I was just browsing and not deeply knowledgeable about the warrior diet but even if you don't eat during the day I think you do not have to worry about not getting enough calories. Over the years I've come to a deep conviction that we eat far more food than our bodies need, especially in America.
If you read up on Calorie Restriction http://www.calorierestriction.org/
you will see some support for this, however due to the loss of nutrition in food, getting enough nutrients is more difficult. Part of the CR plan is to eat foods that are low in calories and high in nutrients. We do not need a lot of calories.
That being said, it makes sense to try to eat a high percentage of nutritious foods if you are restricting (i.e. not eating during the day). Also, in spite of "common" wisdom, I have found personally that dietary fiber in the forms of grains is VERY constipating. What has helped me is taking water with unprocessed Sea Salthttp://www.watercure.com
and eating minimal grains/dairy.