A 60-year-old male complains of pain in both knees coming on gradually over the past 2 years. The pain is relieved by rest and worsened by the movement. There is bony enlargement of the knees with mild inflammation. Crepitation is noted on motion of the knee joint. There are no other findings except for bony enlargement at the distal interphalangeal joint. The patient is 5 feet 9 in. tall and weighs 88 kgs. The best way to prevent disease progression is