Eating once a day is for monks. Because in the Buddhist precepts, only the precepts of monks have the rule of eating once a day.

For lay disciples at home, there is no rule of eating once a day. In the "Bodhisattva Commandments at Home", laymen who are bound by the Bodhisattva Commandments do not eat after noon on the 6th of every month. This shows that when the Buddha formulated the commandments, he must have taken into account the nutrition of lay disciples.

To sum up, Buddhism's one-day diet does not violate health preservation. In fact, we meet many monks over 100 years old who eat once in a while, such as monk Xu Yun and elder Ben Huan.