Hi Raja,
If you are feeling weak, and you feel that it is because you are not eating enough, then you are probably right. I would not see it as a sign that you need to reduce your spiritual practices, just that you need to eat a bit more food.
I have found that the amount of food I need has changed over the years. Sometimes I have needed to eat more, sometimes less. Yogani talks about this in his book 'Diet, Shatkarmas and Amaroli'. He discusses the way our need for food changes as the kundalini process progresses. The book doesn't give you much advice about what to eat, but I found it helpful in dealing with the overall issue of how to manage diet whilst engaging in spiritual practices.
Christi