Matthew 6:17-18

When you fast, put oil on your head and wash your face, so that it will not be obvious to others that you are fasting, but only to your Father, who is unseen; and your Father, who sees what is done in secret, will reward you. 

Martin Luther, in speaking about there being no requirement to fast said,

“Care must be taken, lest out of this freedom [from fasting and abstinence] there grows a lazy indifference about killing the wantonness of the flesh; for the roguish [son of] Adam is exceedingly tricky in looking for permission for himself, and in pleading the ruin of the body or of the mind; so some men jump right in and say it is neither necessary nor commanded to fast or to mortify the flesh, and are ready to eat this and that without fear, just as if they had for a long time had much experience of fasting, although they have never tried it.”
~ (Treatise on Good Works XXI)

In light of Luther’s contention about the devious aspects of our sinful flesh, let’s recenter around God once again.