https://www.theguardian.com/lifeandstyle/wordofmouth/2015/ja...
Sure they did. They didn't start that diet on day one. Between ideas of nutrition during their lifetimes and however long it took to adopt, formalize and tweak their diet regimen it could have taken years or generations even.
The difference now is we have a deeper understanding of everything involved with nutrition and some of the research we do is determining why we see the effects we do as opposed to the Templars just trying to achieve a desired effect.
It's pretty easy to discount the amount of time that was spent on it and the number of missteps along the way and the unavoidable fluff the Templars also likely engaged in. And then compare that to formalized research and imagine that the Templars had some intuitive insight that makes scientific research look redundant or overly complicated...
Similarly the usual days did not have as much animal produce as today.
Remember that these people were professional soldiers with at least a few hours of strenuous exercise a day combined with relative leisure In prayer. (Compared to peasants or even modern day workers.)
A 4 pound chicken will get you about 2000 calories after it is cooked, whereas the same chicken would lay approx 5 eggs/week, each @ 75 calories, or 375 calories/week. So, it would only take 6 weeks for a chicken to output as many calories as exist within it, and chickens lay eggs productively for 4-5 years.