The Maltese Church has issued a handy explainer for the Lenten fast

Catholics around the world today are marking the start of the 40-day Lenten period with Ash Wednesday.

It’s a day dedicated to fasting, although the fast will continue throughout Lent for believers on every Friday of the weeks that follow, and even a further penance to have no sweets over the next 40 days.

But why is fish considered to be an appropriate substitute for meat?

The Maltese church has issued an explainer for Catholics showing what is required of the fast: no meat on Fridays, no snacking or sweets, one regular meal and two smaller meals throughout the day. That is valid for anyone aged between 18 to 60.

The 1963 document Sacrosanctum Concilium, by Pope Paul VI, specifically described the Lenten penance as something that can be “fostered” in ways according to one’s circumstances. However it makes clear that the paschal fast – Paschal derived from the Latin adjective describing Easter or Passover – be celebrated on Good Friday and even prolonged throughout Holy Saturday “so that the joys of the Sunday of the resurrection may be attained with uplifted and clear mind.”

But why is fish considered to be an appropriate substitute for meat?

By the Middle Ages, the strict fast involved avoiding meat, eggs, and dairy. That divide was clearly explained by Saint Thomas Aquinas in his Summa Theologica. To Aquinas, Lent was a time for simplicity, and meat in the 1200s was a luxury: so a feast based on modesty should be celebrated by refusing something as decadent as meat.

That’s simple enough, but there was something else on Aquinas’ mind: sex.

“For, since such like animals are more like man in body, they afford greater pleasure as food, and greater nourishment to the human body, so that from their consumption there results a greater surplus available for seminal matter, which when abundant becomes a great incentive to lust.”

Simply read? Aquinas thought eating too much meat made you horny.

There was a third reason for the avoidance of meat, according to Aquinas: flatulence. “Those who fast are forbidden the use of flesh meat rather than of wine or vegetables, which are flatulent foods.” Again, Aquinas argued that vegetables and their powers of flatulence improved vitality.

However Aquinas argued that the Church considered eating flesh meat afforded more pleasure than eating fish… “Hence the Church forbade those who fast to eat flesh meat, rather than to eat fish.”

Also, St Paul’s first letter to the Corinthians has been used to justify fasting rules. “There is one kind of flesh of men, another flesh of beasts, another of fish, and another of birds” (15:39). Add to that the distinction from Judaism’s dietary restrictions, which separates fleishig (which includes land-locked mammals and fowl) from pareve (which includes fish).