Paleo diets are based on a simple premise – if the cavemen didn’t eat it, you shouldn’t either. So long to refined sugar, dairy, legumes and grains (this is pre-agricultural revolution), and hello to meat, fish, poultry, fruits and veggies. The idea is that by eliminating modern-era foods like highly-processed carbs and dairy, you can avoid or control “diseases of civilization” like Type 2 diabetes and heart disease, and likely lose weight too. What you eat and how much depend on your goals or the specific program you’re on, if you choose to follow one. The high-protein diet is ranked poorly among U.S. News experts, who consider it too restrictive to be healthy or sustainable.