¹ “Shout it aloud, do not hold back.
   Raise your voice like a trumpet.
Declare to my people their rebellion
   and to the descendants of Jacob their sins.
² For day after day they seek me out;
   they seem eager to know my ways,
as if they were a nation that does what is right
   and has not forsaken the commands of its God.
They ask me for just decisions
   and seem eager for God to come near them.
³ ‘Why have we fasted,’ they say,
   ‘and you have not seen it?
Why have we humbled ourselves,
   and you have not noticed?’
   “Yet on the day of your fasting, you do as you please
   and exploit all your workers.
⁴ Your fasting ends in quarreling and strife,
   and in striking each other with wicked fists.
You cannot fast as you do today
   and expect your voice to be heard on high.
⁵ Is this the kind of fast I have chosen,
   only a day for people to humble themselves?
Is it only for bowing one’s head like a reed
   and for lying in sackcloth and ashes?
Is that what you call a fast,
   a day acceptable to the LORD?
 ⁶ “Is not this the kind of fasting I have chosen:
to loose the chains of injustice
   and untie the cords of the yoke,
to set the oppressed free
   and break every yoke?
⁷ Is it not to share your food with the hungry
   and to provide the poor wanderer with shelter—
when you see the naked, to clothe them,
   and not to turn away from your own flesh and blood?
⁸ Then your light will break forth like the dawn,
   and your healing will quickly appear;
then your righteousness will go before you,
   and the glory of the LORD will be your rear guard.
⁹ Then you will call, and the LORD will answer;
   you will cry for help, and he will say: Here am I.
   “If you do away with the yoke of oppression,
   with the pointing finger and malicious talk,
¹⁰ and if you spend yourselves in behalf of the hungry
   and satisfy the needs of the oppressed,
then your light will rise in the darkness,
   and your night will become like the noonday.
¹¹ The LORD will guide you always;
   he will satisfy your needs in a sun-scorched land
   and will strengthen your frame.
You will be like a well-watered garden,
   like a spring whose waters never fail.
¹² Your people will rebuild the ancient ruins
   and will raise up the age-old foundations;
you will be called Repairer of Broken Walls,
   Restorer of Streets with Dwellings.
              –Isaiah 58:1-12

Fasting is about much more than food.  The idea behind our fast is not merely to go without food or something else.  Instead, as we enter into sincere repentance, all of our relationships should begin to change.  As I am fasting, praying more, seeking God more in the scriptures, the way I treat others should also change.  Maybe in your case, you might not quarrel with your spouse as much or raise your voice at your children.  Perhaps you will find yourself treating your boss with more respect or colleagues with less sarcasm.