The Natural Man
The natural man will benefit greatly from a fast directed by the Lord Jesus Christ.
Outcomes from fasting the way Christ says will do more for the spirit than for the natural man. The natural man, however, will experience some wonderful things from Christ and he will think differently. He will respond to problems differently.
What you learn from fasting, as described by God through Isaiah, cannot be obtained any other way - not through books, nor audio, video, or preaching - but by doing as it says. The spirit must dominate the fasting experience, not the flesh (anger, blaming others, malice or strife) which is not pleasing in God's sight.
Gal 5:17 For the flesh lusteth against the Spirit, and the Spirit against the flesh: and these are contrary the one to the other: so that ye cannot do the things that ye would.
The natural man is always with you. There is always a war going on. That's why we are told, among other things, to remain watchful and sober in the Lord because of our adversary, the devil.
1Th 5:6 Therefore let us not sleep, as do others; but let us watch and be sober.
1Th 5:8 But let us, who are of the day, be sober, putting on the breastplate of faith and love; and for an helmet, the hope of salvation.
1Pe 4:7 But the end of all things is at hand: be ye therefore sober, and watch unto prayer.
1Pe 5:8 Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:
The natural man is with you when you are praying, fasting, giving or teaching about Christ. Although it is impossible for him to understand or know the things of Christ, he will always have an opinion about spiritual matters.
He is with you when you are involved in the affairs of this life such as paying bills, working for an employer or having your own business. These cares are your social environment, the school you attend, the decisions you make, or your duty to your family and more.
The natural man has his idea of what paying bills looks like, or what caring for others, love, compassion, socializing with others and etc. look like.
But the Lord has an entirely different perspective. It is for this reason Christ came - to destroy the works of the flesh. If you do not take each of these thoughts and ways to Jesus Christ for correction, then you are still walking in the flesh and making decisions that do not please God, nor create the outcomes that show Jesus Christ as the author of your life.
Pro 3:5 Trust in the LORD with all thine heart; and lean not unto thine own understanding.
Pro 3:6 In all thy ways acknowledge him, and he shall direct thy paths.
Pro 3:7 Be not wise in thine own eyes: fear the LORD, and depart from evil.
"...and lean not unto thine own understanding..." makes it clear that leaning or choosing your understanding above trusting the Lord is forbidden for the saint of God.
Let me be clear; ancient Isreal had no science, technology, or doctors. They only had God as their supplier. As long as Israel obeyed and followed God, they had the protection of his word. If they was disobedient, the other nations were permitted to consume them.
Because you are told to lean not to your own understanding, this leaves you with only one alternative... to listen to Christ and learn from that trust.
Not thinking or having their thoughts recreated in Christ may be difficult for most saints to grasp. What is most important is that your natural way of thinking is not authoring the fasting experience.
The Holy Ghost is responsible for teaching you ALL THINGS. He must rewrite your experiences. He must teach you how to maintain peace or how to deal with difficult people. He will teach you how to maintain your integrity when the people around you have given up theirs.
Want to learn to drive a car, or overcome a fear of spiders? Every thing around you is full of opportunities for spiritual growth. Your life is a canvas.