Is it still valid to fast today?

Fasting is synonymous with intercessory prayer, and prayer warriors typically testify that fasting weakens the flesh and heightens the spiritual senses. Is this biblically true or is this just a noble mindset? 

Before I get into the scriptures, I do want to say that for us in the grace dispensation, fasting is a personal choice and not a biblical instruction. Paul (our apostle, Romans 11:13), does not explicitly instruct us to fast. His only reference is a personal instruction found in 1 Cor.7:5. See more in the footnote*. The person who chooses to fast must understand that it is more for their own purposes; to focus themselves, to buffet their flesh, or to remind them of their cause. Fasting has no spiritual purpose today. It cannot influence God, it cannot make your prayers more effective, it cannot manipulate the outcomes. So, if you choose to fast, know that it's real purpose is more for your personal sake than it is for your prayer sake. It's more to keep your flesh in line with your prayer goals than to add any more spiritual value, power, or effectiveness to your prayers.

Fasting was a requirement for Israel under their law program, but it is not a ritual or a requirement in the Body of Christ today.

For sin shall not have dominion over you: for ye are not under the law, but under grace. Rom.6:14

We do not need fasting, self-sacrifice, or any form of work to add to, or improve our prayer times, or our standing before God. Christ did that for us through His cross work (Rom.6:3-6). Through this most perfect work of grace, we, having died with Christ, are resurrected into a new creation, and freely participate in the mysteries of God's wisdom and grace.

The mystery of Christ in us gives us all spiritual blessings of forgiveness, grace, redemption, salvation, and peace with God through faith in the gospel of Christ (Eph.1:3).

To the praise of the glory of his grace, wherein he hath made us accepted in the beloved. In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace; Wherein he hath abounded toward us in all wisdom and prudence; Having made known unto us the mystery of his will… Eph.1:6-9

What a privilege and a joy to have the riches of God’s grace! We are no longer a child who needs to conform to conditions and regulations. We do not need to be instructed by law, neither do we need to do works to merit God's approval or acceptance. We do not need to be told what to eat or not to eat (1 Tim 4:4). For what spiritual benefit would fasting gain for us that we do not already possess in Christ freely?

Whether we eat or not does not change our position or our blessings in Christ. Neither eating nor fasting commends us to God, but Christ (1 Cor.8:8, Col.1:27).

Let no man therefore judge you in meat, or in drink, or in respect of an holyday… Col.2:16

Those who think that God will answer their prayers if they can prove to Him their sincerity or who think that by their sacrifice God will hear them, end up making it a work of the flesh, a tool to manipulate God's will or boost their egos and spiritual stance with regards to performance or acceptance.

As a matter of fact, fasting should be very carefully considered and practiced, and one's heart should be evaluated to determine the true motive for using this ordinance.

Matthew 6:16-18, Moreover when ye fast, be not, as the hypocrites, of a sad countenance: for they disfigure their faces, that they may appear unto men to fast. Verily I say unto you, They have their reward. 17 But thou, when thou fastest, anoint thine head, and wash thy face; 18 That thou appear not unto men to fast, but unto thy Father which is in secret: and thy Father, which seeth in secret, shall reward thee openly

As an example, notice how fasting in Judaism eventually became a worthless religious practice. The Lord Jesus lamented that some people no longer fasted in faith. They just did it to feel religious, to stroke their egos, to show off, and to brag to others, "Look at how faithful I am to God! I am so holy and pious because I fast often!" Notice how the Pharisee bragged, "I fast twice in the week, I give tithes of all that I possess" (Luke 18:12). The fasting here was not done in faith. It was just some mindless religious ritual performed so one could then boast of his "faithfulness" and his "holiness." We want to avoid this should we choose to fast.

Fasting is a valid practice today, but it is not an instruction from the epistles of Paul and it is not a spiritual tool to fast-track or supercharge prayer. Fasting plays no role in the effectiveness of your prayers, nor does it add any more power to it. It is something one can do by choice for the flesh sake, but remember to check your hearts motives and be careful not to use it to exploit others or to gain from it.

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*The Apostle Paul never tells us that we must fast (no, that would be religion that makes such demands). Saint Paul does instruct that husbands and wives who have agreed not to be intimate for a time, are to "give [themselves] to fasting and prayer" (1 Corinthians 7:5). Why would this be necessary? Remember, the verse continues, "and come together again, that Satan tempt you not for your incontinency [lack of self-control]." One of God's designs in marriage is to fulfill the natural sexual urge (libido). If sexual intercourse is lacking in the marriage relationship, Satan can eventually use this to his advantage. Those desires, if not satisfied by the spouse, can lead to extramarital affairs. Self-control will be gone. Recall that fasting and prayer were done in Scripture during times of peril (danger) or distress (sadness, depression). A marriage without intimacy is vulnerable to Satan's attacks, and people physically separated from their spouses are (or at least should be!) missing them. Evidently, prayer and fasting are the means whereby God strengthens ("self-controls") Christians who cannot be (or have agreed not to be) intimate with their spouses for a specific period. The Pauline doctrine on marriage (1 Corinthians chapter 7) will equip the married saints praying that doctrine. God's Word will effectually work in them that believe, 1 Thessalonians 2:13 says. This paragraph above is verbatim quoted from Shawn Brasseaux here.