Something isn't right here. At the time of the Templars nobody ate like this. Nobody could. Rich or poor, holy or not, food changed according to the season. Vegetables were only available at certain times of the year. The rest of the time it would be a combination of bread (grain) and meat. The diet described in this article would only have been possible in relatively temperate climates with long growing seasons. But even so, there would have been seasons.
The concept of a weekly diet, one that can be followed month after month, is a very modern thing. You ate what was in season. You didn't eat meat when there was plenty of vegetables available. You shoved the extra vegetables into animals, which you then ate during the seasons when the vegetables weren't available. This concept of a "balanced" diet between the two would have been impractical and extremely wasteful.
Also, be careful with the word meat in old texts. The meaning changes depending on context. Western cultures generally don't count fish as meat but others do. Similarly, 'game' and even 'fowl' are sometimes not included, with 'meat' reserved for the slaughter of domesticated animals. So a text about people not eating meat at particular times doesn't necessarily mean they weren't getting a pile of fats and proteins from something that we today would consider meat.
> Rich or poor, holy or not, food changed according to the season.
Tha's true.
> Vegetables were only available at certain times of the year. The rest of the time it would be a combination of bread (grain) and meat.
That's not. Plenty of fruits & vegetables can be put up for quite a long time. Root vegetables can be stored for many months (almost a year) by digging them up and piling in 'silos,' which alternate layers of soil or sand & vegetables. Apples can be stored in barrels. Cabbages can be covered in leaves, or fermented. Beans & peas can be dried. Almonds can be used to make milk (in fact, in the middle ages almond milk was more common than cows' milk).
Christians have been fasting on Wednesdays & Fridays, Lent & Advent for millennia, well before refrigeration and modern foodstuffs.
Try storing food that way for a few months. The results aren't pretty. What survives are carbs. All the vitamins are gone. You have carrots suitable for pottage, not salad. Seeds (peas, nuts, grains etc) can indeed be stored but they too are just blobs of carbs. When we talk about "eating vegetables" we don't mean porridge and dried nuts. Scurvy was a thing for a reason.
Scurvy was a thing on sailing ships. If it had been universal for everybody everywhere, wouldn't we have retained the ability to produce vitamin C like other creatures do - and not lost it through evolution?
I am amazed if you truly cannot imagine a root cellar, just a generation or two ago.
Scurvy "was a thing" because for centuries they didn't know why it happened in the first place.
A Scottish surgeon in the Royal Navy, James Lind, is generally credited with proving that scurvy can be successfully treated with citrus fruit in 1753.
Folks in the middle ages had some confused ideas about where the adult geese came from (thinking they started life as barnacles!) and thus meat from this one particular bird was approved to eat on fast days.
The concept of a weekly diet, one that can be followed month after month, is a very modern thing. You ate what was in season. You didn't eat meat when there was plenty of vegetables available. You shoved the extra vegetables into animals, which you then ate during the seasons when the vegetables weren't available. This concept of a "balanced" diet between the two would have been impractical and extremely wasteful.
Also, be careful with the word meat in old texts. The meaning changes depending on context. Western cultures generally don't count fish as meat but others do. Similarly, 'game' and even 'fowl' are sometimes not included, with 'meat' reserved for the slaughter of domesticated animals. So a text about people not eating meat at particular times doesn't necessarily mean they weren't getting a pile of fats and proteins from something that we today would consider meat.