Hi there,
A good diet is a chapter for another day, another time, but what you may understand is that diet is specific to each person. You would not recommend milk to a lactose intolerant person, nor any meat to a vegan, but a good diet is probably the easiest to achieve because you simply avoid too many carbohydrates, fats, sugar, and other harmful additives.
But nowadays, most bodybuilders are just on boosters and supplements. That's why they cause different health problems like cancer because of the extra use of
supplements and body boosters, but there are a lot of gyms that don't allow supplements and boosters, like EOS Fitness Las Vegas. They only focus on their natural bodies and, without supplements, they provide the best results in just 3 to 6 months.