There is a difference between dieting and fasting. They both have one thing in common, restricting yourself from certain foods or eating altogether. The sole purpose for dieting is the physical health benefits that come with losing weight. Fasting is for the soul, and the purpose is to hear from God. Prayer accompanies fasting because you are seeking God for direction, healing, forgiveness, during times of grief, or for miracles. The foundation scripture above about fasting was preceded by Jesus teaching prayer - Matthew 6:5-13. I believe this was intentional because Jesus wanted to teach followers about prayer first, and then introduce fasting. Throughout scriptures you will see many examples of fasting.
Jesus - Matthew 4:1-4
Daniel - Daniel 9:3, Daniel 10:3
Moses - Exodus 34:28
Esther - Esther 4:16
Jehoshaphat - 2 Chronicles 20:3
David - 2 Samuel 12:16
Reading scriptures during fasting helps to see how God has blessed others during fasting and can help build your faith. This is a practical way to show God you take this time seriously. You want your fast to be focused entirely on speaking to and hearing from God. Fasting should not be for show because God will not honor it. Jesus strictly warns us not to let others know we are fasting. Scripture also tells us that some forms of healing and deliverance can only come by fasting. Fasting doesn’t guarantee you will receive what you are asking. Fasting lets God know you are waiting and seeking Him, and Him alone.
There are many ways to engage in fasting see the link below for guides on fastings.
DAY OF FASTING AND PRAYER GUIDELINES
Authors: Rick Warren, Bill Bright, Lance Witt
https://assets.speakcdn.com/assets/1927/prayer_fasting5.pdf