match their current nutrition plan, therefore I don't like to post in this section of the forum.
Anyway, since you are asking I'll give my two cents...
The concept is that is very rare for an individual to be able to utilize fats efficiently as an energy source, including glycogenesis.
Because we are very opportunistic and sugars are an "easier" form to get glycogen from we tend to embrace the lazy metabolism style of preferring them, especially if an enough amount is constantly given.
When one drops below a certain level of sugars intake the metabolism doesn't just jump on fats for its needs but rather goes in strike mode, it means you don't feel very well at all (low blood sugar).
There are two ways here: either you reduce sugars quite abruptly and suffer for a few days (or weeks) or you reduce them slowly and progressively in order to give time to the metabolism to adapt to new demand without going into strike mode.
Some people manage better than others to abruptly change sugars intake, for some it is almost impossible due to the discomfort implications involved.
Based on an experience developed in many years I suggest the second option even if it is slower and snobbed by many in this fast world where everything as to be accomplished...yesterday.
A very common and huge mistake is to lower sugars intake without at the same time increasing A LOT the consumption of other foods, especially fat rich ones.
Usually whom decide to reduce sugars has a weight loss goal and the concept to INCREASE the total amounts of calories intake is hard to nail in.
The concept of calories itself is a load of crap, but that is another story, or better is the same story but will require a very long discussion I am not sure I am willing to start.
