How real is Matthew 4:1-2 in terms of physical realities? Then Jesus was led by the Spirit out into the wilderness to be tempted by the devil. He fasted for forty days and forty nights after which he was very hungry, and the tempter came to Him (Matt. 4:1-2). 


The forty days and forty nights of fasting how exhaustive and physically weak would a man can endure. The way I understand it, we can live with no food for three days but definitely we must have water to sustain our physical energy. But for Jesus to be still standing for forty days and had the strength to face Satan, is truly an amazing narrative if taken into reality.

Is this passages a metaphor of forty days or strictly speaking this is forty calendar days in our time?
It is humanly possible to fast food for 40 days, though it is generally recommended to be very cautious about making such a decision due to the pressure it will put on your body's health and fitness. That said, several Christian teachers and writers both past and present recommend and teach about the benefits of 40-day fasting as a way to draw closer to God.

It's also noted that Christianity traditionally marks the 40 days of Lent as a period of fasting. While we find that some denominations ease the requirements (or make it purely optional), it can be expected that in earlier times 'pure' fasting would have taken place much more commonly especially within the Catholic church.

Given the above, one can expect it to have been very physically possible for Jesus to have fasted for 40 days, though doubtful that it would have been an easy, enjoyable experience!!