The point I was trying to get across to you is that when you reduce your carbs to where your body enters ketosis carbs are no longer your primary means of energy. You still take in small amounts durning the day to support normal brain function.
So in this diets carbs do not = energy and as other have said it works!
Keep in mind this diet is generally not used to bulk though some use it that way. We are trying to keep muscle here not so much gain. So yes during a bulking stage I intake as even and clean bulking diet that I can carbs help make up the calories in that diet. During this time I do recieve my energy from carbs and enjoy eating almsot everything!
Once your body is buring fat as fuel your energy levels are normal and you have no trouble functioning during normal activities however, when running or heavy leight lifting the carb stores in your body will be used to support energy as the body can not burn fat fast enough to provide the energy needed.
Some runners deplete carb stores during the week and load up before their next run this is known as supersaturation. when the body is in a depleted state it will allow for maxium carb intake past the normal (balanced) levels thus givings runners more energy and endurance. Clearly you would not want to be in a ketosis state trying to run a marathon.
Some info like I said not all runner do this but it has been used.
Eating for Endurance Running | Nutrition for Runners
low carbohydrate diet (less than 50 grams) causes an increase in muscle glycogen storing enzymes. Therefore, starting 6 days from your event, "depleting" muscle glycogen with this 3-day low carb diet (exercising intensely on all three days as well), you can set your body up for a "rebound" of carbohydrate storage during the three days immediately prior to the event. For those next three days, you simply rest, eat a very high carb diet (10 grams of carbohydrate per kilogram of bodyweight), and watch your muscles swell up with energy.