Āhāra means ‘food’ in Sanskrit, the language of ancient Indian philosophy and religion. It is also part of the ayurveda system and includes anything that we consume, either in the solid or liquid form.
For starters, the general rule of yoga (and āhāra) is that for any relatively healthy individual moderation in food and drink is key (as it usually is with most other aspects of human life, e.g. vihāra, the lifestyle).
It is not always easy to ascertain what moderation is for any individual so it is extremely useful to have a teacher or mentor to advise. Our mind is more than often not quite truthful about our actual needs, hiding them behind the veils of five kleśas (which is a much longer topic to expand on). Suffice to say that most of (generally accepted) healthy food and beverages is completely fine to consume in moderation!
Like in any period of the human history, people have been developing (and sticking to) their habits (saṁskāra-s), both in their eating and drinking sphere of life, and in their general lifestyle, including training, etc. Some of those have been based on misapprehension, some closer to the very nature of truth but most of the times all of those were just fashionable ways of reacting to the chaos that human ways of thinking transform into manageable chunks of generally accepted knowledge at the time of our lives.
Usually, when one myth comes up as generally accepted truth, the other (opposite) myth is taken off its pedestal. This is the very nature of humans (as we know of) and it should not be frowned upon. The idea is rather to accept the fact, trying to understand its underlying cause, and make a bit wiser choices about how to progress in life.