I would never advocate that, as an atheist, you should base your morality on what the Bible says, but I would advise you actually have a morality. Ethics isn't just about what is good for you, but what is good for others. Regardless of appeals to history, or to what diet helped our prehistoric ancestors survive inhospitable climates, the fact is most of us do NOT need to exploit, enslave and kill other animals nowadays - there is an endless variety of healthy, delicious vegan food available, so why would you cause suffering unnecessarily?