Let nobody therefore deceive you and say that fasting or vegetable food weakens one's health, for in fact it gives it strength.
Fasting is not a remedy for the spirit alone, but it is also for the body. There have never been any cases were vegetarian food has harmed or weakened anyone.
Daniel and the three young men did not eat meat at the King's table. It was sufficient to eat beans and their health was better than the others. (Dan 1: 15).
Our fathers, the ascetics and the great monks, were very strict in their fasts. Yet we have never heard that fasting weakened their health. On the contrary, they remained strong even in their old age.
No-where is it mentioned that our father Adam became sick or weak from eating vegetarian food. The same applies to Eve and to all the fathers preceding Noah's and the great flood. Therefore, rest assured about your bodily health.