Jesus taught his disciples the method of fasting in which they would gain the most from their sacrifice.
Mt 6:16 Fasting for Success
“Whenever you fast, do not put on a gloomy face as the hypocrites do, for they neglect their appearance so that they will be noticed by men when they are fasting. Truly I say to you, they have their reward in full.
“But you, when you fast, anoint your head and wash your face so that your fasting will not be noticed by men, but by your Father who is in secret; and your Father who sees what is done in secret will reward you.
Many Christians have read this scripture and only seen the part about doing your fasting in “Secret”, and missed the most important point. God wants to reward good behavior and that include fasting.