Although there are proven weight loss advantages to low carb dieting and many people are successful doing it, it doesn't work for everyone (contrary to popular belief). In reality, most people feel better eating a low-to-medium amount of carbohydrates, rather than very low carb (ketogenic).
Roughly half (45-55%) of total calories.
Best If You:
Are an athlete or work out a lot and have good insulin sensitivity. That is, BOTH of the following are true:
You are depleting glycogen regularly through daily (or almost daily) workouts
You function well on carbs: you feel good after eating carbs, with no major energy swings.
Can Also Work If:
You choose Levels 5, 6, and 7 foods (see below) ... eating strictly "low-glycemic index" starches can help loosen stubborn fat much like an overall low-carb diet
You eat strategically to reduce carb impact (eat w/protein, fiber, fat; spread out over multiple meals...see below)
Low-carb: Somewhere above 100 grams per day; May need above 140 grams to avoid ketosis; 20% of total calories is also considered low-carb.
Medium-carb: Roughly 30 - 45% of total calories.
Works Well For:
A wide variety of people both active or inactive who have no need for ketogenic carb levels but want to enjoy the weight loss benefits of lower carb
Lower carb (versus High Carb diet) tends to enhance stubborn body fat mobilization, particularly lower body fat, due to lower muscle glycogen levels
Better hunger control due to 1) fewer total carbs in the diet (fewer energy crashes, particularly if insulin resistant) -- and 2) from greater amounts of protein, fiber, and fats in diet (slows gastric emptying)
You can still eat some Refined Carbs (Level 1 - 3) with fewer energy problems due to overall lower carb intake in diet
Ketogenic (very low-to-no carb)
Less than 100 grams carbs per day. The lower you go, the greater your level of ketosis (higher numbers of ketone bodies from fat burning).
Best If You: (any of the following)
You are currently moderately lean and want to reach the lowest fat levels but have stubborn fat
Are sedentary, inactive or only do low-intensity activity like walking
Have extreme insulin resistance; you should see improved energy, hunger control, better health, and possibly better fat loss
Have extreme carb addiction
Are genetically better suited to burn fat: you feel better running on fat versus carbs
Are on a very-low-calorie or rapid loss diet where you need to reduce all unnecessary calories
Ketogenic diets work tremendously well for some, terribly for others. If you feel terrible on a ketogenic diet, you may still benefit from low-carb -- just not at ketogenic levels. Other people burn carbs or fats equally well (metabolically flexible).
If you are an athlete and/or are exercising with higher intensity you will need to use various carb cycling methods to replenish liver and muscle glycogen (see Carb Refeeds).