What happens when you follow a very low carbohydrate diet?

What happens when you follow a very low carbohydrate diet? 

Info source:

http://www.m.webmd.com/food-recipes/features/how-food-affects-your-moods?page=2

So what happens when you follow a very low carbohydrate diet? According to researchers from Arizona State University, a very low carbohydrate (ketogenic) diet was found to enhance fatigue and reduce the desire to exercise in overweight adults after just two weeks.