No need to cut out beef if you're looking to live healthy.  There are up to 27 lean cuts per beef.  Lean beef is high in protein, lower in fat, contains omega-3s, iron and zinc that are good for eliminating brain fog.  
Here are 6 cuts to get you started:
1-Chuck Roast 
1-Tri Tip Roast 
1-Beef Tenderloin 
1-Flank Steak or Skirt Steak (your choice)
1- Sirloin Tip Steak
1-Top Round Steak