The question focus on the physical realities and since we as human are time bound we normally try to figure the physical realities of the subject 40 days and 40 nights, Is it really 40 calendar days event in our time?
I found the link that forty days are just an expression in the time of Jews.
"At the time among the Jews, the number forty wasn’t generally used to signify >a specific number, per se, but rather more used as a general term for a large >figure. When it was used in terms of time, it simply meant a “long time”. >Thus, the phrase “40 days and 40 nights” was just another way to say a “really long time”. - "The Biblical Expression “40 Days and 40 Nights” Just Means a “Really Long Time”
There are two important characters in the bible who are associated having experienced the forty days, Noah and Moses.
The Forword of the book "When the Divine Will Reigns in Souls" (Book of Heaven, by Mystics name Luisa Picarreta).states the following;
"From time to time it has pleased God to bring about monumental and universal >changes in the affairs of mankind.When these events occur it has been the usual >way with our God to give us a very special persons to be identified in a >particular manner with these changes.
In the beginning when the Decree of Creation brought the human race to >existence, Adam & Eve were chosen to be the first humans to be inserted into >time. They were our first parents in the order of nature.Later, humanity had >grown so steeped in evil that God saw fit to send the "Great Flood".He chose >Noah to build the Ark and lead a tiny remnant through that awesome change in >human affairs.When the chosen people,the Jews were to be lead out of the land >of Egypt, God chose Moses,through whom we are given the Ten Commandments. >Centuries later, the Decree of Redemption was fulfilled and the Only-Begotten >Son of the Father,Jesus became Incarnate in the most pure womb of Mary.She >became the Mother of God, Mother of the Redeemer and cooperated perfectly with >Him for the Redemption of Mankind."(Foreword by Thomas M. Fahy)
We can see the relevance of forty days to the events that happened to Noah signifying the cleansing of the sins of men by Water/Flood to renew the face of the earth. And for Moses the Old Covenant will be renewed by the New Covenant thru Jesus Christ.
The face of the earth will be renewed by the Most Precious Blood of Jesus Christ.
The Blood & Water that gushed forth from the Heart of Jesus is the source of Sanctifying Grace that will restore our friendship with God and become adopted sons thru the Sacraments of Baptism.
Now back to the physical realities of Jesus endurance with the human flesh deprived of food nourishment, can this be real?
Yes, Jesus being docile to the promptings of the Holy Spirit knows fully the tactics of the devil when we are physically weak.And so Jesus in the following verse answer Satan with the strength of Word of God.
"But he answered and said, it is written, Man shall not live by bread alone, >but by every word that proceedeth out of the mouth of God."(Matthew4:4)
and in John4:34, Jesus said;
"My food is to do the will of him who sent me, and to accomplish his work.
This forty days and forty nights prayer & fasting was imitated by a lot of saints like St. Padre Pio and most especially by numerous Mystics of the Church. One notable mystics is Luisa Picarreta in the succeeding foreword of Thomas M. Fahy (When the Divine Will Reigns in Soul, page xviii) it is written;
"Luisa Piccaretta who was confined to bed for 64 years without food or water >and scarcely any sleep, had little more than a first grade in education,but >Jesus would come her everyday and illuminate her mind with the most sublime >mysteries about God..."
Formore info on Luisa Picarreta please visit their site link: Luisa Piccarreta.
Title Page from The Hours of the Passion of the Servant of God,
Luisa Piccarreta, the Little Daughter of the Divine Will
Showing the Nihil Obstat by Francesco Sorrentino (Revisore eccl.)
and Imprimatur by A. Can. Laviano V.G.
Dated February 20, 1915
In closing, Matthew 4:1-2 passages shows Jesus was docile to the voice & promptings of the Holy Spirit, and showing us all believers the power of "prayer & fasting".
When we are called to a Great Mission we must first always seek the Holy Spirit thru prayer & fasting not in the context of 40 days & 40 nights but it requires a "long period of discernment" to accept and follow the Will of God.