The Great Commandment is about loving the Lord with all of our heart.  Sometimes the Lord calls us to special prayer and fasting to zero our whole being toward the supremacy of God in our lives.  We lay aside things we like, enjoy and “love” for the One we are to love supremely.  It is an exercise of the heart and soul for a greater end than today’s pleasures or foods.  It is a good time to break our addictions to unhealthy eating choices.  It can be a first step to a new lifestyle changing the rest of our year. 

”Return to Me with all your heart, And with fasting, weeping and mourning; And rend your heart and not your garments.” Now return to the Lord your God, For He is gracious and compassionate, Slow to anger, abounding in lovingkindness And relenting of evil. Who knows whether He will not turn and relent And leave a blessing behind Him… Joel 2:12-15 (NASB)