The quick down and dirty and gritty on why Carbs as a macronutrient is Key to utilize as a primary energy source for life. Carbs get labeled as bad or the reason for someone being fat/de-conditioned.  The bigger reason may ben that someone is eating the wrong things in either in excess or not enough. When we don't eat enough our body goes into survival mode and will feed off the ready fuel sources (fat comes first at lower energy expenditure levels, aka fat burner mode). However this will be different than doing Intermittent fasting (save that for another episode). I.F. Yes your naturally in a deficit BUT you still need to be eating enough maintenance calories/macros when in the eating window